The Paramagnetic or Spin Crossover Iron(III) Complexes Based-on Pentadentate Schiff Base Ligand: Crystal Structure, and Magnetic Property Investigation

Abstract

A series of bi- or mononuclear hexacoordinate iron(III) complexes, [Fe(L)][Fe(bpb)(CN)2]·CH3OH·0.5H2O (1), [Fe(L)] [Co(bpb)(CN)2]·CH3OH (2) [(Fe (L))2(4,4’-bipy)](BPh4)2 (3), [Fe(L)(py)](BPh4) (4) and [Fe(L)(dmap)](BPh4) (5) (bpb = 1,2-bis(pyridine-2-carboxamido)benzenate, L = N,N’-bis(2-hydroxybenzyliden)-1,7-diamino-4-azaheptane, dmap = 4-dimethylaminopyridine), have been prepared with the pentadentate Schiff base iron(III) compound as assemble precursor and characterized by element analysis, IR and X-ray diffraction. Single crystal structural determination revealed the neutral cyanide-bridged binuclear entity for complexes 1 and 2 and the cationic di- or mononuclear structure for complexes 3–5 with the positive charge(s) balanced by BPh4 – ion(s). The experimental study and theoretical simulation of the magnetic property discovered the ferromagnetic coupling between the Fe(III) ions bridged by cyanide group in complex 1 and the always high spin state of the Fe(III) ion coordinated to the Schiff base ligand in both complexes 1 and 2. The temperature dependent magnetic susceptibility investigation over complexes 3–5 showed the occurrence of the thermo-induced gradual complete spin crossover (SCO) property at about 115, 170 and 200 K, respectively.

Three novel mononuclear 4‐vinylpyridine‐based Fe(III) complexes displaying various spin‐crossover behaviour

“…[31] Subsequently Xu et al synthesized complexes [Fe(L)(py)] and [Fe(L)(dmap)](BPh 4 ) (L = N,N'-bis(2-hydroxybenzyliden)-1,7-diamino-4-azaheptane; dmap = 4-dimethylaminopyridine) using pentadentate Schiff base ligands and pyridine like ligands. [32] The magnetic studies have revealed thermally induced gradually complete SCO behaviour at different temperatures. These studies emphasize the important role of Fe(III) and pentadentate Schiff base ligands in spin-crossover behaviour.…”