Comparative investigation of the copper(II) complexes of (R)-, (S)- and (R,S)-1-phenyl-N,N-bis(pyridine-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

The interaction of the enantiopure (R)- and (S)-1-phenyl-N,N-bis(pyridine-3- ylmethyl)ethanamine ligands, R-L1 and S-L1, with copper(II) chloride followed by addition of hexafluorophosphate resulted in the isolation of the corresponding enantiomeric complexes [Cu(R-L1)Cl](PF6) (1), [Cu(S-L1)Cl](PF6) (2) and [Cu(S-L1)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-L1 was employed in a parallel synthesis, the similar racemic complex [Cu(R,S-L1)Cl](PF6)·0.5MeOH (4) was obtained, in which the L1 ligands in each dimeric unit have opposite hands. In contrast to the complexes of L1, the reaction of Cu(II) chloride with the related ligand, (R)-1-cyclohexyl-N,N-bis(pyridine-3-ylmethyl)ethanamine (R-L2), yielded the mononuclear complex [Cu(R,S-L2)Cl2] (5), displaying a distorted square pyramidal coordination geometry. The structure of this product along with its corresponding circular dichroism spectrum revealed that racemisation of the starting R-L2 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 antiferromagnetic intermolecular interaction is operative for 5.