Dicopper( II ) complexes of novel polyfunctional pyridazines: crystal structure and magnetic properties of bis[µ-pyridazine-3,6-dicarbaldehyde dioximato(1–)-κN 1 ,N′:N 2 ,N″]-bis[aqua(perchlorato-κO)copper( II )]

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.