Bistability and low energy electron transfer : diimine bridged cobalt semiquinonate-catecholate coordination polymers

Intramolecular shifts in charge distribution have been investigated for the coordination polymers of [CoIII(N-N) (SQ)(Cat)]n/[CoII(N-N)(SQ)2]n tautomers (N-N = 4.4′-bipyridine analogs; SQ = 3.6-di-t-butyl- 1.2-semiquinone; Cat = 3,6-di-t-butylcatechol). The polymers remain exclusively in the low-spin CoIII and high-spin CoII limiting forms, with a series of intermediate species that exhibit CoIII/CoII equilibria in the solid state. A significant bistability on temperature has been observed by monitoring the changes in magnetism and the intensity of a low energy transition (2500nm = 4000cm−1) that appears characteristically for the CoIII tautomer.