Decavanadate-based discrete compound and coordination polymer: Synthesis, crystal structures, spectroscopy and nano-materials

摘要

Two decavanadate based compounds, [{HMTAH}_2{Na(H_2O)_6}_2][H_2V_(10_O_(28)]·6H_2O (1) (HMTA = hexamethylenetetramine) and [Na_3(H_2O)_9]_(2n)[V_(10)O_(28)]_n (2), have been synthesized in aqueous medium. Compound 1 (a discrete compound) is synthesized with organic and inorganic cations, whereas compound 2 (a coordination polymer) has been isolated using only inorganic cations. An acidified aqueous solution of sodium metavanadate, on heating at 70 ℃ followed by addition of acetonitrile, results in the isolation of compound 2, the crystal structure of which showing it to be a two-dimensional coordination polymer, formed from the decavanadate cluster anion and the tri-sodium aqua-complex cation. Compounds 1 and 2 have been characterized by routine elemental analyses, FT-IR spectroscopy and unambiguously by single crystal X-ray crystallography. Among these two compounds, compound 2 exhibits an emission in the visible region at room temperature in its solid state (on excitation at 380 nm). Nanocrystals of compound 2 in the size range 50-70 nm were synthesized by ultrasonication of macrocrystals of compound 2 in acetonitrile solvent (0.5 mM). The nanoparticles were characterized by FT-IR and PXRD studies. The morphology of the nanoparticles of compound 2 were studied using FE-SEM, TEM and AFM techniques. As expected, these nanoparticles also display emission spectra at room temperature. The connectivity of the decavanadate oxygens with the metal cations plays an important role in compound 2 exhibiting emission spectra, because decavanadate cluster (as such) containing compounds generally do not show emission.