Dinuclear valence tautomeric 1,2-semiquinonato/catecholatoeobalt complexes containing 1,1,4,7,10,10-hexamethyltriethylenetetramine

Dinuclear 1,2-semiquinonato/catecholatocobalt complexes containing 1,1,4,7,10,10-hexamethyltriethylenetetra-mine (hmdeta) as a potential tetradentate N₄ coligand, [Co₄(hmteta)(dbbq)₄], (dbbq = 3,5- and 3,6-di-tert-butyl-l,2-benzoquinone (3,5-dbbq and 3,6-dbbq)) were synthesized and characterized. The crystal structures proved that [C0 ₂-(hmteta)(3,6-dbbq)₄] · 2C₆H ₅CH₃ ([3,6]) exists as low spin [(3,6-dbsq)(3,6-dbcat) Co^III(hmteta)Co^III(3,6-dbsq)(3,6-dbcat)] (3,6-dbsq = 3,6-di-tert-butyl-l,2-semiquinonato; 3,6-dbcat = 3,6-di-tert-butylcatecholato), while [Co₂(hmteta)-(3,5-dbbq)₄].C₆H ₅CH₃ ([3,5]) approximates to [(3,5-dbsq) ₂Co^II(hmteta)Co^II(3,5-dbsq)₂] in the solid state at ambient temperature. On the basis of the effective magnetic moments, the [Co^III] →[Co^II] 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 [Co^III] whereas [3,5] shifts to [Co ^III] 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.