Structure and UV-Vis spectroscopy of nitrosylthiolatoferrate mononuclear complexes

Density functional calculations for the (RS)_xFe(NO)_4−x]⁻ (R=CH₃) compounds are carried out using the DFT method with the B3LYP functional. The results can be verified by the experimental data only in the case of the (RS)₂Fe(NO)₂]⁻ complex. The experimentally characterised molecular structure of (RS)₂Fe(NO)₂]⁻ (where (RS)₂=(SCH₂CH₂NMeCH₂CH₂CH₂NMeCH₂CH₂S) is properly reproduced by the RB3LYP method. The discrepancy between the calculated spin densities with the integral spin observed experimentally is interpreted in terms of antiferromagnetic coupling between the Fe(III) centre and the NO⁻ ligands. The theoretical analysis gives a good account of some properties observed in these compounds. In particular, the electronic spectrum calculated by the TDDFT method for (CH₃S)₂Fe(NO)₂]⁻ is similar in shape to the experimental one, although is hypsochromically shifted. The LLCT (S_π→π^*_NO), LMCT (S_π→d) or (π^*_NO→d+S_π→d) and MLCT (d→π^*_NO) transitions are mostly responsible for absorption of the (RS)_xFe(NO)_4−x]⁻ complexes within UV-Vis. The chemical reactivity of (RS)₂Fe(NO)₂]⁻ is interpreted basing on the calculated effect of a polar solvent on the ligand polarity and on the character of the HOMO and LUMO orbitals.