Nonparameterized molecular orbital calculations of ligand-bridge Fe2(CO)6X2-type dimers containing metal-metal interactions
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Parameter-free molecular orbital calculations via the Fenske-Hall model have been carried out on representative Fe2B2-bridged complexes of the Fe2(CO)6X2-type dimer (viz., those where X2denotes both the (B…B)-nonbonded (SCH3)2 and (NH2)2 ligands and the corresponding (B—B)-bonded S2 and cis-CH3N=NCH3 ligands) and of the [Fe2(CO)6(PR2)2]n series (n = 0, 1-, 2-). These comparative calculations reveal that the above systematic variation of the bridging ligands (with and without direct B-B bonds) does not markedly affect the nature of the Fe-Fe interactions. The orbital character of the ai HOMO in each natural species is found to correspond closely to the classical “bent” Fe-Fe bond with the b2 LUMO being its antibonding counterpart. Furthermore, the determined MO energy-level ordering and associated eigenvectors for the phosphide-bridged dimers with n = 1- and 2- are consistent with the monoanion possessing one electron and the dianion two electrons in this 4b2 MO of predominantly antibonding diiron character, corresponding formally to a “net” one-electron Fe-Fe bond and a “net” no-electron Fe-Fe bond, respectively. The results of this molecular orbital study, which provides the first detailed description of the electronic structure and bonding characteristics of this important dimeric metal cluster system, are evaluated and correlated with the available spectroscopic and crystallographic data. © 1975, American Chemical Society. All rights reserved.
author list (cited authors)
Hall, M. B., Fenske, R. F., & Dahl, L. F.