Charles H. Winter

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Name: Winter, Charles H.

Organization: Wayne State University , USA

Department: Department of Chemistry

Title: Associate(PhD)

TOPICS

Material Chemistry

Inorganic Chemistry

Organic Chemistry

Chemicals
References

Synthesis, structural characterization, and volatility evaluation of zirconium and hafnium amidate complexes

Co-reporter:Mahesh C. Karunarathne, Joseph W. Baumann, Mary Jane Heeg, Philip D. Martin, Charles H. Winter

Journal of Organometallic Chemistry 2017 Volume 847(Volume 847) pp:

Publication Date(Web):1 October 2017

DOI:10.1016/j.jorganchem.2017.03.003

•Homoleptic Zr(IV) and Hf(IV) amidate complexes were synthesized and characterized.•The complexes adopt monomeric structures with dodecahedral geometry.•Many of the complexes are volatile and highly thermally stable.•The new complexes are promising precursors for ZrO2 and HfO2 films.Treatment of tetrakis(dimethylamido)zirconium or tetrakis(dimethylamido)hafnium with four equivalents of N-tert-butylacetamide, N-isopropylisobutyramide, N-isopropylacetamide, N-methylacetamide, or N-tert-butylformamide in refluxing toluene, followed by sublimation of the crude products at 105–125 °C/0.05 Torr, afforded tetrakis(N-tert-butylacetamido)zirconium (81%), tetrakis(N-isopropylisobutyramido)zirconium (87%), tetrakis(N-isopropylacetamido)zirconium (51%), tetrakis(N-tert-butylacetamido)hafnium (83%), tetrakis(N-isopropyliso-butyramido)hafnium (79%), tetrakis(N-isopropylacetamido)hafnium (67%), tetrakis(N-methylacetamido)zirconium (5%), and tetrakis(N-tert-butylformamido)zirconium (1%) as colorless crystalline solids. The structural assignments for the new complexes were based upon spectral and analytical data and by X-ray crystal structure determinations for tetrakis(N-tert-butylacetamido)zirconium, tetrakis(N-isopropylacetamido)zirconium, tetrakis(N-isopropylacetamido)hafnium, tetrakis(N-methylacetamido)zirconium, and tetrakis(N-tert-butylformamido)zirconium. These complexes are monomeric in the solid state, with eight-coordinate metal centers surrounded by four κ2-N,O-amidate ligands. Six of the eight new complexes undergo sublimation on a preparative scale from 130 to 140 °C at 0.05 Torr, with 84.5–95.8% sublimed recoveries and 0.68–3.06% nonvolatile residues. Tetrakis(N-methylacetamido)zirconium and tetrakis(N-tert-butylformamido)zirconium decompose extensively upon attempted sublimation. Solid state decomposition temperatures for the zirconium complexes range between 218 and 335 °C and 290–360 °C for the hafnium complexes. Tetrakis(N-isopropylisobutyramido)zirconium, tetrakis(N-tert-butylacetamido)hafnium, and tetrakis(N-isopropylacetamido)hafnium exhibit the highest solid state decomposition temperatures in the series, possess good volatility, and have useful properties for chemical vapor deposition and atomic layer deposition precursors.Monomeric zirconium and hafnium complexes of the formula M(RNC(O)R′) were obtained upon treatment of tetrakis(dimethylamido)zirconium or tetrakis(dimethylamido)hafnium with four equivalents of secondary organic amides. These complexes combine good volatility and high thermal stability, and are promising candidates for metal oxide thin film growth precursors.Download high-res image (129KB)Download full-size image

Low Temperature Thermal Atomic Layer Deposition of Cobalt Metal Films

Co-reporter:Joseph P. Klesko, Marissa M. Kerrigan, and Charles H. Winter

Chemistry of Materials 2016 Volume 28(Issue 3) pp:700

Publication Date(Web):January 21, 2016

DOI:10.1021/acs.chemmater.5b03504

Thermal Atomic Layer Deposition of Titanium Films Using Titanium Tetrachloride and 2-Methyl-1,4-bis(trimethylsilyl)-2,5-cyclohexadiene or 1,4-Bis(trimethylsilyl)-1,4-dihydropyrazine

Co-reporter:Joseph P. Klesko, Christopher M. Thrush, and Charles H. Winter

Chemistry of Materials 2015 Volume 27(Issue 14) pp:4918

Publication Date(Web):July 15, 2015

DOI:10.1021/acs.chemmater.5b01707

Less sensitive oxygen-rich organic peroxides containing geminal hydroperoxy groups

Co-reporter:Nipuni-Dhanesha H. Gamage, Benedikt Stiasny, Jörg Stierstorfer, Philip D. Martin, Thomas M. Klapötke and Charles H. Winter

Chemical Communications 2015 vol. 51(Issue 68) pp:13298-13300

Publication Date(Web):20 Jul 2015

DOI:10.1039/C5CC05015D

A series of oxygen-rich organic peroxide compounds each containing two bis(hydroperoxy)methylene groups is described. Energetic testing shows that these compounds are much less sensitive toward impact and friction than existing classes of organic peroxides. The compounds are highly energetic, which may lead to practical peroxide-based explosives.

Reductive Elimination of Hypersilyl Halides from Zinc(II) Complexes. Implications for Electropositive Metal Thin Film Growth

Co-reporter:Chatu T. Sirimanne; Marissa M. Kerrigan; Philip D. Martin; Ravindra K. Kanjolia; Simon D. Elliott

Inorganic Chemistry 2015 Volume 54(Issue 1) pp:7-9

Publication Date(Web):December 9, 2014

DOI:10.1021/ic502184f

Treatment of Zn(Si(SiMe3)3)2 with ZnX2 (X = Cl, Br, I) in tetrahydrofuran (THF) at 23 °C afforded [Zn(Si(SiMe3)3)X(THF)]2 in 83–99% yield. X-ray crystal structures revealed dimeric structures with Zn2X2 cores. Thermogravimetric analyses of [Zn(Si(SiMe3)3)X(THF)]2 demonstrated a loss of coordinated THF between 50 and 155 °C and then single-step weight losses between 200 and 275 °C. The nonvolatile residue was zinc metal in all cases. Bulk thermolyses of [Zn(Si(SiMe3)3)X(THF)]2 between 210 and 250 °C afforded zinc metal in 97–99% yield, Si(SiMe3)3X in 91–94% yield, and THF in 81–98% yield. Density functional theory calculations confirmed that zinc formation becomes energetically favorable upon THF loss. Similar reactions are likely to be general for M(SiR3)n/MXn pairs and may lead to new metal-film-growth processes for chemical vapor deposition and atomic layer deposition.

Low-Temperature Atomic Layer Deposition of Copper Films Using Borane Dimethylamine as the Reducing Co-reagent

Co-reporter:Lakmal C. Kalutarage, Scott B. Clendenning, and Charles H. Winter

Chemistry of Materials 2014 Volume 26(Issue 12) pp:3731

Publication Date(Web):June 4, 2014

DOI:10.1021/cm501109r

The atomic layer deposition (ALD) of Cu metal films was carried out by a two-step process with Cu(OCHMeCH2NMe2)2 and BH3(NHMe2) on Ru substrates and by a three-step process employing Cu(OCHMeCH2NMe2)2, formic acid, and BH3(NHMe2) on Pd and Pt substrates. The two-step process demonstrated self-limited ALD growth at 150 °C with Cu(OCHMeCH2NMe2)2 and BH3(NHMe2) pulse lengths of ≥3.0 and ≥1.0 s, respectively. An ALD window was observed between 130 and 160 °C, with a growth rate of about 0.13 Å/cycle. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) revealed rough Cu films that likely originate from the Cu nanoparticle seed layer. The Cu films exhibited poor electrical conductivity because of their nanoparticulate natures. The three-step process showed self-limited ALD growth on Pd and Pt at 150 °C with Cu(OCHMeCH2NMe2)2, formic acid, and BH3(NHMe2) pulse lengths of ≥3.0, ≥ 0.3, and ≥1.0 s, respectively. ALD windows were observed between 135 and 165 °C on both Pd and Pt, with growth rates of 0.20 Å/cycle on both substrates. Plots of film thickness versus number of cycles showed linear growth behavior on Pd with a growth rate of 0.20 Å/cycle up to 2000 cycles. By contrast, a similar plot for growth on Pt revealed nonlinear growth behavior, with a growth rate of about 0.4 Å/cycle up to 500 cycles, and then a growth rate of about 0.03 Å/cycle between 500 and 2000 cycles. The large difference in growth behavior between Pd and Pt substrates is proposed to occur by formation of a Cu/Pd alloy film and continuous catalytic decomposition of the BH3(NHMe2) by the surface Pd sites. By contrast, there is much less surface Pt in the growing Cu film, and catalytic decomposition of BH3(NHMe2) by the diminishing surface Pt as the Cu film grows leads to a decreased growth rate beyond 500 cycles. X-ray photoelectron spectroscopy reveals the formation of high purity Cu metal for all depositions, with low levels of C, N, O, and B. The Cu films on Pd and Pt showed smooth, continuous films at all thicknesses and had low electrical resistivities.

Precursors and chemistry for the atomic layer deposition of metallic first row transition metal films

Co-reporter:Thomas J. Knisley, Lakmal C. Kalutarage, Charles H. Winter

Coordination Chemistry Reviews 2013 Volume 257(23–24) pp:3222-3231

Publication Date(Web):December 2013

DOI:10.1016/j.ccr.2013.03.019

•We review the growth of first row transition metal films by atomic layer deposition.•Processes are best developed for copper.•Strong reducing co-reagents need to be developed.•Other challenges include formation of continuous films and film nucleation.Recent trends in the microelectronics industry are requiring the growth of metallic first row transition metal films by the atomic layer deposition (ALD) method. The ALD growth of noble metal thin films has been well developed in the past ten years, due to the positive electrochemical potentials of these metal ions and attendant ease of reduction to the metallic state. By contrast, the ALD growth of metallic first row transition metal films remains poorly documented, in large part because of the negative electrochemical potentials of most of the ions and a corresponding lack of powerful reducing co-reagents that can convert precursors in positive oxidation states to the metals. In this short review, we discuss progress that has been made to date in the ALD growth of metallic first row transition metal films. The low temperature ALD of high purity, low resistivity Cu films has been reported, but optimum ALD processes for the other first row transition metals are still elusive. The current state of precursor and reducing co-reagent development is overviewed, and key future challenges are outlined.

Volatile and Thermally Stable Mid to Late Transition Metal Complexes Containing α-Imino Alkoxide Ligands, a New Strongly Reducing Coreagent, and Thermal Atomic Layer Deposition of Ni, Co, Fe, and Cr Metal Films

Co-reporter:Lakmal C. Kalutarage ; Philip D. Martin ; Mary Jane Heeg

Journal of the American Chemical Society 2013 Volume 135(Issue 34) pp:12588-12591

Publication Date(Web):August 15, 2013

DOI:10.1021/ja407014w

Treatment of MCl2 (M = Cu, Ni, Co, Fe, Mn, Cr) with 2 equiv of α-imino alkoxide salts K(RR′COCNtBu) (R = Me, tBu; R′ = iPr, tBu) afforded M(RR′COCNtBu)2 or [Mn(RR′COCNtBu)2]2 in 9–75% yields. These complexes combine volatility and high thermal stability and have useful atomic layer deposition (ALD) precursor properties. Solution reactions between Ni, Co, and Mn complexes showed that BH3(NHMe2) can reduce all to metal powders. ALD growth of Ni, Co, Fe, and Cr films is demonstrated. Mn film growth may be possible, but the films oxidize completely upon exposure to air.

Synthesis, Structure, and Solution Reduction Reactions of Volatile and Thermally Stable Mid to Late First Row Transition Metal Complexes Containing Hydrazonate Ligands

Co-reporter:Lakmal C. Kalutarage, Philip D. Martin, Mary Jane Heeg, and Charles H. Winter

Inorganic Chemistry 2013 Volume 52(Issue 9) pp:5385-5394

Publication Date(Web):April 25, 2013

DOI:10.1021/ic400337m

Treatment of MCl2 (M = Ni, Co, Fe, Mn, Cr) with 2 equiv of the hydrazonate salts K(tBuNNCHCtBuO), K(tBuNNCHCiPrO), or K(tBuNNCMeCMeO) afforded the complexes M(tBuNNCHCtBuO)2 (M = Ni, 65%; Co, 80%; Fe, 83%; Mn, 68%; Cr, 64%), M(tBuNNCHCiPrO)2 (M = Ni, 63%; Co, 86%; Fe, 75%), and M(tBuNNCMeCMeO)2 (M = Ni, 34%; Co, 29%; Fe, 27%). Crystal structure determinations of Co(tBuNNCHCtBuO)2, M(tBuNNCHCiPrO)2 (M = Ni, Co), and M(tBuNNCMeCMeO)2 (M = Ni, Co, Fe) revealed monomeric complexes with tetrahedral geometries about the metal centers. To evaluate the potential of these new complexes as film growth precursors, preparative sublimations, thermogravimetric analyses, solid state decomposition studies, and solution reactions with reducing coreagents were carried out. M(tBuNNCHCtBuO)2 sublime between 120 and 135 °C at 0.05 Torr, whereas M(tBuNNCHCiPrO)2 and M(tBuNNCMeCMeO)2 sublime between 100 and 105 °C at the same pressure. All complexes afforded ≥96% recovery of sublimed material, with ≤3% of nonvolatile residues. The solid state decomposition temperatures were highest for M(tBuNNCHCiPrO)2 (273–308 °C), intermediate for M(tBuNNCHCtBuO)2 (241–278 °C), and lowest for M(tBuNNCMeCMeO)2 (235–250 °C). Treatment of Co(tBuNNCHCtBuO)2 in tetrahydrofuran with hydrazine, BH3(L) (L = NHMe2, SMe2, THF), pinacol borane, and LiAlH4 led to rapid formation of cobalt metal, while analogous reductions of Mn(tBuNNCHCtBuO)2 with BH3(THF), pinacol borane, and LiAlH4 appeared to afford manganese metal. The new complexes M(tBuNNCHCtBuO)2, M(tBuNNCHCiPrO)2, and M(tBuNNCMeCMeO)2 have very promising properties for use as precursors for the growth of the respective metals in atomic layer deposition film growth processes.

Volatility and High Thermal Stability in Mid-to-Late First-Row Transition-Metal Complexes Containing 1,2,5-Triazapentadienyl Ligands

Co-reporter:Lakmal C. Kalutarage, Mary Jane Heeg, Philip D. Martin, Mark J. Saly, David S. Kuiper, and Charles H. Winter

Inorganic Chemistry 2013 Volume 52(Issue 3) pp:1182-1184

Publication Date(Web):January 23, 2013

DOI:10.1021/ic302787z

Treatment of first-row transition-metal MCl2 (M = Ni, Co, Fe, Mn, Cr) with 2 equiv of the potassium 1,2,5-triazapentadienyl salts K(tBuNNCHCHNR) (R = tBu, NMe2) afforded M(tBuNNCHCHNR)2 in 18–73% isolated yields after sublimation. The X-ray crystal structures of these compounds show monomeric, tetrahedral molecular geometries, and magnetic moment measurements are consistent with high-spin electronic configurations. Complexes with R = tBu sublime between 155 and 175 °C at 0.05 Torr and have decomposition temperatures that range from 280 to 310 °C, whereas complexes with R = NMe2 sublime at 105 °C at 0.05 Torr but decompose between 181 and 225 °C. This work offers new nitrogen-rich ligands that are related to widely used β-diketiminate and 1,3,5-triazapentadienyl ligands and demonstrates new complexes with properties suitable for use in atomic-layer deposition.

Synthesis, Structure, and Properties of Group 1 Metal Complexes Containing Nitrogen-Rich Hydrotris(tetrazolyl)borate Ligands

Co-reporter:Christopher J. Snyder;Dr. Philip D. Martin;Dr. Mary Jane Heeg ; Charles H. Winter

Chemistry - A European Journal 2013 Volume 19( Issue 10) pp:3306-3310

Publication Date(Web):

DOI:10.1002/chem.201203990

Metallapyrimidines and Metallapyrimidiniums from Oxidative Addition of Pyrazolate N–N Bonds to Niobium(III), Niobium(IV), and Tantalum(IV) Metal Centers and Assessment of Their Aromatic Character

Co-reporter:T. Hiran Perera, Richard L. Lord, Mary Jane Heeg, H. Bernhard Schlegel, and Charles H. Winter

Organometallics 2012 Volume 31(Issue 17) pp:5971-5974

Publication Date(Web):June 26, 2012

DOI:10.1021/om300490w

Treatment of MCl4(4-tBupy)2 (M = Nb, Ta) with 3 equiv of potassium 3,5-di-tert-butylpyrazolate afforded (2,2,6,6-tetramethyl-5-ketimidehept-3-en-3-imide)bis(3,5-di-tert-butylpyrazolate)chloroniobium(V) (1; 24%) and (2,2,6,6-tetramethyl-5-ketimidehept-3-en-3-imide)bis(3,5-di-tert-butylpyrazolate)chlorotantalum(V) (2; 27%) as deep red and yellow crystalline solids, respectively. Analogous treatment of NbCl4(THF)2 with 3 equiv each of 4-tert-butylpyridine and potassium 3,5-di-tert-butylpyrazolate and excess Na/Hg in diethyl ether afforded (2,2,6,6-tetramethyl-5-ketimidohept-3-en-3-imide)bis(3,5-di-tert-butylpyrazolate)niobium(V) (3, 32%) as deep red crystals. X-ray crystallography established that 1 and 3 each contain two intact η2-3,5-di-tert-butylpyrazolate ligands as well as one 3,5-di-tert-butylpyrazolate ligand that has undergone N–N bond oxidative addition to the niobium center. In 1, one of the nitrogen atoms abstracted a hydrogen atom from tetrahydrofuran solvent, whereas no hydrogen atom abstraction occurred in 3. These complexes represent rare examples of pyrazolate N–N bond cleavage. NICS calculations suggest that the niobacycles are weakly aromatic, in comparison to the highly aromatic 3,5-di-tert-butylpyrazolate ligands and pyrimidine.

Low Temperature Growth of High Purity, Low Resistivity Copper Films by Atomic Layer Deposition

Co-reporter:Thomas J. Knisley, Thiloka C. Ariyasena, Timo Sajavaara, Mark J. Saly, and Charles H. Winter

Chemistry of Materials 2011 Volume 23(Issue 20) pp:4417

Publication Date(Web):September 27, 2011

DOI:10.1021/cm202475e

Poly(pyrazolyl)aluminate Complexes Containing Aluminum–Hydrogen Bonds

Co-reporter:Christopher J. Snyder, Mary Jane Heeg, and Charles H. Winter

Inorganic Chemistry 2011 Volume 50(Issue 19) pp:9210-9212

Publication Date(Web):August 30, 2011

DOI:10.1021/ic201541c

The treatment of LiAlH4 with 2, 3, or 4 equiv of the 3,5-disubstituted pyrazoles Ph2pzH or iPr2pzH afforded [Li(THF)2][AlH2(Ph2pz)2] (97%), [Li(THF)][AlH(Ph2pz)3] (96%), [Li(THF)4][Al(Ph2pz)4] (95%), and [Li(THF)][AlH(iPr2pz)3] (89%). The treatment of ZnCl2 with [Li(THF)][AlH(Ph2pz)3] afforded Zn(AlH(Ph2Pz)3)H (70%). X-ray crystal structures of these complexes demonstrated κ2 or κ3 coordination of the aluminum-based ligands to the Li or Zn ions. The treatment of [Li(THF)][AlH(Ph2pz)3] with MgBr2 or CoCl2 in THF/Et2O solutions, by contrast, afforded the pyrazolate transfer products Mg2Br2(Ph2pz)2(THF)3·2THF (25%) and Co2Cl2(Ph2pz)2(THF)3·THF (23%) as colorless and blue crystalline solids, respectively. An analogous treatment of [Li(THF)][AlH(Ph2pz)3] with MCl2 (M = Mn, Fe, Ni, Cu) afforded metal powders and H2, illustrating hydride transfer from Al to M as a competing reaction path.

Efficient Hydride and Pyrazolyl Redistribution upon Thermolysis of a Calcium Complex Containing Dihydrobis(pyrazolyl)borate Ligands

Co-reporter:Mark J. Saly, Jing Li, Mary Jane Heeg, and Charles H. Winter

Inorganic Chemistry 2011 Volume 50(Issue 16) pp:7385-7387

Publication Date(Web):July 19, 2011

DOI:10.1021/ic2012815

Thermolysis of CaBp2(THF)2 (THF = tetrahydrofuran) at 190–200 °C and 0.05 Torr leads to a redistribution reaction to afford CaTp2 (90%) and CaTp(BH4) (84%). Treatment of CaTp(BH4) with THF affords CaTp(BH4)(THF)2 and [CaTp(BH4)(THF)]4, both of which were structurally characterized. Methanolysis or ethanolysis/hydrolysis of the BH4–-containing complexes affords [TpCa(HOMe)2(μ4-B(OMe)4)Ca(HOMe)2Tp][B(OMe)4] and [{TpCa}3{μ6-B(OB(OEt)3)3]·EtOH.

The Atomic Layer Deposition of SrB2O4 Films Using the Thermally Stable Precursor Bis(tris(pyrazolyl)borate)strontium

Co-reporter:Mark J. Saly;Frans Munnik

Chemical Vapor Deposition 2011 Volume 17( Issue 4-6) pp:128-134

Publication Date(Web):

DOI:10.1002/cvde.201006890

Abstract

The atomic layer deposition (ALD) of strontium borate films is carried out using bis(tris(pyrazolyl)borate)strontium (SrTp₂) and water as precursors. Self-limiting ALD growth is established at 350 °C with SrTp₂ and water pulse lengths of ≥ 2.0 s and ≥ 0.3 s, respectively. An ALD window is observed from 300 to 375 °C, in which the growth rate is 0.47 Å per cycle. The thin film compositions are assessed by elastic recoil detection analysis (ERDA) and X-ray photoelectron spectroscopy (XPS). ERDA suggests compositions of SrB₂O₄ at growth temperatures of < 350 °C, but the boron/strontium and oxygen/strontium ratios are lower than those of SrB₂O₄ at 350 and 400 °C. Within the ALD window, hydrogen concentrations range from 0.37(42) to 0.87(7) at.-%, and the carbon and nitrogen concentrations are below the detection limits. XPS analyses on representative strontium borate thin films show all expected ionizations. X-ray diffraction (XRD) experiments reveal that the as-deposited films are amorphous. The surface morphology is assessed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The rms surface roughness of typical 2 µm × 2 µm areas for films deposited at 325 and 350 °C are 0.3 and 0.2 nm, respectively. SEM images of these films show no cracks or pinholes.

Synthesis, structural characterization, and properties of heavier alkaline earth complexes containing bis(pyrazolyl)borate or bis(3,5-diisopropylpyrazolyl)borate ligands

Co-reporter:Mark J. Saly, Mary Jane Heeg, Charles H. Winter

Polyhedron 2011 30(7) pp: 1330-1338

Publication Date(Web):

DOI:10.1016/j.poly.2011.02.026

Volatility and High Thermal Stability in Mid- to Late-First-Row Transition-Metal Diazadienyl Complexes

Co-reporter:Thomas J. Knisley, Mark J. Saly, Mary Jane Heeg, John L. Roberts, and Charles H. Winter

Organometallics 2011 Volume 30(Issue 18) pp:5010-5017

Publication Date(Web):August 25, 2011

DOI:10.1021/om200626w

Treatment of MCl2 (M = Cr, Mn, Fe, Co, Ni) with 2 equiv of lithium metal and 1,4-di-tert-butyl-1,3-diazadiene (tBu2DAD) in tetrahydrofuran at ambient temperature afforded Cr(tBu2DAD)2 (38%), Mn(tBu2DAD)2 (81%), Fe(tBu2DAD)2 (47%), Co(tBu2DAD)2 (36%), and Ni(tBu2DAD)2 (41%). Crystal structure determinations revealed monomeric complexes that adopt tetrahedral coordination environments and were consistent with tBu2DAD radical anion ligands. To evaluate the viability of M(tBu2DAD)2 (M = Cr, Mn, Fe, Co, Ni) as potential film growth precursors, thermogravimetric analyses, preparative sublimations, and solid-state decomposition studies were performed. Mn(tBu2DAD)2 is the most thermally robust among the series, with a solid-state decomposition temperature of 325 °C, a sublimation temperature of 120 °C/0.05 Torr, and a nonvolatile residue of 4.3% in a preparative sublimation. Thermogravimetric traces of all complexes show weight loss regimes from 150 to 225 °C with final percent residues at 500 °C ranging from 1.5 to 3.6%. Thermolysis studies reveal that all complexes except Mn(tBu2DAD)2 decompose into their respective crystalline metal powders under an inert atmosphere. Mn(tBu2DAD)2 may afford amorphous manganese metal upon thermolysis.

Tetramethylcyclobutadienecobalt(I) complexes containing pyrazolate or tetrazolate ligands with various coordination modes

Co-reporter:Oussama M. El-Kadri, Mary Jane Heeg, Charles H. Winter

Journal of Organometallic Chemistry 2011 696(10) pp: 1975-1981

Publication Date(Web):

DOI:10.1016/j.jorganchem.2010.10.046

Growth of Tantalum(V) Oxide Films by Atomic Layer Deposition Using the Highly Thermally Stable Precursor Ta(NtBu)(iPrNC(Me)NiPr)2(NMe2)

Co-reporter:Monika K. Wiedmann, Mahesh C. Karunarathne, Ronald J. Baird and Charles H. Winter

Chemistry of Materials 2010 Volume 22(Issue 15) pp:4400

Publication Date(Web):July 12, 2010

DOI:10.1021/cm100926r

The atomic layer deposition (ALD) growth of Ta2O5 films was demonstrated using Ta(NtBu)-(iPrNC(Me)NiPr)2(NMe2) and water with substrate temperatures between 225 and 400 °C. At 325 °C, self-limited growth was demonstrated with Ta(NtBu)(iPrNC(Me)NiPr)2(NMe2) and water pulse lengths of ≥0.5 s. An ALD window was observed between 275 and 350 °C, with a growth rate of 0.28 Å/cycle. The growth rates were 0.33 and 0.37 Å/cycle at 250 and 225 °C, respectively. At 375 and 400 °C the growth rate increased slightly to 0.31 Å/cycle, and precursor thermal decomposition may contribute to growth at these temperatures. In a series of films deposited at 325 °C, the film thickness increased linearly with the number of deposition cycles. X-ray photoelectron spectroscopy of films deposited at 300 and 350 °C revealed stoichiometric Ta2O5 with carbon and nitrogen levels below the detection limits. The films were amorphous as deposited, but annealing at 700 °C in dry air resulted in crystallization of hexagonal δ-Ta2O5. Atomic force microscopy found root-mean-square surface roughnesses of 0.6−0.7 nm for 45 nm thick films deposited at 300 and 350 °C. The index of refraction of films grown at 325 °C was determined to be 2.12−2.16 at 633 nm using ellipsometry.

Atomic layer deposition of CaB2O4 films using bis(tris(pyrazolyl)borate)calcium as a highly thermally stable boron and calcium source

Co-reporter:Mark J. Saly, Frans Munnik and Charles H. Winter

Journal of Materials Chemistry A 2010 vol. 20(Issue 44) pp:9995-10000

Publication Date(Web):24 Sep 2010

DOI:10.1039/C0JM02280B

The atomic layer deposition of CaB2O4 was carried out using bis(tris(pyrazolyl)borate)calcium (CaTp2) and water as precursors. CaTp2 melts at 280 °C, undergoes solid state thermal decomposition at 385 °C, and sublimed on a preparative scale at 180 °C/0.05 Torr in about 3 hours with 99.7% recovery and 0.2% non-volatile residue. Self-limited ALD growth was established at 350 °C with CaTp2 and water pulse lengths of ≥2.0 and ≥0.3 s, respectively. An ALD window was observed from 300 to 375 °C, in which the growth rate was between 0.34 and 0.36 Å per cycle. The thin film compositions were assessed by elastic recoil detection analysis (ERDA) and X-ray photoelectron spectroscopy (XPS). The B/Ca ratios for CaB2O4 films deposited at 275, 325, 350, and 400 °C were 1.84(11), 1.85(11), 1.89(13), and 1.42(10), respectively, as determined by ERDA. Within the ALD window, hydrogen concentrations ranged from 0.22(2) to 0.35(4) atom% and the carbon and nitrogen concentrations were below the detection limits. XPS analyses on representative CaB2O4 thin films showed all expected ionizations. X-Ray diffraction experiments revealed that the as-deposited films were amorphous. The surface morphology was assessed by atomic force microscopy and scanning electron microscopy. The rms surface roughness of a typical 2 µm × 2 µm area for films deposited at 325 and 350 °C was 0.3 nm. Scanning electron micrographs of these films showed no cracks or pinholes.

Complexes of the [K(18-Crown-6)]+ Fragment with Bis(tetrazolyl)borate Ligands: Unexpected Boron−Nitrogen Bond Isomerism and Associated Enforcement of κ3-N,N′,H-Ligand Chelation

Co-reporter:Dongmei Lu

Inorganic Chemistry 2010 Volume 49(Issue 13) pp:5795-5797

Publication Date(Web):June 10, 2010

DOI:10.1021/ic100959j

The syntheses and solid-state structures of K(BH2(RCN4)2)(18-crown-6) (R = H, Me, NMe2, and NiPr2) are described. Complexes where R = H and Me have B−N bonds to N1 of the tetrazolyl groups and form one-dimensional polymers, whereas those with R = NMe2 and NiPr2 possess isomeric B−N bonds to N2 of the tetrazolyl moieties and adopt chelating κ3-N,N′,H-coordination modes to the potassium ion.

Highly Distorted κ3-N,N,H Bonding of Bis(3,5-di-tert-butylpyrazolyl)borate Ligands to the Heavier Group 2 Elements†

Co-reporter:Mark J. Saly and Charles H. Winter

Organometallics 2010 Volume 29(Issue 21) pp:5472-5480

Publication Date(Web):July 1, 2010

DOI:10.1021/om100434e

Treatment of MI2 (M = Ca, Sr, Ba) with two equivalents of thallium bis(3,5-di-tert-butylpyrazolyl)borate (TlBptBu2) in tetrahydrofuran at ambient temperature afforded CaBptBu22 (67%), SrBptBu22 (79%), and BaBptBu22(THF) (63%). Sublimation of BaBptBu22(THF) at 205 °C/0.05 Torr afforded BaBptBu22 (37%) along with loss of tetrahydrofuran. Crystal structure determinations of SrBptBu22, BaBptBu22(THF), and BaBptBu22 revealed monomeric structures containing highly distorted κ3-N,N,H-BptBu2 ligands. The M−N−N−B torsion angles in SrBptBu22, BaBptBu22(THF), and BaBptBu22 range from 20.00(8)° to 60.90(1)°, which indicate significant deformation of the 3,5-di-tert-butylpyrazolyl groups in order to avoid intraligand and interligand tert-butyl group steric repulsions. BH2(tBu2pz)(tBu2pzH) was prepared in 78% yield by treatment of Li(BptBu2)(THF) with pivalic acid, and its X-ray crystal structure was determined. To assess the viability of MBptBu22 (M = Ca, Sr, Ba) as potential thin-film growth precursors, solid-state decomposition studies, thermogravimetric analyses, and preparative sublimations were performed. SrBptBu22 is the most thermally stable among the series, with a solid-state decomposition temperature of 325 °C, a sublimation temperature of 190 °C/0.05 Torr, and a nonvolatile residue of 3.6% in a preparative sublimation. The TGA traces of CaBptBu22 and SrBptBu22 show weight loss regimes from 150 to 325 °C, with final percent residues of 20% and 25%, respectively. Several of the new complexes exhibit much higher thermal stability than existing group 2 chemical vapor deposition precursors and, thus, may serve as film growth precursors.

Atomic Layer Deposition Growth of BaB2O4 Thin Films from an Exceptionally Thermally Stable Tris(pyrazolyl)borate-Based Precursor

Co-reporter:Mark J. Saly, Frans Munnik, Ronald J. Baird and Charles H. Winter

Chemistry of Materials 2009 Volume 21(Issue 16) pp:3742

Publication Date(Web):August 4, 2009

DOI:10.1021/cm902030d

Volatility, High Thermal Stability, and Low Melting Points in Heavier Alkaline Earth Metal Complexes Containing Tris(pyrazolyl)borate Ligands

Co-reporter:Mark J. Saly, Mary Jane Heeg and Charles H. Winter

Inorganic Chemistry 2009 Volume 48(Issue 12) pp:5303-5312

Publication Date(Web):April 27, 2009

DOI:10.1021/ic900342j

Treatment of MI2 (M = Ca, Sr) or BaI2(THF)3 with 2 equiv of potassium tris(3,5-diethylpyrazolyl)borate (KTpEt2) or potassium tris(3,5-di-n-propylpyrazolyl)borate (KTpnPr2) in hexane at ambient temperature afforded CaTpEt22 (64%), SrTpEt22 (64%), BaTpEt22 (67%), CaTpnPr22 (51%), SrTpnPr22 (75%), and BaTpnPr22 (39%). Crystal structure determinations of CaTpEt22, SrTpEt22, and BaTpEt22 revealed monomeric structures. X-ray structural determinations for strontium tris(pyrazolyl)borate (SrTp2) and barium tris(pyrazolyl)borate ([BaTp2]2) show that SrTp2 exists as a monomer and [BaTp2]2 exists as a dimer containing two bridging Tp ligands. The thermogravimetric analysis traces, preparative sublimations, and melting point/decomposition determinations demonstrate generally very high thermal stabilities and reasonable volatilities. SrTp2 has the highest volatility with a sublimation temperature of 200 °C/0.05 Torr. [BaTp2]2 is the least thermally stable with a decomposition temperature of 330 °C and a percent residue of 46.5% at 450 °C in the thermogravimetric analysis trace. SrTpEt22, BaTpEt22, CaTpnPr22, SrTpnPr22, and BaTpnPr22 vaporize as liquids between 210 and 240 °C at 0.05 Torr. BaTpEt22 and BaTpnPr22 decompose at about 375 °C, whereas MTpEt22 and MTpnPr22 (M = Ca, Sr) are stable to >400 °C. Several of these new complexes represent promising precursors for chemical vapor deposition and atomic layer deposition film growth techniques.

Volatility and High Thermal Stability in Tantalum Complexes Containing Imido, Amidinate, and Halide or Dialkylamide Ligands

Co-reporter:Monika K. Wiedmann, Mary Jane Heeg and Charles H. Winter

Inorganic Chemistry 2009 Volume 48(Issue 12) pp:5382-5391

Publication Date(Web):May 8, 2009

DOI:10.1021/ic900454g

Treatment of Ta(NtBu)Cl3(py)2 with 2 equiv of Li(iPrNCMeNiPr) or Li(tBuNCMeNtBu) afforded Ta(NtBu)(iPrNCMeNiPr)2Cl and Ta(NtBu)(tBuNCMeNtBu)2Cl in 63% and 61% yields, respectively. Treatment of Ta(NtBu)(iPrNCMeNiPr)2Cl or Ta(NtBu)(tBuNCMeNtBu)2Cl with LiNRR′ afforded Ta(NtBu)(iPrNCMeNiPr)2(NRR′) and Ta(NtBu)(tBuNCMeNtBu)2(NRR′) in 79−92% yields (R, R′ = Me, Et). Treatment of Ta(NtBu)(tBuNCMeNtBu)2Cl with AgBF4 afforded Ta(NtBu)(tBuNCMeNtBu)2F in 54% yield, while treatment of Ta(NtBu)(tBuNCMeNtBu)2Cl with BBr3 afforded Ta(NtBu)(tBuNCMe-NtBu)2Br in 68% yield. X-ray crystal structures of Ta(NtBu)(tBuNCMeNtBu)2F and Ta(NtBu)(tBuNCMeNtBu)2Br revealed that the amidinate ligands exhibit η2-coordination, and that the imido and halide ligands are cis to each other within the distorted octahedral structures. NMR studies indicated that the other complexes have analogous structures. Additionally, variable temperature NMR studies revealed that some of the complexes undergo amidinate rearrangement. The enthalpies, entropies, and free energies of activation for these rearrangements were calculated for Ta(NtBu)(tBuNCMeNtBu)2X (X = F, Cl, Br). When X = F, ΔH‡ = 9.1 ± 0.4 kcal/mol, ΔS‡ = −20.5 ± 1.6 cal/mol·K, and ΔG‡(298 K) = 15.3 ± 0.7 kcal/mol. For X = Cl, ΔH‡ = 12.4 ± 0.3 kcal/mol, ΔS‡ = −20.2 ± 0.8 cal/mol·K, and ΔG‡(298 K) = 18.4 ± 0.3 kcal/mol. When X = Br, ΔH‡ = 12.5 ± 0.5 kcal/mol, ΔS‡ = −21.7 ± 1.5 cal/mol·K, and ΔG‡(298 K) = 19.0 ± 0.7 kcal/mol. All of the complexes are volatile, and they sublime between 120 and 203 °C. In addition, Ta(NtBu)(iPrNCMeNiPr)2NMe2 has a decomposition point that is 65−160 °C higher than widely used film growth precursors and is therefore a promising candidate for use in chemical vapor deposition and atomic layer deposition film growth techniques.

Volatility Enhancement in Calcium, Strontium, and Barium Complexes Containing β-Diketiminate Ligands with Dimethylamino Groups on the Ligand Core Nitrogen Atoms

Co-reporter:Baburam Sedai, Mary Jane Heeg and Charles H. Winter

Organometallics 2009 Volume 28(Issue 4) pp:1032-1038

Publication Date(Web):January 22, 2009

DOI:10.1021/om8006739

Treatment of M(N(SiMe3)2)2(THF)2 with 2 equiv of 4-(2,2-dimethylhydrazino)dimethylhydrazone-3-penten-2-one (LNMe2H) in toluene at ambient temperature afforded Ca(η2-LNMe2)2 (88%), [Sr(η5-LNMe2)(μ-η1:η5-LNMe2)]2 (85%), and [Ba(η5-LNMe2)(μ-η2:η3-LNMe2)]2 (83%) as colorless or pale yellow crystalline solids. The formulations of the new complexes were assigned from spectral and analytical data and by X-ray crystal structure determinations. In the solid state, Ca(η2-LNMe2)2 exists as a tetrahedral monomer. [Sr(η5-LNMe2)(μ-η1:η5-LNMe2)]2 is a dimer that contains a terminal η5-LNMe2 ligand on each strontium ion. The dimer is held together by two μ-η1:η5-LNMe2 ligands, in which one dimethylamino moiety per LNMe2 ligand acts as a donor ligand to the adjacent strontium ion. [Ba(η5-LNMe2)(μ-η2:η3-LNMe2)]2 crystallizes as a dimer that contains a terminal η5-LNMe2 ligand on each barium ion. The two bridging LNMe2 ligands adopt a μ-η2:η3-coordination mode, where each LNMe2 ligand is bonded to one barium ion through the in-plane nitrogen atom lone pairs and to the other barium ion through the out-of-plane π-system of one nitrogen and two carbon atoms. Ca(η2-LNMe2)2, [Sr(η5-LNMe2)(μ-η1:η5-LNMe2)]2, and [Ba(η5-LNMe2)(μ-η2:η3-LNMe2)]2 sublime at 90, 115, and 145 °C, respectively, at 0.05 Torr. These sublimation temperatures are 25 to 55 °C lower than those of previously reported analogous calcium, strontium, and barium complexes that contain isopropyl groups on the β-diketiminate ligand core nitrogen atoms. The increased volatility of complexes containing LNMe2 ligands is attributed to the lattice energy-lowering effects of the dimethylamino group lone pairs of electrons, much like what is observed in group 2 β-diketonate complexes containing fluorinated alkyl groups. The relevance to film growth precursor design is discussed.

Synthesis, structure, properties, volatility, and thermal stability of molybdenum(II) and tungsten(II) complexes containing allyl, carbonyl, and pyrazolate or amidinate ligands

Co-reporter:Oussama M. El-Kadri, Mary Jane Heeg, Charles H. Winter

Journal of Organometallic Chemistry 2009 694(24) pp: 3902-3911

Publication Date(Web):

DOI:10.1016/j.jorganchem.2009.08.001

A low valent metalorganic precursor for the growth of tungsten nitride thin films by atomic layer deposition

Co-reporter:Charles L. Dezelah, Oussama M. El-Kadri, Kaupo Kukli, Kai Arstila, Ronald J. Baird, Jun Lu, Lauri Niinistö and Charles H. Winter

Journal of Materials Chemistry A 2007 vol. 17(Issue 11) pp:1109-1116

Publication Date(Web):02 Jan 2007

DOI:10.1039/B610873C

The atomic layer deposition growth of tungsten nitride films was demonstrated using the precursors W2(NMe2)6 and ammonia with substrate temperatures between 150 and 250 °C. At 180 °C, surface saturative growth was achieved with W2(NMe2)6 pulse lengths of ≥2.0 s. The growth rates were between 0.74 and 0.81 Å cycle−1 at substrate temperatures between 180 and 210 °C. Growth rates of 0.57 and 0.96 Å cycle−1 were observed at 150 and 220 °C, respectively. In a series of films deposited at 180 °C, the film thicknesses varied linearly with the number of deposition cycles. Films grown at 180 and 210 °C exhibited resistivity values between 810 and 4600 μΩ cm. Time-of-flight elastic recoil detection analysis on tungsten nitride films containing a protective AlN overlayer demonstrated slightly nitrogen-rich films relative to W2N, with compositions of W1.0N0.82C0.13O0.26H0.33 at 150 °C, W1.0N0.74C0.20O0.33H0.28 at 180 °C, and W1.0N0.82C0.33O0.18H0.23 at 210 °C. In the absence of an AlN overlayer, the oxygen and hydrogen levels were much higher, suggesting that the films degrade in the presence of ambient atmosphere. The as-deposited films were amorphous. Amorphous films containing a protective AlN overlayer were annealed to 600–800 °C under a nitrogen atmosphere. X-Ray diffraction patterns suggested that crystallization does not occur at or below 800 °C. Similar annealing of films that did not contain the AlN overlayer afforded X-ray diffraction patterns that were consistent with orthorhombic WO3. Atomic force microscopy showed root-mean-square surface roughnesses of 0.9, 0.8, and 0.7 nm for films deposited at 150, 180, and 210 °C, respectively.

The growth of ErxGa2−xO3 films by atomic layer deposition from two different precursor systems

Co-reporter:Charles L. Dezelah, Pia Myllymäki, Jani Päiväsaari, Kai Arstila, Lauri Niinistö and Charles H. Winter

Journal of Materials Chemistry A 2007 vol. 17(Issue 13) pp:1308-1315

Publication Date(Web):12 Jan 2007

DOI:10.1039/B616443A

The atomic layer deposition (ALD) growth of ErxGa2−xO3 (0 ≤ x ≤ 2) thin films was demonstrated using two precursor systems: Er(thd)3, Ga(acac)3, and ozone and Er(C5H4Me)3, Ga2(NMe2)6, and water at substrate temperatures of 350 and 250 °C, respectively. Both processes provided uniform films and exhibited surface-limited ALD growth. The value of x in ErxGa2−xO3 was easily varied by selecting a pulse sequence with an appropriate erbium to gallium precursor ratio. The Er(thd)3, Ga(acac)3, and ozone precursor system provided stoichiometric ErxGa2−xO3 films with carbon, hydrogen, nitrogen, and fluorine levels of <0.2, <0.2, <0.3, and 0.6–2.2 atomic percent, respectively, as determined by Rutherford backscattering spectrometry (RBS) and time of flight-elastic recoil detection analysis (TOF-ERDA). The film growth rate was between 0.25 and 0.28 Å cycle−1. The effective permittivity of representative samples was between 10.8 and 11.3. The Er(C5H4Me)3, Ga2(NMe2)6, and water precursor system provided stoichiometric ErxGa2−xO3 films with carbon, hydrogen, nitrogen, and fluorine levels of 2.0–6.1, 5.0–10.3, <0.3–0.7, and ≤0.1 atom percent, respectively, as determined by RBS and TOF-ERDA. The film growth rate was between 1.0 and 1.5 Å cycle−1 and varied as a function of the Er(C5H4Me)3 to Ga2(NMe2)6 pulse ratio. The effective permittivity of representative samples was between 9.2 and 10.4. The as-deposited films of both precursor systems were amorphous, but crystallized either to Er3Ga5O12 or to a mixture of β-Ga2O3 and Er3Ga5O12 upon annealing between 900 and 1000 °C under a nitrogen atmosphere. Atomic force microscopy showed root mean square surface roughnesses of <1.0 nm for typical films regardless of precursor system or film composition.

Synthesis, structural characterization, and properties of chromium(III) complexes containing amidinato ligands and η2-pyrazolato, η2-1,2,4-triazolato, or η1-tetrazolato ligands

Co-reporter:Oussama M. El-Kadri, Mary Jane Heeg and Charles H. Winter

Dalton Transactions 2006 (Issue 37) pp:4506-4513

Publication Date(Web):31 Jul 2006

DOI:10.1039/B607903B

Treatment of anhydrous chromium(III) chloride with 2 or 3 equivalents of 1,3-di-tert-butylacetamidinatolithium or 1,3-diisopropylacetamidinatolithium in tetrahydrofuran at ambient temperature afforded Cr(tBuNC(CH3)NtBu)2(Cl)(THF) and Cr(iPrNC(CH3)NiPr)3 in 78% and 65% yields, respectively. Treatment of Cr(tBuNC(CH3)NtBu)2(Cl)(THF) with the potassium salts derived from pyrazoles and 1,2,4-triazoles afforded Cr(tBuNC(CH3)NtBu)2(X), where X = 3,5-disubstituted pyrazolato or 3,5-disubstituted 1,2,4-triazolato ligands, in 65–70% yields. X-Ray crystal structure analyses of Cr(tBuNC(CH3)NtBu)2(Me2pz) (Me2pz = 3,5-dimethylpyrazolato) and Cr(tBuNC(CH3)NtBu)2(Me2trz) (Me2trz = 3,5-dimethyl-1,2,4-triazolato) revealed η2-coordination of the Me2pz and Me2trz ligands. Treatment of Cr(tBuNC(CH3)NtBu)2(Cl)(THF) with trifluoromethyltetrazolatosodium (NaCF3tetz) in the presence of 4-tert-butylpyridine afforded Cr(tBuNC(CH3)NtBu)2(CF3tetz)(4-tBupy) in 30% yield. An X-ray crystal structure determination showed η1-coordination of the tetrazolato ligand through the 2-nitrogen atom. The complexes Cr(iPrNC(CH3)NiPr)3 and Cr(tBuNC(CH3)NtBu)2(X) are volatile and sublime with <1% residue between 120 and 165 °C at 0.05 Torr. In addition, these complexes are thermally stable at >300 °C under an inert atmosphere such as nitrogen or argon. Due to the good volatility and high thermal stability, these new compounds are promising precursors for the growth of chromium-containing thin films using atomic layer deposition.

Synthesis, structure and properties of volatile lanthanide complexes containing amidinate ligands: application for Er2O3 thin film growth by atomic layer deposition

Co-reporter:Jani Päiväsaari, Charles L. Dezelah, IV, Dwayne Back, Hani M. El-Kaderi, Mary Jane Heeg, Matti Putkonen, Lauri Niinistö and Charles H. Winter

Journal of Materials Chemistry A 2005 vol. 15(Issue 39) pp:4224-4233

Publication Date(Web):17 Aug 2005

DOI:10.1039/B507351K

Treatment of anhydrous rare earth chlorides with three equivalents of lithium 1,3-di-tert-butylacetamidinate (prepared in situ from the di-tert-butylcarbodiimide and methyllithium) in tetrahydrofuran at ambient temperature afforded Ln(tBuNC(CH3)NtBu)3 (Ln = Y, La, Ce, Nd, Eu, Er, Lu) in 57–72% isolated yields. X-Ray crystal structures of these complexes demonstrated monomeric formulations with distorted octahedral geometry about the lanthanide(III) ions. These new complexes are thermally stable at >300 °C, and sublime without decomposition between 180–220 °C/0.05 Torr. The atomic layer deposition of Er2O3 films was demonstrated using Er(tBuNC(CH3)NtBu)3 and ozone with substrate temperatures between 225–300 °C. The growth rate increased linearly with substrate temperature from 0.37 Å per cycle at 225 °C to 0.55 Å per cycle at 300 °C. Substrate temperatures of >300 °C resulted in significant thickness gradients across the substrates, suggesting thermal decomposition of the precursor. The film growth rate increased slightly with an erbium precursor pulse length between 1.0 and 3.0 s, with growth rates of 0.39 and 0.51 Å per cycle, respectively. In a series of films deposited at 250 °C, the growth rates varied linearly with the number of deposition cycles. Time of flight elastic recoil analyses demonstrated slightly oxygen-rich Er2O3 films, with carbon, hydrogen and fluorine levels of 1.0–1.9, 1.7–1.9 and 0.3–1.3 atom%, respectively, at substrate temperatures of 250 and 300 °C. Infrared spectroscopy showed the presence of carbonate, suggesting that the carbon and slight excess of oxygen in the films are due to this species. The as-deposited films were amorphous below 300 °C, but showed reflections due to cubic Er2O3 at 300 °C. Atomic force microscopy showed a root mean square surface roughness of 0.3 and 2.8 nm for films deposited at 250 and 300 °C, respectively.

Synthesis, Structure, and Properties of Zirconium and Hafnium Complexes Containing η2-Pyrazolato Ligands

Co-reporter:Elena Sebe;Ilia A. Guzei;Mary Jane Heeg;Louise M. Liable-Ss;Arnold L. Rheingold

European Journal of Inorganic Chemistry 2005 Volume 2005(Issue 19) pp:

Publication Date(Web):31 AUG 2005

DOI:10.1002/ejic.200500378

Treatment of tetrakis(dimethylamido)zirconium with four equiv. of 3,5-dimethylpyrazole, 3,5-di-tert-butylpyrazole, or 3,5-diphenylpyrazole in refluxing toluene afforded tetrakis(η²-3,5-dimethylpyrazolato)zirconium (86 %), tetrakis(η²-3,5-di-tert-butylpyrazolato)zirconium (88 %), and tetrakis(η²-3,5-diphenylpyrazolato)zirconium (85 %), respectively, as colorless crystalline solids. The analogous hafnium complexes were prepared through treatment of hafnium tetrachloride with four equiv. of the potassium salts of 3,5-dimethylpyrazolate, 3,5-di-tert-butylpyrazolate, or 3,5-diphenylpyrazolate in tetrahydrofuran to afford tetrakis(η²-3,5-dimethylpyrazolato)hafnium (75 %), tetrakis(η²-3,5-di-tert-butylpyrazolato)hafnium (58 %), and tetrakis(η²-3,5-diphenylpyrazolato)hafnium·toluene (38 %), respectively, as colorless crystalline solids. X-ray crystal structures of representative members of these complexes revealed monomeric species containing four η²-pyrazolato ligands and approximate dodecahedral geometry about the metal centers. Treatment of tetrakis(η²-3,5-dimethylpyrazolato)hafnium with 3,5-dimethylpyrazole in a 1:1 molar ratio afforded tris(η²-3,5-dimethylpyrazolato)(η¹-3,5-dimethylpyrazolato)(η¹-3,5-dimethylpyrazole)hafnium as colorless crystals (84 %). Tris(η²-3,5-dimethylpyrazolato)(η¹-3,5-dimethylpyrazolato)(η¹-3,5-dimethylpyrazole)hafnium contains three η²-3,5-dimethylpyrazolato, one η¹-3,5-dimethylpyrazolato, and one η¹-3,5-dimethylpyrazole ligands. The η¹-3,5-dimethylpyrazolato and η¹-3,5-dimethylpyrazole ligands are connected through a N–H···N hydrogen bond. Tetrakis(η²-3,5-dimethylpyrazolato)hafnium did not form an adduct with pyridine or tetrahydrofuran, suggesting that the formation of a hydrogen bond is important to the stability of adducts. Attempted sublimation of all of the new pyrazolato complexes led to some decomposition, as evidenced by the formation of the free pyrazoles in the sublimates and significant amounts of nonvolatile residues. This work greatly expands the number of zirconium and hafnium complexes that contain η²-pyrazolato ligands. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Synthesis, Structure, and Ligand Redistribution Equilibria of Mixed Ligand Complexes of the Heavier Group 2 Elements Containing Pyrazolato andβ-Diketiminato Ligands

Co-reporter:Hani M. El-Kaderi;Mary Jane Heeg

European Journal of Inorganic Chemistry 2005 Volume 2005(Issue 11) pp:

Publication Date(Web):1 JUN 2005

DOI:10.1002/ejic.200500087

Treatment of M[N(SiMe₃)₂]₂(THF)₂ (M = Ca, Sr, Ba) with various stoichiometries of N-tert-butyl-4-(tert-butylimino)-2-penten-2-amine (L^tBuH) and 3,5-di-tert-butylpyrazole (tBu₂pzH) afforded [(η²-tBu₂pz)Ca(μ-η⁵:η²-tBu₂pz)(μ-η²:η²-tBu₂pz)Ca(η⁵-L^tBu)] (17 %), [Sr(μ-η⁵:η²-tBu₂pz)(η⁵-L^tBu)]₂ (50 %), and [Ba(μ-η⁵:η²-tBu₂pz)(η⁵-L^tBu)]₂ (66 %) as colorless crystalline solids. The formulations of the new complexes were assigned from spectral and analytical data and by X-ray crystal structure determinations. In the solid state, [(η²-tBu₂pz)Ca(μ-η⁵:η²-tBu₂pz)(μ-η²:η²-tBu₂pz)Ca(η⁵-L^tBu)] exists as a dimer that is held together by μ-η⁵:η²- and μ-η²:η²-pyrazolato ligands, with a terminal η²-tBu₂pz ligand on one calcium ion and an η⁵-L^tBu ligand on the other. The dimeric structures of [Sr(μ-η⁵:η²-tBu₂pz)(η⁵-L^tBu)]₂ and [Ba(μ-η⁵:η²-tBu₂pz)(η⁵-L^tBu)]₂ are connected by two μ-η⁵:η²-pyrazolato ligands, and the coordination sphere of each metal ion is capped with an η⁵-L^tBu ligand. In toluene solution, [(η²-tBu₂pz)Ca(μ-η⁵:η²-tBu₂pz)(μ-η²:η²-tBu₂pz)Ca(η⁵-L^tBu)] exists as an equilibrium mixture of at least four compounds. In toluene solution, [Sr(μ-η⁵:η²-tBu₂pz)(η⁵-L^tBu)]₂ exists in equilibrium with Sr(η⁵-L^tBu)₂ and Sr₄(tBu₂pz)₈. A van’t Hoff analysis of this equilibrium between 46 and 104 °C afforded ΔH° = 22.2 ± 0.7 kcal/mol, ΔS° = 43.7 ± 1.9 cal/mol·K, and ΔG°(298 K) = 9.2 ± 0.9 kcal/mol. [Ba(μ-η⁵:η²-tBu₂pz)(η⁵-L^tBu)]₂ exists in toluene solution as a single, pure species between –60 and +80 °C. The overall results suggest that the η⁵-L^tBu ligand is better at saturating the coordination sphere of the metal ion to which it coordinates than is the tBu₂pz ligand, and is suggested as a more promising ligand for the construction of practical, volatile chemical vapor deposition film growth precursors. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Synthesis, Characterization, and Hydrolysis Products of (η2-tBu2pz)AlH(μ:η1,η1-tBu2pz)2AlH2 − Structural Characterization of a Complex Containing η1-, η2-, and μ:η1,η1-Pyrazolato Ligands and a Complex Containing a Terminal Hydroxo Ligand

Co-reporter:Zhengkun Yu;John E. Knox;Andrey V. Korolev;Mary Jane Heeg;H. Bernhard Schlegel;Charles H. Winter

European Journal of Inorganic Chemistry 2005 Volume 2005(Issue 2) pp:

Publication Date(Web):18 NOV 2004

DOI:10.1002/ejic.200400660

Treatment of alane−ethyldimethylamine with 3,5-di-tert-butylpyrazole (tBu₂pzH) in a 2:3 molar ratio afforded [(η²-tBu₂pz)AlH(μ:η¹,η¹-tBu₂pz)₂AlH₂] in 57% yield. Hydrolysis of [(η²-tBu₂pz)AlH(μ:η¹,η¹-tBu₂pz)₂AlH₂] afforded variable mixtures of Al(tBu₂pz)₃, [(η²-tBu₂pz)AlH(μ:η¹,η¹-tBu₂pz)₂AlH(OH)], and [(η²-tBu₂pz)AlH(μ:η¹,η¹-tBu₂pz)₂AlH(η¹-tBu₂pz)]. The structures of all new complexes were assigned from spectral and analytical data. In addition, the X-ray crystal structures of [(η²-tBu₂pz)AlH(μ:η¹,η¹-tBu₂pz)₂AlH(OH)] and [(η²-tBu₂pz)AlH(μ:η¹,η¹-tBu₂pz)₂AlH(η¹-tBu₂pz)] were determined. [(η²-tBu₂pz)AlH(μ:η¹,η¹-tBu₂pz)₂AlH(OH)] crystallizes as a dimeric molecule, and contains two bridging pyrazolato ligands, one η²-pyrazolato ligand, as well as terminal hydrido and hydroxo ligands. The hydroxo and η²-pyrazolato ligands possess a syn-relationship within the dimer. The hydroxy group proton does not participate in dihydrogen bonding, and instead appears to be intramolecularly hydrogen-bonded to the π-cloud of the η²-pyrazolato ligand. The overall structure of [(η²-tBu₂pz)AlH(μ:η¹,η¹-tBu₂pz)₂AlH(η¹-tBu₂pz)] is very similar to that of [(η²-tBu₂pz)AlH(μ:η¹,η¹-tBu₂pz)₂AlH(OH)], except that the η¹- and η²-pyrazolato ligands have an anti-disposition within the dimer. Molecular orbital calculations were carried out on [(η²-tBu₂pz)AlH(μ:η¹,η¹-tBu₂pz)₂AlH(OH)] to understand the hydrogen bonding and the η²-pyrazolato ligand coordination. The calculations predict that there is a 1.4 kcal/mol energy difference between η¹- and η²-pyrazolato ligand coordination, which implies that the observed η²-pyrazolato ligand occurs due to accommodation of the bulky tert-butyl groups. The intramolecular hydrogen bond between the hydroxo ligand proton and the π-cloud of the η²-pyrazolato ligand is estimated to have a bond strength of 3.7 kcal/mol. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Synthesis and structural characterization of unsymmetrical osmocenes containing the pentamethylcyclopentadienyl ligand

Co-reporter:Shamindri M. Arachchige, Mary Jane Heeg, Charles H. Winter

Journal of Organometallic Chemistry 2005 Volume 690(Issue 19) pp:4356-4365

Publication Date(Web):1 October 2005

DOI:10.1016/j.jorganchem.2005.07.039

Treatment of dibromo(pentamethylcyclopentadienyl)osmium(III) dimer with alkali metal salts of a variety of cyclopentadienyl derivatives provides a simple approach to the synthesis of unsymmetrical osmocenes containing the pentamethylcyclopentadienyl ligand. Furthermore, the reaction of dibromo(pentamethylcyclopentadienyl)osmium(III) with alkali metal salts of pyrrole and 3,5-di-tert-butylpyrazole afforded the corresponding pentamethylcyclopentadienylosmium complexes containing η5-pyrrolyl or η5-3,5-di-tert-butylpyrazolato ligands. This overall synthetic approach afforded pentamethylosmocene (64%), (η5-pentamethylcyclopentadienyl)(η5-indenyl)osmium (36%), (η5-pentamethylcyclopentadienyl)(η5-fluorenyl)osmium (30%), (η5-pyrrolyl)(η5-pentamethylyclopentadienyl)osmium (30%), and (η5-3,5-di-tert-butylpyrazolato)(η5-pentamethylcyclopentadienyl)osmium (38%). The new complexes were characterized by spectroscopic and analytical techniques, and by single crystal X-ray structural determinations. In the solid state, all of the new complexes exist as eclipsed metallocenes.Treatment of dibromo(pentamethylcyclopentadienyl)osmium(III) dimer with alkali metal salts of a variety of cyclopentadienyl derivatives provides a simple approach to pentamethylosmocene, (η5-pentamethylcyclopentadienyl)(η5-indenyl)osmium, (η5-pentamethylcyclopentadienyl)(η5-fluorenyl)osmium, (η5-pyrrolyl)(η5-pentamethylyclopentadienyl)osmium, and (η5-3,5-di-tert-butylpyrazolato)(η5-pentamethylcyclopentadienyl)osmium. The molecular structures have been determined by X-ray crystal structure analyses.

Synthesis and Characterization of Potassium Complexes Containing Terminal η2-Pyrazolato Ligands

Co-reporter:Wenjun Zheng;Mary Jane Heeg;Charles H. Winter

European Journal of Inorganic Chemistry 2004 Volume 2004(Issue 13) pp:

Publication Date(Web):26 APR 2004

DOI:10.1002/ejic.200400025

The potassium complexes [K(η²-3,5-R₂pz)(η⁶-18-crown-6)] (R = Ph, tBu; pz = pyrazolato) were prepared by treatment of 3,5-diphenylpyrazole or 3,5-di-tert-butylpyrazole with potassium hydride in the presence of 18-crown-6. These complexes contain η⁶-18-crown-6 and terminal η²-pyrazolato ligands, and constitute the first examples of group 1 metal complexes with this pyrazolato ligand coordination mode. In contrast to [K(η²-3,5-Ph₂pz)(η⁶-18-crown-6)] and [K(η²-3,5-tBu₂pz)(η⁶-18-crown-6)], the aqua complex [K(η²-3,5-Me₂pz)(H₂O)(η⁶-18-crown-6)] was obtained when 3,5-dimethylpyrazole was treated with potassium hydride and 18-crown-6 in the presence of a small amount of water. [K(η²-3,5-Me₂pz)(H₂O)(η⁶-18-crown-6)] contains an η²-pyrazolato ligand that is bent towards being co-facial with the best plane of the 18-crown-6 ligand, to allow hydrogen bonding between the pyrazolato ligand nitrogen atoms and the coordinated aqua ligand. The hydrogen bonding thus confers a novel terminal π-facial η²-bonding mode to the pyrazolato ligand. All compounds were characterized by elemental analysis, NMR spectroscopy, and mass spectrometry. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Synthesis, structure, and properties of magnesium complexes containing cyclopentadienyl and amidinate ligand sets

Co-reporter:Aibing Xia, Hani M El-Kaderi, Mary Jane Heeg, Charles H Winter

Journal of Organometallic Chemistry 2003 Volume 682(1–2) pp:224-232

Publication Date(Web):1 October 2003

DOI:10.1016/S0022-328X(03)00787-3

N,N′-Bis(2,6-diisopropylphenyl)(tert-butyl)amidine and N,N′-bis(2,4,6-trimethyl-phenyl)(tert-butyl)amidine were prepared and treated with [CpMgMe(Et2O)]2 in diethyl ether or tetrahydrofuran to afford the monomeric amidinate complexes [CpMg(η2-tBuC(N(2,6-iPr2C6H3))2] (87%) and [CpMg(η2-tBuC(N(2,4,6-Me3C6H2))2)(THF)] (76%). The solid-state structures of the amidines and resultant magnesium complexes were determined by X-ray diffraction methods. In the solid-state, the magnesium complexes are monomeric and contain one η5-cyclopentadienyl ligand and one η2-amidinate ligand, as well as one tetrahydrofuran ligand for the latter. [CpMg(η2-tBuC(N(2,6-iPr2C6H3))2)] can be sublimed unchanged with 80% recovery at 180 °C/0.05 torr, while [CpMg(η2-tBuC(N(2,4,6-Me3C6H2))2)(THF)] decomposes to Cp2Mg (77%) and [Mg(η2-tBuC(N(2,4,6-Me3C6H2)))2] (83%) under similar conditions. [Mg(η2-tBuC(N(2,4,6-Me3C6H2)))2] was prepared independently through treatment of dibutylmagnesium with two equivalents of N,N′-bis(2,4,6-trimethylphenyl)(tert-butyl)amidine in toluene at ambient temperature.Treatment of [CpMgCH3(Et2O)]2 with two new bulky amidines affords the complexes [CpMg(η2-tBuC(N(2,6-iPr2C6H3))2] (87%) and [CpMg(η2-tBuC(N(2,4,6-Me3C6H2))2)(THF)] (76%). [CpMg(η2-tBuC(N(2,6-iPr2C6H3))2)] can be sublimed unchanged with 80% recovery at 180 °C/0.05 torr, while [CpMg(η2-tBuC(N(2,4,6-Me3C6H2))2)(THF)] decomposes to Cp2Mg (77%) and [Mg(η2-tBuC(N(2,4,6-Me3C6H2)))2] (83%) under similar conditions. The molecular structures were determined by single crystal X-ray analyses.

Coordination of 3,5-Diisopropyl-1,2,4-triazolato and 5-Phenyltetrazolato Ligands to the [K([18]crown-6)]+ Fragment: Structural Insight into the Coordination of Nitrogen-Rich Azolato Ligands to Single Metal Centers

Co-reporter:Wenjun Zheng Dr.;Mary Jane Heeg Dr. Professor Dr.

Angewandte Chemie 2003 Volume 115(Issue 24) pp:

Publication Date(Web):17 JUN 2003

DOI:10.1002/ange.200250485

Durch asymmetrische η²-Koordination über zwei Stickstoffdonoren binden die heterocyclischen Liganden in K([18]Krone-6)-diisopropyltriazolat und K([18]Krone-6)-phenyltetrazolat an das Kaliumion (siehe Bild). Die Verbindungen sind Beispiele für die seltene terminale η²-Koordination stickstoffreicher Azolatliganden.

Co-reporter:Wenjun Zheng Dr.;Mary Jane Heeg Dr. Professor Dr.

Angewandte Chemie International Edition 2003 Volume 42(Issue 24) pp:

Publication Date(Web):17 JUN 2003

DOI:10.1002/anie.200250485

Potassium slips a disk: A novel slipped η²-coordination mode with differing KN separations is found in the complexes (3,5-diisopropyltriazolato)([18]crown-6)potassium and (phenyltetrazolato)([18]crown-6)potassium (see diagram), which are thus extremely rare examples of terminal η² coordination of nitrogen-rich azolato ligands.

Synthesis, Structure, and Molecular Orbital Calculations of (Pyrazolato)vanadium(III) Complexes − Understanding η2-Pyrazolato Ligand Coordination on d2 Metal Centers

Co-reporter:Karl R. Gust;John E. Knox;Mary Jane Heeg;H. Bernhard Schlegel;Charles H. Winter

European Journal of Inorganic Chemistry 2002 Volume 2002(Issue 9) pp:

Publication Date(Web):7 AUG 2002

DOI:10.1002/1099-0682(200209)2002:9<2227::AID-EJIC2227>3.0.CO;2-F

The cover picture shows the structures of several vanadium(III) complexes that contain η²-pyrazolato ligands, along with orbital interactions that stabilize the η²-pyrazolato ligand bonding mode. Details are discussed in the article by C. H. Winter et al. on p. 2327 ff.

Synthesis, Structure, and Molecular Orbital Calculations of (Pyrazolato)vanadium(III) Complexes − Understanding η2-Pyrazolato Ligand Coordination on d2 Metal Centers

Co-reporter:Karl R. Gust;John E. Knox;Mary Jane Heeg;H. Bernhard Schlegel;Charles H. Winter

European Journal of Inorganic Chemistry 2002 Volume 2002(Issue 9) pp:

Publication Date(Web):2 AUG 2002

DOI:10.1002/1099-0682(200209)2002:9<2327::AID-EJIC2327>3.0.CO;2-9

Treatment of trichlorotris(tetrahydrofuran)vanadium(III) with (3,5-di-tert-butylpyrazolato)potassium (1, 2, or 3 equiv.) in tetrahydrofuran afforded V(tBu₂Pz)Cl₂(THF)₂ (48%), V(tBu₂Pz)₂Cl(THF)₂ (67%), and V(tBu₂Pz)₃(THF) (77%), respectively, as purple crystalline solids. The X-ray crystal structures of V(tBu₂Pz)Cl₂(THF)₂, V(tBu₂Pz)₂Cl(THF)₂, and V(tBu₂Pz)₃(THF) reveal six- and seven-coordinate vanadium centers with η²-pyrazolato ligands. Molecular orbital calculations were carried out to understand the electronic nature of pyrazolato coordination to transition metal centers containing d electrons. It is demonstrated that η²-pyrazolato ligand coordination occurs through interaction of filled symmetric and antisymmetric combinations of the nitrogen lone pairs with empty d_z and d_yz orbitals. The complexes described herein are the first examples of η²-pyrazolato ligand coordination to a d² metal center. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Synthesis, Structure, and Molecular Orbital Calculations of Chromium(III) and Iron(III) Complexes Containing η2-Pyrazolato Ligands

Co-reporter:Karl R. Gust;John E. Knox;Mary Jane Heeg Dr.;H. Bernhard Schlegel Dr. Dr.

Angewandte Chemie International Edition 2002 Volume 41(Issue 9) pp:

Publication Date(Web):2 MAY 2002

DOI:10.1002/1521-3773(20020503)41:9<1591::AID-ANIE1591>3.0.CO;2-D

η² coordination of pyrazolato ligands is currently unknown for d-block metal complexes with d² or higher electronic configurations, and all known Group 6–11 metal–pyrazolato complexes contain η¹, μ:η¹,η¹, or η⁵ ligands. Tris(3,5-di-tert-butylpyrazolato)chromium(III) and tris(3,5-di-tert-butylpyrazolato)iron(III) (see picture), which contain η²-pyrazolato ligands, have been synthesized, and molecular-orbital calculations indicate that η²-pyrazolato coordination is less stable than η¹ coordination in a model iron(III) complex.

A bridging ethyl complex of aluminium

Co-reporter:Zhengkun Yu, Mary Jane Heeg and Charles H. Winter

Chemical Communications 2001 (Issue 4) pp:353-354

Publication Date(Web):07 Feb 2001

DOI:10.1039/B008047K

Treatment of triethylaluminium (2 equiv.) with diphenylpyrazole (1 equiv) affords a pyrazolate-bridged dialuminium complex that contains a bridging ethyl group between the two aluminium centers; this complex has been structurally characterized and its reactivity and properties are described.

The growth of ErxGa2−xO3 films by atomic layer deposition from two different precursor systems

Co-reporter:Charles L. Dezelah, Pia Myllymäki, Jani Päiväsaari, Kai Arstila, Lauri Niinistö and Charles H. Winter

Journal of Materials Chemistry A 2007 - vol. 17(Issue 13) pp:NaN1315-1315

Publication Date(Web):2007/01/12

DOI:10.1039/B616443A

A low valent metalorganic precursor for the growth of tungsten nitride thin films by atomic layer deposition

Co-reporter:Charles L. Dezelah, Oussama M. El-Kadri, Kaupo Kukli, Kai Arstila, Ronald J. Baird, Jun Lu, Lauri Niinistö and Charles H. Winter

Journal of Materials Chemistry A 2007 - vol. 17(Issue 11) pp:NaN1116-1116

Publication Date(Web):2007/01/02

DOI:10.1039/B610873C

Atomic layer deposition of CaB2O4 films using bis(tris(pyrazolyl)borate)calcium as a highly thermally stable boron and calcium source

Co-reporter:Mark J. Saly, Frans Munnik and Charles H. Winter