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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 18, Number 6
BKCSDE 18(6)
June 20, 1997 

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)
Ok-Sang Jung, Du Hwan Jo, Sung Ho Park, Youn Soo Sohn
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 CoⅢ (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 CoⅡ(dmppz)2(3,6-dbsq)2 form in the solid state. At the temperature range of 350-390 K 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° 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.
628 - 631
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