Synthesis, characterization and photophysical properties of some water soluble Zn(II) azide complexes with (E)-2,4-dimethoxy-N-((pyridin-2-yl)methylene)benzenamine derived from 2-pyridinecarboxaldehyde

Five new zinc(II) azide complexes with the composition [Zn(N₃)₂(Lⁿ)], where Lⁿ = (E)-2,4-dimethoxy-N-((pyridin-2-yl)methylene)benzenamine, are reported herein. The complexes were characterized using UV-vis, fluorescence, IR, and ¹H NMR spectroscopy, along with elemental analysis. The single-crystal structural analysis of compound <b>1</b> is presented. The mononuclear Zn(II) complex crystallized in the monoclinic system with the centrosymmetric space group <i>P₂1/n</i>. The asymmetric unit of complex <b>1</b> consists of two crystallographically independent molecules with quite similar geometries. The five-coordination geometry of the Zn(II) ions in <b>1</b> is irregular, best described as halfway between trigonal bipyramidal and square pyramidal geometries. Efforts to obtain single crystals of compounds <b>2</b>–<b>5</b> suitable for X-ray crystal structure analysis were unsuccessful. However, based on spectroscopic data and the structures of related zinc(II) complexes reported in the literature, complex <b>2</b> is proposed to have a geometry similar to that of complex <b>1</b>, and complexes <b>3</b>–<b>5</b> are anticipated to have a four-coordinated tetrahedral geometry. All complexes were obtained in moderate-to-good yields and behave as non-electrolytes in acetonitrile solution. UV-vis and fluorescence spectral studies of complexes <b>1</b>–<b>5</b> indicate ligand-to-ligand (intra-ligand, π-π*) charge transfer transitions.