Three zinc(II) and cadmium(II) complexes containing 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole and polynitrile ligands: synthesis, molecular and supramolecular structures, and photoluminescence properties

Abstract

Three photoluminescent complexes containing either Zn^II or Cd^II have been synthesized and their structures determined. Bis[4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole-κ²N¹,N⁵]bis(dicyanamido-κN¹)zinc(II), [Zn(C₁₂H₁₀N₆)₂(C₂N₃)₂], (I), bis[4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole-κ²N¹,N⁵]bis(dicyanamido-κN¹)cadmium(II), [Cd(C₁₂H₁₀N₆)₂(C₂N₃)₂], (II), and bis[4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole-κ²N¹,N⁵]bis(tricyanomethanido-κN¹)cadmium(II), [Cd(C₁₂H₁₀N₆)₂(C₄N₃)₂], (III), all crystallize in the space group P-1, with the metal centres lying on centres of inversion, but neither analogues (I) and (II) nor Cd^II complexes (II) and (III) are isomorphous. A combination of N-H...N and C-H...N hydrogen bonds and π-π stacking interactions generates three-dimensional framework structures in (I) and (II), and a sheet structure in (III). The photoluminescence spectra of (I)-(III) indicate that the energies of the π-π* transitions in the coordinated triazole ligand are modified by minor changes of the ligand geometry associated with coordination to the metal centres.

Keywords: crystal structure; hydrogen bonding; photoluminescence; polynitrile ligands; solvothermal synthesis; π–π stacking interactions.