Co-existing intermolecular halogen bonding, aryl packing and hydrogen bonding in driving the self-assembly process of Keggin polyoxometalates

A new series of supramolecular architectures based on Keggin polyoxometalates (POMs): (Hbpy)3[PMo12O40]·2.2H2O (1), (H3/4bppy)4H2[PMo12O40]·3H2O (2), (Hbppy)4H2[SiW12O40]·3H2O (3) and (Hppy)4H2[SiMo12O40] (4) (bpy = 4-(5-chloropyridin-2-yl)pyridine, ppy = 4-(5-phenylpyridin-2-yl)pyridine and bppy = 4-(5-(4-bromophenyl)pyridin-2-yl)pyridine), has been prepared and characterized. In compound 1, no direct interaction occurs among POM anion clusters, and the anions together with organic molecule bpys construct the supramolecular frameworks to accommodate guest water molecules. In compounds 2 and 3, Keggin anions form one-dimensional pillar-like inorganic chains as a ‘guest’ to occupy the supramolecular spaces formed by compact organic array, while POMs form two-dimensional layers and alternative array with organic layers in compound 4. Noncovalent interactions of hydrogen bonding, aryl packing and halogen bonding coexist in compounds 1–3. The C–X⋯O (X = Cl or Br) synthon is introduced for the first time to drive self-assembly process of POMs. The crystal structure analyses reveal that the substituted groups of organic bipyridine have a major influence on the packing arrangement of crystals. Additionally, the different cation ∶ anion ratios (3 in 1, and 4 in the other compounds) may also in part affect the packing modes of the organic and inorganic moieties.