Transformation of Tri-Titanium(IV)-Substituted α-Keggin Polyoxometalate (POM) into Tetra-Titanium(IV)-Substituted POMs : Reaction Products of Titanium(IV) Sulfate with the Dimeric Keggin POM Precursor under Acidic Conditions

Reaction products of titanium(IV) sulfate in HCl-acidic aqueous solution with the dimeric species linked through three intermolecular Ti-O-Ti bonds of the two trititanium(IV)-substituted α-Keggin polyoxometalate (POM) subunits are described. Two novel titanium(IV)-containing α-Keggin POMs were obtained under different conditions. One product was a dimeric species through two intermolecular Ti-O-Ti bonds of the two tetra-titanium(IV)-substituted α-Keggin POM subunits, i.e., [[{Ti(H2O)3}2(μ-O)](αPW9Ti2O38)]2 (1). The other product was a monomeric α-Keggin species containing the tetra-titanium(IV) oxide cluster and two coordinated sulfate ions, i.e., [{Ti4(μO)3(SO4)2(H2O)8}(α-PW9O34)] (2). Molecular structures of 1 and 2 were also discussed based on host (lacunary site)-guest (titanium atom) chemistry.