In this study we investigated the interaction of trivacant polyoxometalate, [A-α-PW9O34]9- with lanthanide ions of Sm(III), Dy(III), Er(III) and Yb(III) in aqueous solution. Sandwich-type polyoxometalates of [(A-α-PW9O34)2(MOH2)3(CO3)]11- (M = Yb(III), Dy(III), Er(III)) are formed by stoichiometric reaction of trivacant polyoxometalate, [A-α-PW9O34]9- with metal ions M(III) in aqueous 0.1M carbonate solution. The complexes are characterized by elemental analysis (ICP), infrared spectroscopy (IR), UV-Vis spectroscopy and thermogravimetry analysis (TGA). The structure of complexes consist of two lacunary [A-α-PW9O34]9- moieties which linked by a (M3CO3) belt. The syntheses of complexes require presence of carbonate anion and decomposition take place with loss of it. We obtained new tetramer complexes with Sm(III) and Dy(III) of [(PW10M2O38)4(W3O8(H2O)2(OH)4)]22- under different conditions. the Sm(III) derivative obtained under the sandwich-type polyoxometalates syntheses conditions but the Dy(III) derivative obtained by reaction of [A-α-PW9O34]9- with Dy(III) ions in 1:1 mole ratio and without carbonate solution. The later complexes are characterized by elemental analysis (ICP), infrared spectroscopy (IR), UV-Vis spectroscopy, thermogravimetry analysis (TGA) and X-ray single crystal structure analysis. The structure of complexes can be viewed as the confluence of four [PW10O37]9- units each incorporating 2M(III) ions to create four Keggin-like anions that are further tied together by three additional tungstate atoms. The unexpected complexes of [M(PW11O39)2]11- is formed by interaction of [A-α-PW9O34]9- with Yb(III) and Er(III) ions in 1:1 mole ratio. The structures consist of two [PW11O39]7- moieties which linked by a lanthanide atom.
