Intramolecular change distribution and related properties in a series of 3,6-di-tert-butylbenzoquinonatocobalt complexes containing piperidine

A series of cobalt-benzoquinone complexes containing piperidine derivatives as a coligand, [Co(3,6-dbq)₂(N-N)], (N-N = 1,1′-methylenedipiperidine (mdp), 1,1′-methylenebis(3-methylpiperidine) (mbmp), 1-methyl-4-(methylamino)piperidine (mmap); 3,6-dbq = 3,6-di-tert-butyl-1,2-benzoquinone) have been prepared and characterized. The crystal structure of [Co(3,6-dbq)₂(mmap)].0.5Me₂CO (P1, a = 11.524(2) Å, b = 12.565(4) Å, c = 14.160(3) Å, α = 80.65(2)°, β = 82.15(2)°, γ= 87.39(2)°, V = 2003.6(8) ų, R = 0.0763) proves that the molecule exists as low-spin [Co^III(3,6-db-sq) (3,6-dbcat)(mmap)] (3,6-dbsq = 3,6-di-tert-butyl-1,2-semiquinonato; 3,6-dbcat = 3,6-di-tert-butylcatecholato) in the solid state. According to magnetic, spectroscopic, and thermal analyses, [Co^III(3,6-dbsq)(3,6-dbcat)(mmap)] is locked up to 431 K while [Co^II(3,6-dbsq)₂(mdp)] and [Co^II(3,6-dbsq)2(mbmp)] are changed to their corresponding low spin Co^III forms at (below) T_1/2 = 215 K and 271 K, respectively. The transition temperature (T_1/2) between Co^III/Co^II varies as mbmp < mdp ≪ mmap, which appears to be associated with electronic versus steric effects of the piperidine coligands. In particular, [Co(3,6-dbq)₂(mdp)] reveals a two-step spin conversion centered at 208 K and 298 K with a plateau of 90 deg.