Dimetallic complexes of acyclic pyridine-armed ligands derived from 3,6-diformylpyridazine

Abstract

A bis(pyridine-armed) acyclic Schiff base ligand L1 has been synthesised from 3,6-diformylpyridazine and two equivalents of 2-(2-aminoethyl)pyridine. Reduction of this ligand using NaBH₄ resulted in the formation of the amine analogue L2. Complexes of the form [M₂L1(μ-X)]Y₂ClO₄ [where: M = Cu(II), X = OH⁻ and Y = ClO₄⁻1, Cl⁻2, Br⁻3 or I⁻4; M = Co(II), X = OH⁻ and Y = ClO₄⁻5; M = Ni(II), X = SCN⁻6 or X = N₃⁻7 and Y = ClO₄⁻], and [Cu₂L2(μ-OH)](ClO₄)₃8 were prepared and characterised. The complexes 1 and 5–7 have been characterised by single-crystal X-ray diffraction. The acyclic ligand L1 provides three nitrogen donor atoms per metal centre, including a pyridazine bridge between the metal centres, and the anion X also bridges the two metal centres. As required, coordinating solvent molecules or additional anions make up the remainder of the coordination sphere. The two copper centres of 1 are very strongly antiferromagnetically coupled (2J = −1146 cm⁻¹) via the pyridazine and hydroxide ion bridges, whereas the competing antiferromagnetic pyridazine bridging pathway and ferromagnetic 1,1-bridging azide pathway resulted in the observation of weak antiferromagnetic exchange in the dinickel(II) complex 7 (2J = −14 cm⁻¹). Electrochemical examination of L1, L2 and complexes 1 and 5–8 revealed multiple redox processes. These have been tentatively assigned to a mixture of metal centred and ligand centred redox processes on the basis of cyclic voltammetry and coulometry results and comparisons with literature examples.