Hydrothermal Synthesis, Crystal Structure And Characterization Of Polyoxotungstates Containing Transition Metal

In this paper, five unreported organic-inorganic hybrid compounds have beensynthesized by utilizing a flexible ligand with long spacer, bpp, an organic chelating ligand,2,2'-bipy, or a bridging ligand, 4,4'-bipy, as organic composition and polyoxoanions asinorganic building units, and by adjusting reaction conditions and reaction materials. Thesecompounds have been structurally characterized by elemental analyses, UV, IR, TG andsingle crystal X-ray diffractions. The magnetic properties of compound 1and 3have beenstudied.1. Four transition-metal derivatives of the Keggin polyoxometalates have beenhydrothermally synthesized and structurally characterized:It is interesting to note that bpp is transformed into pyridine-4-carboxylic acid. This isthe first time that oxidation cracking reaction of C-C bonds of an N-heterocyclic ligandoccured and pyridine-4-carboxylic acid (PCA) ligand was formed in metal/organic/POMreaction system under hydrothermally conditions. The reaction mechanism is not clear but asis well-known, polyoxometalates (POMs) have catalytic-oxidation activity, and underpresence of POM, the bpp might be oxidized partially by the oxidative materials, such as CuII,NO3-, and O2 in the acid system under hydrothermal conditions, although CuI have notappeared in the product. In 1and 2, Keggin polyoxometalates, copper coordination cationsand waters are linked through the hydrogen bonds into three-dimensional supramoleculararchitectures. In 3adjacent [α-FeW12O42]5- polyanions are linked by water molecules via Hbond,forming a ladder chain structure. These chains create a layer structure throughhydrogen bonds. That is, the anion acts as the hydrogen bond acceptor forming a 2Dhydrogen bond net work. In 4a 3D supramolecular architecture is assembled by thetungstoferrate anions, protonized 4,4'-bipyridinium cations and water molecules through thehydrogen bonding interactions between them.2. A new polyoxometalate compound on the base of Dawson type polyoxoanion clusterdecorated by Cu-4,4'-bipy coordination ion has been hydrothermally synthesized andstructurally characterized: Compound 5is a supramolecular compound. Dawson anion regarded as mono-dentateligand provides its two terminal oxygen atoms and coordinates to a {Cu(4,4'-Hbipy)2}3+cation, forming a polymeric chain. The protonated organic cations H2bpp2+ link the chainsvia hydrogen bonds.