Mixed-valence {Fe II2Fe III4} hexanuclear complexes with thermally induced Fe(iii) spin-crossover behavior

Abstract

Cyano-bridged mixed-valence {Fe₆} hexanuclear complexes {[Tp^4-MeFe^II(CN)₃]₂[Fe^III(Tpa)]₂[Fe^III(OR)(Tpa)]₂}·6ClO₄·S (Tp^4-Me = tri(4-methyl-pyrazol-1-yl)borate, Tpa = tris(2-pyridylmethyl)amine; R = –CH₃, S = 8MeOH 1, R = –C₂H₅, S = 6EtOH 2) have been obtained by building the units of [Tp^4-MeFe(CN)₃]⁻ and [Fe(Tpa)]²⁺ in methanol and ethanol, respectively. Complex 1 exhibited single-crystal-to-single-crystal (SCSC) transformation to give {[Tp^4-MeFe^II(CN)₃]₂[Fe^III(Tpa)]₂[Fe^III(OH)(Tpa)]₂}·6ClO₄·8H₂O (3) in water. Detailed analysis of the coordination environment of the Fe^III centers on the square lattice and magnetic susceptibility measurements of all the complexes confirmed their Fe³⁺ spin-crossover (SCO) properties (T_1/2 = 178 K, 1; 185 K, 2; 208 K, 3).