A 1,8-naphthalenediol-based unsymmetrical dinucleating ligand

Abstract

A facile synthesis of 2-formyl-1,8-naphthalenediol is reported. Its potential as a general precursor for the preparation of unsymmetrical multidentate chelating ligand systems based on 1,8-naphthalenediol is demonstrated by the synthesis of the dinucleating ligand L⁴⁻ (H₄L = N,N′-bis(2-(1,8-naphthalenediol)methylidene)propylenediamine). Reaction of H₄L with copper acetate results in the formation of the unsymmetrical dinuclear Cu^II complex [LCu₂] (3), which has been structurally characterized by single-crystal X-ray diffraction. One Cu^II ion is coordinated by a N₂O₂ compartment of L⁴⁻ and the other Cu^II ion is coordinated by an O₄ compartment of L⁴⁻ while they are bridged by two aryloxide functions of L⁴⁻. A dimerization of two molecules of 3 to a tetranuclear entity 3₂ occurs through formation of weak apical Cu–O interactions. Analysis of the temperature dependent magnetic susceptibility measurements (2–290 K) established a strong intradimer exchange coupling J₁₂ = −371 cm⁻¹. This strong superexchange interaction fits nicely in a magneto-structural correlation which has been established for dinuclear bis(phenoxide)-bridged Cu^II complexes demonstrating the electronic equivalence of the aryloxides of a phenol and 1,8-naphthalenediol.