Influence of Peripheral Substituents on Fe(II) Spin State in Complexes with Tridentate Schiff‐Base Ligands.

Six Fe(II) complexes with substituted 6‐((quinoline‐8‐ylimino)methyl)phenolates (R2qsal) were synthesized. X‐ray crystal structure determination for [Fe(R2qsal)2], where R=F (1), Cl (2), Br (3), I (4), CF3/H (5), or CN/H (6), revealed mononuclear complexes that crystallize either solvent‐free in case of 1, 5, and 6 or as CH2Cl2 solvates in the case of 2, 3, and 4. Complexes 1–4, which contain π‐donating substituents, exhibit only high‐spin (HS) state, as shown by crystal structure analysis and magnetic measurements. In contrast, complexes 5 and 6, which contain electron‐withdrawing substituents, exist in the low‐spin (LS) state at lower temperatures but exhibit crossover to the HS state above 300 K. Electronic structure calculations show a good correlation between the relative energies of the LS and HS states and the experimentally observed behavior. [ABSTRACT FROM AUTHOR]