Abstract: The electronic structure and chemical bonding of the five coordinate iron clusters [Fe(XCHCHS)_2]_2~n-[X=O, (Ⅰ); X=S, (Ⅱ); n=2, 3, 4] and their monomers have been studied. The calculated data of the quadrupole splitting and chemical isomer shift are in good agreement with those of experiments.The multiplet of the iron in the oxidized ground state of cluster(Ⅰ) is 6, while that of (Ⅱ) is 4, in accordance with the experimental results. The calculation result shows that the oxidation-reduction process in fact takes place on iron, but the electrons gained or lost transfer to the ligand atoms through charge relaxation. The formation of these clusters can be considered as dimerization of two fragments through interaction of their orbitals in the frontier region. An explanation about the configuration difference between (I) and (II) is proposed.

Key words: Five coordinate iron clusters, Electronic structure