Square-planar copper(II) halide complexes of tridentate ligands with π-π stacking interactions and alternating short and long Cu•••Cu distances

The preparation of a new tridentate N2O-donor ligand N-(2-pyridylmethyl)-3-methoxysalicylaldiminato (HL) is described, together with the corresponding copper(II) complexes [Cu(L)X] (X = Cl-, Br-). The compounds were characterized by elemental analysis, spectral, magnetic and crystallographic studies. In both compounds, the local molecular structure of the Cu(II) ion involves a square-planar CuN2OX chromophore, consisting of a deprotonated phenolate oxygen, an imine nitrogen, the pyridine nitrogen and X. In the solid state, pi-pi stacking interactions are dominantly present, involving the pyridine and phenolate rings of neighboring molecules, which lead to a one-dimensional arrangement with alternating short and long (CuCu)-Cu-... distances of [3.720, 4.599 Angstrom] for the bromo complex and of [3.698, 4.696 Angstrom] for the chloro complex. The temperature-dependent magnetic measurements and EPR data of polycrystalline samples, as well as of frozen solutions in CHCl3 show that there is no observable exchange interaction between the Cu ions. The EPR parameters (g(parallel to), A(parallel to)) agree with a perfect planar geometry, just as found in the X-ray analysis. (C) 2004 Elsevier B.V. All rights reserved.