Two rare {M 2 (MoO 4 ) 2 } n chain-containing molybdate-based metal–organic complexes with a bis-pyrazole-bis-amide ligand: fluorescent sensing and photocatalysis performance

By introducing a bis-pyrazole-bis-amide ligand, N,N'-bis(1H-pyrazole-4-carboxamide)-1,4-benzene (L), two molybdate-based metal-organic complexes containing {M2(MoO4)2} n (M = Co, Zn), [Co2L2(MoO4)2]·H2O (1), [Zn2L2(MoO4)2]·H2O (2), have been prepared under hydrothermal/solvothermal conditions. X-ray diffraction analyses reveal that both 1 and 2 are isostructural. An interesting structural feature is that a kind of {M2(MoO4)2} n chain could be found in 1 and 2, although different raw materials [Mo7O24]6- and [PMo12O40]3- anions were utilized. Then these chains are further linked by L ligands into a two dimensional (2D) structure. The title complexes represent the first examples containing {MoO4} units and pyrazole-/or amide-derivative ligands. Complexes 1 and 2 exhibit distinct performances due to different metal centers, with 2 acting as a fluorescent sensor for Fe3+, MnO4 -, CrO4 2- and Cr2O7 2-, but 1 being a better photocatalyst towards degradation of cationic dyes methylene blue (MB) and neutral red (NR).