Organic-inorganic hybrids consisting of organic cations and polyanions are promising functional materials due to their various compositions and structures. An important aspect of these materials is the interactions between the organic and inorganic components, which not only produce the final structures, but also influence the properties. Here, we investigated the interactions between organic cations and polyanions using protonated 2-aminopyridinium (Hap) as the cation, and successfully obtained two polyoxometalate-based hybrids, namely (C5H7N2)4[Mo8O26], (I), and (C5H7N2)2[NiMo6O16(OH)2{CH3C(CH2O)3}2]·4H2O, (II). In the crystal structure of (I), every Hap cation links with two polyanions by donating one or two N-H...O hydrogen bonds, and every polyanion is surrounded by eight Hap cations via terminal or bridging O atoms. Conversely, in compound (II), every Hap cation only links with one polyanion decorated by a triol ligand; this organic-inorganic component further assembles via uncoordinated water molecules. In the extended structures, Hap plays a key role, not only providing a counter charge, but also acting as `glue' linking polyanions in the role of hydrogen-bond donors. In both compounds, as the nodes of the supramolecular network, the polyanions exhibit an ordered two-dimensional arrangement due to strong hydrogen bonds and electrostatic interactions between the organic and inorganic parts. The electrochemistry of compound (I) shows that redox sourcing from polyanions is a surface-controlled process. Conversely, the magnetic behaviour of compound (II) indicates dominant antiferromagnetic properties.
Keywords: POM; crystal structure; hybrids; polyoxometalate; pyridinium; supramolecular interactions.