Synthesis and pH-variable ultracentrifugation molecular weight measurements of the dimeric, Ti–O–Ti bridged anhydride form of a novel di-TiIV-1,2-substituted α-Keggin polyoxotungstate. Molecular structure of the [(α-1,2-PW10Ti2O39)2]10− polyoxoanion

摘要: The preparation and characterization of a Keggin-type, novel di-TiIV-1,2-substituted polyoxotungstate are described. dimeric, Ti–O–Ti bridged anhydride form the α-Keggin polyoxotungstate, K10[α,α-P2W20Ti4O78]·12H2O 1, was unexpectedly found in varied molar-ratio reactions tri-lacunary precursor Na9[A-PW9O34]·19H2O with Ti(SO4)2 aqueous solution. Although this compound first as minor product tri-TiIV-1,2,3-substituted species, K10H2[α,α-P2W18Ti6O77]·17H2O 3, it successfully prepared main work structurally characterized. Compound analytically pure, homogeneous colorless needle crystals, obtained major 29.2% yield (2.7 g scale) from recrystallization under acidic conditions (at pH 2.2) 1 ∶ 2 reaction product. X-Ray structure analysis revealed that molecular consisted dimeric formed by two bonds linking [α-1,2-PW10Ti2O40]7− Keggin units. Interestingly, ultracentrifugation weight (MW) measurements solution showed pH-dependent interconversion between monomer [α-1,2-PW10Ti2O40]7−2 dimer [α,α-P2W20Ti4O78]10−1; present less (pH 7.8), while more 1.0 2.2). Characterization also accomplished complete elemental analyses, TG/DTA, FTIR (31P 183W) NMR spectroscopy.