Two Supramolecular Inorganic-Organic Hybrids of 12-Silicotungstic Acid Heteropolyoxometalate and Trinuclear Lanthanide Clusters: Syntheses, Structures, and Magnetic Properties

Hydrothermal synthesis of two novel inorganic-organic hybrid assemblies, {Na[Ln(pydc-OH)(H2O)(4)](3)}[SiW12O40]center dot 15H(2)O [Ln = Nd (1) and Ln = Sm, (2); pydc-OH = 4-hydroxypyridine-2,6-dicarboxy], and their characterization is described. Structural characterizations by single-crystal X-ray diffraction reveal that these compounds are isostructural, and each consists of [SiW12O40](4-) Keggin-type polyoxometalates (POMs) linked by three lanthanide ions to yield discrete trinuclear lanthanide clusters. These discrete molecules are further packed into 3D supramolecular assemblies by means of hydrogen-bonding and anion-pi interactions. Both compounds exhibit remarkable thermal stability. The temperature variation in the magnetic susceptibility chi(m) and of the chi T-m product and Bohr magnetons of the Nd-III(1)- and Sm-III (2)-based compounds are considered. The magnetic data have been interpreted relative to data presented in the literature.