A Hydrogen‐Bonded Cyanide‐Bridged [Co₂Fe₂] Square Complex Exhibiting a Three‐Step Spin Transition

Abstract

Co-crystallization of a cyanide-bridged tetranuclear complex [Co₂ Fe₂ ] with 4-cyanophenol (CP) gave a hydrogen bonding donor-acceptor system, [Co₂ Fe₂ (bpy*)₄ (CN)₆ (tp*)₂ ](PF₆ )₂ ⋅2 CP⋅8 BN (1). 1 exhibited a three-step phase transition between HT, IM1, IM2, and LT phases upon temperature variation. Variable temperature magnetic measurements and structural analyses revealed that the three-step spin transition is caused by electron-transfer-coupled spin transitions (ETCSTs) accompanied with alteration of the hydrogen bonding interactions.