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

Abstract

Abstract Co‐crystallization of a cyanide‐bridged tetranuclear complex [Co 2 Fe 2 ] with 4‐cyanophenol (CP) gave a hydrogen bonding donor–acceptor system, [Co 2 Fe 2 (bpy*) 4 (CN) 6 (tp*) 2 ](PF 6 ) 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.