Solvent Dependent Spin-State Behaviour via Hydrogen Bonding in Neutral FeII Diimine Complexes

We report the syntheses, structures, and magnetic properties of cis-[Fe(pizR)2(NCS)2] complexes based on the pyridyl imidazoline ligands 2-(20-pyridinyl)-4,5-dihydroimidazole (pizH, 1) and 2-(20-pyridinyl)-4,5-dihydro-1-methylimidazole (pizMe, 2). The ligands, complexes, and magnetic measurements are chosen to separate hydrogen-bonding and intrinsic ligand field properties, so as to improve our understanding of the effect of hydrogen-bonding interactions on spin-state switching. In the solid state, both complexes are high spin between 5 and 300K. In deuterated methanol and acetonitrile solutions, both complexes show gradual thermal spin crossover. Complex 1, capable of hydrogen bonding, shows solvent-sensitive spin crossover, whereas spin crossover in the methylated analogue 2 is insensitive to solvent identity