Solvent-induced Keggin-based Cd(II)/Ni(II) complexes constructed from pyridyl-tetrazole: Assembly, structures and properties

•Three Keggin-based CdII/NiII complexes were obtained under solvothermal conditions.•The reports on polyoxometalate-based CdII/NiII complexes are very limited.•Methanol plays an important role in the construction of the title complexes.•The different metal ions show great effect on the structures of complexes 1–3.•The electrochemical and photocatalytic properties of title complexes were studied.

Three Keggin-based CdII/NiII transition metal complexes, namely, [Cd(3-Hptz)4(CH3O)2](H3PMo12O40)·2H2O (1), [Cd(4-Hptz)4(CH3O)2](H3PMo12O40)·2H2O (2) and {[Ni3(4-ptz)2(4-Hptz)2(μ3-O)(H2O)2](HPMo12O40)}·5H2O (3) [3-ptzH = 5-(3-pyridyl)-1H-tetrazole, 4-ptzH = 5-(4-pyridyl)-1H-tetrazole], have been synthesized under solvothermal conditions and characterized by IR spectroscopy and single-crystal X-ray diffraction. The mixture of methanol and water was used as the solvent, which play an important role in the formation of compounds 1–3. Compounds 1 and 2 are isostructural. In 1, four 3-Hptz ligands and two methanol molecules coordinate with one CdII ion to form a [Cd(3-Hptz)4(CH3O)2] metal–organic unit, which links the adjacent discrete PMo12O403− (PMo12) anions through hydrogen bonding interactions to construct a 2D supramolecular layer. In compound 3, the tetrazole groups from one 4-Hptz and two 4-ptz ligands coordinate with three Ni ions to form a flat trinuclear subunit, which is further covered by another 4-Hptz vertically, resulting in a {[Ni3(4-ptz)2(4-Hptz)2(μ3-O)(H2O)2]2+ cluster. Adjacent trinuclear clusters connect with each other through pyridyl group of 4-ptz ligands to form a 1D chain. The PMo12 anions hang on both sides of the 1D chain, and methanol molecules may act as structure-directing agent in 3. The effect of central metals on the structures of the title compounds was discussed. In addition, the photocatalytic activities of the title complexes for the degradation of methylene blue under UV and sunlight irradiation have been investigated in detail.

Graphical abstractThree novel Keggin-based CdII/NiII metal–organic complexes constructed from two isomeric ligands 5-(x-pyridyl)-1H-tetrazole (x = 3, 4) have been successfully synthesized under CH3OH/H2O mixed solvents. The CH3OH solvent plays important and different roles in the construction of the title compounds.Figure optionsDownload full-size imageDownload as PowerPoint slide