| 17514334 |
Jimenez CA, Belmar JB, Alderete J, Delgado FS, Lopez-Rodriguez M, Pena O, Julve M, Ruiz-Perez C: New anionic cobalt complexes using highly hindered bis-amides with varying donor abilities as ligands. Dalton Trans. 2007 Jun 7;(21):2135-44. Epub 2007 Apr 23.
Four potential tetradentate ligands of formulae 1,2-bis-(3,5-di-tert-butyl-2-hydroxybenzamido) ethane (H (4) L (1), 1), 1,2-bis-(3,5-di-tert-butyl-2-hydroxybenzamido) propane (H (4) L (2), 2), 1,2-bis-(3,5-di-tert-butyl-2-hydroxybenzamido) benzene (H (4) L (3), 3) and 1,8-bis-(3,5-di-tert-butyl-2-hydroxybenzamido) naphthalene (H (4) L (4), 4) have been prepared and the crystal structures of three of them (1, 3 and 4) determined by single crystal X-ray diffraction. The investigation of their complexing ability toward Co (II) afforded the compounds of formulae [Co (III)(L (3)) Na (I)(H (2) O)(2)] (5), [Co (III)(L (n)) Li (I)(H (2) O) 2] with n = 1 (6), 2 (7) and 3 (8) and [Co (II)(L (4)) Li (I)(2)] (9). Complexes 5-8 are square planar Co (III) species, as corroborated by the crystal structure of 5. In this compound, two amide-nitrogen and two phenolate-oxygen atoms of a fully deprotonated (L (3))(4-) anion build a slightly distorted square planar surrounding around the cobalt atom, the Co-N distances [1.858 (3) and 1.861 (3) A] being somewhat longer than the Co-O ones [1.798 (3) and 1.801 (3) A]. Magnetic and 1H NMR data at room temperature for 6-8 support the occurrence of an intermediate S = 1 low-lying state for the Co (III) center which is stabilized by the strong donating ability of the fully deprotonated bis-amidate ligands. In the case of the compound with the naphthalene derivative (9), the analytical and spectroscopic data suggest the occurrence of a low spin Co (II) complex. The weakening of the ligand field strength of the tetradentate bis-amidate ligand in the naphthalene derivative (5-6-5 ring-membered fused chelate) when compared to the situation in complexes 5-8 (5-5-5 ring-membered fused chelate) would account for this feature. |
31(0,1,1,1) |