Hydrogen-bonding interactions, geometrical selectivity and spectroscopic properties of cobalt(III) complexes with unsymmetrical tridentate amine-amidato-phenolato type ligands

Four cobalt(III) complexes with the formula of [Co(Ln)2]− bearing tridentate amine-amidato-phenolato-type ligands (Ln: n = 1–4) were synthesized. All of the complexes were characterized by 1H NMR spectroscopy and X-ray analysis. The geometrical selectivity was found to depend on the flexibility of the amine-amidato chelate in combination with the planar 2-oxybenzamido 6-membered chelate; that is, the amine-amidato 5-membered chelate took the mer-type geometry, and the 6-membered chelate took the fac-type geometry. In most of the mer-type complexes, intermolecular double hydrogen bonds via amidato(O) and amino group were selectively formed between their enantiomeric pairs of mononuclear complexes. In the case of two chiral ligands {L22– = 2-amino-1-(2-oxybenzamido)propane; L32− = trans-1-amino-2-(2-oxybenzamido)cyclohexane}, [Co(L3)2]− showed diastereoselectivity while [Co(L2)2]− did not. Furthermore, PPh4[Co(L1)2] (L12− = 2-amino-1-(2-oxybenzamido)-2-methylpropane) showed an apparent solvatochromic behavior in several solvents. Although the molecular structures of [Co(L2 or L3)2]− are quite similar to that of [Co(L1)2]−, these complexes did not exhibit such a solvatochromic behavior.