Ab initio calcns. were performed for complexes Fe2S2(SH)42- and Fe2S2 (SH)43- by utilizing 2 kinds of Gaussian basis sets. The 1st set is identical to that previously used for dealing with Fe2S2Cl42-, while the 2nd is a larger one in which 4p-like functions are included for Fe atom. The energy level sequences obtained are comparable with each other. The highest occupied orbitals are of terminal S character in the dianion and change into species mainly involving bridged S components upon reduction This is in agreement with the evidence that the terminal and bridged S atoms are the active sites undergoing substitution and dimerization, resp.

Key words: CALCULATION, MOLECULAR ORBIT, IRON COMPLEX, FERRITIN, CHEMICAL BONDS, ENERGY LEVELS, AB INITIO CALCULATION, SEQUENCE, SULFIDE COMPLEX, METALLOPROTEIN