Syntheses, structure and properties of dinuclear Co complexes with bis(catecholate) ligands – Effect of a quinoline ring in the terminal group

Six dinuclear Co complexes with bis(catecholate) ligands, where the two catechol moieties are connected by acetylene spacer, have been synthesized and characterized. For [Co2(L1)(tpa)2](ClO4)2 (H4L1 = 5,5′-(buta-1,3-diyne-1,4-diyl)bis(3-t-butylcatechol)) it appears that both cobalt ions have an octahedral sphere and the spin states are ls-Co(III) from X-ray crystal structure analysis. On the other hand, complex 6, [Co2(L2)(pbqa)2](PF6)2 (H4L2 = 5,5′-(ethyne-1,2-diyl)bis(3-t-butylcatechol)), was isolated with the mixed valent state CoII(hs)-[Sq-Cat]-CoIII(ls) and shows a spin transition behavior that depends on temperature.