A DFT and Mossbauer spectroscopy investigation of spin-crossover iron(II) complexes with 2,6-bis(1H-imidazol-2-yl)pyridines

A quantum chemical study was carried out for a number of iron(II) complexes [FeL2]A(i)& BULL;nH(2)O (L = 2,6-bis(1H-imidazole-2-yl)pyridine (L-1); 2,6-(4,5-dimethyl-1H-imidazole-2-yl)pyridine (L-2); 2,6-bis(1H-benzimidazole-2-yl)pyridine (L-3); A = ReO4-, B10H102-, B12H122-; n = 0-2). These complexes exist in the low spin (LS) form (1)A(1) (total electron spin S = 0) at room temperature and switch to the high spin (HS) form T-5(2) (S = 2) upon heating. The experimental isomeric shift and quadrupole splitting values for compounds with L-2 exceed those for compounds with L-1 and L-3 by mm/s and mm/s, respectively (for LS forms). Such a discrepancy between MS parameters can be explained by the assumption that chemical bonding between the iron ion and the surrounding nitrogen atoms in the compounds with L-2 may be more ionic in character than that in the compounds with L-1 and L-3. At the same time, the results obtained with the TPSSh hybrid meta-GGA functional gave a better agreement with the experimental data than those obtained with the B3LYP exchange-correlation functional.