Molecular structure of orthosilicic acid, silanol, and H/sub 3/SiOH x AlH/sub 3/ complex: models of surface hydroxyls in silica and zeolites
Journal Article
·
· J. Phys. Chem.; (United States)
Geometries are obtained by gradient methods from nonempirical quantum chemical SCF calculations. The basis set employed (6-31G*) includes d-type polarization functions on both silicon and oxygen atoms. For the minimum-energy structure of orthosilicic acid (belonging to the S/sub 4/ point group) the SiO geometry deviates from a regular tetrahedron, but this does not seriously affect the results of other bond angles and lengths. Passing from terminal hydroxyls in H/sub 3/SiOH to bridged hydroxyls in H/sub 3/SiOH x AlH/sub 3/, the O-H bond becomes longer by 0.44 pm and and the SiOH angle becomes smaller by 0.4/sup 0/. The Al-O bond in the H/sub 3/SiOH x AlH/sub 3/ complex is longer (203 pm) and weaker (70kJ/mol) than previously estimated. In the complex, the deprotonation energy is lowered by 165 kJ/mol compared with that of silanol. Evidence is produced for a linear relation between deprotonation energy and net charge on the proton for hydroxyl of different type (free, hydrogen-bonded, bridged). Predictions are made for the local structures of terminal and bridged hydroxyls. An unusually long Al-O bond is found (194 +/- 5 pm for triple bond Si single bond O(H) single bond Al triple bond groups, which shrinks up to 172 +/- 3 pm on deprotonation.
- Research Organization:
- Central Institute of Physical Chemistry, Berlin, East Germany
- OSTI ID:
- 6540936
- Journal Information:
- J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 91:9; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALUMINIUM COMPOUNDS
ALUMINIUM HYDRIDES
BOND ANGLE
BOND LENGTHS
CHALCOGENIDES
COMPLEXES
DATA
DIMENSIONS
HYDRIDES
HYDROGEN COMPOUNDS
HYDROXY COMPOUNDS
INFORMATION
INORGANIC ACIDS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
LENGTH
MATERIALS
MINERALS
MOLECULAR STRUCTURE
NUMERICAL DATA
ORGANIC COMPOUNDS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
SELF-CONSISTENT FIELD
SILICA
SILICIC ACID
SILICON COMPOUNDS
SILICON OXIDES
THEORETICAL DATA
ZEOLITES
400201* -- Chemical & Physicochemical Properties
ALUMINIUM COMPOUNDS
ALUMINIUM HYDRIDES
BOND ANGLE
BOND LENGTHS
CHALCOGENIDES
COMPLEXES
DATA
DIMENSIONS
HYDRIDES
HYDROGEN COMPOUNDS
HYDROXY COMPOUNDS
INFORMATION
INORGANIC ACIDS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
LENGTH
MATERIALS
MINERALS
MOLECULAR STRUCTURE
NUMERICAL DATA
ORGANIC COMPOUNDS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
SELF-CONSISTENT FIELD
SILICA
SILICIC ACID
SILICON COMPOUNDS
SILICON OXIDES
THEORETICAL DATA
ZEOLITES