Niobium uptake by {P2W12} polyoxoanion with [NbO(C2O4)2(H2O)2]− as Nb source

Reaction of (NH4)[NbO(C2O4)2(H2O)2]·3H2O with K12[H2P2W12O48]∙24H2O in aqueous solution at pH 1.7 leads to the formation of mixed Nb/W species based on [(P2M18O60)2(µ-O)2]n− (M is a Nb/W mixture, when Nb ratio ranges from 6 to 8 and charge differs from 14- to 16- correspondingly) archetype. Direct crystallization from the reaction media results in colorless crystals with the composition formulated as K9(NH4)5[cis-(P2W15Nb3O61)2]·48H2O (1). Crystallization in the presence of (NMe2H2)Cl yields two phases (2a and 2b), containing the same [trans-(P2W14.7Nb3.3O61)2]14.6− anions but different cation/H2O compositions. Both phases are present in a mixture with bulk composition corresponding to (NMe2H2)14.6[P2W14.7Nb3.3O61]2·28H2O (2). The solution behavior of 1 and 2 was studied with HR-ESI-MS and HPLC-ICP-AES. During XRPD study of 2 we found blue coloration of the thin film of the complex. This effect has only surface nature and was studied by diffuse reflectance spectra.