pH, solvent and metal ion induced octamolybdate-based metal-organic complexes decorated with a pyridyl-carboxylate ligand containing an amide group

Three octamolybdate-based metal-organic complexes constructed from a pyridyl-carboxylate ligand containing an amide group, 3-(2-pyridinecarboxylic acid) amido pyridine (HPCAP), namely, H-2{[Cu-3(PCAP)(4)(H2O)(2)](beta-Mo8O26)}center dot 10H(2)O (1), H{[Cu(PCAP)(H2O)](beta-Mo8O26)(0.5)} (2) and H-2[Co(H2O)(6)][Co-2-(PCAP)(4)(gamma-Mo8O26)(H2O)(2)]center dot 10H(2)O (3), have been successfully synthesized under hydrothermal or solvothermal (methanol-water mixed solvent) conditions. Single-crystal X-ray analyses reveal that compound 1 is a 2D layer based on infinite 1D [Cu-3(PCAP)(4)](n)(2n+) chains and bidentate beta-Mo8O264- anions. In compound 2, 1D thin centipede [Cu-2(PCAP)(2)](n)(2n+) chains were connected by tetradentate beta-Mo8O264- anions through the Cu-O bond to form a 2D network. In compound 3, gamma-Mo8O264- anions were connected by adjacent [Co-2(PCAP)(4)(H2O)(2)] moieties through Co-O and Mo-N bonds forming an uncommon 1D fat centipede chain. The adjacent chains were further extended to a 2D supramolecular network through hydrogen bonding interactions. The title compounds represent the first examples of introducing a pyridyl-carboxylate ligand containing an amide group into the POM system. The pH value, solvent and metal ions play key roles in the construction of the final architectures and show a great influence on the structural diversities of the title compounds. The electrochemical properties of compound 1 and the photocatalysis properties of the title compounds have been reported.