Charge transfer phase transition with reversed thermal hysteresis loop in the mixed-valence Fe9[W(CN)8]6•xMeOH cluster

A bimetallic pentadecanuclear cyanido-bridged {Fe-9[W(CN)(8)](6) (MeOH)(24)}center dot xMeOH cluster of an Fe-II/III-W-IV/V mixed valence nature, reveals a reversible single-crystal-to-single-crystal transformation, concomitant with metal-to-metal charge transfer between Fe and W ions. The dominance of Fe-HS(II)-NC-W-V units at a high temperature, and Fe-HS(III)-NC-W-IV units at a low temperature, leads to an unprecedented reversed thermal hysteresis loop in magnetic measurements.