The μ2-scaled Hückel method is used to calculate the electronic energy surfaces of the four boranes BnHn 2- (n=8-11) and the carborane C2B8H 102-. These electronic energy surfaces and their minimum energy geometries are directly compared to both the single crystal x-ray determined structures and to Hartree-Fock optimized geometries. Bond distances differ on the average by 0.04 Å between alternate methods. It is shown that μ2-scaled Hückel results may be directly interpreted by analysis of the highest occupied and lowest unoccupied molecular orbitals. Also studied by the μ2-scaled Hückel and Hartree-Fock methods are the isomerization pathways of B8H82-, B 11H112-, and C2B8H 102-. Reaction barriers and transition state geometries found by the two different calculational methods are in fair agreement with each other and known literature values. Using the μ2-scaled Hückel method one can readily deduce that the B8H 82- and B11H112- isomerizations are Woodward-Hoffmann allowed reactions. In the case of B 8H82- this allowed mechanism is contrasted to an alternate Woodward-Hoffmann forbidden pathway. Hartree-Fock calculations on the C2B8H102- confirm earlier μ2-scaled Hückel based findings, that a second less stable isomer of C2B8H102- exists which, in contradiction to Wade's rules of electron deficient clusters, has a pair of open square faces in the cluster.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry