The factors affecting the assembly of Keggin–metal–bimb systems: charge/polarity of Keggin polyanions and coordination modes of metal cations

Abstract

To explore the influence of the charge/polarity of Keggin polyanions and coordination modes of transition metal cations on the construction of polyoxometalate (POM)-based hybrid compounds, we design two synthetic routes and obtain six new POM-based inorganic–organic hybrid compounds, namely, [Co₅(H₂O)₆(bimb)₈(PW^VI₁₀W^V₂O₄₀)₂]·14H₂O (1), [Co₂(bimb)₂(GeW₁₂O₄₀)][bimb]·2H₂O (2), [Co₂(bimb)₂(BW₁₂O₄₀)][Hbimb]·2H₂O (3), [Co₂(bimb)₂(H₂W₁₂O₄₀)][H₂bimb]·2H₂O (4), [Cu(bimb)(BW₁₂O₄₀)][H₂bimb]₂·2H₂O (5) and [Ag₂(bimb)₂(BW₁₂O₄₀)][H₃bimb]·2H₂O (6) (bimb = 1,4-bis(1-imidazolyl)benzene). All compounds were characterized by elemental analyses, IR spectroscopy, powder X-ray diffraction and single-crystal X-ray diffraction. Compound 1 represents the first POM-based three-dimensional (3D) self-penetrating structure composed of a unique metal–organic polycatenated framework and tridentate Keggin clusters. Compounds 2, 3, 4 and 6 are isostructural, which show POMOF structures consisting of Keggin cluster guests and a metal–organic nanotube host. The structure of compound 5 is a simple 2D grid layer. The isolation of the title compounds is very informative for systematically understanding the effect of the charge/polarity of POMs and coordination modes of transition metal cations on the structures of POM-based hybrids. The effect of the charge/polarity of POMs and coordination modes of transition metal cations is discussed in this work. Additionally, the luminescence and electrochemical properties of 1–6 have been investigated in detail.