Dehydration-actuated single-molecule magnet behavior in a cyanide-bridged [Fe2Co2] cluster featuring zigzag structure

Abstract

A rare zigzag cyanide-bridged tetranuclear complex, {[(Tp*)FeIII(CN)3]2[CoII(tphz)1/2(SCN)(MeOH)]2}·4H2O (1·4H2O) (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate, tphz = tetrapyridophenazine) was successfully isolated and characterized structurally and magnetically. Single-crystal structural analysis indicates the Fe3+ and Co2+ ions are linked by cyanides while the inverse two Co2+ are bridged by the pyrazine of tphz. Magnetic studies for 1·4H2O revealed the ferromagnetic coupling (JFeCo = +3.2 cm−1) between the Fe3+ and Co2+ ions and antiferromagnetic interaction (JCoCo = −2.7 cm−1) between the Co2+ ions of the cluster. After the release of crystallized water molecules, however, the magnetic behaviors were drastically tuned indicated by the notable changes in the magnetic couplings for FeIIICoII (JFeCo = +3.9 cm−1) and CoIICoII (JCoCo = −3.5 cm−1). Reduced magnetization reveals the uniaxial magnetic anisotropy of the dehydrated molecule with the zero-field splitting parameter D = −10.3 cm−1. Additionally, field-supported single-molecule magnet behavior was observed with the effective energy barrier Ueff = 38.2 K, making complex 1 the first example of a zigzag Fe2Co2 single-molecule magnet. This work provides not only a rare dynamic switching molecular complex but also highlights the important influence of guest water molecules in magnetic behaviors.