Synthesis and properties of [CuLCl₂] and [CuL(N₃)(OClO₃)]·H₂O (L=α,α'-bis(pyrazolyl)-m-xylene): X-ray structure of [CuLCl₂]₂

Abstract

Using an m-xylyl based dinucleating ligand α,α'-bis(pyrazolyl)-m-xylene (L), providing only one pyrazole nitrogen coordination to each copper(II) centre, two copper(II) complexes [CuLCl₂] (1) and [CuL(N₃)(OClO₃)]·H₂O (2) have been synthesized. Complex 1 has been structurally characterized, revealing that the coordination sphere of each copper(II) ion is distorted square pyramidal. Two pyrazole nitrogens from two different ligands and two chloride ions form the equatorial plane and an additional weak bonding interaction by a chloride ion from an adjacent layer provide axial coordination. The dimeric repeat unit [CuLCl₂]₂ having a Cu₂Cl₂ bridging unit gives rise to an extended network. Based on physicochemical studies, a similar structure has been proposed for 2; however, in 2 one azide ion and a coordinating perchlorate ion are in the equatorial plane. Magnetic susceptibility measurements (25-300 K) reveal that the two copper(II) centres in each 'pseudo dicopper(II) unit' are weakly antiferromagnetically coupled, with the relevant 2J values of ≈-10 cm^-1 for 1 and ≈-9 cm^-1 for 2. The square pyramidal stereochemistry of the copper(II) centres is revealed by absorption and EPR spectral properties.