
TY  - JOUR
A1  - McLarnan, TJ 
A1  - Hill, RJ 
A1  - Gibbs, GV 
T1  - A CNDO/2 Molecular Orbital Study of Shared Tetrahedral Edge Conformations in Olivine-Type Compounds
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1979
VL  - 32
IS  - 5
SP  - 949
EP  - 959
KW  - 
UR  - https://doi.org/10.1071/CH9790949 
N2  - Semi-empirical molecular orbital calculations have been used to study the shortening of tetrahedral shared edges in olivine-type compounds. The shared edge conformation in forsterite was modelled by a cluster of SiO3(OH)Mg3(OH)107- composition, consisting of a silicate tetrahedron sharing edges with three magnesium-containing octahedra. Predicted tetrahedron edge lengths agree well with observed values. Calculations on similar clusters representing shared edge conformations in sinhalite, chrysoberyl, and &#947;-Na2BeF4 also predict shortening of shared edges with d(X2-X3) < d(X3-X3), (X = O,F), as observed. Calculations on Mg2SiS4 fail to predict shortened shared edges. Detailed analysis of the individual molecular orbital energy terms indicates that the minimum energy configuration is determined by a complex sum of one- and two-centre energies. Distortions due to dimensional misfit of polyhedra in olivine structure space group P bnm appear to have relatively little importance in shortening the shared edges of the tetrahedron. 
ER  -

