Dinuclear Valence Tautomeric 1,2-Semiquinonato/Catecholatocobalt Complexes Containing 1,1,4,7,10,10-Hexamethyltriethylenetetramine

Abstract

Abstract Dinuclear 1,2-semiquinonato/catecholatocobalt complexes containing 1,1,4,7,10,10-hexamethyltriethylenetetramine (hmdeta) as a potential tetradentate N4 coligand, [Co2(hmteta)(dbbq)4], (dbbq = 3,5- and 3,6-di-tert-butyl-1,2-benzoquinone (3,5-dbbq and 3,6-dbbq)) were synthesized and characterized. The crystal structures proved that [Co2(hmteta)(3,6-dbbq)4]·2C6H5CH3 ([3,6]) exists as low spin [(3,6-dbsq)(3,6-dbcat)CoIII(hmteta)CoIII(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), while [Co2(hmteta)(3,5-dbbq)4]·C6H5CH3 ([3,5]) approximates to [(3,5-dbsq)2CoII(hmteta)CoII(3,5-dbsq)2] in the solid state at ambient temperature. On the basis of the effective magnetic moments, the [CoIII] → [CoII] conversion of [3,6] underwent a relatively abrupt transition around 330 K while that of [3,5] occurs in a wide range of temperature. Electronic absorption spectra showed that [3,6] shifts predominantly to [CoIII] whereas [3,5] shifts to [CoII] valence tautomer in solution at room temperature. The charge distribution of [3,6] exhibited significant solvent effects at room temperature. These prominent features between [3,5] and [3,6] appeared to be associated with difference between delicate electronic and steric effects of the two dbbq ligands.