Magneto-structural study on a tetracopper(II) Schiff base complex stabilizing a decanuclear water aggregate

Abstract

A new tetranuclear copper(II) complex [Cu 4L 2(3-ppz) 2] ( 1) has been prepared from the reaction of [Cu 2LBr] and 3-phenylpyrazole (3-ppz), where H 3L is a pentadentate Schiff base N, N′-(2-hydroxypropane-1,3-diyl)bis(salicylaldimine). The complex as 1 · 6H 2O has been structurally characterized by X-ray crystallography. The structure shows the presence of a tetranuclear copper(II) complex with a core showing Cu⋯Cu distances in the range of 3.261(1)–3.492(1) Å. The tetrameric complex is formed from the self-assembly of two dimeric {Cu 2L} + units in the presence of two anionic 3-ppz ligands as linkers. The alkoxo oxygen atoms bind three copper(II) centers giving two equatorial and one axially elongated Cu–O bond. The variable temperature magnetic susceptibility data in the range 300–17 K show antiferromagnetic spin–spin coupling giving magnetic moments of 3.3 μ B at 300 K and 0.56 μ B at 17 K for the Cu 4 unit. A theoretical fitting to the magnetic data gives J values of −86.3, −47.32 and 11.13 cm −1 with a diamagnetic ground state. The crystal structure shows the presence of two complexes and 12 water molecules in the unit cell belonging to the triclinic space group P 1 ¯ . Among them, 10 water molecules form an aggregate in which six water molecules are in a chair conformation of the cyclohexane-type with two water dimers hydrogen bonded to the cyclic structure. The discrete decameric water assembly is anchored onto the metalloorganic host involving four phenoxo oxygen atoms of two Cu 4 units and four water molecules of the cyclic chair hexameric unit through hydrogen bonding interactions.