Tunable transition-metal-linked Preyssler type polyoxometalate frameworks: Synthesis, structural characterization and optical proprieties
Polyoxometalates (POMs), a class of molecularly defined transition metal-oxide clusters (TM= Cr, V, Mo, W, Nb), have been developed due to their properties in the field of catalysis, magnetism, electronics, gas sensor, supramolecular chemistry and drug deliver. Among all POMs, tungsten oxide (WOx), as a nontoxic and photostable semiconductor with a narrow bandgap about 2.6 eV, is the most attractive cluster for the researchers. Due to the narrow bandgap of WOx, only the blue and near ultraviolet regions of the solar spectrum can be excited. The photocatalytic performance of WOx can be increased by doping numerous elements to reduce bandgap effectively. POMs offer the advantage of precisely placed atoms and well-defined W:O ratios. Besides, POMs can be used as building blocks for frameworks in which the POMs are linked with all-inorganic linkers. All-inorganic frameworks have high stability, high catalytic activity, photochemical and electrochemical activity. Here, we develop a strategy to synthesize six frameworks based on the Preyssler cluster [P5W30O110]15- linked with various transition metals such as Mn, Fe, Co, Ni, Cu and Zn. Besides, bimetallic POM frameworks have been prepared where the transition metals are distributed homogeneously within all crystals of the sample. In addition, the transition metal ratio was varied from 0 to 1, affording materials with absorption that varies as a function of metal identity and content. The diffuse reflectance from single metallic POM frameworks to bimetallic POM frameworks were shown to illustrate the tunable optical properties of these POM frameworks.