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

Abstract

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)(μ-Cl)]₂(PF₆)₂, [Cu(3)(μ-Cl)]₂(PF₆)₂·0.5CH₂Cl₂, Cu(4)(ClO₄)₂, Cu(5)₂(ClO₄)₂, [Cu(6)(ClO₄)₂(H₂O)]·0.5H₂O, Cu₂(7)(ClO₄)₄, [Cu₂(8)(Cl)₄] and [Cu₂(9+H)(μ-OCH₃)₂(H₂O)](ClO₄)₃·C₄H₁₀O were isolated and X-ray structures of [Cu(2)(μ-Cl)]₂(PF₆)₂, [Cu(3)(μ-Cl)]₂(PF₆)₂·0.5CH₂Cl_2, [Cu(6)₂(ClO₄)₂(H₂O)]·0.5H₂O, [Cu₂(8)Cl₄] and [Cu₂(9+H)(μ-OCH₃)₂(H₂O)](ClO₄)₃·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)]·0.5H₂O includes a chain-like structure formed by unusual intermolecular π-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)(μ-Cl)]₂(PF₆)₂ and [Cu(3)(μ-Cl)]₂(PF₆)₂·0.5H₂O 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.