Controllable assembly of four new POM-based supramolecular compounds by altering the POM secondary building units from pseudo-Keggin to classical Keggin

Abstract

Four new supramolecular compounds, namely, [HMn^II(bix)₄][PMo^VI₈V^V₄O₄₀(V^IVO)₂]·2H₂O (1), [Zn(bix)₄][PMo^VI₉V^V₃O₄₀(V^IVO)₂]·2H₂O (2), [Cu(bix)₄][PMo^VI₉V^V₃O₄₀(V^IVO)₂]·4H₂O (3) and [Cu^I(bix)]₂[Cu^I(bix)](bix)[PMo₁₂O₄₀]·4H₂O (4) (bix = 1,4-Bis(imidazol-1-ylmethyl)benzene), have been synthesized under hydrothermal conditions, which are constructed from Keggin/pseudo-Keggin polyoxometalate (POM) secondary building units (SBUs) and transition metal complexes. Compound 1 consists of an infinite 1D chain constructed from [HMn^II(bix)₄]³⁺ cations and the reduced bi-capped pseudo-Keggin polyoxoanions [PMo^VI₈V^V₄O₄₀(V^IVO)₂]³⁻. With the aid of hydrogen bonds, these 1D chains extend to 3D supramolecular frameworks. Compounds 2 and 3 are isostructural and consist of the bi-supporting Keggin polyoxoanions [PMo^VI₉V^V₃O₄₀(V^IVO)₂]²⁻ and [M(bix)₄]²⁺ (M = Zn, Cu) coordination polymer fragments, resulting in the 3D supramolecular frameworks via weak interactions. Compound 4 is composed of the 1D ladder-like chains [Cu(bix)]_nⁿ⁺ which are filled in the 3D supramolecular cavities and stabilize the whole framework structures viahydrogen bonds. Interestingly, 3D architectures have been obviously changed by altering the POM SBUs from pseudo-Keggin to classical Keggin. Here, all these compounds are characterized by elemental analyses, IR, TG analyses and single-crystal X-ray diffractions. In addition, the electrochemical properties and photocatalytic properties of compounds 1–4 have been investigated.