title: New anionic cobalt complexes using highly hindered bis-amides with varying donor abilities as ligands.
abstract: 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.
authors.affiliation: Dpto. Química Orgánica, Facultad de Ciencias Químicas, Universidad de Concepción, Casilla 160-C, Concepción, Chile. cjimenez@udec.cl
authors.forename: Claudio A
authors.initials: CA
authors.lastname: Jiménez
authors.forename: Julio B
authors.initials: JB
authors.lastname: Belmar
authors.forename: Joel
authors.initials: J
authors.lastname: Alderete
authors.forename: Fernando S
authors.initials: FS
authors.lastname: Delgado
authors.forename: Matías
authors.initials: M
authors.lastname: López-Rodríguez
authors.forename: Octavio
authors.initials: O
authors.lastname: Peña
authors.forename: Miguel
authors.initials: M
authors.lastname: Julve
authors.forename: Catalina
authors.initials: C
authors.lastname: Ruiz-Perez
mesh_terms: D000577:Amides / Q000737:chemistry*; D000838:Anions; D003035:Cobalt / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008280:Magnetics; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013696:Temperature
chemical_list: D000577:Amides; D000838:Anions; D008024:Ligands; D009942:Organometallic Compounds; D003035:Cobalt