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Theory of chemical bonds in metalloenzymes V: Hybrid‐DFT studies of the inorganic [8Fe–7S] core
Author(s) -
Shoji M.,
Koizumi K.,
Kitagawa Y.,
Yamanaka S.,
Okumura M.,
Yamaguchi K.,
Ohki Y.,
Sunada Y.,
Honda M.,
Tatsumi K.
Publication year - 2006
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.21201
Subject(s) - singlet state , chemistry , density functional theory , antiferromagnetism , chemical bond , ground state , bond order , atomic orbital , electronic structure , cubane , computational chemistry , spin (aerodynamics) , spin states , bond length , condensed matter physics , atomic physics , crystallography , quantum mechanics , physics , thermodynamics , inorganic chemistry , crystal structure , organic chemistry , excited state , electron
The electronic and spin structures of the [8Fe–7S] inorganic model complex (1) have been investigated using the density functional theory (DFT) UB3LYP and UBLYP methods. The experimental geometry of 1 was used to calculate the sets of exchange interactions ( J values) between Fe‐spin centers within spin Hamiltonian models. The experimental temperature‐dependent paramagnetism is well reproduced on the basis of the calculated J values. The calculated low‐lying energy levels are also consistent with those of the experiments. This indicates that the ground spin state of 1 is singlet (S = 0) for the weak antiferromagnetic coupling between two [4Fe–3S] cubane units, which take the Fe(III)Fe(II) 3 formal charge and S = 7/2 spin states. The first‐order density matrix of the most stable broken‐symmetry (BS) solution has been diagonalized to elucidate the natural molecular orbitals (MOs) and their occupation number of 1, which are hardly obtained by the symmetry‐adapted (SA) CASSCF approach. Several chemical indices such as the effective bond orders before and after spin projection are also calculated by using the occupation numbers to provide the SA MO picture of labile chemical bonds of 1. It is found that the BS MO calculation followed by spin‐projected SA analysis is an effective and practical alternative to the CASSCF MO approach for the multinuclear transition metal clusters. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006