Solvent-induced Mn(ii)/Zn(ii)/Co(ii) organopolymolybdate compounds constructed by bis-pyridyl-bis-amide ligands through the Mo–N bond: synthesis, structures and properties

Abstract

Three transition metal organopolymolybdate hybrid compounds, namely, H₂[Mn(H₂O)₄L₃(γ-Mo₈O₂₆)] 8H₂O (1), H[M₂(CH₃O)(H₂O)₆L₃(γ-Mo₈O₂₆)] [M = Zn (2) and Co (3)] [L = 1,4-bis(3-pyridinecarboxamido)benzene] have been synthesized under solvothermal conditions and characterized by IR spectroscopy, TG analysis, powder XRD and single-crystal X-ray diffraction. Compounds 1–3 were obtained by the one-pot method, and the mixture of methanol and water with different ratios was used as the solvent. In compound 1, the γ-Mo₈ anions were connected with pyridine groups of ligand L by the Mo–N bond, forming an uncommon 1D γ-Mo₈–L chain. The adjacent chains were connected by [MnL₂(H₂O)₄]²⁺ moieties through hydrogen bonding interaction to construct a 2D supramolecular network. Compounds 2 and 3 are isostructural, which show a 3D 2,4,6-connected {4⁴·6²}{4⁴·6⁶·8⁴·10}{6} framework. The γ-Mo₈ anions were connected by [M(H₂O)₂(CH₃O)]⁺ [M = Zn (2) and Co (3)] subunits forming 1D M–Mo₈ chains, which were connected by [ML₂(H₂O)₄]²⁺ moieties to construct a 2D layer. In compounds 2 and 3, there also exist the same 1D γ-Mo₈–L chains as in 1, which extended the 2D networks to 3D frameworks. The Mo–N bond with pyridyl groups was formed under the solvothermal conditions, which is scarcely reported to our knowledge. The effect of the solvent on the assembly of the title compounds and the formation of the Mo–N bond, as well as the role of metal–organic moieties on the construction of diverse organopolymolybdate compounds have been discussed in detail. Furthermore, the electrochemical and photocatalytic properties of 1–3 have been investigated.