Interaction of an extended series of N-substituted di(2-picolyl)amine derivatives with copper(II). Synthetic, structural, magnetic and solution studies

The interaction of Cu(II) with the following secondary N-substituted derivatives of di(2-picolyl)amine (1) are reported: N-cyclohexylmethyl-di(2-picolyl)amine (2), N-benzyl-di(2-picolyl)amine (3), N-(4-pyridylmethyl)-di(2-picolyl)amine (4), N-(4-carboxymethylbenzyl)-di(2-picolyl)amine (5), N-(9-anthracen-8-ylmethyl)-di(2-picolyl)amine (6), 1,3-bis[di(2-picolyl)aminomethyl]benzene (7), 1,4-bis[di(2-picolyl)aminomethyl]benzene (8) and 2,4,6-tris[di(2-picolyl)amino]triazine (9). The solid complexes [Cu(2)(mu-Cl)](2)(PF6)(2), [Cu(3)(mu-Cl)](2)(PF6)(2)center dot 0.5CH(2)Cl(2), Cu(4)(ClO4)(2), Cu(5)(2)(ClO4)(2), [Cu(6)(ClO4)(2)(H2O)]center dot 0.5H(2)O, Cu-2(7)(ClO4)(4), [Cu-2(8)(Cl)(4)] and [Cu-2(9+H)(mu-OCH3)(2)(H2O)]( ClO4)(3)center dot C4H10O were isolated and X-ray structures of [Cu(2)(mu-Cl)](2)(PF6)(2), [Cu(3)(mu-Cl)](2)(PF6)(2)center dot 0.5CH(2)Cl(2), [Cu(6)(2)(ClO4)(2)(H2O)]center dot 0.5H(2)O, [Cu-2(8)Cl-4] and [Cu-2(9+H)(mu-OCH3)(2)(H2O)](ClO4)(3)center dot C4H10O were obtained. The series is characterised by a varied range of coordination geometries and lattice architectures which in the case of [Cu(6)(ClO4)(2)(H2O)]center dot 0.5H(2)O includes a chain-like structure formed by unusual intermolecular pi-interactions between metal bound perchlorate anions and the aromatic rings of adjacent anthracenyl groups. Variable temperature magnetic susceptibility measurements have been performed for [Cu(2)(mu-Cl)](2)(PF6)(2) and [Cu(3)(mu-Cl)](2)(PF6)(2)center dot 0.5H(2)O over the range 2-300 K. Both compounds show Curie-Weiss behaviour, with the data indicating weak antiferromagnetic interaction between the pairs of copper ions in each complex. Liquid-liquid (H2O/CHCl3) extraction experiments involving 1-3 and 7-9 as extractants showed that, relative to the parent (unsubstituted) dipic ligand 1, substitution at the secondary amine site in each case resulted in an increase in extraction efficiency towards Cu(II) (as its perchlorate salt); at least in part, this increase may be attributed to the enhanced lipophilicities of the N-substituted derivatives.