Synthesis, spectral and structural characterization of two polymeric 1:1 complexes of 2,3-dimethylpyridine and 5-ethyl-2-methylpyridine with copper(II) azide; Cu(2,3-dimethylpyridine) (N3)2 and Cu(2-methyl-5-ethylpyridine) (N3)2

Two new 1:1 ligand complexes of copper(II) azide with disubstituted pyridine ligands, namely catena-di-μ(1,3)-azido-di-μ(1,1)-azidobis(2,3-lutidine)dicopper(II)] (1) and catena-di-μ(1,1)-azidodi-μ(1,1)-azidobis(2-methyl-5-ethylpyridine)dicopper(II)] (2), have been synthesized and characterized by spectroscopic and X-ray crystallographic methods. The polymeric complex 1 features monodentate 2,3-lut ligands, centrosymmetric di-μ(1,1)-azido-bridged Cu₂N₂ rings, distorted square-pyramidal copper(II) coordination geometry and di-μ(1,3)-azido bridges which link the centrosymmetric binuclear Cu₂(2,3-lut)₂(N₃)₂ moieties to form sheets within the ab plane. In the monoclinic crystals of complex 2, the copper(II) centres are pentacoordinated via N(11), N(21), N(11b) and N(21a) from the azido ligands Cu---N distances 1.971(5)–2.286(5) Å] and N(1) from the organic molecule at a Cu---N bond length of 2.001(5) Å. Both azido ligands function as μ(1,1) bridges to form chains of polyhedra along the short a-axis of the unit cell. The IR absorption spectra reveal that each of these complexes contains two independent azide ligands. The solid and solution electronic spectra of complexes 1 and 2 show at least three and two strong absorption bands, respectively, associated with N₃^? → Cu^II charge transfer transitions. The EPR spectra of powder samples and DMSO solutions at room temperature were recorded and are discussed.