Tuning of spin-crossover behavior in two cyano-bridged mixed-valence Fe III2FeII trinuclear complexes based on a TpR ligand

Abstract

Spin-crossover (SCO) complexes have been extensively studied in the past few decades owing to their bistable nature which find application in a myriad of areas. In order to enhance and optimize the SCO behavior, considerable attention is being paid towards the synthesis of discrete multinuclear spin-crossover complex systems. Here, two mixed-valence Fe^III₂Fe^II trinuclear complexes of the formula {[Fe^II(TPMA)][Fe^III(Tp^R)(CN)₃]₂}·MeOH·2H₂O (1) and {[Fe^II(TPMA)][Fe^III(Tp^R)(CN)₃]₂}·H₂O (2) [where TPMA = tris(2-pyridylmethyl)amine, Tp = tris(pyrazol-1-yl)borate, R = 3,5-dimethyl for 1 and H for 2] were synthesized and characterized. Magnetic measurements confirmed that complex 1 undergoes SCO at a high temperature (T_1/2 = 410 K for the fresh sample and T_1/2 = 406 K for the dried sample), while complex 2 displays near room temperature SCO (T_1/2 = 283 K for the fresh sample and T_1/2(↑) = 283 K and T_1/2(↓) = 257 K for the dried sample). To the best of our knowledge, complex 1 has the highest transition temperature reported among trinuclear SCO complexes so far, which is a remarkable feature of multinuclear materials. Slight structural modifications tend to upend the SCO behavior which paves the way for fine tuning SCO.