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T-O bond length

Table IV. Observed Mean T—O Bond Lengths and T-O-T Angles... Table IV. Observed Mean T—O Bond Lengths and T-O-T Angles...
T-O bond length increases owing to an additional coordination of Ca to an oxygen. [Pg.270]

More interestingly the unit cell parameters are sensitive to the T-O bond length. Shorter T-O bonds (than Si-O) result in lower unit cell parameters and volume. For example, the first positive evidence for the incroporation of boron in MFl was provided by NOTARI et al. (20) who showed, for the first time, that the unit cell volume decreased as the boron content increased in the as synthesized MFL Conversely, the unit cell volume increases when the T-0 bond is larger than Si-O. Fe-MFI and Ga-MFI where shown to have larger unit cell volumes than pure silicalite and even than Al-MFI (21). However, it is necessary to mention that the unit cell parameters are also dependent on the presence of non-framework species within the pores of the zeolite. Care must then be taken to ensure the investigated sample be devoid of such species. If not, that effect must be taken into account. [Pg.294]

The neutron diffraction studies confirmed earlier X-ray results about other important structural changes with temperature [2.5] the mean Si-0 and Al-0 tetrahedral distances were found to decrease continuously with temperature, whereas the Li-0 distances increased see Table 2.2. The decrease in the Si-O and Al-0 distances is comparable to the decrease in the Si-0 distance measured in quartz, also listed in Table 2.2. In fact, zero expansion or slight apparent contraction of T-O bond lengths with temperature has been found in high-temperature structural analyses of many silicates. Hazen and Finger compiled data for silicates and other compounds and evaluated them statistically [2.33]. The large positive thermal expansion of the Li-0 bonds in /3-eucryptite is also in line with their findings for electrostatically weak M-0 bonds. [Pg.23]

Tetrahedron T-O Bond Length From Bond Length From Chemical Analysis... [Pg.231]

Similar effects were observed in the structures of the lithium salts of ester enolates [43] studied by Seebach et al. (1985). Here too systematic differences in angles are observed compared with amide and ketone enolates, and there is a correlation between the bond angles and the difference in the two C-O bond lengths at the reaction centre for three compounds [43], consistent with incipient elimination of t-butoxide to give the ketene [44] (Ferretti et al., 1991). [Pg.119]

Mg contents (such as the studied Mg-substituted hydroxyapatites, with up to lOmol.% Mg with respect to the total cationic concentration), the authors reported a Mg MAS NMR spectrum containing a complex line-shape. This was tentatively attributed to the existence of several local environments around Mg sites, leading to a distribution of quadrupole parameters. DFT calculations (supported by H, and Ca NMR and other experimental results) yielded Mg NMR parameters (Cq, /q and 5iso) that differed depending on the t)rpe of Ca site substituted by Mg. The Cq values were particularly sensitive to the details of the local Mg environment in the substituted hydroxyapatites. Even with the observed preference for Mg substitution into Ca(II) sites, small deviations in Mg—O bond lengths could cause large Cq variations, which explains the complex and featureless lineshape observed in the Mg NMR spectrum. [Pg.101]

A natural question that arises is whether there is any correlation between Si—O—Si (T——T) angles (0) and Si—O (T— X) bond lengths, /. Geometrically, the Si Si(T T) distance, d, and I are related by the expression, / = (d/2) cosec (0/2). A correlation between / and 0 should exist when cations are in contact d is constant). When 0 is large, no Si Si contact exists and therefore there should be no correlation between d and /. A correlation would exist between / and d when 0 < 145°, thus indicating that tetrahedral structures are determined by T— X and T T interactions rather than X X interactions. [Pg.46]

The foregoing account will have shown that a good deal of direct and significant information about hydrogen bonds has been collected from studies of neutron diffraction over the past four or five years. These show quite clearly the correlation between the 0 H and 0—O bond lengths and the possibility that ih hydroge. d m t. v lie elat d... [Pg.32]

A parameter, which is of special importance for the description of M(OR)n in addition to the coordination polyhedron of the central atom and the M-O bond lengths, is the M-O-C bond angle. Bradley [198] was the first to emphasize the role of unshared electron pairs at the oxygen atoms that can be involved into interaction with the vacant t/-orbitals of the transition metal. Thus in the molecules containing maingroup metals such as Bi, Sn, Ge, Te, and Al. the values of these angles usually do not exceed 120 to 130°, while in those of... [Pg.40]


See other pages where T-O bond length is mentioned: [Pg.5662]    [Pg.62]    [Pg.257]    [Pg.29]    [Pg.188]    [Pg.223]    [Pg.259]    [Pg.297]    [Pg.90]    [Pg.365]    [Pg.158]    [Pg.592]    [Pg.19]    [Pg.35]    [Pg.5662]    [Pg.62]    [Pg.257]    [Pg.29]    [Pg.188]    [Pg.223]    [Pg.259]    [Pg.297]    [Pg.90]    [Pg.365]    [Pg.158]    [Pg.592]    [Pg.19]    [Pg.35]    [Pg.24]    [Pg.285]    [Pg.72]    [Pg.70]    [Pg.67]    [Pg.91]    [Pg.109]    [Pg.18]    [Pg.1447]    [Pg.340]    [Pg.430]    [Pg.431]    [Pg.515]    [Pg.46]    [Pg.437]    [Pg.18]    [Pg.101]    [Pg.352]    [Pg.245]    [Pg.465]    [Pg.31]    [Pg.249]    [Pg.497]    [Pg.524]    [Pg.528]    [Pg.153]   
See also in sourсe #XX -- [ Pg.253 , Pg.263 ]




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