Electron transfer coupled spin transition in cyano-bridged mixed-valence {FeIII2FeII2} molecular squares

By selecting the N4 ligand bnbpen, a mixed-valence cyano-bridged homometallic iron square complex {[Fe III (Tp)(CN) 3 ] 2 [Fe II (bnbpen)] 2 }(ClO 4 ) 2 ·8CH 3 OH and solvo-free form were prepared. Both have thermally reversible electron transfer-coupled spin transition (ETCST) behavior.