Formation of novel cadmium(II) tetrazolato complexes with Schiff bases as co-ligands via in situ [3+2] cyclo-addition

Five cadmium(II) complexes, [Cd(PZTZ)2(OH2)2] (1), [Cd2(L1)2(Cl)2]·0.11CH3OH (2), [Cd(PRTZ)(L1)(OH2)] (3), [Cd(PRTZ)(L2)(OH2)] (4) and [Cd(PZTZ)(L2)(OH2)]·0.25H2O (5) {HL1 = 2-(3-(methylamino)propylimino)methyl)phenol; HL2 = 2-(3-(dimethylamino)propylimino)methyl)phenol; HPZTZ = 2-pyrazinyltetrazole and HPRTZ = 2-pyridyltetrazole} have been synthesized and characterized. Single crystal X-ray diffraction studies have confirmed the structures of the complexes. Complex 2 crystallizes in triclinic space group P1¯, and all others crystallize in monoclinic space group P21/c. Complex 1 consists of a discrete centrosymmetric mononuclear unit, in which cadmium(II) is octahedrally coordinated by two pyrazene and two tetrazolate nitrogen atoms of two PZTZ− moieties and two oxygen atoms of two water molecules. The asymmetric unit of complex 2 contains a double phenoxo bridged dinuclear cadmium(II) species and 0.11 fraction of a methanol molecule. In the dinuclear unit, each cadmium(II) is penta-coordinated. In each of the complexes 3, 4 and 5, cadmium(II) is coordinated meridionally by a depronated terdentate Schiff base {(L1)− for 3 and (L2)− for 4 and 5} and two nitrogen atoms of the (PRTZ)− in 3 and 4 and two nitrogen atoms of the (PZTZ)− in 5. Water molecules coordinate in the sixth coordination sites of cadmium(II) in the complexes to complete their distorted octahedral geometries. All the complexes show photoluminescence in DMSO solution at room temperature upon the irradiation of ultraviolet light. The life times of the excited states are in the range of 8.32–12.22 ns. Weak interactions like C–H⋯π/O–H⋯π/π⋯π with multiple hydrogen bonds promote the formation of supramolecular architectures in these complexes.

Graphical abstractFive photo-luminescent cadmium(II) complexes have been synthesized and characterized. Weak interactions promote the formation of supramolecular architectures in these complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide