Temperature-dependent redox isomerism via intramolecular electron transfer. Synthesis and properties of Co(dmppz)(2)(3,6-dbq)(2)(dmppz=1,4-dimethylpiperazine; 3,6-dbq=3,6-di-tert-butyl-1,2-quinone)

Abstract

The preparation and characterization of Co(dmppz)(2)(3,6-dbq)(2) (dmppz = 1,4-dimethylpiperazine; 3,6-dbq = 3,6-di-tert-butyl-1,2-quinone) are established. Temperature-dependent magnetic moments (100-400 K), variable-temperature IR, and electronic spectra are presented to show that the title complex exhibits an equilibrium via a catechol to cobalt intramolecular electron transfer. At temperatures below 350 K, the charge distribution of the complex is Co-III(dmppz)(2)(3,6-dbsq)(3,6-dbcat) (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 complex is predominantly Co-II(dmppz)(2)(3, 6-dbsq)2 form in the solid state. At the temperature range of 350-390K a mixture of Co((III)) and Co((II)) redox isomers exist at equilibrium. The transition temperature (Tc) of Co(III)/Co(II) in solution is approximately 50 degrees lower than that in the solid state. In particular, thermal analysis on solid sample of the complex discloses that the transition for the Co(III)Co(II) is accompanied by the change in heat content of 12.30 kcal/mol.