1
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Li L, Yuan F. Unexpected C=N bond cleavage in H3salmp: Synthesis and structures of [LnNa(salmp)(sal)]2·6EtOH (Ln = Sm, Er; H3salmp = 2-bis(salicylidieneamino) methylphenol; sal = salicylaldehydato). J STRUCT CHEM+ 2017. [DOI: 10.1134/s0022476617070319] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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2
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Yu F, Cao ZH, Ge JY, Sun YC, Ouyang ZW, Zuo JL, Wang Z, Kurmoo M. Magnetostructural relationship for μ2-phenoxido bridged ferric dimers. Dalton Trans 2017; 46:4317-4324. [DOI: 10.1039/c7dt00110j] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The magneto-structural correlation between μ2-phenoxido bridged iron(iii) complexes are studied by structural analyses, magnetic, HF-EPR measurements, and DFT calculations. The magnetic exchange coupling is governed by the Fe–O–Fe angle and the crossover point from AF to F interactions is θ at 97.83°.
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Affiliation(s)
- Fei Yu
- State Key Laboratory of Coordination Chemistry
- School of Chemistry and Chemical Engineering
- Collaborative Innovation Center of Advanced Microstructures
- Nanjing University
- Nanjing
| | - Zi-Heng Cao
- State Key Laboratory of Coordination Chemistry
- School of Chemistry and Chemical Engineering
- Collaborative Innovation Center of Advanced Microstructures
- Nanjing University
- Nanjing
| | - Jing-Yuan Ge
- State Key Laboratory of Coordination Chemistry
- School of Chemistry and Chemical Engineering
- Collaborative Innovation Center of Advanced Microstructures
- Nanjing University
- Nanjing
| | - Yi-Chen Sun
- Wuhan National High Magnetic Field Center
- Huazhong University of Science and Technology
- Wuhan
- P. R. China
| | - Zhong-Wen Ouyang
- Wuhan National High Magnetic Field Center
- Huazhong University of Science and Technology
- Wuhan
- P. R. China
| | - Jing-Lin Zuo
- State Key Laboratory of Coordination Chemistry
- School of Chemistry and Chemical Engineering
- Collaborative Innovation Center of Advanced Microstructures
- Nanjing University
- Nanjing
| | - Zhenxing Wang
- Wuhan National High Magnetic Field Center
- Huazhong University of Science and Technology
- Wuhan
- P. R. China
| | - Mohamedally Kurmoo
- Institut de Chimie de Strasbourg
- Université de Strasbourg
- CNRS-UMR 7177
- 67008 Cedex Strasbourg
- France
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3
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Nasonova DI, Presniakov IA, Sobolev AV, Verchenko VY, Tsirlin AA, Wei Z, Dikarev EV, Shevelkov AV. Role of iron in synthetic tetrahedrites revisited. J SOLID STATE CHEM 2016. [DOI: 10.1016/j.jssc.2016.03.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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4
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Nasonova DI, Presniakov IA, Sobolev AV, Verchenko VY, Tsirlin AA, Wei Z, Dikarev EV, Shevelkov AV. Role of iron in synthetic tetrahedrites revisited. J SOLID STATE CHEM 2016. [DOI: 10.1016/j.jssc.2015.12.015] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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5
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Li L, Zhou Y, Yuan F. Bis(μ-2-{bis-[(2-oxidobenzyl-idene)amino]-meth-yl}phenolato)bis-[(tetra-hydro-furan)-samarium(III)] tetra-hydro-furan disolvate. Acta Crystallogr Sect E Struct Rep Online 2012; 68:m603-4. [PMID: 22590109 PMCID: PMC3344343 DOI: 10.1107/s1600536812015759] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2012] [Accepted: 04/11/2012] [Indexed: 11/24/2022]
Abstract
In the centrosymmetric binuclear complex of the title solvate, [Sm2(C21H15N2O3)2(C4H8O)2]·2C4H8O, the SmIII is coordinated in a distorted monocapped octahedral geometry by four O atoms and two N atoms from two tridentate deprotonated 2-{bis[(2-oxidobenzylidene)amino]methyl}phenolate ligands and an O atom of a tetrahydrofuran (THF) molecule. The Sm⋯Sm distance in the complex is 3.8057 (4) Å. Parts of the coordinating THF molecule are disordered over two sets of sites in a 0.56 (3):0.44 (3) ratio. The complex and solvent molecules are linked into a three-dimensional structure via C—H⋯O hydrogen-bonding interactions.
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Affiliation(s)
- Li Li
- School of Chemistry and Biochemistry, University of Science and Technology of Suzhou, Suzhou 215009, People's Republic of China
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6
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Guo D, Knight TE, McCusker JK. Angular Momentum Conservation in Dipolar Energy Transfer. Science 2011; 334:1684-7. [DOI: 10.1126/science.1211459] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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7
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Zueva EM, Sameera WMC, Piñero DM, Chakraborty I, Devlin E, Baran P, Lebruskova K, Sanakis Y, McGrady JE, Raptis RG. Experimental and theoretical Mössbauer study of an extended family of [Fe8(μ4-O)4(μ-4-R-px)12X4] clusters. Inorg Chem 2010; 50:1021-9. [PMID: 21188980 DOI: 10.1021/ic101691q] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Six [Fe(8)(μ(4)-O)(4)(μ-4-R-pyrazolato)(12)X(4)] complexes containing an identical Fe(8)(μ(4)-O)(4) core have been structurally characterized and studied by Mössbauer spectroscopy. In each case, an inner μ(4)-O bridged Fe(III) cubane core is surrounded by four trigonal bipyramidal iron centers, the two distinct sites occurring in a 1:1 ratio. The Mössbauer spectrum of each of the clusters consists of two quadrupole doublets, which, with one exception (X = NCS, R = H), overlap to give three absorption lines. The systematic variation of X and R causes significant changes in the Mössbauer spectra. A comparison with values for the same clusters computed using density functional theory allows us to establish an unequivocal assignment of these peaks in terms of a nested model for the overlapping doublets. The changes in Mössbauer parameters (both experimental and computed) for the 1-electron reduced species [Fe(8)(μ(4)-O)(4)(μ-4-Cl-pyrazolato)(12)Cl(4)](-) are consistent with a redox event that is localized within the cubane core.
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Affiliation(s)
- Ekaterina M Zueva
- Department of Inorganic Chemistry, Kazan State Technological University, Kazan, Russia
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8
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Guo D, McCusker JK. Spin exchange effects on the physicochemical properties of tetraoxolene-bridged bimetallic complexes. Inorg Chem 2007; 46:3257-74. [PMID: 17371015 DOI: 10.1021/ic070005y] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The synthesis, physical, and spectroscopic properties of a series of metal complexes bridged by the redox-active chloranilate ligand are described. Compounds containing the (CAcat,cat)4- ligand, where (CAcat,cat)4- represents the fully reduced aromatic form of chloranilate, have been prepared by two different routes from H2CA and H4CA starting materials; the corresponding (CAsq,cat)3- analogue was obtained by one-electron oxidation with decamethylferrocenium tetrafluoroborate. Homo- and heterobimetallic complexes containing CrIII and GaIII with chloranilate have been prepared, yielding the following six complexes: [Ga2(tren)2(CAcat,cat)](BPh4)2 (1), [Ga2(tren)2(CAsq,cat)](BPh4)2(BF4) (2), [GaCr(tren)2(CAcat,cat)](BPh4)2 (3), [GaCr(tren)2(CAsq,cat)](BPh4)2(BF4) (4), [Cr2(tren)2(CAcat,cat)] (BPh4)2 (5), and [Cr2(tren)2(CAsq,cat)](BPh4)2(BF4) (6) (where tren is tris(2-aminoethyl)amine). Single-crystal X-ray structures have been obtained for complexes 1, 3, and 5; nearly identical C-C bond distances within the quinoidal ligand confirm the aromatic character of the bridge in each case. Complex 2 exhibits a temperature-independent magnetic moment of microeff = 1.64 +/- 0.04 microB in the solid state between 4 and 350 K, consistent with the CAsq,cat formulation of the ligand and an S = 1/2 ground state for complex 2. Complex 3 exhibits a value of microeff = 3.44 +/- 0.09 microB that is also temperature-independent, indicating an S = 3/2 ground state. Complexes 4-6 are all influenced by Heisenberg spin exchange. The temperature-independent behavior of complexes 4 and 6 indicate the presence of strong antiferromagnetic exchange between the CrIII and the (sq,cat) bridging radical yielding well-isolated ground states of S = 1 and 5/2 for 4 and 6, respectively. In contrast, complex 5 exhibits a weak intramolecular antiferromagnetic exchange interaction between the two CrIII centers (J = -2 cm-1 for H = -2Jŝ1.ŝ2) via superexchange through the diamagnetic CAcat,cat bridge. The absorption spectra of the CAsq,cat-containing complexes exhibit a number of sharp, relatively intense features in fluid solution. Group theoretical arguments coupled with a qualitative ligand-field analysis including the effects of Heisenberg spin exchange suggest that several of the observed transitions are a consequence of exchange interactions in both the ground- and excited-state manifolds of the compounds.
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Affiliation(s)
- Dong Guo
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA
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9
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Belinsky MI. Spin–orbit coupling in the double exchange model 2. Comparison of the antisymmetric double exchange with the Dzialoshinsky–Moriya antisymmetric exchange, spin canting and ZFS. Chem Phys 2006. [DOI: 10.1016/j.chemphys.2005.12.020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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10
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Spin–orbit coupling in the double exchange model 1. Antisymmetric double exchange in a valence-delocalized [Fe2.5+Fe2.5+] cluster. Chem Phys 2006. [DOI: 10.1016/j.chemphys.2005.12.019] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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11
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Berlinguette CP, Dragulescu-Andrasi A, Sieber A, Güdel HU, Achim C, Dunbar KR. A Charge-Transfer-Induced Spin Transition in a Discrete Complex: The Role of Extrinsic Factors in Stabilizing Three Electronic Isomeric Forms of a Cyanide-Bridged Co/Fe Cluster. J Am Chem Soc 2005; 127:6766-79. [PMID: 15869299 DOI: 10.1021/ja043162u] [Citation(s) in RCA: 132] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A series of bimetallic, trigonal bipyramidal clusters of type {[Co(N-N)(2)](3)[Fe(CN)(6)](2)} are reported. The reaction of {Co(tmphen)(2)}(2+) with [Fe(CN)(6)](3)(-) in MeCN affords {[Co(tmphen)(2)](3)[Fe(CN)(6)](2)} (1). The cluster can exist in three different solid-state phases: a red crystalline phase, a blue solid phase obtained by exposure of the red crystals to moisture, and a red solid phase obtained by desolvation of the blue solid phase in vacuo. The properties of cluster 1 are extremely sensitive to both temperature and solvent content in each of these phases. Variable-temperature X-ray crystallography; (57)Fe Mossbauer, vibrational, and optical spectroscopies; and magnetochemical studies were used to study the three phases of 1 and related compounds, Na{[Co(tmphen)(2)](3)[Fe(CN)(6)](2)}(ClO(4))(2) (2), {[Co(bpy)(2)](3)[Fe(CN)(6)](2)}[Fe(CN)(6)](1/3) (3), and {[Ni(tmphen)(2)](3)[Fe(CN)(6)](2)} (4). The combined structural and spectroscopic investigation of 1-4 leads to the unambiguous conclusion that 1 can exist in different electronic isomeric forms, {Co(III)(2)Co(II)Fe(II)(2)} (1A), {Co(III)Co(II)(2)Fe(III)Fe(II)} (1B), and {Co(II)(3)Fe(III)(2)} (1C), and that it can undergo a charge-transfer-induced spin transition (CTIST). This is the first time that such a phenomenon has been observed for a Co/Fe molecule.
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Affiliation(s)
- Curtis P Berlinguette
- Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, TX 77842-3012, USA
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12
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Belinsky MI. Anisotropic double exchange in mixed-valence dimeric clusters of transition metal ions. Chem Phys 2005. [DOI: 10.1016/j.chemphys.2004.07.043] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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13
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Stubna A, Jo DH, Costas M, Brenessel WW, Andres H, Bominaar EL, Münck E, Que L. A structural and Mössbauer study of complexes with Fe(2)(micro-O(H))(2) cores: stepwise oxidation from Fe(II)(micro-OH)(2)Fe(II) through Fe(II)(micro-OH)(2)Fe(III) to Fe(III)(micro-O)(micro-OH)Fe(III). Inorg Chem 2004; 43:3067-79. [PMID: 15132612 DOI: 10.1021/ic030296k] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Dinuclear non-heme iron clusters containing oxo, hydroxo, or carboxylato bridges are found in a number of enzymes involved in O(2) metabolism such as methane monooxygenase, ribonucleotide reductase, and fatty acid desaturases. Efforts to model structural and/or functional features of the protein-bound clusters have prompted the preparation and study of complexes that contain Fe(micro-O(H))(2)Fe cores. Here we report the structures and spectroscopic properties of a family of diiron complexes with the same tetradentate N4 ligand in one ligand topology, namely [(alpha-BPMCN)(2)Fe(II)(2)(micro-OH)(2)](CF(3)SO(3))(2) (1), [(alpha-BPMCN)(2)Fe(II)Fe(III)(micro-OH)(2)](CF(3)SO(3))(3) (2), and [(alpha-BPMCN)(2)Fe(III)(2)(micro-O)(micro-OH)](CF(3)SO(3))(3) (3) (BPMCN = N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane). Stepwise one-electron oxidations of 1 to 2 and then to 3 demonstrate the versatility of the Fe(micro-O(H))(2)Fe diamond core to support a number of oxidation states with little structural rearrangement. Insight into the electronic structure of 1, 2', and 3 has been obtained from a detailed Mössbauer investigation (2' differs from 2 in having a different complement of counterions). Mixed-valence complex 2' is ferromagnetically coupled, with J = -15 +/- 5 cm(-)(1) (H = JS(1).S(2)). For the S = (9)/(2) ground multiplet we have determined the zero-field splitting parameter, D(9/2) = -1.5 +/- 0.1 cm(-)(1), and the hyperfine parameters of the ferric and ferrous sites. For T < 12 K, the S = (9)/(2) multiplet has uncommon relaxation behavior. Thus, M(S) = -(9)/(2) <--> M(S) = +(9)/(2) ground state transition is slow while deltaM(S) = +/-1 transitions between equally signed M(S) levels are fast on the time scale of Mössbauer spectroscopy. Below 100 K, complex 2' is trapped in the Fe(1)(III)Fe(2)(II) ground state; above this temperature, it exhibits thermally assisted electron hopping into the state Fe(1)(II)Fe(2)(III). The temperature dependence of the isomer shifts was corrected for second-order Doppler shift, obtained from the study of diferrous 1. The resultant true shifts were analyzed in a two-state hopping model. The diferric complex 3 is antiferromagnetically coupled with J = 90 +/- 15 cm(-)(1), estimated from a variable-temperature Mössbauer analysis.
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Affiliation(s)
- Audria Stubna
- Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA
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14
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Vrajmasu V, Münck E, Bominaar EL. Density functional study of the electric hyperfine interactions and the redox-structural correlations in the cofactor of nitrogenase. Analysis of general trends in (57)Fe isomer shifts. Inorg Chem 2003; 42:5974-88. [PMID: 12971768 DOI: 10.1021/ic0301371] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The influence of the interstitial atom, X, discovered in a recent crystallographic study of the MoFe protein of nitrogenase, on the electric hyperfine interactions of (57)Fe has been investigated with density functional theory. A semiempirical theory for the isomer shift, delta, is formulated and applied to the cofactor. The values of delta for the relevant redox states of the cofactor are predicted to be higher in the presence of X than in its absence. The analysis strongly suggests a [Mo(4+)4Fe(2+)3Fe(3+)] oxidation state for the S = 3/2 state M(N). Among C(4-), N(3-), and O(2-), oxide is found to be the least likely candidate for X. The analysis suggests that X should be present in the cofactor states M(OX) and M(R) as well as in the alternative nitrogenases. The calculations of the electric field gradients (EFGs) indicate that the small values for DeltaE(Q) in M(N) result from an extensive cancellation between valence and ligand contributions. X emerges from the analysis of the hyperfine interactions as an ionically bonded species. Its major effect is on the asymmetry parameters for the EFGs at the six equatorial sites, Fe(Eq). A spin-coupling scheme is proposed for the state [Mo(4+)4Fe(2+)3Fe(3+)] that is consistent with the measured (57)Fe A-tensors and DeltaE(Q) values for M(N) and identifies the unique site exhibiting the small A value with the terminal Fe site, Fe(T). The optimized structure of a cofactor model has been calculated for several oxidation states. The study reveals a contraction in the average Fe-Fe distance upon increasing the number of electrons stored in the cluster, in accord with extended X-ray absorption fine structure studies. The reliability of the adopted methodology for predicting redox-structural correlations is tested for cuboidal [4Fe-4S] clusters. The calculations reveal a systematic increase in the S...S sulfide distances, in quantitative agreement with the available data. These trends are rationalized by a simple electrostatic model.
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Affiliation(s)
- Vladislav Vrajmasu
- Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA 15213, USA
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15
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Picraux LB, Weldon BT, McCusker JK. Intramolecular excimer formation in a naphthalene-appended dinuclear iron-oxo complex. Inorg Chem 2003; 42:273-82. [PMID: 12693207 DOI: 10.1021/ic026054m] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The synthesis, structure, and physical properties of a Heisenberg exchange-coupled cluster containing naphthalene groups are described. [Fe2(O)(O2CCH2C10H7)2(TACN-Me3)2]2+ (3) crystallizes in space group P1 with unit cell parameters a = 12.94(2) A, b = 14.84(2) A, c = 15.23(2) A, alpha = 101.12(7) degrees, beta = 90.8(1) degrees, gamma = 114.14(7) degrees, V = 2605(6) A3, and Z = 2 with R = 0.0425 and wR2 = 0.1182. Variable-temperature magnetic susceptibility data indicate that the two high-spin FeIII centers are antiferromagnetically coupled with J = -105 cm-1 (H = -2 JS1.S2), which is typical for this class of compounds. The room-temperature static emission spectrum of the compound in deoxygenated CH3CN solution is centered near 335 nm and has features reminiscent of both methyl-2-naphthylacetate (1) and [Zn2(OH)(O2CCH2C10H7)2(TACN-Me3)2]+ (2) with the following two caveats: (1) the overall emission intensity is roughly a factor of 10 less than that of the free ester (1, phi = 0.13) or the ZnII analogue (2, phi = 0.14), and (2) there is significant broadening of the low-energy shoulder of the emission envelope. Time-correlated single photon counting data revealed biphasic emission for 3 with tau 1 = 4.6 +/- 1 ns and tau 2 = 47 +/- 1 ns. The latter compares favorably with that found for 2 (tau = 47 +/- 1 ns) and is assigned as the S0-S1 fluorescence of naphthalene. Emission anisotropy, time-gated emission spectra, and nanosecond time-resolved absorption measurements all support the assignment of the 4.6 ns component as being due to a singlet excimer that forms between the two naphthylacetate groups of 3, a process that is likely mediated by the structural constraints of the oxo-bis-carboxylato diiron core. No direct evidence for intramolecular electron and/or energy transfer from the photoexcited naphthyl group to the iron-oxo core was obtained, suggesting that the short-lived excimer may contribute to circumventing such pathways in this type of system.
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Affiliation(s)
- Laura B Picraux
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA
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Egdal RK, Hazell A, Larsen FB, McKenzie CJ, Scarrow RC. A dihydroxo-bridged Fe(II)-Fe(III) complex: a new member of the diiron diamond core family. J Am Chem Soc 2003; 125:32-3. [PMID: 12515497 DOI: 10.1021/ja027219t] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The first structurally characterized Fe(II)-Fe(III) complex containing a M2(mu-OH)2 diamond core is a Robin and Day class II mixed-valence complex.
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Affiliation(s)
- Rune Kirk Egdal
- Department of Chemistry, University of Southern Denmark, Odense Campus, 5230 Odense M, Denmark.
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Lee D, DuBois JL, Pierce B, Hedman B, Hodgson KO, Hendrich MP, Lippard SJ. Structural and spectroscopic studies of valence-delocalized diiron(II,III) complexes dupported by carboxylate-only bridging ligands. Inorg Chem 2002; 41:3172-82. [PMID: 12054996 DOI: 10.1021/ic011050n] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The synthesis, molecular structures, and spectroscopic properties of a series of valence-delocalized diiron(II,III) complexes are described. One-electron oxidation of diiron(II) tetracarboxylate complexes afforded the compounds [Fe(2)(mu-O(2)CAr(Tol))(4)L(2)]X, where L = 4-(t)BuC(5)H(4)N (1b), C(5)H(5)N (2b), and THF (3b); X = PF(6)(-) (1b and 3b) and OTf(-) (2b). In 1b-3b, four mu-1,3 carboxylate ligands span relatively short Fe...Fe distances of 2.6633(11)-2.713(3) A. Intense (epsilon = 2700-3200 M(-1) cm(-1)) intervalence charge transfer bands were observed at 620-670 nm. EPR spectroscopy confirmed the S = (9)/(2) ground spin state of 1b-3b, the valence-delocalized nature of which was probed by X-ray absorption spectroscopy. The electron delocalization between paramagnetic metal centers is described by double exchange, which, for the first time, is observed in diiron clusters having no single-atom bridging ligand(s).
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Affiliation(s)
- Dongwhan Lee
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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18
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Weldon BT, Wheeler DE, Kirby JP, McCusker JK. Bimolecular electron and energy transfer reactivity of exchange-coupled dinuclear iron(III) complexes. Inorg Chem 2001; 40:6802-12. [PMID: 11735494 DOI: 10.1021/ic010659l] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Bimolecular quenching between photosensitizers and exchange-coupled transition metal complexes has been studied in an effort to experimentally establish a link between Heisenberg spin exchange and chemical reactivity. The acceptors are members of the oxo/hydroxo-biscarboxylato class of dinuclear Fe(III) compounds, where protonation of the oxo bridge provides a means for modulating the magnitude of spin exchange within the cluster. Photoexcitation of solutions containing Ru(II) polypyridyl sensitizers and the Fe(III) complexes results in quenching of emission from the (3)MLCT excited state of the Ru(II) chromophores; nanosecond time-resolved absorption measurements demonstrate that quenching occurs, in part, by electron transfer. Decoupling electron transfer driving force (DeltaG(0)(ET)) from changes in the magnitude of spin exchange was achieved by varying the bridging carboxylate to afford a series of complexes of the form [Fe(2)O(H)(O(2)CR)(2)(Tp)(2)](n)(+) (n = 0, 1, 2). Electrochemical measurements reveal a greater than 500 mV shift in cluster reduction potential across the series (i.e., R = CH(3) to CF(3)), whereas variable-temperature magnetic susceptibility measurements demonstrate a corresponding invariance in spin exchange between the metal centers (J(oxo) = -119 +/- 4 cm(-1) and J(hydroxo) = -18 +/- 2 cm(-1) for H = -2JS(1).S(2)). Structural analyses suggest that reorganization energies (lambda) associated with electron transfer should be identical for all molecules within a given series (i.e., oxo or hydroxo bridged); likewise Deltalambda between the series is expected to be small. A comparison of quenching rates for the two extended series firmly establishes that neither reorganization energy nor electron transfer driving force considerations can account for differences in reactivity between oxo-bridged (large spin exchange) and hydroxo-bridged (small spin exchange) quenchers. Upon consideration of energy transfer contributions, it is determined that reactivity differences between the oxo- and hydroxo-bridged quenchers must lie in the relative rates of Dexter energy transfer and/or electron transfer, with the origin of the latter linked to something other than DeltaG(0)(ET) or lambda. Finally, the extent to which spin exchange within the dinuclear Fe(III) quenchers can be identified as the key variable influencing these reactivity patterns is discussed.
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Affiliation(s)
- B T Weldon
- Department of Chemistry, University of California at Berkeley, Berkeley, California 94720, USA
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