Controllable self-assembly of four new metal-organic frameworks based on different phosphomolybdate clusters by altering the molar ratio of H3PO4 and Na2MoO4

By adjusting the molar ratio of the reactants H3PO4 and Na2MoO4, four new metal-organic frameworks, namely, CoH(bix)(4)[(PMo8V4O40)-V-VI-O-V((VO)-O-IV)(2)] (1), (H(2)bix)(2)(NaHP2Mo5O23)center dot 2H(2)O(2), H-2(bix)(4)[Cd(H2O)(4)][Cd(HPO4)(4)(H2PO4)(4)(MoO2)(12)(OH)(6)]center dot 10H(2)O (3) and (H(2)en)(3)(Co3P4Mo4O28) (4) (bix 1,4-bis(imidazol-1-ylmethyl) benzene, en 1,2-ethylenediamine), have been hydrothermally prepared and characterized by elemental analyses, IR spectroscopy, TG analyses, and single-crystal X-ray diffraction. Compound 1 consists of straight chains based on pseudo-Keggin (PMo8V4O40)-V-VI-O-V((VO)-O-IV)(2)](3-) polyanions and [CoH(bix)4](3+) complex fragments, which are further connected into a three-dimensional (3D) open framework by hydrogen bonding interactions between polyanions and organic bix ligands. Compound 2 shows 3D supramolecular networks constructed from weak interactions between free biprotonated bix, water and oxygen atoms of polyanions [P2Mo5O23](6-). In compound 3, [Cd(HPO4)(4)(H2PO4)(4)(MoO2)(12)(OH)(6)](4-) polyanions are linked by [Cd(H2O)(4)](2+) cations to build one-dimensional (1D) chains. Then weak interactions between free bix ligands, water and oxygen atoms of the polyanions extend these 1D chains to 3D supramolecular frameworks. Compound 4 exhibits open-framework structures. Interestingly, it also shows 1D left and right-handed helical chains and 2D (6,3)-layers. The molar ratio of the reactants H3PO4 and Na2MoO4 influence the transformation of the phosphomolybdate clusters in compounds 1-4. The electrochemistry and photocatalysis properties of these compounds have also been investigated in this paper.