Effect of the chemical structure of an equatorial ligand on the spin crossover properties of the Fe(III) complex with 4-styrylpyridine axial ligands

In order to study the effect of the chemical structure of the equatorial ligand on the spin state of the Fe(iii) ion in complexes with invariable photoisomerizable 4-styrylpyridine axial ligands and different tetradentate Schiff bases, several new Fe(iii) complexes have been first synthesized, characterized, and studied by UV-vis, NMR, and EPR spectroscopies. The general chemical formula of the complexes is [Fe(SB)Sp₂]BPh₄·MeOH, where Sp is trans-4-styrylpyridine and SB are dianions of Schiff bases: salen, bzacen, and acen [salen = N,N'-ethylenebis(salicylaldimine) 1, acen = N,N'-ethylenebis(acetylacetonylideneimine) 2, and H₂bzacen = N,N'-ethylenebis(benzoylacetonylideneimine) 3]. The results of the EPR and NMR measurements of the complexes both in the solid state and in solutions showed that the more methyl groups and less aromatic rings in the equatorial ligand, the more abrupt spin-crossover was observed in the complex. The dependence of the magnetic properties of the complexes on the state of matter and the presence of a solvent (powder, liquid solutions, and vitrified solutions) are noted.