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, [CdLCl 2 ] n ( 1 ), α-{[CdLCl 2 ]·H 2 O} n ( 2 ), β-{[CdLCl 2 ]·H 2 O} n ( 3 ), and [Cd 4 L 2 (H 2 O) 2 Cl 8 ]·2H 2 O ( 4 ), with 3,5-bis(pyrimidin-2-yl)-4 H -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 ,N 1 triazole ) or bis -bidentate (N′ pyrimidine ,N 1 triazole ,N 2 triazole ,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 [Cd 4 L 2 (H 2 O) 2 Cl 8 ] complex molecules with μ 2 - and μ 3 -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 4 L 2 (OH 2 ) 2 Cl 8 ]·2H 2 O 2 ]·H 2 O} n .