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(PWVI10WV2O40)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.