Co-reporter:Zhen Yao, Charles E. Schulz, Nana Zhan, and Jianfeng Li
Inorganic Chemistry October 16, 2017 Volume 56(Issue 20) pp:12615-12615
Publication Date(Web):October 5, 2017
DOI:10.1021/acs.inorgchem.7b02092
A new sterically hindered “picket fence-like” porphyrin with chelates for the second metal atom, H2TImPP (TImPP = meso-tetrakis[α,α,α,α-o-(5-imidazolecarboxylaminophenyl)]porphyrinato), is developed and used in the synthesis of four iron(II) bis(imidazole) derivatives, which are characterized by single crystal X-ray and other spectroscopies. The comprehensive studies on the crystal structures revealed noteworthy features including new axial ligand arrangements, deformed porphyrin planes, and strongly tilted pickets which can be rationalized by analysis of the intra- and intermolecular interactions. Solid-state Mössbauer experiments on [Fe(TImPP)(1-MeIm)2] were conducted at several temperatures from 295 to 25 K. The quadrupole splitting (ΔEQ) in the range of 1.01–1.03 mm/s confirmed the low-spin state of the iron.
Co-reporter:Yulong Liu, Wei Xu, Jing Zhang, William Fuller, Charles E. Schulz, and Jianfeng Li
Journal of the American Chemical Society April 12, 2017 Volume 139(Issue 14) pp:5023-5023
Publication Date(Web):March 24, 2017
DOI:10.1021/jacs.7b01722
The five-coordinate iron porphyrin carbene complexes [Fe(TPP) (CCl2)] (TPP = tetraphenylporphyrin), [Fe(TTP) (CCl2)] (TTP = tetratolylporphyrin) and [Fe(TFPP) (CPh2)] (TFPP = tetra(pentafluorophenyl)porphyrin), utilizing two types of carbene ligands (CCl2 and CPh2), have been investigated by single crystal X-ray, XANES (X-ray absorption near edge spectroscopy), Mössbauer, NMR and UV–vis spectroscopies. The XANES suggested the iron(II) oxidation state of the complexes. The multitemperature and high magnetic field Mössbauer experiments, which show very large quadrupole splittings (QS, ΔEQ), determined the S = 0 electronic configuration. More importantly, combined structural and Mössbauer studies, especially the comparison with the low spin iron(II) porphyrin complexes with strong diatomic ligands (CS, CO and CN–) revealed the covalent bond nature of the carbene ligands. A correlation between the iron isomer shifts (IS, δ) and the axial bond distances is established for the first time for these donor carbon ligands (:C–R).
Co-reporter:Mingrui He, Xiangjun Li, Yanhong Liu, and Jianfeng Li
Inorganic Chemistry 2016 Volume 55(Issue 12) pp:5871
Publication Date(Web):May 26, 2016
DOI:10.1021/acs.inorgchem.6b00173
Three five-coordinate high-spin (cyano)manganese(II) complexes, utilized tetraphenylporphyrin (TPP), tetratolylporphyrin (TTP), and tetramesitylporphyrin (TMP) as ligands, are prepared and studied by single-crystal X-ray, FT-IR, UV–vis, and EPR spectroscopies. The crystal structure studies revealed noteworthy structural features including unexpectedly wide tilting angles of the axial Mn–CCN bonds, which is contrasted to the isoelectronic Fe(III)–CCN bonds. Solid-state EPR measurements (90 K) and simulations are applied to obtain the ZFS parameters (D, E, and E/D (λ)), which are compared to Mn(II) porphyrin analogues of hemes to understand the ligand field of the cyanide. The solution EPR studies gave new insights into the chemical equilibrium of four- and five-coordinate species, which has been monitored by UV–vis spectroscopy.
Co-reporter:Bin Hu, Mingrui He, Zhen Yao, Charles E. Schulz, and Jianfeng Li
Inorganic Chemistry 2016 Volume 55(Issue 19) pp:9632-9643
Publication Date(Web):September 22, 2016
DOI:10.1021/acs.inorgchem.6b01364
The synthesis and characterization of several electron-poor iron(II) porphyrin (FeTFPPBr8) complexes with axial imidazole ligands are reported. The single-crystal X-ray structures have been studied by a combination of crystal packing and Hirshfeld surface calculations, which explained the unusual axial-ligand geometries, e.g., the strong tilt of the Fe–NIm bonds and the imidazole planes. The six-coordinate [Fe(TFPPBr8)(1-MeIm)2] was studied by multiple-temperature solid-state Mössbauer spectroscopy, which suggested that it is a low-spin complex with δ ∼ 0.32–0.38 mm/s and ΔEQ ∼ 1.0 mm/s.
Co-reporter:Baiyin He, Xiangjun Li, Jianfeng Li
Journal of Organometallic Chemistry 2016 Volume 809() pp:14-20
Publication Date(Web):1 May 2016
DOI:10.1016/j.jorganchem.2016.02.023
•Modified “picket fence” porphyrin and iron carbonyl derivatives are synthesized.•The smallest FeCO angle of 172.10(13)° is a result of the rare carbonyl disorder.•Interactions found between terminal oxygen of CO and carbon atoms of the pickets.A new modified “picket fence” porphyrin is synthesized and its six-coordinate iron(II) carbonyl derivatives [Fe(MmacTpivPP)(CO)(Py)] and [Fe(MmacTpivPP)(CO)(1-MeIm)] are characterized by single-crystal X-ray, UV-vis and IR spectroscopies. X-ray structural determinations revealed that both [Fe(MmacTpivPP)(CO)(Py)] and [Fe(MmacTpivPP)(CO)(1-MeIm)] are crystallized in the C2/c space group with 2-fold axes passing through the Fe atoms. The FeCO angle of [Fe(MmacTpivPP)(CO)(Py)] is as small as 172.1°, contrasted to 180° of the same angle in [Fe(MmacTpivPP)(CO)(1-MeIm)]. Short intramolecular interactions are found between the terminal oxygen atom of CO and the carbon atoms of the pickets in [Fe(MmacTpivPP)(CO)(Py)]. The characteristic CO stretching frequencies (νCO) of the two complexes are same at 1965 cm−1.Iron(II) porphyrin complexes [Fe(MmacTpivPP)(CO)(Py)] and [Fe(MmacTpivPP)(CO)(1-MeIm)] were characterized. The smallest FeCO angle of 172.10(13)° is observed in the structure of [Fe(MmacTpivPP)(CO)(Py)], which is a result of the rare carbonyl disorder and attributed to the intramolecular interactions between the terminal oxygen atom of CO and carbon atoms of the pickets.
Co-reporter:Jianfeng Li, Bruce C. Noll, Charles E. Schulz, and W. Robert Scheidt
Inorganic Chemistry 2015 Volume 54(Issue 13) pp:6472-6485
Publication Date(Web):June 22, 2015
DOI:10.1021/acs.inorgchem.5b00780
The synthesis of six new bis(cyano) iron(III) porphyrinate derivatives is reported. The anionic porphyrin complexes utilized tetraphenylporphyrin, tetramesitylporphyrin, and tetratolylporphyrin as the porphyrin ligand. The potassium salts of Kryptofix-222 and 18-C-6 were used as the cations. These complexes have been characterized by X-ray structure analysis, solid-state Mössbauer spectroscopy, and EPR spectroscopy, both in frozen CH2Cl2 solution and in the microcrystalline state. These data show that these anionic complexes can exist in either the (dxz,dyz)4(dxy)1 or the (dxy)2(dxz,dyz)3 electronic configuration and some can clearly readily interconvert. This is a reflection that these two states can be very close in energy. In addition to the effects of varying the porphyrin ligand, subtle effects of the cyanide ligand environment in the solid state and in solution are sufficient to shift the balance between the two electronic states.
Co-reporter:Baiyin He, Charles E. Schulz and Jianfeng Li
Dalton Transactions 2015 vol. 44(Issue 30) pp:13651-13661
Publication Date(Web):24 Jun 2015
DOI:10.1039/C5DT00941C
A new, modified “picket fence” porphyrin is synthesized and its bis(imidazole)-ligated iron(II) derivative [Fe(MbenTpivPP)(1-MeIm)2] is investigated. X-ray structure determinations demonstrate that [Fe(MbenTpivPP)(1-MeIm)2] has structural features of a near planar porphyrin plane, a relative perpendicular ligand orientation, and one unusually large absolute ligand orientation (φ). The combination of these features leads to a new type of species that is different from previously reported analogues. Further structural examination reveals a strong correlation between the mutual ligand orientations (θ) and the axial Fe–NIm bond distances, which is detailed for the first time. Mössbauer spectroscopic characterization shows that the low spin derivative has a quadrupole splitting of 0.99 mm s−1 at 100 K.
Co-reporter:Qiang Yu;Xiangjun Li;Diansheng Liu
Acta Crystallographica Section C 2015 Volume 71( Issue 7) pp:545-548
Publication Date(Web):
DOI:10.1107/S2053229615009304
`Picket-fence' porphyrin compounds are used in the investigation of interactions of hemes with dioxygen, carbon monoxide, nitric monoxide and imidazole ligands. (Cryptand-222)potassium chlorido[meso-tetra(α,α,α,α-o-pivalamidophenyl)porphyrinato]manganese tetrahydrofuran monosolvate (cryptand-222 is 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane), [K(C18H36N2O6)][Mn(C64H64N8O4)Cl]·C4H8O or [K(222)][Mn(TpivPP)Cl]·THF [systematic name for TpivPP: 5,10,15,20-tetrakis(2-tert-butanamidophenyl)porphyrin], is a five-coordinate high-spin manganese(II) picket-fence porphyrin complex. It crystallizes with a potassium cation chelated inside a cryptand-222 molecule; the average K—O and K—N distances are 2.83 (4) and 2.995 (13) Å, respectively. All four protecting tert-butyl pickets of the porphyrin are ordered. The porphyrin plane is nearly planar, as indicated by the atomic displacements and the dihedral angles between the mean planes of the pyrrole rings and the 24-atom mean plane. The axial chloride ligand is located inside the molecular cavity on the hindered porphyrin side and the Mn—Cl bond is tilted slightly off the normal to the porphyrin plane by 3.68 (2)°. The out-of-plane displacement of the metal centre relative to the 24-atom mean plane (Δ24) is 0.7013 (4) Å, indicating a noticeable porphyrin core doming.
Co-reporter:Bin Hu ; Jianfeng Li
Angewandte Chemie International Edition 2015 Volume 54( Issue 36) pp:10579-10582
Publication Date(Web):
DOI:10.1002/anie.201505166
Abstract
The first X-ray single-crystal structure of a {FeNO}8 porphyrin complex [Co(Cp)2][Fe(TFPPBr8)(NO)], and the structure of the {FeNO}7 precursor [Fe(TFPPBr8)(NO)] are determined at 100 K. The two complexes are also characterized by FTIR and UV/Vis spectroscopy. [Fe(TFPPBr8)(NO)]− shows distinct structural features in contrast to a nitrosyl iron(II) porphyrinate on the FeNO− moiety, which include a much more bent FeNO− angle (122.4(3)°), considerably longer FeNO− (1.814(4)) and NO− (1.194(5) Å) bond distances. These and the about 180 cm−1 downshift νN-O stretch (1540 cm−1) can be understood by the covalently bonding nature between the iron(II) and the NO− ligand which possesses a two-electron-occupied π* orbital as a result of the reduction. The overall structural features of [Fe(TFPPBr8)(NO)]− and [Fe(TFPPBr8)(NO)] suggest a low-spin state of the iron(II) atom at 100 K.
Co-reporter:Bin Hu ; Jianfeng Li
Angewandte Chemie 2015 Volume 127( Issue 36) pp:10725-10728
Publication Date(Web):
DOI:10.1002/ange.201505166
Abstract
The first X-ray single-crystal structure of a {FeNO}8 porphyrin complex [Co(Cp)2][Fe(TFPPBr8)(NO)], and the structure of the {FeNO}7 precursor [Fe(TFPPBr8)(NO)] are determined at 100 K. The two complexes are also characterized by FTIR and UV/Vis spectroscopy. [Fe(TFPPBr8)(NO)]− shows distinct structural features in contrast to a nitrosyl iron(II) porphyrinate on the FeNO− moiety, which include a much more bent FeNO− angle (122.4(3)°), considerably longer FeNO− (1.814(4)) and NO− (1.194(5) Å) bond distances. These and the about 180 cm−1 downshift νN-O stretch (1540 cm−1) can be understood by the covalently bonding nature between the iron(II) and the NO− ligand which possesses a two-electron-occupied π* orbital as a result of the reduction. The overall structural features of [Fe(TFPPBr8)(NO)]− and [Fe(TFPPBr8)(NO)] suggest a low-spin state of the iron(II) atom at 100 K.
Co-reporter:Qiang Yu;Diansheng Liu;Xiangjun Li
Acta Crystallographica Section C 2015 Volume 71( Issue 10) pp:856-859
Publication Date(Web):
DOI:10.1107/S2053229615015478
As representative porphyrin model compounds, the structures of `picket-fence' porphyrins have been studied intensively. The title solvated complex salt {systematic name: (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane)potassium(I) [5,10,15,20-tetrakis(2-tert-butanamidophenyl)porphyrinato]iron(II) n-hexane monosolvate}, [K(C18H36N2O6)][Fe(C64H64N8O4)Cl]·C6H14 or [K(222)][Fe(TpivPP)Cl]·C6H14 [222 is cryptand-222 or 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane, and TpivPP is meso-α,α,α,α-tetrakis(o-pivalamidophenyl)porphyrinate(2−)], [K(222)][Fe(TpivPP)Cl]·C6H14, is a five-coordinate high-spin iron(II) picket-fence porphyrin complex. It crystallizes with a potassium cation chelated inside a cryptand-222 molecule; the average K—O and K—N distances are 2.81 (2) and 3.05 (2) Å, respectively. One of the protecting tert-butyl pickets is disordered. The porphyrin plane presents a moderately ruffled distortion, as suggested by the atomic displacements. The axial chloride ligand is located inside the molecular cavity on the hindered porphyrin side and the Fe—Cl bond is tilted slightly off the normal to the porphyrin plane by 4.1°. The out-of-plane displacement of the metal centre relative to the 24-atom mean plane (Δ24) is 0.62 Å, indicating a noticeable doming of the porphyrin core.
Co-reporter:Jianfeng Li ; Qian Peng ; Allen G. Oliver ; E. Ercan Alp ; Michael Y. Hu ; Jiyong Zhao ; J. Timothy Sage ;W. Robert Scheidt
Journal of the American Chemical Society 2014 Volume 136(Issue 52) pp:18100-18110
Publication Date(Web):December 9, 2014
DOI:10.1021/ja5105766
Oriented single-crystal nuclear resonance vibrational spectroscopy (NRVS) has been used to obtain all iron vibrations in two {FeNO}6 porphyrinate complexes, five-coordinate [Fe(OEP)(NO)]ClO4 and six-coordinate [Fe(OEP)(2-MeHIm)(NO)]ClO4. A new crystal structure was required for measurements of [Fe(OEP)(2-MeHIm)(NO)]ClO4, and the new structure is reported herein. Single crystals of both complexes were oriented to be either parallel or perpendicular to the porphyrin plane and/or axial imidazole ligand plane. Thus, the FeNO bending and stretching modes can now be unambiguously assigned; the pattern of shifts in frequency as a function of coordination number can also be determined. The pattern is quite distinct from those found for CO or {FeNO}7 heme species. This is the result of unchanging Fe–NNO bonding interactions in the {FeNO}6 species, in distinct contrast to the other diatomic ligand species. DFT calculations were also used to obtain detailed predictions of vibrational modes. Predictions were consistent with the intensity and character found in the experimental spectra. The NRVS data allow the assignment and observation of the challenging to obtain Fe–Im stretch in six-coordinate heme derivatives. NRVS data for this and related six-coordinate hemes with the diatomic ligands CO, NO, and O2 reveal a strong correlation between the Fe–Im stretch and Fe–NIm bond distance that is detailed for the first time.
Co-reporter:Jianfeng Li ; Bruce C. Noll ; Allen G. Oliver ; Charles E. Schulz ;W. Robert Scheidt
Journal of the American Chemical Society 2013 Volume 135(Issue 41) pp:15627-15641
Publication Date(Web):September 11, 2013
DOI:10.1021/ja408431z
Disorder in the position of the dioxygen ligand is a well-known problem in dioxygen complexes and, in particular, those of picket fence porphyrin species. The dynamics of Fe–O2 rotation and tert-butyl motion in three different picket fence porphyrin derivatives has been studied by a combination of multitemperature X-ray structural studies and Mössbauer spectroscopy. Structural studies show that the motions of the dioxygen ligand also require motions of the protecting pickets of the ligand binding pocket. The two motions appear to be correlated, and the temperature-dependent change in the O2 occupancies cannot be governed by a simple Boltzmann distribution. The three [Fe(TpivPP)(RIm)(O2)] derivatives studied have RIm = 1-methyl-, 1-ethyl-, or 2-methylimidazole. In all three species there is a preferred orientation of the Fe–O2 moiety with respect to the trans imidazole ligand and the population of this orientation increases with decreasing temperature. In the 1-MeIm and 1-EtIm species the Fe–O2 unit is approximately perpendicular to the imidazole plane, whereas in the 2-MeHIm species the Fe–O2 unit is approximately parallel. This reflects the low energy required for rotation of the Fe–O2 unit and the small energy differences in populating the possible pocket quadrants. All dioxygen complexes have a crystallographically required 2-fold axis of symmetry that limits the accuracy of the determined Fe–O2 geometry. However, the 80 K structure of the 2-MeHIm derivative allowed for resolution of the two bonded oxygen atom positions and provided the best geometric description for the Fe–O2 unit. The values determined are Fe–O = 1.811(5) Å, Fe–O–O = 118.2(9)°, O–O = 1.281(12) Å, and an off-axis tilt of 6.2°. Demonstration of the off-axis tilt is a first. We present detailed temperature-dependent simulations of the Mössbauer spectra that model the changing value of the quadrupole splitting and line widths. Residuals to fits are poorer at higher temperature. We believe that this is consistent with the idea that population of the two conformers is related to the concomitant motions of both Fe–O2 rotations and motions of the protecting tert-butyl pickets.
Co-reporter:Jianfeng Li, Qian Peng, Alexander Barabanschikov, Jeffrey W. Pavlik, E. Ercan Alp, Wolfgang Sturhahn, Jiyong Zhao, J. Timothy Sage, and W. Robert Scheidt
Inorganic Chemistry 2012 Volume 51(Issue 21) pp:11769-11778
Publication Date(Web):October 19, 2012
DOI:10.1021/ic301719v
The low-frequency vibrational characterization of the spin-crossover complex, five-coordinate cyano(tetraphenylporphyrinato)iron(II), [Fe(TPP)(CN)]−, is reported. Nuclear resonance vibrational spectroscopy has been used to measure all low-frequency vibrations involving iron at several temperatures; this yields vibrational spectra of both the low- (S = 0) and high-spin (S = 2) states. Multitemperature oriented single-crystal measurements facilitate assignments of the vibrational character of all modes and are consistent with the DFT-predicted spectra. The availability of the entire iron vibrational spectrum allows for the complete correlation of the modes between the two spin states. These data demonstrate that not only do the frequencies of the vibrations shift to lower values for the high-spin species as would be expected owing to the weaker bonds in the high-spin state, but also the mixing of iron modes with ligand modes changes substantially. Diagrams illustrating the changing character of the modes and their correlation are given. The reduced iron–ligand frequencies are the primary factor in the entropic stabilization of the high-spin state responsible for the spin crossover.
Co-reporter:Baiyin He, Charles E. Schulz and Jianfeng Li
Dalton Transactions 2015 - vol. 44(Issue 30) pp:NaN13661-13661
Publication Date(Web):2015/06/24
DOI:10.1039/C5DT00941C
A new, modified “picket fence” porphyrin is synthesized and its bis(imidazole)-ligated iron(II) derivative [Fe(MbenTpivPP)(1-MeIm)2] is investigated. X-ray structure determinations demonstrate that [Fe(MbenTpivPP)(1-MeIm)2] has structural features of a near planar porphyrin plane, a relative perpendicular ligand orientation, and one unusually large absolute ligand orientation (φ). The combination of these features leads to a new type of species that is different from previously reported analogues. Further structural examination reveals a strong correlation between the mutual ligand orientations (θ) and the axial Fe–NIm bond distances, which is detailed for the first time. Mössbauer spectroscopic characterization shows that the low spin derivative has a quadrupole splitting of 0.99 mm s−1 at 100 K.
![Iron(1 ), diaqua[5,10,15,20-tetraphenyl-21H,23H-porphinato(2-)-κN21,κN22,κN23,κN24]-, (OC-6-12)-, perchlorate (1:1)](/data/chemimg/1498100/65893-70-1.png)
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![Silane, [methylenebis(4,1-phenylene-2,1-ethynediyl)]bis[trimethyl-](http://img.cochemist.com/ccimg/77200/77123-71-8.png)
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![N-BENZYL-N-[(2-CHLORO-8-METHYL-3-QUINOLINYL)METHYL]-2-FURAMIDE](http://img.cochemist.com/ccimg/75900/75867-44-6.png)
![N-BENZYL-N-[(2-CHLORO-8-METHYL-3-QUINOLINYL)METHYL]-2-FURAMIDE](http://img.cochemist.com/ccimg/75900/75867-44-6_b.png)
![Manganese, [5,10,15,20-tetraphenyl-21H,23H-porphinato(2-)-κN21,κN22,κN23,κN24]-, (SP-4-1)-](/data/chemimg/546000/31004-82-7.png)
![Manganese, [5,10,15,20-tetraphenyl-21H,23H-porphinato(2-)-κN21,κN22,κN23,κN24]-, (SP-4-1)-](/data/chemimg/546000/31004-82-7_b.png)
![Iron, chloro[2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(2,3,4,5,6-pentafluorophenyl)-21H,23H-porphinato(2-)-κN21,κN22,κN23,κN24]-, (SP-5-12)-](/data/chemimg/926300/131917-66-3.png)
![Iron, chloro[2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(2,3,4,5,6-pentafluorophenyl)-21H,23H-porphinato(2-)-κN21,κN22,κN23,κN24]-, (SP-5-12)-](/data/chemimg/926300/131917-66-3_b.png)
![4,7,13,16,21,24-Hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane](http://img.cochemist.com/ccimg/24000/23978-09-8.png)
![4,7,13,16,21,24-Hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane](http://img.cochemist.com/ccimg/24000/23978-09-8_b.png)
![Ferrate(2-), [7,12-diethenyl-3,8,13,17-tetramethyl-21H,23H-porphine-2,18-dipropanoato(4-)-κN21,κN22,κN23,κN24]-, hydrogen (1:2), (SP-4-2)-](/data/chemimg/522800/14875-96-8.png)
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