A number of dicopper(II) complexes containing binucleating, primarily nitrogen donor ligands havingm-xylyl spacers between the coordination units of relevance to tyrosinase activity and a brief account of the recent results obtained using a new non-Schiff base binucleating ligand providing only two-nitrogen coordination at each copper centre are described in this paper. This new system exhibits tyrosinase activity. A dihydroxo-bridged copper(II) complex has also been obtained with a novel ligand assembly formed as an impurity during our desired ligand synthesis. A brief review has been presented in this field emphasising the nature of the ligand systems and the reaction conditions.

Activation of dioxygen on dicopper(I) centres was systematically investigated using a group of open-chain and a macrocyclicm-xylyl-based dinucleating ligand from a bioinorganic viewpoint. Even though intermediate peroxodicopper(II) species was not detected (even at −80°C for the open-chain system), the putative intermediate reacted with C–H groups in ligands giving oxygenated products (C–OH groups). Absorption, spectroscopic and magnetic properties of the final dicopper(II) complexes have been investigated.

A novel trinuclear copper(II) compound [{(L³)Cu(OClO₃)}₃(μ₃-OCO₂)][ClO₄] has been synthesised using an N-tridentate symmetrical pyridylalkylamine ligand, N-methyl-N,N-bis(2-pyridylmethyl) amine (L³). The structure of the complex has been determined by X-ray crystallography; it is found to crystallise in the hexagonal space group P6₃/m with a = 13·936(2), b = 13·936(2), c = 14·895(3) Å, α = β = 90°, γ = 120°. The complex possesses a 6̅ symmetry axis passing through the carbon atom of the triply bridging carbonate ion, with the three symmetry related copper ions connected to one another through the oxygen atoms from the bridging carbonato group, giving an equilateral triangular array of copper centres. Each copper ion has distorted square pyramidal environment with the basal plane formed by three nitrogen atoms of the ligand L³ and the oxygen atom of the bridging carbonato group. The apical position at each copper is provided by the weak oxygen coordination from the perchlorate ion.

Reaction of 𝑁-(phenyl)-2-pyridinecarboxamide (HL¹) and 𝑁-(𝑝-tolyl)-2-pyridinecarboxamide (HL²) ligands with MnCl₂.4H₂O affords complexes [(HL¹)₂MnCl₂] 1 and [(HL²)₂MnCl₂] 2. The structures of 1 and 2 were determined by three-dimensional X-ray crystallography revealing that the Mn^II ions assume distorted octahedral geometry with coordination by two HL¹/HL² ligands providing two pyridine N and two amide O and two chloride ions. Notably, secondary interactions [C-H$\cdots$Cl (pyridine 3-H hydrogen) and N-H$\cdots$Cl (amide NH hydrogen)] triggered by Mn^II-coordinated chloride ions acting as hydrogen bonding acceptors generate self-complementary dimeric tectons, which lead to 2D supramolecular architectures.