An evidence for conversion of A-PW9O349− derivatives to A-PW10O379− derivatives. Synthesis and characterization of [(A-PW9O34)2(H2OM)3CO3]11− (M = Sm(III), Eu(III) and Gd(III)) and [(PW10Sm2O38)4(W3O8(H2O)2(OH)4)]22− (M = Sm(III) and Gd(III))

Abstract

In this study, we show that the A-PW9O349− anion reacts with aqueous carbonate solutions of samarium(III), europium(III) and gadolinium(III), and yields different products. Under heating to 80°C, the main products for Eu(III) and Gd(III) are new sandwich type polyoxometalates, [(A-PW9O34)2(H2OM)3CO3]11−, while a samarium(III) derivative analogous to [(A-PW9O34)2(H2OSm)3CO3]11− is produced when the reaction is maintained under room temperature (30°C). Under heating, the main product for Sm(III) is a new tetramer species of [(PW10Sm2O38)4(W3O8(H2O)2(OH)4)]22−. We obtained a gadolinium(III) derivative analogous to [(PW10Gd2O38)4(W3O8(H2O)2(OH)4)]22− as by-product from the filtrate of the respective sandwich type polyoxometalate synthesis. On the other hand, 31P NMR shows decomposition of the sandwich type compound to a tetramer species for the Eu(III) derivative in aqueous solution. The structures of sandwich type polyoxometalates consist of a (MOH2)3CO3 belt encapsulated by two A-PW9O34 groups. The structure of the tetramer species consist of four PW10O379− units each incorporating two Sm(III) ions to create four Keggin-like anions that are further tied together by three additional tungstate units. The new complexes in these two categories have been isolated and characterized by elemental analysis, IR, 31P NMR spectroscopy thermogravimetric analysis (TGA) and X-ray single crystal structure analysis.