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)].0.5Me(2)CO (P (1) over bar, a = 11.524(2) Angstrom, b = 12.565(4) Angstrom, c = 14.160(3) Angstrom, alpha = 80.65(2)degrees, beta = 82.15(2)degrees, gamma = 87.39(2)degrees, V = 2003.6(8) Angstrom (3), R = 0.0763) proves that the molecule exists as low-spin [Co-III(3,6-dbsq)(3,6-dbcat)(mmap)] (3,6-dbsq = 3,6-di-tert-butyl-1,2-semiquinonato; 3,6-dbcat = 3,6-di-tert-butyrcatecholato) 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.