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GREEN SYNTHESES OF ANDERSON-EVANS POLYANIONS {XMo6O24} IN ONE-POT PROCEDURE

Ioana Cristina Pistea, Carmen Roba, Cristina Rosu

Abstract

Polyoxometalates (POMs) are discrete, anionic metal-oxygen clusters of early d bloc metal ions in high oxidation status (e.g. MoVI, WVI) with a very large structural and compositional variety, leading to interest in many different areas (catalysts in homogeneous and heterogeneous catalytic oxidation of organic compounds or biochemical reactions, activity in enzymatic redox processes, as antitumoral, antibacterial and antiviral treatments etc). An important subclass of POMs is the {XMo6O24} structure type, Anderson-Evans structure, in which an octahedral XO6 hetero group is surrounded by six edge-shared MoO6 octaedra. In the literature almost all syntheses of the subclass Anderson-Evans polyanions are of the hydrothermal type, yielding crystalline compounds in low yields and, after one or two recrystallizations, the obtained crystals are good for single X-ray investigation. The major problems of these syntheses are low reproducibility and low yields (14 пїЅ 35%). Here, we report two green methods of synthesis of {XMo6O24} Anderson-Evans polyanions, where X = Cr(III), Mn(II), Co(II), Ni(II) and Cu(II), in one-pot procedure, under conventional пїЅopen beakerпїЅ conditions, in aqueous solutions, controlling the final pH and without heating. Slow evaporation at room temperature for Cr(III) and Mn(II) compounds for 2-6 hours led to the formation of well formed crystals and excellent yields (70-75%). Slow evaporation in a refrigerator at 60C for Co(II), Ni(II) and Cu(II) compounds for 2-5 days led to the formation of small crystals and good yields (60- 65%). The two green methods described in this paper are simple, rapid, reproducible, inexpensive, and the resulting compounds are crystalline and high yields (60-75%). The molecular formula of Anderson-Evans polyanions were determined by elemental and thermo-gravimetric analysis, UV-Vis and FTIR spectroscopy.

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DOI resolver: doi.org/10.5593/sgem2017/61/s24.021

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