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

Abstract

A new tetranuclear copper(II) complex [Cu₄L₂(3-ppz)₂] (1) has been prepared from the reaction of [Cu₂LBr] and 3-phenylpyrazole (3-ppz), where H₃L is a pentadentate Schiff base N,N'-(2-hydroxypropane-1,3-diyl)bis(salicylaldimine). The complex as 1·6H₂O has been structurally characterized by X-ray crystallography. The structure shows the presence of a tetranuclear copper(II) complex with a core showing CuCu distances in the range of 3.261(1)-3.492(1) Å. The tetrameric complex is formed from the self-assembly of two dimeric {Cu₂L}₊ 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 Cu₄ 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 P1^-. 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 Cu₄ units and four water molecules of the cyclic chair hexameric unit through hydrogen bonding interactions.