Chelate-Ring-Dependent Shifts in Redox Isomerism for the Co(Me2N(CH2)nNMe2)(3,6-DBQ)2(n= 1−3) Series, Where 3,6-DBQ Is the Semiquinonate or Catecholate Ligand Derived from 3,6-Di-tert-butyl-1,2-benzoquinone

Intramolecular electron transfer between Co II (SQ) and Co III (Cat) redox isomers has been investigated for the series of complexes Co(N-N)(3,6-DBQ) 2, where 3,6-DBQ is the semiquinonate or catecholate form of 3,6-di- tert -butyl-1,2-benzoquinone and N-N is tetramethylmethylenediamine (tmmda), tetramethylethylenediamine (tmeda), or tetramethylpropylenediamine (tmpda). Measurements of magnetic properties and changes in electronic spectra indicate that the transition temperature ( T 1/2 ) for Co(III)/Co(II) redox isomerism in the solid state and in toluene solution is the lowest for Co(tmpda)(3,6-DBQ) 2 . This is attributed to the flexibility of the six-membered chelate ring of Co(tmpda) and a positive contribution to Δ S for the equilibrium. Transition temperatures for the tmmda and tmeda analogues are more than 150 deg higher than that for the tmpda species. Structural characterization of Co III (tmmda)(3,6-DBSQ)(3,6-DBCat), Co III (tmeda)(3,6-DBSQ)(3,6-DBCat), and Co II (tmpda)(3,6-DBSQ) 2 has shown that the Co(tmmda) and Co(tmeda) chelate rings are conformationally ordered, while there is considerable disorder in the Co(tmpda) chelate ring. In toluene solution, T 1/2 is approximately 15 deg higher for Co(tmeda)(3,6-DBSQ) 2 than for the tmmda analogue due to the more contracted chelate ring of Co III (tmmda)(3,6-DBSQ)(3,6-DBCat). For the Co(N-N)(3,6-DBQ) 2 series, T 1/2 varies as tmpda ≪ tmmda < tmeda.