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

Abstract

By adjusting the molar ratio of the reactants H3PO4 and Na2MoO4, four new metal–organic frameworks, namely, CoH(bix)4[PMoVI8VV4O40(VIVO)2] (1), (H2bix)2(NaHP2Mo5O23)·2H2O (2), H2(bix)4[Cd(H2O)4][Cd(HPO4)4(H2PO4)4(MoO2)12 (OH)6]·10H2O (3) and (H2en)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 [PMoVI8VV4O40(VIVO)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.