Electron density distributions and bonded interactions for the fibrous zeolites natrolite, mesolite and scolecite and related materials

For the fibrous zeolites natrolite, Na-2[Al2Si3O10]. 8H(2)O, mesolite, Na2C a2[Al2Si3O10](3). 8H(2)O, and scolecite, Ca[Al2Si3O10]. 3H(2)O, with topolo gically identical aluminosilicate framework structures, accurate single-cry stal X-ray diffraction data have been analyzed by least-squares refinements using generalized scattering factor (GSF) models. The final agreement indi ces were R(F) = 0.0061, 0.0165, and 0.0073, respectively. Ensuing calculati ons of static deformation [Delta rho(r)], and total, [rho(r)], model electr on density distributions served to study chemical. bonding, in particular b y topological electron density analyses yielding bond critical point (bcp) properties and in situ cation electronegativities. The results for 32 SiO, 24 AlO, 14 CaO, and 12 NaO unique bonds are compiled and analyzed in terms of both mean values and correlations between bond lengths, bonded oxygen ra dii, bcp densities, curvatures at the bcps, and electronegativities. Compar ison with recent literature data obtained from both experimental electron d ensity studies on minerals and model calculations for geometry-optimized mo lecules shows that the majority of the present findings conforms well with chemical expectation and with the trends observed from molecular modeling. For the SiO bond, the shared interaction is indicated to increase with decr easing bond length, whereas the AlO bond is of distinctly more polar nature , as is the NaO bond compared to CaO. Also, the observed ranges of the Si a nd Al in situ electronegativities and their mean electronegativities agree well with both Pauling's values and model calculation results, and statisti cally significant correlations are obtained which are consistent with trend s described for oxide and nitride molecules.