MNDO studies of basicity in borate glasses |
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| Affiliation: | 1. School of Civil Engineering, Changsha University of Science and Technology, Changsha, 410114, China;3. Research group LIWET, Department of Green Chemistry and Technology, Ghent University, Campus Kortrijk, Graaf Karel De Goedelaan 5, Kortrijk B-8500, Belgium;4. School of Transportation, Civil Engineering and Architecture, Foshan University, Foshan, 528225, China;1. Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachi-Oji, Tokyo 192-0397, Japan;2. Institute of Chemistry, Eötvös Loránd University Pázmány P. s., 1/A, Budapest 1117, Hungary;3. National Institute of Materials Science, Sengen 1-2-1, Tsukuba, Ibaraki, 305-0047, Japan;4. Division of Materials Chemistry, Ruđer Bosković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia |
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| Abstract: | The cluster approximation was adopted for the borate glasses. The geometries and basicity of various isomers of H8B9O18−, H8B11O21− and H8B12O232− were studied by the MNDO semi-empirical molecular orbital method. The optimized geometries of pentaborate, triborate and diborate structure in the clusters showed good agreement with the experimentally determined ones. The changes of bond length and charge rearrangements accompanying the formation of a four-fold coordinated boron atom (4B) accorded with the prediction of Gutmann's bond length variation rule. The basicity in the borate glass was defined as the electron donability of oxygens in the glass network. MO interaction between the occupied orbitals of the clusters and the LUMO of the acidic site in (H2B9O14)2O and the proton affinity of the clusters were estimated. The basicities of the clusters which contained 4B and that of the clusters which contained non-bridging oxygen atoms (NBO) were compared. The appearance of NBO in high alkali borate glass was interpreted. |
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