Molecular assemblies based on polytungstate clusters and the flexible organic ligand 1,3-bis(4-pyridyl)propane

Four polyoxometalate (POM) assemblies based on the flexible organic ligand 1,3-bis(4-pyridyl) propane (bpp) have been synthesized and fully characterized, including (Hbpp)(3)-[PW12O40] (1), [Cu(bpp)](2)[Cu-2(bpp)(3)][SiW12O40] (2), [Cu-2-(Hbpp)(4)](H(2)bpp)(0.5)H-2[SbW18O60]center dot 3H(2)O (3), and (H(2)bpp)(5)-[Ni-4(OH2)(2)(AsW9O34)(2)]center dot 0.5H(2)O (4). Compounds 1 and 2 were prepared by the reaction of the classical Keggin-type anions with organic bpp under hydrothermal conditions. The difference between these compounds is that protonated bpp is found in 1, whereas in 2 Cu-I-bpp fragments are present. In the framework of 1, organic and hybrid chains, built upon supramolecular interactions, coexist. Compound 2, which crystallizes in a chiral space group, has a 2D wave-like structure consisting of {Cu-6(bpp)(6)} grids that accommodate {[Cu-2(bpp)(2)][SiW12O40]}(2-) fragments. The nonclassical anionic clusters in 3 and 4 are obtained from simple inorganic salts or oxides under hydrothermal conditions. The inorganic moiety in 3 exhibits a pseudo-Dawson-like [SbW18O60](9-) cluster, and in 4 a sandwich-type [Ni-4(H2O)(2)(AsW9O34)(2)](10-) anion is present. The organic ligand bpp, with a freely rotatable -(CH2)(3)- group, is present in various conformations in the four compounds. Structure-analyses results indicate that the flexibility of bpp plays a significant role in the fabrication of these kinds of inorganic-organic arrangements. The thermal and electrochemistry properties of all four compounds have also been studied.