Abrupt spin crossover in iron(iii) complexes with aromatic anions

Abstract

Two iron(III) spin crossover complexes, [Fe(qsal-X)₂]OTs·nH₂O, (Br 1·H₂O; I, 2·2H₂O or non-solvated 1, 2) have been prepared and fully characterized. Structural studies of 1·H₂O and 2·2H₂O reveal the presence of 1D π–π chains linking the Fe(III) centres and a strong X⋯O halogen bond. In both complexes the 1D π–π chains are angled relative to each other, enforced by C–H⋯X interactions. Magnetic studies reveal abrupt spin crossover in 1 (T_1/2↓ = 258 K and T_1/2↑ = 260 K) and 2 (T_1/2 = 298 K) with T_1/2 increasing on going from Br to I. The presence of abrupt spin crossover in both complexes shows that aromatic anions can be effective in the design of cooperative spin crossover systems.