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Stoian SA, Moshari M, Ferentinos E, Grigoropoulos A, Krzystek J, Telser J, Kyritsis P. Electronic Structure of Tetrahedral, S = 2, [Fe{(EP iPr 2) 2N} 2], E = S, Se, Complexes: Investigation by High-Frequency and -Field Electron Paramagnetic Resonance, 57Fe Mössbauer Spectroscopy, and Quantum Chemical Studies. Inorg Chem 2021; 60:10990-11005. [PMID: 34288665 DOI: 10.1021/acs.inorgchem.1c00670] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In this work, we assessed the electronic structures of two pseudotetrahedral complexes of FeII, [Fe{(SPiPr2)2N}2] (1) and [Fe{(SePiPr2)2N}2] (2), using high-frequency and -field EPR (HFEPR) and field-dependent 57Fe Mössbauer spectroscopies. This investigation revealed S = 2 ground states characterized by moderate, negative zero-field splitting (zfs) parameters D. The crystal-field (CF) theory analysis of the spin Hamiltonian (sH) and hyperfine structure parameters revealed that the orbital ground states of 1 and 2 have a predominant dx2-y2 character, which is admixed with dz2 (∼10%). Although replacing the S-containing ligands of 1 by their Se-containing analogues in 2 leads to a smaller |D| value, our theoretical analysis, which relied on extensive ab initio CASSCF calculations, suggests that the ligand spin-orbit coupling (SOC) plays a marginal role in determining the magnetic anisotropy of these compounds. Instead, the dx2-y2β → dxyβ excitations yield a large negative contribution, which dominates the zfs of both 1 and 2, while the different energies of the dx2-y2β → dxzβ transitions are the predominant factor responsible for the difference in zfs between 1 and 2. The electronic structures of these compounds are contrasted with those of other [FeS4] sites, including reduced rubredoxin by considering a D2-type distortion of the [Fe(E-X)4] cores, where E = S, Se; X = C, P. Our combined CASSCF/DFT calculations indicate that while the character of the orbital ground state and the quintet excited states' contribution to the zfs of 1 and 2 are modulated by the magnitude of the D2 distortion, this structural change does not impact the contribution of the excited triplet states.
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Affiliation(s)
- Sebastian A Stoian
- Department of Chemistry, University of Idaho, Moscow, Idaho 83844, United States
| | - Mahsa Moshari
- Department of Chemistry, University of Idaho, Moscow, Idaho 83844, United States
| | - Eleftherios Ferentinos
- Inorganic Chemistry Laboratory, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis, Zografou, 15771 Athens, Greece
| | - Alexios Grigoropoulos
- Inorganic Chemistry Laboratory, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis, Zografou, 15771 Athens, Greece
| | - J Krzystek
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, United States
| | - Joshua Telser
- Department of Biological, Physical, and Health Sciences, Roosevelt University, Chicago, Illinois 60605, United States
| | - Panayotis Kyritsis
- Inorganic Chemistry Laboratory, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis, Zografou, 15771 Athens, Greece
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Levesanos N, Liyanage WPR, Ferentinos E, Raptopoulos G, Paraskevopoulou P, Sanakis Y, Choudhury A, Stavropoulos P, Nath M, Kyritsis P. Investigating the Structural, Spectroscopic, and Electrochemical Properties of [Fe{(EPiPr2)2N}2] (E = S, Se) and the Formation of Iron Selenides by Chemical Vapor Deposition. Eur J Inorg Chem 2016. [DOI: 10.1002/ejic.201600833] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- Nikolaos Levesanos
- Inorganic Chemistry Laboratory; Department of Chemistry; National and Kapodistrian University of Athens; Panepistimiopolis 15771 Athens Greece
| | - Wipula P. R. Liyanage
- Department of Chemistry; Missouri University of Science and Technology; 65409 Rolla Missouri USA
| | - Eleftherios Ferentinos
- Inorganic Chemistry Laboratory; Department of Chemistry; National and Kapodistrian University of Athens; Panepistimiopolis 15771 Athens Greece
| | - Grigorios Raptopoulos
- Department of Chemistry; Missouri University of Science and Technology; 65409 Rolla Missouri USA
| | - Patrina Paraskevopoulou
- Department of Chemistry; Missouri University of Science and Technology; 65409 Rolla Missouri USA
| | - Yiannis Sanakis
- Institute of Nanoscience and Nanotechnolgy; N.C.S.R. “Demokritos”; Aghia Paraskevi 15310 Attiki Greece
| | - Amitava Choudhury
- Department of Chemistry; Missouri University of Science and Technology; 65409 Rolla Missouri USA
| | - Pericles Stavropoulos
- Department of Chemistry; Missouri University of Science and Technology; 65409 Rolla Missouri USA
| | - Manashi Nath
- Department of Chemistry; Missouri University of Science and Technology; 65409 Rolla Missouri USA
| | - Panayotis Kyritsis
- Inorganic Chemistry Laboratory; Department of Chemistry; National and Kapodistrian University of Athens; Panepistimiopolis 15771 Athens Greece
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Hazra S, Sasmal S, Fleck M, Grandjean F, Sougrati MT, Ghosh M, Harris TD, Bonville P, Long GJ, Mohanta S. Slow magnetic relaxation and electron delocalization in an S = 9/2 iron(II∕III) complex with two crystallographically inequivalent iron sites. J Chem Phys 2011; 134:174507. [PMID: 21548699 DOI: 10.1063/1.3581028] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The magnetic, electronic, and Mössbauer spectral properties of [Fe(2)L(μ-OAc)(2)]ClO(4), 1, where L is the dianion of the tetraimino-diphenolate macrocyclic ligand, H(2)L, indicate that 1 is a class III mixed valence iron(II∕III) complex with an electron that is fully delocalized between two crystallographically inequivalent iron sites to yield a [Fe(2)](V) cationic configuration with a S(t) = 9∕2 ground state. Fits of the dc magnetic susceptibility between 2 and 300 K and of the isofield variable-temperature magnetization of 1 yield an isotropic magnetic exchange parameter, J, of -32(2) cm(-1) for an electron transfer parameter, B, of 950 cm(-1), a zero-field uniaxial D(9∕2) parameter of -0.9(1) cm(-1), and g = 1.95(5). In agreement with the presence of uniaxial magnetic anisotropy, ac susceptibility measurements reveal that 1 is a single-molecule magnet at low temperature with a single molecule magnetic effective relaxation barrier, U(eff), of 9.8 cm(-1). At 5.25 K the Mössbauer spectra of 1 exhibit two spectral components, assigned to the two crystallographically inequivalent iron sites with a static effective hyperfine field; as the temperature increases from 7 to 310 K, the spectra exhibit increasingly rapid relaxation of the hyperfine field on the iron-57 Larmor precession time of 5 × 10(-8) s. A fit of the temperature dependence of the average effective hyperfine field yields |D(9∕2)| = 0.9 cm(-1). An Arrhenius plot of the logarithm of the relaxation frequency between 5 and 85 K yields a relaxation barrier of 17 cm(-1).
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Affiliation(s)
- Susanta Hazra
- Department of Chemistry, University of Calcutta, Kolkata, India
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Vrajmasu VV, Münck E, Bominaar EL. Theoretical Analysis of the Three-Dimensional Structure of Tetrathiolato Iron Complexes. Inorg Chem 2004; 43:4867-79. [PMID: 15285661 DOI: 10.1021/ic040049w] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The three-dimensional structures of a number of [M(SR)(4)](n-) complexes, where M is a 3d transition metal and R is an alkyl or aryl group, have been analyzed using density functional theory (DFT). Special attention is paid to the Fe(II)/Fe(III) mimics of rubredoxin. The Fe(II) model complex [Fe(SCH(3))(4)](2-) has an equilibrium conformation with D2d symmetry. The DFT energy has been decomposed into contributions for ligand-ligand and metal-ligand interactions. The latter contribution is analyzed with the angular overlap model (AOM) and constitutes the dominant stereospecific interaction in the Fe(II) complex. The sulfur lone-pair electrons exert anisotropic pi interactions on the 3d(6) shell of Fe(II), which are controlled by the torsion angles, omega(i), for the rotations of the S(i)-C(beta) bonds around the Fe-S(i) axes. In contrast, the pi interactions acting on the high-spin 3d(5) shell of Fe(III) are isotropic. As a consequence, the stereochemistry of the Fe(III) complexes is determined by the Coulomb repulsions between the ligands and has S(4) symmetry. The electrostatic repulsions between the lone pairs of the sulfurs are an essential component of the ligand-ligand interaction. The lone-pair repulsions distort the 90 degree angle SFeS' angles (delta + delta(t)) and give rise to a correlation between delta and omega, which is confirmed by crystallographic data. Both the Fe(II) and Fe(III) complexes exhibit structural bistability due to the presence of low-lying equilibrium conformations with S(4) symmetry in which the complex can be trapped by the crystalline host.
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Affiliation(s)
- Vladislav V Vrajmasu
- Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA 15213, USA
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Sanakis Y, Power PP, Stubna A, Münck E. Mössbauer study of the three-coordinate planar Fe(II) thiolate complex [Fe(SR)(3)](-) (R = C(6)H(2)-2,4,6-tBu(3)): model for the trigonal iron sites of the MoFe(7)S(9):homocitrate cofactor of nitrogenase. Inorg Chem 2002; 41:2690-6. [PMID: 12005493 DOI: 10.1021/ic0111278] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The cofactor (M-center) of the MoFe protein of nitrogenase, a MoFe(7)S(9):homocitrate cluster, contains six Fe sites with a (distorted) trigonal sulfido coordination. These sites exhibit unusually small quadrupole splittings, Delta E(Q) approximately 0.7 mm/s, and isomer shifts, delta approximately 0.41 mm/s. Mössbauer and ENDOR studies have provided the magnetic hyperfine tensors of all iron sites in the S = 3/2 state M(N). To assess the intrinsic zero-field splittings and hyperfine parameters of the cofactor sites, we have studied with Mössbauer spectroscopy two salts of the three-coordinated Fe(II) thiolate complex [Fe(SR)(3)](-) (R = C(6)H(2)-2,4,6-tBu(3)). One of the salts, [Ph(4)P][Fe(SR)(3)] x 2MeCN x C(7)H(8), 1, has a planar geometry with idealized C(3h) symmetry. This S = 2 complex has an axial zero-field splitting with D = +10.2 cm(-1). The magnetic hyperfine tensor components A(x) = A(y) = -7.5 MHz and A(z) = -29.5 MHz reflect an orbital ground state with d(z(2)) symmetry. A(iso) = (A(x) +A(y) +A(z))/3 = -14.9 MHz, which includes the contact interaction (kappa P = -21.9 MHz) and an orbital contribution (+7 MHz), which is substantially smaller than A(iso) approximately -22 MHz of the tetrahedral Fe(II)(S-R)(4) sites of both rubredoxin and [PPh(4)](2)[Fe(II)(SPh)(4)]. The largest component of the electric field gradient (EFG) tensor is negative, as expected for a d(z(2)) orbital. However, Delta E(Q) = -0.83 mm/s, which is smaller than expected for a high-spin ferrous site. This reduction can be attributed to a ligand contribution, which in planar complexes provides a large positive EFG component perpendicular to the ligand plane. The isomer shift of 1, delta = 0.56 mm/s, approaches the delta-values reported for the six trigonal cofactor sites. The parameters of 1 and their importance for the cofactor cluster of nitrogenase are discussed.
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Affiliation(s)
- Yiannis Sanakis
- Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA
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Fukui K, Masuda H, Ohya-Nishiguchi H, Kamada H. Effects of CoS torsion angle variation in a cobalt(II)-thiolate complex: X-ray crystal structure analysis, single-crystal EPR measurements and ligand-field calculations. Inorganica Chim Acta 1995. [DOI: 10.1016/0020-1693(95)04683-z] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Ding X, Bill E, Trautwein AX, Winkler H, Kostikas A, Papaefthymiou V, Simopoulos A, Beardwood P, Gibson JF. Exchange interactions, charge delocalization, and spin relaxation in a mixed‐valence di‐iron complex studied by Mössbauer spectroscopy. J Chem Phys 1993. [DOI: 10.1063/1.465881] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Trautwein AX, Bill E, Bominaar EL, Winkler H. Iron-containing proteins and related analogs — complementary Mössbauer, EPR and magnetic susceptibility studies. STRUCTURE AND BONDING 1991. [DOI: 10.1007/3-540-54261-2_1] [Citation(s) in RCA: 147] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Bill E, Haas C, Ding XQ, Maret W, Winkler H, Trautwein AX, Zeppezauer M. Fe(II)-substituted horse liver alcohol dehydrogenase, a model for non-heme iron enzymes. Various states of iron-dioxygen interaction investigated by Mössbauer and EPR spectroscopy. EUROPEAN JOURNAL OF BIOCHEMISTRY 1989; 180:111-21. [PMID: 2539999 DOI: 10.1111/j.1432-1033.1989.tb14621.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The catalytic Zn(II) ion of horse liver alcohol dehydrogenase (EE isozyme) was replaced by Fe(II), providing a novel iron protein with the unusual coordination of Fe(II) to two cysteines residues, one histine residue and water. The electronic structure of iron in this system was characterized by Mössbauer spectroscopy at various temperatures as well as applied magnetic fields and analysed in terms of the spin Hamiltonian formalism. The novelty we found is an unusually weak spin coupling (/J/ less than 0.1 cm-1) of a paramagnet (S = 1) with iron (S = 2). From EPR and biochemical studies we conclude that the corresponding chemical species is triplet oxygen (O2). The quantitative determination of the coupling energy was possible utilizing the competition between Zeemann interaction and spin coupling at weak magnetic fields and low temperature. Oxidation experiments followed by Mössbauer spectroscopy showed that the spin-coupled system is an outer-sphere Fe(II) . (O2)aq complex occurring as an intermediate during a Fe(II)-catalyzed dioxygen activation. We observed two additional Fe(II) species after treatment with O2 and dithionite. The spin Hamiltonian parameters of iron in the coupled system are presented. The results are compared with those of iron in other non-heme iron proteins.
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Affiliation(s)
- E Bill
- Institut für Physik, Medizinische Universität, Lübeck, Federal Republic of Germany
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