Comparative Investigation of the copper(II) complexes of (R)-, (S)- and (R,S)-1-phenyl-N,N-bis(pyriclIne-3-ylmethyl)ethanamine along with the related complex of (R,S)-1-cyclohexyl-N,N-bis(pyridine-3-ylmethyl)ethanamine. Synthetic, magnetic, and structural studies

摘要

The interaction of the enantiopure (R)- and (S)-1-phenyl-N,N-bis(pyridine-3- ylmethyl)ethanamine ligands, R-L~1 and S-L~1, with copper(II) chloride followed by addition of hexafluorophosphate resulted in the isolation of the corresponding enantiomeric complexes [Cu(i?-L1)C1](PF6) (1), [Cu(S-L~1)Cl](PF6) (2) and [Cu(5-L~1)Cl](PF6)·0.5Et2O (3), in which dimerization occurs through two long Cu···Cl interactions, the μ-chloro bridges being thus strongly asymmetric. The organic ligand is bound to the metal centre via its N3-donor dipyridylmethylamine fragment in a planar fashion, such that each copper centre is in a square planar environment (or distorted square pyramidal with a long axial bond length if the additional interaction is considered). When R,S-L~1 was employed in a parallel synthesis, the similar racemic complex [Cu(R,S-L~1)Cl](PF6)·0.5MeOH(4) was obtained, in which the L~1 ligands in each dimeric unit have opposite hands. In contrast to the complexes of L~1, the reaction of Cu(II) chloride with the related ligand, (R)-1-cyclohexyl-N,N-bis(pyridine-3-ylmethyl)ethanamine (R-L~2), yielded the mononuclear complex [Cu(R,S-L~2)Cl2] (5), displaying a distorted square pyramidal coordination geometry. The structure of this product along with its corresponding circular dichroism spectrum revealed that rac-emisation of the starting R-L~2 ligand has occurred under the relatively mild (basic) conditions employed for the synthesis. A temperature-dependent magnetic studies of the complexes 1, 2 and 5 indicate that a week ferromagnetic interaction is operative in each dicopper core in 1 and 2 with 2J = 1.2 cm~(-1). On the other hand, a week antiferromag-netic intermolecular interaction is operative for 5.