Thermodynamics of Molecular Metal Formation: Metallophthalocyanine and Tetrathiafulvalene Iodides
William B. Euler, Mary E. Melton, Brian M. Hoffman, Journal of the American Chemical Society, 1982, 104, 5966 – 5971
Abstract
Solid-state electrochemical cells are employed to investigate the formation reaction of several iodinated materials, DIx, where D is a metallophthalocyanine (M(Pc), M = H2, Ni, Co, Cu) or tetrathiafulvalene (TTF). I2 and [(CH3)4N]I3 cells were also studied as controls. The M(Pc)I constitute a set of isostructural and isoionic molecular conductors; in contrast, the TTFIx (x = 0.7, 2, 3) differ in structure, level of oxidation, and the state of the iodine. For none of the DIx studied does the formation reaction of the parent D and molecular iodine have free energy more favorable than –5.2 kcal/mol. This is so despite the highly favorable lattice stabilization energies, L, that are calculated from appropriate Born-Haber cycles: L ranges from –103 to –117 kcal/mol in the nonintegrally (partially) oxidized materials while L = –164 ± 5 kcal/mol in the integrally oxidized TTFI3. Individual contributions to L, namely the nonbonded, ionic, and mixed-valence, or carrier-delocalization, contributions, are also discussed. The first two of these are large and contribute in different proportions for the M(Pc)I and (TTF)Ix. The third, though small, can be of the same magnitude as or greater than the total free energy of formation.