Synthesis, Structure and Catalytic Activity of ... - Jacobs University

K8[Ti4O4(C2O4)8] (K-1) (Ti4) that crystallizes from any saturated aqueous
solution of K2TiO(C2O4)2. The reaction of Ti4 with Na9[A-α-PW9O34], on the
other hand, lead to a peculiar structure 5, which exhibits unusual dimerization
fashion with the help of oxalate groups attached to the sandwiched titanium
atoms.
Attempts were fruitful with the lone pair containing POM precursor Na9[B-α-
AsW9O33], where polyanions 6 and 7 containing two and eight titanium atoms
respectively were obtained. The only Wells-Dawson based structure is the
dimeric polyanion 8 harboring four titanium atoms incorporated into the
tungstate framework and two external ones linking the two half-units.
Two crystallographically disordered molecules 9 and 10 were also briefly
reported on.
In Chapter IV, Catalytic studies were discussed for p-xylene oxidation reaction
using four organo-ruthenium polyanions (11-14) as heterogeneous catalysts.
For all four ruthenium-containing polyanions the yields were comparable and
significantly higher than those for the blank and the corresponding “alltungsten”
derivatives, that is considered as evidence of the importance of the
ruthenium centers for the overall catalytic efficiency of the POMs for this type
of reactions. The second part of the chapter dealt with the two novel zirconium
and hafnium polyanions (15 and 16 respectively). They contain an
unprecedented octahedral Zr6/Hf6 assembly which is stabilized by two (B-α-
AsW9O33) groups and five terminal acetate ligands. The TBA-salts of both 15
and 16 revealed high catalytic activity and selectivity in the liquid-phase
oxidation of organic compounds with aqueous H2O2. A heterolytic oxidation
mechanism is manifested by the high yields of epoxide and diol in the oxidation
of cyclohexene.
iv