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Münster K, Baabe D, Kintzel B, Böhme M, Plass W, Raeder J, Walter MD. Low-Coordinate Iron(II) Amido Half-Sandwich Complexes with Large Internal Magnetic Hyperfine Fields. Inorg Chem 2022; 61:18883-18898. [DOI: 10.1021/acs.inorgchem.2c02768] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Katharina Münster
- Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Hagenring 30, Braunschweig38106, Germany
| | - Dirk Baabe
- Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Hagenring 30, Braunschweig38106, Germany
| | - Benjamin Kintzel
- Institut für Anorganische und Analytische Chemie, Friedrich-Schiller-Universität Jena, Humboldtstraße 8, Jena07743, Germany
| | - Michael Böhme
- Institut für Anorganische und Analytische Chemie, Friedrich-Schiller-Universität Jena, Humboldtstraße 8, Jena07743, Germany
| | - Winfried Plass
- Institut für Anorganische und Analytische Chemie, Friedrich-Schiller-Universität Jena, Humboldtstraße 8, Jena07743, Germany
| | - Jan Raeder
- Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Hagenring 30, Braunschweig38106, Germany
| | - Marc D. Walter
- Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Hagenring 30, Braunschweig38106, Germany
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Hakey BM, Leary DC, Xiong J, Harris CF, Darmon JM, Petersen JL, Berry JF, Guo Y, Milsmann C. High Magnetic Anisotropy of a Square-Planar Iron-Carbene Complex. Inorg Chem 2021; 60:18575-18588. [PMID: 34431660 DOI: 10.1021/acs.inorgchem.1c01860] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Among Earth-abundant catalyst systems, iron-carbene intermediates that perform C-C bond forming reactions such as cyclopropanation of olefins and C-H functionalization via carbene insertion are rare. Detailed descriptions of the possible electronic structures for iron-carbene bonds are imperative to obtain better mechanistic insights and enable rational catalyst design. Here, we report the first square-planar iron-carbene complex (MesPDPPh)Fe(CPh2), where [MesPDPPh]2- is the doubly deprotonated form of [2,6-bis(5-(2,4,6-trimethylphenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine]. The compound was prepared via reaction of the disubstituted diazoalkane N2CPh2 with (MesPDPPh)Fe(thf) and represents a rare example of a structurally characterized, paramagnetic iron-carbene complex. Temperature-dependent magnetic susceptibility measurements and applied-field Mössbauer spectroscopic studies revealed an orbitally near-degenerate S = 1 ground state with large unquenched orbital angular momentum resulting in high magnetic anisotropy. Spin-Hamiltonian analysis indicated that this S = 1 spin system has uniaxial magnetic properties arising from a ground MS = ±1 non-Kramers doublet that is well-separated from the MS = 0 sublevel due to very large axial zero-field splitting (D = -195 cm-1, E/D = 0.02 estimated from magnetic susceptibility data). This remarkable electronic structure gives rise to a very large, positive magnetic hyperfine field of more than +60 T for the 57Fe nucleus along the easy magnetization axis observed by Mössbauer spectroscopy. Computational analysis with complete active space self-consistent field (CASSCF) calculations provides a detailed electronic structure analysis and confirms that (MesPDPPh)Fe(CPh2) exhibits a multiconfigurational ground state. The majority contribution originates from a configuration best described as a singlet carbene coordinated to an intermediate-spin FeII center with a (dxy)2{(dxz),(dz2)}3(dyz)1(dx2-y2)0 configuration featuring near-degenerate dxz and dz2 orbitals.
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Affiliation(s)
- Brett M Hakey
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Dylan C Leary
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Jin Xiong
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Caleb F Harris
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Jonathan M Darmon
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
| | - Jeffrey L Petersen
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
| | - John F Berry
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Yisong Guo
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Carsten Milsmann
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
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Tarrago M, Römelt C, Nehrkorn J, Schnegg A, Neese F, Bill E, Ye S. Experimental and Theoretical Evidence for an Unusual Almost Triply Degenerate Electronic Ground State of Ferrous Tetraphenylporphyrin. Inorg Chem 2021; 60:4966-4985. [PMID: 33739093 DOI: 10.1021/acs.inorgchem.1c00031] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Iron porphyrins exhibit unrivalled catalytic activity for electrochemical CO2-to-CO conversion. Despite intensive experimental and computational studies in the last 4 decades, the exact nature of the prototypical square-planar [FeII(TPP)] complex (1; TPP2- = tetraphenylporphyrinate dianion) remained highly debated. Specifically, its intermediate-spin (S = 1) ground state was contradictorily assigned to either a nondegenerate 3A2g state with a (dxy)2(dz2)2(dxz,yz)2 configuration or a degenerate 3Egθ state with a (dxy)2(dxz,yz)3(dz2)1/(dz2)2(dxy)1(dxz,yz)3 configuration. To address this question, we present herein a comprehensive, spectroscopy-based theoretical and experimental electronic-structure investigation on complex 1. Highly correlated wave-function-based computations predicted that 3A2g and 3Egθ are well-isolated from other triplet states by ca. 4000 cm-1, whereas their splitting ΔA-E is on par with the effective spin-orbit coupling (SOC) constant of iron(II) (≈400 cm-1). Therfore, we invoked an effective Hamiltonian (EH) operating on the nine magnetic sublevels arising from SOC between the 3A2g and 3Egθ states. This approach enabled us to successfully simulate all spectroscopic data of 1 obtained by variable-temperature and variable-field magnetization, applied-field 57Fe Mössbauer, and terahertz electron paramagnetic resonance measurements. Remarkably, the EH contains only three adjustable parameters, namely, the energy gap without SOC, ΔA-E, an angle θ that describes the mixing of (dxy)2(dxz,yz)3(dz2)1 and (dz2)2(dxy)1(dxz,yz)3 configurations, and the ⟨rd-3⟩ expectation value of the iron d orbitals that is necessary to estimate the 57Fe magnetic hyperfine coupling tensor. The EH simulations revealed that the triplet ground state of 1 is genuinely multiconfigurational with substantial parentages of both 3A2g (<88%) and 3Eg (>12%), owing to their accidental near-triple degeneracy with ΔA-E = +950 cm-1. As a consequence of this peculiar electronic structure, 1 exhibits a huge effective magnetic moment (4.2 μB at 300 K), large temperature-independent paramagnetism, a large and positive axial zero-field splitting, strong easy-plane magnetization (g⊥ ≈ 3 and g∥ ≈ 1.7) and a large and positive internal field at the 57Fe nucleus aligned in the xy plane. Further in-depth analyses suggested that g⊥ ≫ g∥ is a general spectroscopic signature of near-triple orbital degeneracy with more than half-filled pseudodegenerate orbital sets. Implications of the unusual electronic structure of 1 for CO2 reduction are discussed.
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Affiliation(s)
- Maxime Tarrago
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany
| | - Christina Römelt
- Max-Planck-Institut für Chemische Energiekonversion, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany
| | - Joscha Nehrkorn
- Max-Planck-Institut für Chemische Energiekonversion, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany
| | - Alexander Schnegg
- Max-Planck-Institut für Chemische Energiekonversion, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany
| | - Frank Neese
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany
| | - Eckhard Bill
- Max-Planck-Institut für Chemische Energiekonversion, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany
| | - Shengfa Ye
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany.,State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
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Reiners M, Baabe D, Harms K, Maekawa M, Daniliuc CG, Freytag M, Jones PG, Walter MD. N-Heterocyclic carbene adducts to [Cp′FeI]2: synthesis and molecular and electronic structure. Inorg Chem Front 2016. [DOI: 10.1039/c5qi00235d] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Adducts [Cp′FeI(NHC)] exhibit a highly anisotropic magnetic Ms = ±2 ground state resulting in unusual large spin–lattice (Orbach) relaxation barriers observed by zero-field 57Fe Mössbauer spectroscopy.
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Affiliation(s)
- Matthias Reiners
- Institut für Anorganische und Analytische Chemie
- Technische Universität Braunschweig
- 38106 Braunschweig
- Germany
| | - Dirk Baabe
- Institut für Anorganische und Analytische Chemie
- Technische Universität Braunschweig
- 38106 Braunschweig
- Germany
| | - Kristoffer Harms
- Institut für Anorganische und Analytische Chemie
- Technische Universität Braunschweig
- 38106 Braunschweig
- Germany
| | - Miyuki Maekawa
- Institut für Anorganische und Analytische Chemie
- Technische Universität Braunschweig
- 38106 Braunschweig
- Germany
| | - Constantin G. Daniliuc
- Institut für Anorganische und Analytische Chemie
- Technische Universität Braunschweig
- 38106 Braunschweig
- Germany
| | - Matthias Freytag
- Institut für Anorganische und Analytische Chemie
- Technische Universität Braunschweig
- 38106 Braunschweig
- Germany
| | - Peter G. Jones
- Institut für Anorganische und Analytische Chemie
- Technische Universität Braunschweig
- 38106 Braunschweig
- Germany
| | - Marc D. Walter
- Institut für Anorganische und Analytische Chemie
- Technische Universität Braunschweig
- 38106 Braunschweig
- Germany
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Observation and interpretation of 157.5 T internal magnetic field in Fe[C(SiMe3)3]2 coordination compound. Struct Chem 2009. [DOI: 10.1007/s11224-009-9440-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Stoian SA, Vela J, Smith JM, Sadique AR, Holland PL, Münck E, Bominaar EL. Mössbauer and computational study of an N2-bridged diiron diketiminate complex: parallel alignment of the iron spins by direct antiferromagnetic exchange with activated dinitrogen. J Am Chem Soc 2007; 128:10181-92. [PMID: 16881648 DOI: 10.1021/ja062051n] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This work reports Mössbauer and DFT studies of the diiron-N2 complex LMeFeNNFeLMe (L = beta-diketiminate), 1a. Complex 1a, formally diiron(I), has a system spin S = 3 with an isolated MS = +/-3 quasi-doublet as a ground state; the MS = +/-2 doublet is >100 cm-1 higher in energy. Complex 1a exhibits at 4.2 K a large, positive magnetic hyperfine field, Bint = +68.1 T, and an effective g value of 16 +/- 2 along the easy magnetization axis of the ground doublet; this value is significantly larger than the spin-only value (g = 12). These results have been rationalized by DFT calculations, which show that each Fe site donates significant electron density into the pi* orbitals of dinitrogen, resulting in a configuration best described as two high-spin FeII (Sa = Sb = 2) bridged by triplet N22- (Sc = 1). In this description the minority spin electron of each iron is accommodated by two nonbonding, closely spaced 3d orbitals, z2 and yz (z is perpendicular to the diketiminate planes, x is along the Fe...Fe vector). Spin-orbit coupling between these orbital states generates a large unquenched orbital momentum along the iron-iron vector. The S = 3 ground state of 1a results from strong antiferromagnetic direct exchange couplings of the Fe spins (Sa = Sb = 2) to the N22- spin (Sc = 1) and can be formulated as ((Sa,Sb)Sab = 4, Sc = 1), S = 3>; H = J(Sa + Sb).Sc with J approximately 3500 cm-1.
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Affiliation(s)
- Sebastian A Stoian
- Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA
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Stoian SA, Yu Y, Smith JM, Holland PL, Bominaar EL, Münck E. Mössbauer, electron paramagnetic resonance, and crystallographic characterization of a high-spin Fe(I) diketiminate complex with orbital degeneracy. Inorg Chem 2005; 44:4915-22. [PMID: 15998018 DOI: 10.1021/ic050321h] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The synthesis and X-ray structure of the low-coordinate, high-spin Fe(I) compound LFe(HCCPh) (L = HC(C[tBu]N[2,6-diisopropylphenyl])2]-), 1, are reported. Low-temperature Mössbauer and electron paramagnetic resonance (EPR) spectroscopies reveal that the electronic ground state is a Kramers doublet with uniaxial magnetic properties (effective g values g(x) = 8.9, 0 < g(y), g(z) < 0.3) that is well isolated from the excited states. The observation of a large and positive magnetic hyperfine field, B(int) = +68.8(3) T, demonstrates that the orbital angular moment is essentially unquenched along one spatial direction. Relaxation rates obtained from variable-temperature Mössbauer spectra were fit to an Orbach process, yielding delta = 130-190 cm(-1) for the energy gap ("zero-field splitting") between the two Kramers doublets of the S = 3/2 multiplet. Density functional theory (DFT) and time-dependent DFT calculations give insight into the electronic structures of the ground and excited states. The oxidation state of the iron and the bond order of the phenylacetylene ligand in complex 1 are analyzed using DFT, showing a substantial back-bonding interaction. Spin-orbit coupling acting in the subspace of quasi-degenerate z2 and yz orbitals provides a consistent description of both the zero-field splitting and magnetic hyperfine parameters that fits the EPR and Mössbauer data for 1. Interestingly, the spin-orbit coupling involves the same two orbitals (z2, yz) as in the analogous three-coordinate Fe(II) compounds, because back-bonding significantly lowers the energy of the xy orbital, making it the lowest doubly occupied d orbital. Despite the different oxidation state and different number of atoms in the first coordination sphere, the electronic structure of LFe(I)(HCCPh) can be interpreted similarly to that of three-coordinate Fe(II) diketiminate complexes, but with a substantial effect of back-bonding. To our knowledge, this is the first detailed Mössbauer and EPR study of a structurally characterized high-spin Fe(I) complex.
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Affiliation(s)
- Sebastian A Stoian
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
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Reiff WM, LaPointe AM, Witten EH. Virtual free ion magnetism and the absence of Jahn-Teller distortion in a linear two-coordinate complex of high-spin iron(II). J Am Chem Soc 2004; 126:10206-7. [PMID: 15315408 DOI: 10.1021/ja030632w] [Citation(s) in RCA: 123] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Mössbauer spectroscopy and dc magnetization measurements have been used to characterize the low temperature magnetism of a rigorously linear, two-coordinate complex of high-spin Fe(II), Fe[(C(Si(CH3)3]2 (1). The local C-Fe-C chromophore of 1 exhibits novel slow, single-ion paramagnetic relaxation and fully resolved magnetic hyperfine splitting of its zero field Mössbauer spectrum over the range approximately 100 to approximately 50K. The hyperfine field at 4.2 K is 152 T! This is the largest magnetic hyperfine field observed for iron to date regardless of spin, oxidation state, or coordination environment. This observation is attributable to the large unquenched orbital angular momentum corresponding to the degenerate ground (dxy, dx2-y2) orbital pair of 1 in local Dinfinityh symmetry. Maintenance of the ground-state degeneracy is required by the Jahn-Teller theorem leading to the unprecedented result that the magnitude of the magnetic moment of 1's 5Deltag ground state is essentially that of the parent free ion (5D4) ground term.
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Affiliation(s)
- William M Reiff
- Department of Chemistry and Chemical Biology, Northeastern University, 360 Huntington Avenue, Boston, MA 02115, USA.
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Klatyk J, Schnelle W, Wagner FR, Niewa R, Novák P, Kniep R, Waldeck M, Ksenofontov V, Gütlich P. Large orbital moments and internal magnetic fields in lithium nitridoferrate(I). PHYSICAL REVIEW LETTERS 2002; 88:207202. [PMID: 12005596 DOI: 10.1103/physrevlett.88.207202] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2001] [Indexed: 05/23/2023]
Abstract
The iron nitridometalates Li2[(Li(1-x)Fe(I)(x))N] display ferromagnetic ordering and spin freezing. Large magnetic moments up to 5.0mu(B)/Fe are found in the magnetization. In Mössbauer effect studies huge hyperfine magnetic fields up to 696 kOe are observed at specific Fe sites. These extraordinary fields and moments originate in an unusual ligand field splitting for those Fe species leading [within local spin density approximation (LSDA)] to a localized orbitally degenerate doublet. Including spin-orbit interaction and strong intra-atomic electron correlation (LDA+SO+U) gives rise to a large orbital momentum.
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Affiliation(s)
- J Klatyk
- Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Strasse 40, 01187 Dresden, Germany
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Andres H, Bominaar EL, Smith JM, Eckert NA, Holland PL, Münck E. Planar three-coordinate high-spin Fe(II) complexes with large orbital angular momentum: Mössbauer, electron paramagnetic resonance, and electronic structure studies. J Am Chem Soc 2002; 124:3012-25. [PMID: 11902893 DOI: 10.1021/ja012327l] [Citation(s) in RCA: 165] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Mössbauer spectra of [LFe(II)X](0) (L = beta-diketiminate; X = Cl(-), CH(3)(-), NHTol(-), NHtBu(-)), 1.X, were recorded between 4.2 and 200 K in applied magnetic fields up to 8.0 T. A spin Hamiltonian analysis of these data revealed a spin S = 2 system with uniaxial magnetization properties, arising from a quasi-degenerate M(S) = +/-2 doublet that is separated from the next magnetic sublevels by very large zero-field splittings (3/D/ > 150 cm(-1)). The ground levels give rise to positive magnetic hyperfine fields of unprecedented magnitudes, B(int) = +82, +78, +72, and +62 T for 1.CH(3), 1.NHTol, 1.NHtBu, and 1.Cl, respectively. Parallel-mode EPR measurements at X-band gave effective g values that are considerably larger than the spin-only value 8, namely g(eff) = 10.9 (1.Cl) and 11.4 (1.CH(3)), suggesting the presence of unquenched orbital angular momenta. A qualitative crystal field analysis of g(eff) shows that these momenta originate from spin-orbit coupling between energetically closely spaced yz and z(2) 3d-orbital states at iron and that the spin of the M(S) = +/-2 doublet is quantized along x, where x is along the Fe-X vector and z is normal to the molecular plane. A quantitative analysis of g(eff) provides the magnitude of the crystal field splitting of the lowest two orbitals, /epsilon(yz) - epsilon(2)(z)/ = 452 (1.Cl) and 135 cm(-1) (1.CH(3)). A determination of the sign of the crystal field splitting was attempted by analyzing the electric field gradient (EFG) at the (57)Fe nuclei, taking into account explicitly the influence of spin-orbit coupling on the valence term and ligand contributions. This analysis, however, led to ambiguous results for the sign of epsilon(yz) - epsilon(2)(z). The ambiguity was resolved by analyzing the splitting Delta of the M(S) = +/-2 doublet; Delta = 0.3 cm(-1) for 1.Cl and Delta = 0.03 cm(-)(1) for 1.CH(3). This approach showed that z(2) is the ground state in both complexes and that epsilon(yz) - epsilon(2)(z) approximately 3500 cm(-1) for 1.Cl and 6000 cm(-1) for 1.CH(3). The crystal field states and energies were compared with the results obtained from time-dependent density functional theory (TD-DFT). The isomer shifts and electric field gradients in 1.X exhibit a remarkably strong dependence on ligand X. The ligand contributions to the EFG, denoted W, were expressed by assigning ligand-specific parameters: W(X) to ligands X and W(N) to the diketiminate nitrogens. The additivity and transferability hypotheses underlying this model were confirmed by DFT calculations. The analysis of the EFG data for 1.X yields the ordering W(N(diketiminate)) < W(Cl) < W(N'HR), W(CH(3)) and indicates that the diketiminate nitrogens perturb the iron wave function to a considerably lesser extent than the monodentate nitrogen donors do. Finally, our study of these synthetic model complexes suggests an explanation for the unusual values for the electric hyperfine parameters of the iron sites in the Fe-Mo cofactor of nitrogenase in the M(N) state.
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Affiliation(s)
- Hanspeter Andres
- Departments of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA 15213, USA
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