TEMPERATURE-DEPENDENT REDOX ISOMERISM VIA INTRAMOLECULAR ELECTRON-TRANSFER - SYNTHESIS AND PROPERTIES OF DMPPZ)(2)(3,6-DBQ)(2)(DMPPZ=1,4-DIMETHYLPIPERAZINE - 3,6-DBQ=3,6-DI-TERT-BUTYL-1,2-QUINONE)

The preparation and characterization of Co(dmppz)(2)(3,6-dbq)(2) (dmpp z = 1,4-dimethylpiperazine; 3,6-dbq = 3,6-di-tert-butyl-1,2-quinone) a re established. Temperature-dependent magnetic moments (100-400 K), va riable-temperature IR, and electronic spectra are presented to show th at the title complex exhibits an equilibrium via a catechol to cobalt intramolecular electron transfer. At temperatures below 350 K, the cha rge distribution of the complex is Co-III(dmppz)(2)(3,6-dbsq)(3,6-dbca t) (3,6-dbsq = 3,6-di-tert-butyl-1,2-semiquinoato; 3,6-dbcat = 3,6-di- tert-butylcatecholato) whereas at the temperature beyond 390 K, the co mplex is predominantly Co-II(dmppz)(2)(3, 6-dbsq)2 form in the solid s tate. At the temperature range of 350-390K a mixture of Co((III)) and Co((II)) redox isomers exist at equilibrium. The transition temperatur e (Tc) of Co(III)/Co(II) in solution is approximately 50 degrees lower than that in the solid state. In particular, thermal analysis on soli d sample of the complex discloses that the transition for the Co(III)C o(II) is accompanied by the change in heat content of 12.30 kcal/mol.