Tetra- and polynuclear cadmium(II) complexes with 3,5-bis(pyrimidin-2-yl)-4H-1,2,4-triazol-4-amine. Synthesis, polymorphism, lone pair–π interactions and luminescence

• Cadmium(II) complexes with 3,5-bis(pyrimidin-2-yl)-4H-1,2,4-triazol-4-amine.
• Impact of metal-to-ligand molar ratio and solvent on the phase and chemical composition of the complexes.
• Blue emission of cadmium(II) complexes.
• Double lone pair–π interactions.

Cadmium(II) complexes, [CdLCl2]n (1), α-{[CdLCl2]·H2O}n (2), β-{[CdLCl2]·H2O}n (3), and [Cd4L2(H2O)2Cl8]·2H2O (4), with 3,5-bis(pyrimidin-2-yl)-4H-1,2,4-triazol-4-amine (L), have been synthesized. They are the first examples of structurally characterized metal complexes with L. In these structures, the ligand L adopts either bidentate (N′pyrimidine,N1triazole) or bis-bidentate (N′pyrimidine,N1triazole,N2triazole,N″pyrimidine) coordination. The complexes 1–3 are linear coordination polymers, the compounds 2 and 3 are polymorphs. The linear chains are assembled into 2D supramolecular structure due to π–π stacking interactions between practically planar L molecules. The structure of 4 consists of [Cd4L2(H2O)2Cl8] complex molecules with μ2- and μ3-chlorido-bridged quasi-cubane tetracadmium core and non-coordinated water molecules. In the structure of 4, the intermolecular lone pair–π interactions were observed between Cl atom and π-deficient triazole ring. The photoluminescent properties of L, 3, and 4 were studied in the solid state. These compounds were found to display bright blue luminescence. The relative intensity of emission increases in the order L < [Cd4L2(OH2)2Cl8]·2H2O < β-{[CdLCl2]·H2O}n.

A series of cadmium(II) complexes, [CdLCl2]n (1), α-{[CdLCl2]·H2O}n (2), β-{[CdLCl2]·H2O}n (3), and [Cd4L2(H2O)2Cl8]·2H2O (4), with 3,5-bis(pyrimidin-2-yl)-4H-1,2,4-triazol-4-amine (L), have been synthesized. Lone pair–π interactions between Cl atom and the triazole ring were observed in the structure of [Cd4L2(H2O)2Cl8]·2H2O. The complexes β-{[CdLCl2]·H2O}n and [Cd4L2(H2O)2Cl8]·2H2O show blue emission in the solid state.Figure optionsDownload as PowerPoint slide