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

Abstract

Three octamolybdate-based metal–organic complexes constructed from a pyridyl-carboxylate ligand containing an amide group, 3-(2-pyridinecarboxylic acid)amido pyridine (HPCAP), namely, H₂{[Cu₃(PCAP)₄(H₂O)₂](β-Mo₈O₂₆)}·10H₂O (1), H{[Cu(PCAP)(H₂O)](β-Mo₈O₂₆)_0.5} (2) and H₂[Co(H₂O)₆][Co₂(PCAP)₄(γ-Mo₈O₂₆)(H₂O)₂]·10H₂O (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 [Cu₃(PCAP)₄]_n²ⁿ⁺ chains and bidentate β-Mo₈O₂₆⁴⁻ anions. In compound 2, 1D “thin centipede” [Cu₂(PCAP)₂]_n²ⁿ⁺ chains were connected by tetradentate β-Mo₈O₂₆⁴⁻ anions through the Cu–O bond to form a 2D network. In compound 3, γ-Mo₈O₂₆⁴⁻ anions were connected by adjacent [Co₂(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.