Pyridyl-Thioethers as Capping Ligands for the Design of Heteroleptic Fe(II) Complexes with Spin-Crossover Behavior

Abstract

Mononuclear heteroleptic complexes [Fe(tpma)(bimz)](ClO4)2 (1a), [Fe(tpma)(bimz)](BF4)2 (1b), [Fe(bpte)(bimz)](ClO4)2 (2a), and [Fe(bpte)(bimz)](BF4)2 (2b) (tpma = tris(2-pyridylmethyl)amine, bpte = S,S′-bis(2-pyridylmethyl)-1,2-thioethane, bimz = 2,2′-biimidazoline) were prepared by reacting the corresponding Fe(II) salts with stoichiometric amounts of the ligands. All complexes exhibit temperature-induced spin crossover (SCO), but the SCO temperature is substantially lower for complexes 1a and 1b as compared to 2a and 2b, indicating the stronger ligand field afforded by the N2S2-coordinating bpte ligand relative to the N4-coordinating tpma. Our findings suggest that ligands with mixed N/S coordination can be employed to discover new SCO complexes and to tune the transition temperature of known SCO compounds by substituting for purely N-coordinating ligands.

High spin iron(ii) complexes based on imidazolyl- and 1,2,3-triazolyl-thione ligands and NCE (E = S, Se or BH3) co-ligands: effect of the S-functional group on the structural and magnetic properties

“…It has been shown that S-containing ligands can be utilised to obtain iron( ii ) spin crossover (SCO) complexes 1–13 in some of which the iron( ii ) centres have a {N 4 S 2 } coordination sphere. SCO materials can reversibly switch between the high spin (HS) and low spin (LS) states by and external stimulus, such as temperature, pressure, applied magnetic field, light irradiation, solvation, etc.…”

“…1, and so far just a few examples of SCO-active octahedral iron( ii ) complexes comprising {N 4 S 2 } coordination spheres are known. 1–4,6–8,12,13 Moreover, the presence of S-donors in iron( ii ) metal complexes provides a double advantage to this type of systems. Firstly, a protection of the metallic centre avoiding its oxidation towards iron( iii ), which has already been observed in systems based on some redox-active sulphur ligands, 22 and secondly, maintaining the magnetic properties of these SCO-active systems.…”