Formation in solution, synthesis, crystal structure, and magnetic properties of µ-hydroxo-µ-perchlorato-bis[(diethylenetriamine) perchloratocopper(II)]

Abstract

A new binuclear complex [Cu₂(dien)₂(OH)(ClO₄)₃](dien = diethylenetriamine) has been synthesized and its crystal and molecular structure determined by X-ray diffraction. It crystallizes in the monoclinic space group P2₁, with Z= 2, a= 11.896(7), b= 9.424(3), c= 11.468(7)Å, and β= 117.97(4)°. The structure consists of discrete binuclear molecules where the two copper(II) ions are bridged by a single hydroxo group with a Cu(1)–OH–Cu(2) angle of 128.1(4)°, the intramolecular copper–copper separation being 3.435(1)Å. A pseudo-mirror plane passes through the copper atoms, hydroxo bridge, and central nitrogen atom of the dien ligands. The co-ordination geometry around each copper(II) ion is approximately elongated tetragonal octahedral. The hydroxo group and the three nitrogen atoms of dien occupy the equatorial sites. The apical sites are filled by perchlorate oxygen atoms. Two perchlorate anions act as unidentate ligands whereas the third bridges the copper atoms through one of its oxygen atoms. The solid-state magnetic behaviour has been investigated in the temperature range 4.2–300 K. There is a large antiferromagnetic interaction between the two copper(II) ions [J(singlet–triplet gap)=–374 cm^–1]. The formation of hydroxo complexes of [Cu(dien)(H₂O)]²⁺ has been studied by potentiometry in aqueous solutions[equations (i) and (ii); log K₁=–9.168(2) and log K₂=–8.26(1)(25 °C, 0.1 mol dm^–3NaNO₃)]. [Cu(dien)(H₂O)]²⁺ [graphic omitted] [Cu(dien)(OH)]⁺+ H⁺(i), 2[Cu(dien)(H₂O)]²⁺ [graphic omitted] [Cu₂(dien)₂(OH)]³⁺+ H⁺+ H₂O (ii)