Optimized Structures and Relative Stabilities of the Carboranes from Ab Initio Calculations

Abstract

A b initio calculations at the STO-3G level were performed on almost all of the possible isomers for the entire series of closo-carboranes, C2Bn-2Hn, 5 5 n 5 12. Geometry optimizations using the gradient method were also included in all calculations. We report here the relative energies obtained for the various isomers as well as the optimized structures. These calculations confirm our previous predictions of relative stabilities obtained from topological charge stabilization. Comparisons of our structures with those from experimental data provide us with a measure of reliability for bond distances obtained using a b initio SCF MO calculations at the STO-3G level. Results from the geometry optimization substantiated the experimentally known fluxional behavior of the 8 and 11 atom polyhedra.

Ab Initio Study of the Eight-Vertex closo-Heteroboranes X2B6H6 (X = CH, SiH, GeH, SnH, and PbH). Is the Hexagonal Bipyramid a Viable Alternative?

“…Hence, C 2 B 6 H 8 prefers the alternate BDS skeleton. 6,15 On the other hand, Si, Ge, and Sn, which are larger in size and possess more diffuse p orbitals (Table 2), optimize their interaction effectively with the ring π orbitals leading to more stable HBP arrangements (Table 1).…”

Thermochemistry of icosahedral closo-dicarboranes: a composite ab initio quantum-chemical perspective

“…closo-dicarboranes were the subject of extensive theoretical investigations. 8,9,10,11,12,13,14,15 However, there have been only a small number of correlated ab initio investigations of their thermochemical properties. Schleyer and Najafian (SN) calculated the relative stabilities of the para, meta, and ortho isomers at the MP2/6-31G(d) level of theory and found that the meta and ortho isomers lie 3.5 and 19.1 kcal mol -1 above the most stable para isomer.…”

Structures of two carbon-to-boron bridged o-carboranes

“…For instance, the bonds to the C and B atoms shared with the exocage ring are slightly longer than the related bonds on the other side of the molecule. Table 4 summarizes the situation and provides a comparison of all bond lengths with the results of calculations by Ott & Gimarc (1986) on o-carborane itself.…”