Antiferromagnetism induced by successive protonation of terminal phenol groups of a bis(μ-phenoxide)-bridged dicopper(ii,ii) complex

Abstract

The reaction of a tripodal ligand (H₂L = N,N-bis(2-hydroxybenzyl)-N′,N′-dimethylethylenediamine) with Cu(NO₃)₂·3H₂O and Cu(ClO₄)₂·6H₂O in methanol yielded [Cu₂(HL)₂](NO₃)₂·H₂O (1) and [Cu₂(HL)₂](ClO₄)₂ (1′), respectively. When H₂L was allowed to react with CuSO₄·5H₂O in the presence of triethylamine (1 ∶ 1 ∶ 2) in methanol, the neutral dicopper(II,II) complex [Cu₂(L)₂] (2) was obtained. The monopositive species [Cu₂(L)(HL)]ClO₄·CH₃OH·H₂O (3) crystallized on mixing 1′ and 2 (1 ∶ 1) in methanol–dichloromethane. The crystal structures of 1, 2, and 3 were determined by X-ray crystallography. All of the complexes consist of a discrete dinuclear molecule with bis(μ-phenoxide)-bridges. The tripodal ligand functions as a tetradentate ligand and one of the phenolic oxygen atoms serves as a bridging ligand. Protonation/deprotonation takes place at the terminal phenol moiety and as the phenol group is deprotonated the coordination geometry changes from a distorted square pyramid to a distorted trigonal bipyramid. The two copper ions in 1–3 are antiferromagnetically coupled with 2J = −714 (1), −19.9 (2), and −277 cm⁻¹ (3). The results clearly demonstrate that protonation/deprotonation causes a change in coordination geometry, which in turn drastically affects magnetic exchange interactions.