Study of spin crossover in an iron(II) tris(diimine) system tuned by counter anions.

Investigations of spin-crossover in an iron(II) tris(diimine) system, based on the ligands L 1 (4,5-dimethy-2-(pyridine-2-yl)imidazole) and L 2 (1-acetic ethyl-2-(pyridine-2-yl)-imidazole), have been presented in this paper. The methyl groups at adjacent sites to the donor atoms in the ligand L 1 generated the crossover situation for complexes Fe( L 1 ) 3 (ClO 4 − ) 2 ( 1 ), Fe( L 1 ) 3 (BF 4 − ) 2 ( 2 ), Fe( L 1 ) 3 (PF 6 − ) 2 ( 3 ) and Fe( L 1 ) 3 (SbF 6 − ) 2 ( 4 ), while the acetic ethyl group at the non-coordinating NH site of the ligand L 2 resulted in an increase in the ligand field and generated a low-spin (LS) state for the complex Fe( L 2 ) 3 (ClO 4 − ) 2 ( 5 ). Complexes 1 and 5 were structurally characterized by single-crystal X-ray diffraction at different spin-states, while the phase purity of complexes 2 – 4 was confirmed by PXRD. Raman, IR and UV–Vis absorption spectra and magnetic properties of 1 – 4 were obtained, which revealed the influence of different counter anions on the spin transition temperatures. The blue-shift of IR and Raman spectra, red-shift and decrease in molar absorptivity of UV–Vis absorption spectra all follow the sequence 1 < 3 < 2 < 4 . [ABSTRACT FROM AUTHOR]