Dicopper(II) complexes of novel polyfunctional pyridazines: crystal structure and magnetic properties of bis[µ-pyridazine-3,6-dicarbaldehyde dioximato(1–)-κN1,N′:N2,N″]-bis[aqua(perchlorato-κO)copper(II)]

Abstract

Two novel pyridazine ligands with 3,6-CRNOH (R = H, H₂L¹; Ph, H₂L²) oxime side chains were synthesised. The related copper(II) dinuclear complexes [Cu₂(HL¹)₂(ClO₄)₂(H₂O)₂]1 and [Cu₂(HL²)₂(ClO₄)₂(MeOH)_n]2 were obtained subsequently. The crystal structure of 1 was determined: space group P2₁/n, a= 12.031(6), b= 9.517(4), c= 9.973(5)Å, β= 100.16(4)° and Z= 2. The copper(II) ions of the binuclear unit are bridged by the two diazine fragments of the two essentially planar tetradentate ligands with the oxime nitrogen atoms completing the equatorial co-ordination. Two intra-complex hydrogen bridges link the terminal oximato moieties to give dinucleating macrocyclic complexes. In complexes 1 and 2 the copper(II) is in a classical 4 + 2 environment. The magnetic properties of those compounds revealed a spin-singlet ground state in each case. The singlet-triplet energy gaps were found to be –536(2) for 1 and –545(4) cm^–1 for 2. The low-lying states of the complexes are discussed in relation to the nearly planar structure of the macrocyclic complexes.