Mossbauer-Effect and Fenske-Hall Molecular Orbital Study of the Electronic Structure of Several Trinuclear Iron Carbonyl Clusters


Fenske-Hall molecular orbital calculations have been carried out on the trinuclear carbonyl clusters Fe3(CO)12, [Fe3(CO)10CH]−, [Fe3(CO)9CCO]2−, and [Fe2Co(CO)9CCO]−, and their Mössbauer spectra have been measured at 78 K. The iron 4s Mulliken atomic population shows the expected increase as the Mössbauer-effect isomer shift decreases. Further, we find an excellent correlation between the observed isomer shift and the sum of the iron 4s population and the effective nuclear charge they experience. A calculation of the electric field gradients at the iron nuclei, based on the Mulliken atomic charges and the iron wave functions derived from the Fenske–Hall molecular orbital calculations, reveals that the valence contribution by far predominates over the lattice contribution to the electric field gradient at the iron-57 nucleus. There is a rather good correlation between the calculated and observed quadrupole splittings in the iron clusters. © 1993, American Chemical Society. All rights reserved.


Chemistry and Biochemistry

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