Transformation between monovalent and divalent ionic solids : An ionic(I)-ionic(II) phase transition in a biferrocene-F1TCNQ charge-transfer complex

An “ionic(I)–ionic(II)” charge-transfer transition has been observed in a new molecular solid composed of dineopentylbiferrocene (D) and fluorotetracyanoquinodimethane (A). The material is a monovalent solid (D + A 3 - ) at room temperature and changes to a divalent solid (D 2+ A 3 2- ) at low temperatures, in association with a broad first-order phase transition at around 120 K.