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

Reaction of (NH4)[NbO(C2O4)(2)(H2O)(2)]center dot 3H(2)O with K-12[H2P2W12O48]center dot 24H(2)O in aqueous solution at pH 1.7 leads to the formation of mixed Nb/W species based on [(P2M18O60)(2)(mu-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 K-9(NH4)(5) [cis-(P2W15Nb3O61)(2)]center dot 48H(2)O (1). Crystallization in the presence of (NMe2H2)Cl yields two phases (2a and 2b), containing the same 1trans-(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)center dot 28H(2)O (2). The solution behavior of 1 and 2 was studied with HR-ESIMS 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.