Syntheses, structures, and fluorescent properties of three Zn(II) and Cu(II) complexes of different ligands derived from 3,6-bis(2-pyridyl)-1,2-dihydro-1,2,4,5-tetrazine

Three supramolecular complexes [Zn(HL1 )2(H2O)2(ZnCl4)2] (1), [Cu(L2 )2Cl2] (2), and [Zn(L3 )Cl2] (3) have been synthesized and characterized by single crystal X-ray diffraction analysis (L1 = 3,5-di(2-pyridyl)-4-amino-1,2,4-triazole, L2 = 3,5-di(2-pyridyl)-1,2,4-triazole, and L3 = 2-pyridinecarboxylic acid (pyridin-2-ylmethylene)-hydrazide). In 1, anion–π interactions between Cl− and the π-systems of L1 are observed and anion–π, hydrogen bonding and π–π stacking interactions link the two complex units of [Zn(HL1 )2(H2O)2]4+ and [ZnCl4]2− to form a 3-D supramolecular network. In 2, π–π stacking interactions between aromatic rings of 1,2,4-triazole and pyridine rings are observed; in 3, hydrogen bonding of Cl ··· H–N and π–π stacking interactions between parallel pyridine rings of L 3 are observed. The mechanisms of rearrangement reactions of L to L1 –L3 are discussed. The fluorescent properties for solid 1 and 3 are also investigated.