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

Abstract A quantum chemical study was carried out for a number of iron(II) complexes [FeL 2 ]A i · n H 2 O (L = 2,6‐bis(1 H ‐imidazole‐2‐yl)pyridine (L 1 ); 2,6‐(4,5‐dimethyl‐1 H ‐imidazole‐2‐yl)pyridine (L 2 ); 2,6‐bis(1 H ‐benzimidazole‐2‐yl)pyridine (L 3 ); A = ReO 4 − , B 10 H 10 2− , B 12 H 12 2− ; 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 5 T 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 <0.02> mm/s and <0.1> 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.