Structural, electrochemical, spectroelectrochemical, magnetic and spectroscopic studies are reported for the octahedral cobalt beta-diketonate complexes, [Co(beta-diketonate)(2)(N-N)] {beta-diketonate = 2,2,6,6-tetramethylheptane-3,5-dionate (tmhd); N-N = 1,10-phenanthroline (phen) 1, 2,2'-bipyridine (2,2'-bpy) 2 and dimethylaminoethylamine (dmae) 3; beta-diketonate = 1,3-diphenylpropane-1,3-dionate (dbm); N-N = phen 4, 2,2'-bpy 5, dmae 6). X-ray crystallographic studies of the redox pair [Co(tmhd)(2)(2,2'-bipy)] (0/+)2/2(+) show a shortening of the Co-ligand bond lengths by between 0.18 and 0.22 angstrom upon oxidation and a significantly more regular octahedral geometry around the cobalt in the cation consistent with spin crossover in addition to a change in oxidation state. Cyclic voltammetry of 1-6 reveals an irreversible one-electron oxidation to Co-III with large peak separations between the oxidation and reduction peaks, indicative of redox coupled-spin crossover (RCSCO); i.e. [Co(beta-diketonate)(2)(N-N)](S = 3/2) <-> [Co(beta-dike-tonate)(2)(N-N)](+) + e(-) (S = 0). Moreover, the complexes represent rare examples of RCSCO species with a CoO4N2 coordination sphere. The tmhd complexes are more easily oxidized than the respective dbm analogues with the oxidation peak potentials in the order bipy < phen < dmae. Oxidation of 1-6 with AgBF4 yields the corresponding Co-III cations, [Co(beta-diketonate)(2)(N-N)]BF4 1(+)-6(+) which has been confirmed by H-1 NMR spectroscopy. Spectroelectrochemistry of the redox pairs [Co(beta-diketonate)(2)(N-N)(0/+) is consistent with the isolated compounds being identical to the species formed at the electrode. Theoretical studies reveal that the SOMO is essentially metal d-orbital and beta-diketonate based, consistent with the strong effect of the beta-diketonate ligand on the oxidation potential. In addition, there are substantial changes in the relative stabilities of the various spin states compared with [Co(tacn)(2)](2+/3+) such that the high spin states become more accessible. The above results are consistent with a square scheme mechanism. (c) 2012 Elsevier Ltd. All rights reserved.