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)

摘要

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ゲ (dmppz)2(3,6-dbsq)(3,6-dbcat) (3,6-dbsq=3,6-di-tert-butyl-1,2-semiquinonato; 3,6-dbcat=3,6-di-tert-butylcatecholato) whereas at the temperature beyond 390 K, the complex is predominantly Coケ(dmppz)2(3,6-dbsq)2 form in the solid state. At the temperature range of 350-390 K a mixture of Co(ゲ) and Co(ケ) redox isomers exist at equilibrium. The transition temperature (Tc) of Co(ゲ)/Co(ケ) in solution is approximately 50∑ lower than that in the solid state. In particular, thermal analysis on solid sample of the complex discloses that the transition for the Co(ゲ)/Co(ケ ) is accompanied by the change in heat content of 12.30 kcal/mol.