Molybdate ions, tetrahedral

Molecular recognition, calmodulin, 46 447 Mollusks, arsenic in, 44 150, 167, 168, 170 Molten salts electrolysis, 31 11 oxygen activation, 44 328-329 Molybdate ions, tetrahedral, 39 194-195 Molybdenite, 17 108 Molybdenum, 45 1 acetylene complexes of, 4 104 alkoxides... 

Mo-MCM-41 (1.0 Mo wt%) exhibits a photoluminescence spectrum at around 400-600 nm upon excitation at around 295 nm (defined as X), which coincides with the photoluminescence spectrum of the tetrahedrally coordinated Mo-oxides hi ly dispersed on Si02, as shown in Fig. 1 [11]. The excitation and emission spectra are attributed to the following charge transfer processes on the Mo-0 moieties of the tetrahedral molybdate ions (MoO, ), involving an electron transfer from the O to Mo ions and a reverse radiative decay from the charge transfer excited triplet state [2,11]. 

It is interesting to note that and k are much lower than the rate constants which have been reported for the reaction of ligands with tetrahedral molybdenum(vi) to give products of increased co-ordination number perhaps addition occurs much more readily than straight substitution at this centre.) The pathways involving two molybdate ions, k and k, correspond to reactions of dimolybdate(vi), a species which has not previously been detected in aqueous solution. 

More recently Buckler et al. (210) and Lutz et al. (211) have studied the isotope effect on Mo shielding in molybdate ( 0/ 0) and tetrathiomolybdate ( " S/ S). In the latter case the isotope peak can be observed at the natural abundance of (4-2%) on the species (14%). An isotope effect of 0-25 ppm towards lower frequencies is observed upon exchange of one by The isotope shift induced by (relative to S) in M0S4" was found to be 0 09 ppm to low frequency. This represents a rare case where the shielding isotope effects are known for two isotope pairs and identical molecular geometries since both ions are tetrahedrally coordinated. As a first approximation the isotope effect on the shielding should be proportional to (mi" — ) with mi and m2 representing the mass... 

Thus, a combination of UV-vis and TPR seems suitable to discriminate between monomeric tetrahedral and polymeric octahedral forms of surface Mo s. However, other important distinctions may be overlooked, especially between grafted (covalent bonding, presence of Mo-O-Al) and ion exchanged (electrostatic bonding, no Mo-O-Al) forms of surface molybdates. 

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