•Disposable, colorimetric probe for 1.35-L of H2S gas.•Safe, green, more sensitive alternative to the commonly used Pb-based test papers.•Enhanced sensitivity with a base and moist coating to trap weakly acidic H2S.Hydrogen sulfide (H2S) is a regulated industrial hazard, as it is a chemical asphyxiant with acute toxicity. The characteristic rotten egg smell of hydrogen sulfide is not a suitable indicator for the presence of the gas, as the olfactory system is often overwhelmed and desensitized to the gas. A new probe utilizing the copper(II) complex of 1-(2-pyridylazo)-2-naphthol (Cu-PAN) on a moist, porous, paper-like substrate has been developed to replace commercial lead acetate-based test papers for the detection of hydrogen sulfide gas at low concentrations. The reaction between H2S gas and the copper complex produces a distinct color change from purple to yellow/orange. The color change is observable to the naked eye for concentrations as low as 30 ppb H2S in a small, 1.35-L of gas, a typical volume of human breath. In comparison, the commercial Pb(II)(acetate)2 test papers require large volumes of 5 ppm H2S gas. Incorporation of a base in the current probe aids in trapping weakly acidic H2S. The moist probe enhances the kinetics of the reaction between H2S gas and the base/Cu-PAN. These features increase the sensitivity of the probe, making it potentially suitable for both human breath tests and industrial H2S monitoring. The utilization of a handheld colorimeter allows for quantitative analysis of gaseous H2S, with a limit of detection (LoD) of 16 ppb and a limit of quantification (LoQ) of 53 ppb. The probe, offering rapid detection, is easy to prepare, inexpensive, disposable, and a green alternative to the commonly used lead acetate test papers.Download high-res image (75KB)Download full-size image

•NMR chemical shifts of d0 transition metal compounds show two trends.•α Atoms of single-bonded ligands in 1st & 3rd row complexes are less shielded than 2nd row analogs.•α Atoms of multiple-bonded ligands are more shielded down a group in the periodic table.•NMR shifts of lanthanum(III) complexes help interpret Trend 1 in Group 3 congeners.•Scandide and lanthanide contractions and relativistic effects are used to explain the trends.NMR chemical shifts of d0 transition metal compounds show the following trends: (1) For single-bonded ligands such as M-H, M-CR3, M←NR3, M-SiR3 and M←PR3, 1H, 13C, 15N, 29Si and 31P shifts of these α atoms in the complexes of both first- and third-row transition metals are typically downfield from (or at higher frequencies than) those of second-row analogs with a “V-shape” (Trend 1). (2) For multiple-bonded ligands including those with d-p π bonds, such as M=CHR, M≡CR, M=NR, M=O and MF, 13C, 15N, 17O and 19F shifts of the α atoms in the complexes of first-, second- and third-row transition metals move consecutively upfield (or to lower frequencies) (Trend 2). NMR shifts of lanthanum(III) complexes help interpret Trend 1 in Group 3 congeners. Scandide (d-block) and lanthanide (f-block) contractions and relativistic effects are believed to contribute to the NMR shifts, leading to the observed trends. Comparisons are made with NMR chemical shifts of dn complexes and organic compounds. Since many chemical properties of the second- and third-row congeners such as Zr and Hf are similar, as a result of lanthanide contraction, the NMR chemical shifts are a rare property to distinguish compounds of the otherwise nearly identical congeners. The current paper points out the trends with our narrative interpretations of the trends.NMR chemical shifts of (Left) single-bonded complexes and (Right) double-bonded complexes. NMR chemical shifts of d0, first-, second- and third-row transition metal compounds show two unique trends for single-bonded and multiple-bonded ligands, respectively. Scandide (d-block) and lanthanide (f-block) contractions and relativistic effects are believed to contribute to the NMR shifts, leading to the observed trends.Download high-res image (173KB)Download full-size image

A new sensor for the detection of hydrogen sulfide (H2S) gas has been developed to replace commercial lead(II) acetate-based test papers. The new sensor is a wet, porous, paper-like substrate coated with Bi(OH)3 or its alkaline derivatives at pH 11. In contrast to the neurotoxic lead(II) acetate, bismuth is used due to its nontoxic properties, as Bi(III) has been a reagent in medications such as Pepto-Bismol. The reaction between H2S gas and the current sensor produces a visible color change from white to yellow/brown, and the sensor responds to ≥30 ppb H2S in a total volume of 1.35 L of gas, a typical volume of human breath. The alkaline, wet coating helps the trapping of acidic H2S gas and its reaction with Bi(III) species, forming colored Bi2S3. The sensor is suitable for testing human bad breath and is at least 2 orders of magnitude more sensitive than a commercial H2S test paper based on Pb(II)(acetate)2. The small volume of 1.35-L H2S is important, as the commercial Pb(II)(acetate)2-based paper requires large volumes of 5 ppm H2S gas. The new sensor reported here is inexpensive, disposable, safe, and user-friendly. A simple, laboratory setup for generating small volumes of ppb–ppm of H2S gas is also reported.

Three mononuclear cobalt(II) tetranitrate complexes (A)2[Co(NO3)4] with different countercations, Ph4P+ (1), MePh3P+ (2), and Ph4As+ (3), have been synthesized and studied by X-ray single-crystal diffraction, magnetic measurements, inelastic neutron scattering (INS), high-frequency and high-field EPR (HF-EPR) spectroscopy, and theoretical calculations. The X-ray diffraction studies reveal that the structure of the tetranitrate cobalt anion varies with the countercation. 1 and 2 exhibit highly irregular seven-coordinate geometries, while the central Co(II) ion of 3 is in a distorted-dodecahedral configuration. The sole magnetic transition observed in the INS spectroscopy of 1–3 corresponds to the zero-field splitting (2(D2 + 3E2)1/2) from 22.5(2) cm–1 in 1 to 26.6(3) cm–1 in 2 and 11.1(5) cm–1 in 3. The positive sign of the D value, and hence the easy-plane magnetic anisotropy, was demonstrated for 1 by INS studies under magnetic fields and HF-EPR spectroscopy. The combined analyses of INS and HF-EPR data yield the D values as +10.90(3), +12.74(3), and +4.50(3) cm–1 for 1–3, respectively. Frequency- and temperature-dependent alternating-current magnetic susceptibility measurements reveal the slow magnetization relaxation in 1 and 2 at an applied dc field of 600 Oe, which is a characteristic of field-induced single-molecule magnets (SMMs). The electronic structures and the origin of magnetic anisotropy of 1–3 were revealed by calculations at the CASPT2/NEVPT2 level.

•Direct Pd(II) electroanalysis in pharmaceutical ingredients without pretreatment.•First electroanalysis of a catalytic metal in a DMSO-based solution.•Unmodified glassy carbon electrodes in both aqueous and DMSO solutions.•LODs in the μg L−1 (ppb) range in the presence of pharmaceutical ingredients.•Sensitive, robust, and inexpensive alternative to ICP-based approaches.Anodic stripping voltammetry, a classical electroanalytical method has been optimized to analyze trace Pd(II) in active pharmaceutical ingredient matrices. The electroanalytical approach with an unmodified glassy carbon electrode was performed in both aqueous and 95% DMSO/5% water (95/5 DMSO/H2O) solutions, without pretreatment such as acid digestion or dry ashing to remove the organics. Limits of detection (LODs) in the presence of caffeine and ketoprofen were determined to be 11 and 9.6 μg g−1, with a relative standard deviation (RSD) of 5.7% and 2.3%, respectively. This method is simple, highly reproducible, sensitive, and robust. The instrumentation has the potential to be portable and the obviation of sample pretreatment makes it an ideal approach for determining lost catalytic metals in pharmaceutical-related industries. Furthermore, the simultaneous detection of Pd(II) with Cd(II) and Pb(II) in the low μg L−1 range indicates that this system is capable of simultaneous multi-analyte analysis in a variety of matrices.

•Cr(VI) detection: 5–300 μg L− 1 range; 0.8 μg L− 1 detection limit•Sol-gel thin film electrodeposited over a carboxylated SWNT layer on GCE surface•Sol-gel doped with 2-pyridinium to preconcentrate HCrO4−•Lowering detection limit by three orders of magnitude through the use of SWNTsA pyridine-functionalized thin film has been fabricated to selectively preconcentrate Cr(VI) anions for electrochemical detection in the 5–300 μg L− 1 range. Glassy carbon electrodes were modified through physical deposition of single-walled carbon nanotubes (SWNTs) on the electrode surface, followed by electrochemical deposition of a sol-gel containing a 2-pyridine functional group. The use of SWNTs has increased sensitivity for Cr(VI) detection in aqueous solutions, providing a detection limit of 0.8 μg L− 1.

Zr(NR2)2[MeC(NiPr)2]2 (R = Me, 1; Et, 2) have been prepared through aminolysis and their reactions with O2 and water have been studied. Two major products from the reactions are the oxo dimer {(μ-O)Zr[MeC(NiPr)2]2}2 (3) and its insoluble polymer {(μ-O)Zr[MeC(NiPr)2]2}n (4). Over time the dimer 3 polymerizes to 4. Zr peroxo trimer {(μ-η2:η2-O2)Zr[MeC(NiPr)2]2}3 (5) was also observed from the reaction of 1 with O2 and its crystal structure is reported. DFT calculations show that the reaction of 1 with O2 follows a radical process, yielding the peroxo trimer 5. Mass spectrometric studies of the reactions of water in air with 1 and 2 show the formation of the oxo monomer (O=)Zr[MeC(NiPr)2]2 (6), oxo dimer {(μ-O)Zr[MeC(NiPr)2]2}2 (3), and the dihydroxy monomer (HO)2Zr[MeC(NiPr)2]2 (7). In addition, the cations {Zr(NR2)[MeC(NiPr)2]2}+ (R = Me, Et) were observed. 2 revealed an interesting dynamic NMR behavior. Variable-temperature (VT) NMR spectroscopy has been used to study the Bailar twist process in 2, giving activation parameters ΔH‡ = 10.9(1.1) kcal mol−1, ΔS‡ = −11(4) eu and ΔG‡303 K = 14(2) kcal mol−1.Zr(NMe2)2[MeC(NiPr)2]2 (1) reacts with O2 forming peroxo trimer {(μ-η2:η2-O2)Zr[MeC(NiPr)2]2}3 and then oxo dimer {(μ-O)Zr[MeC(NiPr)2]2}2 and its insoluble polymer {(μ-O)Zr[MeC(NiPr)2]2}n through a radical process, as DFT studies show. Reaction of 1 with H2O yields dihydroxy monomer (HO)2Zr[MeC(NiPr)2]2, oxo monomer (O=)Zr[MeC(NiPr)2]2, and the dimer, as revealed by MS.

Optical thin film sensors have been developed to detect chloroform in aqueous and nonaqueous solutions. These sensors utilize a modified Fujiwara reaction, one of the only known methods for detecting halogenated hydrocarbons in the visible spectrum. The modified Fujiwara reagents, 2,2′-dipyridyl and tetra-n-butyl ammonium hydroxide (n-Bu4NOH or TBAH), are encapsulated in an ethyl cellulose (EC) or sol–gel film. Upon exposure of the EC sensor film to HCCl3 in petroleum ether, a colored product is produced within the film, which is analyzed spectroscopically, yielding a detection limit of 0.830 ppm (parts per million v/v or μL/L hereinafter) and a quantification limit of 2.77 ppm. When the chloroform concentration in pentane is ≥5 ppm, the color change of the EC sensor is visible to the naked eye. In aqueous chloroform solution, reaction in the sol–gel sensor film turns the sensor from colorless to dark yellow/brown, also visible to the naked eye, with a detection limit of 500 ppm. This is well below the solubility of chloroform in water (ca. 5,800 ppm). To our knowledge, these are the first optical quality thin film sensors using Fujiwara reactions for halogenated hydrocarbon detection.

Zero-field splitting (ZFS) parameters of nondeuterated metalloporphyrins [Fe(TPP)X] (X = F, Br, I; H2TPP = tetraphenylporphyrin) have been directly determined by inelastic neutron scattering (INS). The ZFS values are D = 4.49(9) cm–1 for tetragonal polycrystalline [Fe(TPP)F], and D = 8.8(2) cm–1, E = 0.1(2) cm–1 and D = 13.4(6) cm–1, E = 0.3(6) cm–1 for monoclinic polycrystalline [Fe(TPP)Br] and [Fe(TPP)I], respectively. Along with our recent report of the ZFS value of D = 6.33(8) cm–1 for tetragonal polycrystalline [Fe(TPP)Cl], these data provide a rare, complete determination of ZFS parameters in a metalloporphyrin halide series. The electronic structure of [Fe(TPP)X] (X = F, Cl, Br, I) has been studied by multireference ab initio methods: the complete active space self-consistent field (CASSCF) and the N-electron valence perturbation theory (NEVPT2) with the aim of exploring the origin of the large and positive zero-field splitting D of the 6A1 ground state. D was calculated from wave functions of the electronic multiplets spanned by the d5 configuration of Fe(III) along with spin–orbit coupling accounted for by quasi degenerate perturbation theory. Results reproduce trends of D from inelastic neutron scattering data increasing in the order from F, Cl, Br, to I. A mapping of energy eigenvalues and eigenfunctions of the S = 3/2 excited states on ligand field theory was used to characterize the σ- and π-antibonding effects decreasing from F to I. This is in agreement with similar results deduced from ab initio calculations on CrX63– complexes and also with the spectrochemical series showing a decrease of the ligand field in the same directions. A correlation is found between the increase of D and decrease of the π- and σ-antibonding energies eλX (λ = σ, π) in the series from X = F to I. Analysis of this correlation using second-order perturbation theory expressions in terms of angular overlap parameters rationalizes the experimentally deduced trend. D parameters from CASSCF and NEVPT2 results have been calibrated against those from the INS data, yielding a predictive power of these approaches. Methods to improve the quantitative agreement between ab initio calculated and experimental D and spectroscopic transitions for high-spin Fe(III) complexes are proposed.

•Direct Cd2+ and Pb2+ analysis/quantification in pharmaceutical ingredients.•No acid digestion/dry ashing and an inexpensive alternative to ICP-based analyses.•Electroanalysis on unmodified glassy C electrodes in aqueous and DMSO/H2O solutions.•First heavy metal analysis in DMSO/water solutions by anodic stripping voltammetry.•LODs in the μg L−1 (ppb) range in the presence of organic matrices.A new electrochemical method has been developed to detect and quantify the elemental impurities, cadmium(II) (Cd2+) and lead(II) (Pb2+), either simultaneously or individually in pharmaceutical matrices. The electro-analytical approach, involving the use of anodic stripping voltammetry (ASV) on an unmodified glassy carbon electrode, was performed in both aqueous and in a 95/5 dimethyl sulfoxide (DMSO)/water solutions, without acid digestion or dry ashing to remove organic matrices. Limits of detection (LODs) in the μg L−1 [or parts per billion (ppb), mass/volume] range were obtained for both heavy metals - in the presence and absence of representative pharmaceutical components. To the best of our knowledge, the work demonstrates the first analysis of heavy metals in DMSO/water solutions through ASV. The strong reproducibility and stability of the sensing platform, as well as obviation of sample pretreatment show the promise of utilizing ASV as a sensitive, robust, and inexpensive alternative to inductively-coupled-plasma (ICP)-based approaches for the analysis of elemental impurities in, e.g., pharmaceutical-related matrices.

Reaction of TaCl2(═NSiMe3)[N(SiMe3)2] (1) with alkylating reagents form the alkyl amide imide complexes TaR2(═NSiMe3)[N(SiMe3)2] (R = Me (2), CH2Ph (3)) and mixed amide imide compounds Ta(NR′2)2(═NSiMe3)[N(SiMe3)2] (R′ = Me (4), Et (5)). The reaction of 2 and 0.5 equiv of O2 leads to preferential oxygen insertion into one Ta–Me bond, yielding the alkoxy-bridged alkyl dimer Ta2(μ-OMe)2Me2(═NSiMe3)2[N(SiMe3)2]2 (6) as cis and trans isomers. Crystallization of the cis-6 and trans-6 mixture gave only crystals of trans-6. When the crystals of trans-6 were dissolved in benzene-d6, conversion of trans-6 to cis-6 occurred until the trans-6 ⇌ cis-6 equilibrium was reached with Keq = 0.79(0.02) at 25.0(0.1) °C. Kinetic studies of the exchange gave the rate constants k = 0.018(0.002) min–1 for the trans-6 → cis-6 conversion and k′ = 0.022(0.002) min–1 for the reverse cis-6 → trans-6 conversion at 25.0(0.1) °C. Complex 6 reacts with additional O2, forming the dialkoxy dimer Ta2(μ-OMe)2(OMe)2(═NSiMe3)2[N(SiMe3)2]2 (7) as cis and trans isomers. Solid-state structures of 3 and trans-6 have been determined by X-ray diffraction analyses. The mixed amide imide compounds Ta(NR′2)2(═NSiMe3)[N(SiMe3)2] (R′ = Me (4), Et (5)) have also been prepared by salt metathesis reactions employing TaCl3[N(SiMe3)2]2 (8). The pathway from 8 to 4 and 5 eliminates Me3Si–NR′2 (R′ = Me, Et), converting the amide N(SiMe3)2 ligand to the imide ═NSiMe3 ligand. Such intramolecular imidation is rare. The mechanism of this process has been computationally probed, and α-elimination involving the mixed amide species TaCl2(NMe2)[N(SiMe3)2]2 (9) is discussed. Diffusion-ordered spectroscopy (DOSY) studies of 1–6 and 8 show that only the alkoxy-bridged cis-6 and trans-6 are dimers in benzene-d6 solution at 25 °C.

Reaction of d0 Zr(NMe2)2[MeC(NiPr)2]2 (1) with O2 at −30 °C gives three Zr containing products: a peroxo trimer {(μ-η2:η2-O2)Zr[MeC(NiPr)2]2}3 (2), an oxo dimer {(μ-O)Zr[MeC(NiPr)2]2}2 (3), and an oxo polymer {(μ-O)Zr[MeC(NiPr)2]2}n (4). 2 is a rarely observed peroxo complex from the reaction of a d0 complex with O2.

Zero field splitting (ZFS) parameters of several nondeuterated metalloporphyrins [M(TPP)Cl] and [Mn(TPP)] (H2TPP = tetraphenylporphyrin) have been directly determined by inelastic neutron scattering (INS). The ZFS values are the following: D = 6.33(8) cm–1 for [Fe(TPP)Cl], −2.24(3) cm–1 for [Mn(TPP)Cl], 0.79(2) cm–1 for [Mn(TPP)], and |D|= 0.234(12) cm–1 for [Cr(TPP)Cl]. The work shows that compounds with magnetic excitations below ∼30 cm–1 could be determined using nondeuterated samples.

A variable-temperature (VT) crystal structure study of [Fe(TPP)Cl] (TPP2– = meso-tetraphenylporphyrinate) and Hirshfeld surface analyses of its structures and previously reported structures of [M(TPP)(NO)] (M = Fe, Co) reveal that intermolecular interactions are a significant factor in structure disorder in the three metalloporphyrins and phase changes in the nitrosyl complexes. These interactions cause, for example, an 8-fold disorder in the crystal structures of [M(TPP)(NO)] at room temperature that obscures the M–NO binding. Hirshfeld analyses of the structure of [Co(TPP)(NO)] indicate that the phase change from I4/m to P1̅ leads to an increase in void-volume percentage, permitting additional structural compression through tilting of the phenyl rings to offset the close-packing interactions at the interlayer positions in the crystal structures with temperature decrease. X-ray and neutron structure studies of [Fe(TPP)Cl] at 293, 143, and 20 K reveal a tilting of the phenyl groups away from being perpendicular to the porphyrin ring as a result of intermolecular interactions. Structural similarities and differences among the three complexes are identified and described by Hirshfeld surface and void-volume calculations.

(Me3SiCH2)3(Me3SiC)W←OPMe3 (1), an adduct between (Me3SiCH2)3WCSiMe3 (2) and OPMe3, reacts with O2 to give OW(OSiMe3)(CH2SiMe3)3 (3) and CO2. Reaction of 2 with H2O yields 3 and the trimer [(μ-O)W(CH2SiMe3)2(O)(THF)]3 (4). In the reaction of D2O with 2, 3-dn and methane isotopologues CH2D2, CHD3 and CD4 have been observed.

The ability to detect biodiesel at various concentrations in diesel is an important goal in several industries. A simple, solvatochromic dye-doped optical sensor is presented for quick and direct detection of 0.5 ppm–20% v/v FAME/biodiesel in diesel.

Reactions of the zirconium amide guanidinates (R2N)2M[iPrNC(NR2)NiPr]2 (R = Me, M = Zr, 1; M = Hf, 2; R = Et, M = Zr, 3) with O2 or H2O give products that are consistent with the oxo dimers {M(μ-O)[iPrNC(NR2)NiPr]2}2 (R = Me, M = Zr, 4; M = Hf, 5; R = Et, M = Zr, 6) and polymers {M(μ-O)[iPrNC(NR2)NiPr]2}n (R = Me, M = Zr, 7; M = Hf, 8; R = Et, M = Zr, 9). Mass spectrometric (MS) analyses of the reactions of water in air with 1 and 2 show formation of the Zr monomer Zr(═O)[iPrNC(NMe2)NiPr]2 (10), oxo dimers 4 and 5, and dihydroxyl complexes M(OH)2[iPrNC(NMe2)NiPr]2 (M = Zr, 11; Hf, 12). Similar MS analyses of the reaction of diethylamide guanidinate 3 with water in air show the formation of Zr(═O)[iPrNC(NEt2)NiPr]2 (13), Zr(OH)2[iPrNC(NEt2)NiPr]2 (14), 6, and {(Et2N)Zr[iPrNC(NEt2)NiPr]2}+ (15). Kinetic studies of the reaction between 1 and a continuous flow of 1.0 atm of O2 at 80–105 °C indicate that it follows pseudo-first-order kinetics with ΔH⧧ = 8.7(1.1) kcal/mol, ΔS⧧ = −54(3) eu, ΔG⧧358 K = 28(2) kcal/mol, and a half-life of 213(1) min at 85 °C.

Ta(NMe2)4[N(SiMe3)2] (1) undergoes the elimination of Me3Si-NMe2 (2), converting the −N(SiMe3)2 ligand to the ═NSiMe3 ligand, to give the imide “Ta(NMe2)3(═NSiMe3)” (3) observed as its dimer 4. CyN═C═NCy captures 3 to yield guanidinates Ta(NMe2)3–n(═NSiMe3)[CyNC(NMe2)NCy]n [n = 1 (5), 2 (6)]. The kinetic study of α-SiMe3 abstraction in 1 gives ΔH⧧ = 21.3(1.0) kcal/mol and ΔS⧧ = −17(2) eu.

The reactions of FeCl2 and CoCl2 with a bistriazolium salt yields the NHC complexes [FeIII(L1111)2]I·H2O, [FeIII(L2222)2]PF6·CH3CN and [CoIII(L1111)2]I·0.5CH3CN, through an unusual ring opening of one of the triazoyl rings, which leads to the formation of C,N,O tridentate ligands L1111 or L2222. Furthermore, a Fe(II) species [FeII(L1111)2]·CH2Cl2 was also obtained.

The synthesis and characterization of three new ruthenium(II) carbonyl complexes with a bistriazole-2-ylidene (bitz) ligand are reported. These complexes have been fully characterized by elemental analyses, infrared, and 1H and 13C NMR spectroscopies. Their molecular structures were determined by single-crystal X-ray diffraction. The ruthenium(II) ion is in a distorted octahedral environment, in which the donor atoms are provided by two carbene carbon atoms of the bitz ligands, two carbonyl groups, and two halides. All compounds exhibit the cis(CO)-trans(halogen) conformation. The bite angles of these three complexes, 77.58(12)°, 77.13(14)° and 77.14(11)°, are small as a consequence of the chelation of the bitz ligands.Graphical abstractThree ruthenium(II) carbonyl complexes with a bistriazole-2-ylidene (bitz) ligand have been prepared and characterized. The molecular structures were determined by single-crystal X-ray diffraction, which exhibit the six-coordinate distorted octahedral geometry with two carbene carbon atoms, two carbonyl groups, and two halide atoms. The bite angles, 77.58(12)°, 77.13(14)° and 77.14(11)°, are small as a consequence of the chelation of the bitz ligands.Highlights► Three ruthenium(II) complexes containing the bistriazole-2-ylidene ligand were prepared. ► Crystal structures for these complexes were determined by X-ray diffraction analysis. ► These complexes exhibit a distorted octahedral geometry around the Ru atom.

Direct insertion of 1 equiv of CyN═C═NCy (1; Cy = cyclohexyl) into the Zr–NMe2 bonds in (Me2N)3Zr[N(SiMe3)2] (2) and (Me2N)3Zr[Si(SiMe3)3] (3) gave exclusively [CyNC(NMe2)NCy]Zr(NMe2)2[N(SiMe3)2] (5) and [CyNC(NMe2)NCy]Zr(NMe2)2[Si(SiMe3)3] (6), respectively. The reaction between 2 and guanidine CyNHC(NMe2)═NCy (9) gave 5 and HNMe2 through the preferred cleavage of a Zr–NMe2 bond in 2. The reaction between 3 and 9 led to the preferred cleavage of the Zr–Si(SiMe3)3 bond in 3, yielding [CyNC(NMe2)NCy]Zr(NMe2)3 (7) and HSi(SiMe3)3 and, upon cleavage of another Zr–NMe2 bond, forming [CyNC(NMe2)NCy]2Zr(NMe2)2 (8). The aminolysis of Zr(NMe2)4 (4) by 9 first afforded 7 and then 8. The structures of 5, 6, and 9 have been determined by X-ray diffraction.

A new trinuclear species containing a Ta(IV)–Ta(IV) bond, Ta3(μ-H)(μ-NMe2)(μNBut)2(NBut)(NMe2)5, has been formed by reductive elimination of H2. Ta2H2(μ-NMe2)2(NMe2)2(NBut)2 has also been isolated. O2 oxidizes the Ta(IV)–Ta(IV) bond to yield Ta3(μ3-O)(H)(μNBut)(μ-NMe2)2(NMe2)4(NBut)2 under ligand exchange. Delocalization of d electrons is discussed.

The reaction of Nb(NMe2)5 with O2 gives three complexes: monomeric (Me2N)nNb(η2-ONMe2)5−n (n = 3, 4) and dimeric (Me2N)4Nb2[η2-N(Me)CH2NMe2]2(μ-O)2. Nb(NEt2)5 was prepared in a mixture of pentane and THF, leading to its purification and characterization by single-crystal X-ray diffraction. Unlike Nb(NMe2)5, which adopts a square pyramidal structure, Nb(NEt2)5 is a distorted trigonal bipyramid. The reaction of Nb(NEt2)5 with O2 gives an insoluble white solid.

The alkyl amide imide complex Ta(═NSiMe3)[N(SiMe3)2](CH2But)2 (2) has been prepared from the reaction of {Ta(μ-Cl)Cl(═NSiMe3)[N(SiMe3)2]}2 (1) with LiCH2But. Reaction of 2 with O2 leads to the preferential insertion of oxygen into the two Ta−alkyl bonds, yielding an alkoxy complex, Ta(═NSiMe3)[N(SiMe3)2](OCH2But)2 (3). 3 undergoes a ligand exchange to give Ta2(μ-NSiMe3)2(OCH2But)6 (4) and Ta(═NSiMe3)[N(SiMe3)2]2(OCH2But) (5). The exchange reaches an equilibrium: 2 3 ⇌ 1/2 4 + 5; Keq = 2.10(11) × 10−4 at 296 K; ΔG°296K = 4.98(3) kcal. 3 and 5 have also been prepared from the reactions of 1 with LiOCH2But, and LiN(SiMe3)2 and LiOCH2But, respectively. 2 and 4 have been characterized by single-crystal X-ray diffraction.

A bismuth bulk electrode (BiBE) has been investigated as an alternative electrode for the anodic stripping voltammetric (ASV) analysis of Pb(II), Cd(II), and Zn(II). The BiBE, which is fabricated in-house, shows results comparable to those of similar analyses at other Bi-based electrodes. Metal accumulation is achieved by holding the electrode potential at −1.4 V (vs. Ag/AgCl) for 180 s followed by a square wave voltammetric stripping scan from −1.4 to −0.35 V. Calibration plots are obtained for all three metals, individually and simultaneously, in the10–100 μg L−1 range, with a detection limit of 93, 54, and 396 ng L−1 for Pb(II), Cd(II), Zn(II), respectively. A slight reduction in slope is observed for Cd(II) and Pb(II) when the three metals are calibrated simultaneously vs. individually. Comparing the sensitivities of the metals when calibrated individually vs. in a mixture reveals that Zn(II) is not affected by stripping in a mixture. However, Pb(II) and Cd(II) have decreasing sensitivities in a mixture. The optimized method has been successfully used to test contaminated river water by standard addition. The results demonstrate the ability of the BiBE as an alternative electrode material in heavy metal analysis.

Pentaneopentyltantalum, Ta(CH2But)5 (1), was directly observed earlier in the formation of the archetypical alkylidene complex (ButCH2)3Ta═CHBut (2) from the reaction of either (ButCH2)3TaCl2 (3) with 2 equiv of ButCH2Li or (ButCH2)4TaCl (4) with 1 equiv of ButCH2Li. Ta(CH2But)5 (1) was, however, short-lived, and its 1H NMR resonances were mixed with those of (ButCH2)3Ta═CHBut (2), ButCH2Li, (ButCH2)3TaCl2 (3), (ButCH2)4TaCl (4), and CMe4 in a fairly narrow region. In the current work, deuterium-labeled Ta(CD2But)5 (1-d10) has been prepared from the reactions of (ButCD2)3TaCl2 (3-d6) with 2 equiv of ButCD2Li as well as (ButCD2)4TaCl (4-d8) with 1 equiv of ButCD2Li. Due to a kinetic isotope effect, Ta(CD2But)5 (1-d10) has a much longer life than 1. In addition, there are fewer peaks in the 1H NMR spectra of Ta(CD2But)5 (1-d10). 2H NMR spectroscopy can also be used to characterize 1-d10. These properties provide an opportunity to identify and study 1-d10 in detail. Kinetic studies of the Ta(CD2But)5 (1-d10) → (ButCD2)3Ta═CDBut (2-d7) and Ta(CH2But)5 (1) → (ButCH2)3Ta═CHBut (2) conversions yield a kinetic isotope effect (KIE) = 14.1(0.8) at 273 K. In addition, kinetic studies of the 1-d10 → 2-d7 conversion at 273−298 K give ΔH⧧D = 21.1(1.5) kcal/mol and ΔS⧧D = −4(6) eu for the α-deuterium abstraction reaction.

(Me2N)4Ta−SiButPh2 (1) reacts with O2 to give (Me2N)4Ta(OSiButPh2) (2), (Me2N)3Ta(ONMe2)(OSiButPh2) (3), and the unusual μ-oxo amino (Me2N)2(Ph2ButSiO)2(μ,η2-Me2NCH2NMe)2Ta2(μ-O)2 (4) containing two bridging chelating (aminomethyl)amides -N(Me)CH2NMe2. The dimer 4 was characterized by X-ray crystallography. 2 also reacts with O2 to give both 3 and 4. Reaction pathways in the formation of these complexes are discussed. In reactions of O2 with d0 1 and 2, oxidation of the ligands is the prevailing pathway.

Reaction of TaCl(NMe2)4 (1) with KTp* [Tp* = tris(3,5-dimethylpyrazolyl)borohydride] yields two products: Tp*Ta(NMe2)4 (2), in which one N atom of the Tp* ligand binds to Ta, and [Tp*Ta(NMe2)4]·2KTp* (3) where three N atoms of the Tp* ligand in [Tp*Ta(NMe2)4] (2a) bind to Ta. Addition of excess 1 to 3 did not exclude KTp*. Further reaction of 2 with oxygen affords Tp*BH(NMe2) (4). TpTa(NMe2)4 (5) has been synthesized by a similar procedure through the reaction of 1 with TpK [Tp = tris(pyrazolyl)borohydride]. Reactions of 3 and 5 with oxygen were also studied. 2, 4, and 5 were characterized by NMR, EA, and single-crystal X-ray diffraction.

The reaction of W(CH2SiMe3)3(≡CSiMe3) (1) with DMPE (DMPE = Me2PCH2CH2PMe2) gives an adduct W(CH2SiMe3)3(≡CSiMe3)(DMPE-P) (4a), which undergoes a rarely observed reversible transformation to its bis-alkylidene tautomer W(CH2SiMe3)2(═CHSiMe3)2(DMPE-P) (4b) through α-H migration. The DMPE ligands in both 4a and 4b contain a dangling P atom (P). Thermodynamic and kinetic studies of the 4a ⇌ 4b exchange show that it is slightly endothermic with ΔH° = 5.1(1.1) kcal/mol and ΔS° = 24(4) eu; ΔH1⧧ = 7.5(0.9) kcal/mol, ΔS1⧧ = −51(2) eu for the 4a → 4b forward reaction; ΔH−1⧧ = 2.0(0.8) kcal/mol, ΔS−1⧧ = −76(1) eu for the 4b → 4a reverse reaction. Activation entropies are the major contributors to the activation barriers of the exchange: ΔG1⧧278K = 21.7(1.5) kcal/mol and ΔG−1⧧278K = 23.1(1.1) kcal/mol. The 4a ⇌ 4b exchange at 283 K is faster than that of the previously reported PMe3 analogs W(CH2SiMe3)3(≡CSiMe3)(PMe3) (2a) ⇌ W(CH2SiMe3)2(═CHSiMe3)2(PMe3) (2b).(1) The 4a ⇌ 4b mixture undergoes an α-H abstraction, yielding alkyl alkylidene alkylidyne complexes W(CH2SiMe3)(═CHSiMe3)(≡CSiMe3)(DMPE) (syn, 7a; anti, 7b) containing chelating DMPE ligand with the following activation parameters: ΔH2⧧ = 13.2(1.3) kcal/mol and ΔS2⧧ = −36(4) eu. The formation of 7a,b is faster than the formation of W(CH2SiMe3)(═CHSiMe3)(≡CSiMe3)(PR3)2 (PR3 = PMe3, 5a,b; PMe2Ph, 6a,b).

Amidinate amide complexes M[CyNC(Me)NCy]2(NR2)2 (M = Ti, R = Me (1); M = Zr, R = Me (2), R = Et, (3); M = Hf, R = Me (4); Cy = cyclohexyl) have been prepared, and their crystal structures show distorted-octahedral coordination spheres. Variable-temperature NMR studies give ΔH⧧ = 2.8(0.2) kcal mol−1, ΔS⧧ = −36(1) eu and ΔH⧧= 0.5(0.3) kcal mol−1, ΔS⧧ = −44(1) eu for interconversions in 2 and 3, respectively.

Group 4 amide chloride complexes (Me2N)2Hf[N(SiMe3)2]Cl (1b), [(Me3Si)2N]2MCl2Li(THF)3Cl (M = Zr, 2a; Hf, 2b), and [(Me3Si)2N]2MCl2(THF) (M = Zr, 3a; Hf, 3b) and their X-ray crystal structures are reported. An improved synthesis of {[(Me3Si)2N]Ti(μ-NSiMe3)Cl}2 (4) and its use to prepare amide imide {[(Me3Si)2N]Ti(μ-NSiMe3)(NMe2)}2 (5) are also presented. X-ray crystal structures of 5 and previously reported complexes (Me2N)2Zr[N(SiMe3)2]Cl (1a), [(Me3Si)2N]2TiCl2 (6), and [(Me3Si)2N]ZrCl3(THF)2 (7) have been determined. Both 1a and 1b are dimers {[(Me3Si)2N]-(Me2N)2M(μ-Cl)}2 (M = Zr, Hf) in the solid state.

Reactions of O2 with the four-membered cyclic complexes {(Me2N)[(Me3Si)2N]M[N(SiMe3)SiMe2CH2]}2 (M = Zr (1a), Hf (1b)), containing both M−C and M−N bonds, give the five-membered cyclic complexes {(Me2N)[(Me3Si)2N]M[N(SiMe3)SiMe2CH2O]}2 (M = Zr (2a), Hf (2b)) with rarely observed selective O insertion into the M−C bonds. Both dimeric products exist as interesting cis and trans isomers.

Reactions of MCl5 (M = Nb, Ta) with LiNMe2 have been found to yield M(NMe2)4(η2-MeNCH2NMe2) (M = Nb, 2a; Ta, 2b) containing a chelating ligand (dimethylaminomethylene)methylamide, as confirmed by NMR spectroscopy, DFT calculations, and their reactivity studies.

This Account describes recent work in the development and applications of sol–gel sensors for concentrated strong acids and bases and metal ions. The use of sol–gel films doped with organic indicators for the optical sensing of concentrated strong acids (HCl, 1–10 M) and bases (NaOH, 1–10 M) has been explored, and the development of dual optical sensor approaches for ternary systems (HCl–salt–H2O and NaOH–alcohol–H2O) to give acid and salt, as well as base and alcohol, concentrations is discussed. The preparation of transparent, ligand-grafted sol–gel monoliths is also described, and their use in the analysis of both metal cations (Cu2+) and metal anions [Cr(VI)] is presented. A new model using both metal ion diffusion and immobilization by the ligands in such monoliths has been developed to give metal concentrations using the optical monolith sensors. In addition to optical sensing, a method utilizing ligand-grafted sol–gel films for analyte preconcentration in the electrochemical determination of Cr(VI) has been explored and is discussed.

Transparent, pyridine-functionalized sol–gel monoliths have been formed and their use in Cr(VI) sensing applications is demonstrated. The monoliths were immersed in acidic Cr(VI)-containing solutions, and the Cr(VI) uptake was monitored using UV–vis and atomic absorption spectroscopies. At concentrations at the ppm level, the monoliths exhibit a yellow color change characteristic of Cr(VI) uptake, and this can be measured by monitoring the absorption change at about 350 nm using UV–vis spectroscopy. Concentrations at the ppb level are below the limit of detection using this wavelength of 350 nm for measurement. However, by adding a diphenylcarbazide solution to monoliths that have been previously immersed in ppb-level Cr(VI) solutions, a distinct color change takes place within the gels that can be measured at about 540 nm using UV–vis spectroscopy. Concentrations as low as 10 ppb Cr(VI) can be measured using this method. The monoliths can then be regenerated for subsequent sensing cycles by thorough washing with 6.0 M HCl. The factors affecting monolith uptake of Cr(VI) have been explored. In addition, the gels have been characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) measurements.

A new method for the quantitative determination of palladium(II) by the electrochemical quartz crystal microbalance (EQCM) technique has been developed. Using a bare carbon-coated quartz crystal, Pd(II) ions are directly deposited from aqueous solution as palladium metal onto the crystal surface, and the Pd(II) concentration is determined with a detection limit of 0.0156 mM, or 1.66 ppm. No complexing agent or preconcentration of palladium is required for the analysis. The palladium is stripped from the crystal through its electrochemical oxidation, regenerating the crystal for subsequent multi-cycle palladium analyses. A conventional gold-coated quartz crystal was incapable of carrying out the same measurements. The EQCM technique presented is simple, sensitive, and reproducible for the detection of this widely used precious metal.

The Fujiwara reaction is the only known reaction for detecting halocarbons spectrophotometrically in the visible region, and it has been conducted with toxic, offensive-smelling pyridine and a strong base such as NaOH. New alternative approaches to conducting the Fujiwara reactions have been developed using solid pyridine derivatives and new bases for the detection of chloroform and carbon tetrachloride. The reactions of these halocarbons with 2,2′-dipyridyl (or 4,4′-dipyridyl) and tetra-n-butylammonium hydroxide (n-Bu4NOH) or potassium tert-butoxide (KO-t-Bu) were found to give colored species with detection limits of 0.17 mg/L for chloroform and 0.50 mg/L for CCl4 (using 2,2′-dipyridyl and n-Bu4NOH). The use of potassium tert-butoxide as the base in the Fujiwara reactions allows for the detection of the halocarbons in systems sensitive to water.

Reaction of (ArN)2MoCl2(DME) (Ar=2,6-Pri 2C6H3, DME=dimethoxyethane) with LiNMe2 and Li(THF)3Si(SiMe3)3 was found to give a Mo imide amide silyl complex (ArN)2Mo(NMe2)[Si(SiMe3)3] (1). Imide amide complexes (ArN)2Mo(NMe2)2 (2) and (ArN)2Mo(NMe2)[N(SiMe3)2] (4) were prepared from the reactions of (ArN)2MoCl2(DME) with lithium amide reagents and characterized. X-ray structural studies of 1, 2 and 4 are presented. An intermediate to 4, (ArN)2MoCl[N(SiMe3)2] (3), was obtained from the reaction of (ArN)2MoCl2(DME) with LiN(SiMe3)2 and structurally characterized. In addition, a new X-ray structure of previously reported complex (ArN)2Mo(NHAr)2 (5) is reported.Mo imide amide silyl complex (ArN)2Mo(NMe2)[Si(SiMe3)3] (1), imide amide complexes (ArN)2Mo(NMe2)2 (2) and (ArN)2Mo(NMe2)[N(SiMe3)2] (4), and an intermediate to 4, (ArN)2MoCl[N(SiMe3)2] (3), were prepared and characterized. The X-ray structures of these complexes show that they adopt pseudo-tetrahedral geometry around the metal centers.

The ability to detect biodiesel at various concentrations in diesel is an important goal in several industries. A simple, solvatochromic dye-doped optical sensor is presented for quick and direct detection of 0.5 ppm–20% v/v FAME/biodiesel in diesel.

(Me3SiCH2)3(Me3SiC)W←OPMe3 (1), an adduct between (Me3SiCH2)3WCSiMe3 (2) and OPMe3, reacts with O2 to give OW(OSiMe3)(CH2SiMe3)3 (3) and CO2. Reaction of 2 with H2O yields 3 and the trimer [(μ-O)W(CH2SiMe3)2(O)(THF)]3 (4). In the reaction of D2O with 2, 3-dn and methane isotopologues CH2D2, CHD3 and CD4 have been observed.

A new trinuclear species containing a Ta(IV)–Ta(IV) bond, Ta3(μ-H)(μ-NMe2)(μNBut)2(NBut)(NMe2)5, has been formed by reductive elimination of H2. Ta2H2(μ-NMe2)2(NMe2)2(NBut)2 has also been isolated. O2 oxidizes the Ta(IV)–Ta(IV) bond to yield Ta3(μ3-O)(H)(μNBut)(μ-NMe2)2(NMe2)4(NBut)2 under ligand exchange. Delocalization of d electrons is discussed.

Reaction of d0 Zr(NMe2)2[MeC(NiPr)2]2 (1) with O2 at −30 °C gives three Zr containing products: a peroxo trimer {(μ-η2:η2-O2)Zr[MeC(NiPr)2]2}3 (2), an oxo dimer {(μ-O)Zr[MeC(NiPr)2]2}2 (3), and an oxo polymer {(μ-O)Zr[MeC(NiPr)2]2}n (4). 2 is a rarely observed peroxo complex from the reaction of a d0 complex with O2.

The reactions of FeCl2 and CoCl2 with a bistriazolium salt yields the NHC complexes [FeIII(L1111)2]I·H2O, [FeIII(L2222)2]PF6·CH3CN and [CoIII(L1111)2]I·0.5CH3CN, through an unusual ring opening of one of the triazoyl rings, which leads to the formation of C,N,O tridentate ligands L1111 or L2222. Furthermore, a Fe(II) species [FeII(L1111)2]·CH2Cl2 was also obtained.