Molecular structure of 1,5-dicarba-closo-pentaborane-(5) and 1,6-dicarba-closo-hexaborane(6) by gas-phase electron diffraction

Abstract

Gas-phase electron diffraction patterns of 1,5-dicarba-closo-pentaborane and 1,6-dicarba-closo-hexaborane were recorded at room temperature. Least-squares analyses of the reduced intensity data confirmed theD,h and D4h symmetry of the respective carboranes in the gas phase. The carbon atoms are located at apical positions in the polyhedra and may be considered as bonded to a planar girdle of three and four boron atoms, respectively. The bond lengths for the 1,5-dicarbacloso-pentaborane (5) withD,h symmetry are B-C = 1.556 A, B-B = 1.853 A, C-H= 1.071 A, and B-H= 1.183 A. The bond angles are BCC = 73.05", CBB = 53.48", and CBC = 93.16". The distance from the apical carbon atom to the belt is 1.131 A. The bond lengths for the 1,6-dicarba-closo-hexaborane(6) withD,h symmetry are B-C = 1.633 A, B-B = 1.720A. C-H= 1 . 1 0 3 A , a n d B -H = 1.244 A. ThebondanglesareB,CB3=63.56",CBB=58.22",CBC= 83.73",andB2CB4=96.26". The distance from the apical carbon atom to the belt of four boron atoms is 1.090 A. Comparisons were made with related compounds whose structures were determined from microwave spectra or X-ray diffraction data.

1,1,1-Trisborylalkanes as Precursors for Dicarbapentaboranes(5) − Synthesis, Reactivity, and Structures ofcloso-1,5-Bis(neopentyl)-2,3,4-trichloro-1,5-dicarbapentaborane and Its Derivatives

“…In the C 2 B 3 framework, the BϪB [1.842(3)Ϫ1.855 (3) Å ] and BϪC distances [1.541(3)Ϫ1.586(3) Å ] are in the range of the corresponding values for the parent closo-C 2 B 3 H 5 , determined by electron diffraction. [17] The BϪB bond lengths are substantially shorter than the structure data [1.965(8) Å ] published by Meller et al, [7,8] who classified their molecules as bicycles. The BϪB distances in 6a are somewhat shorter than those in the carborane C 2 B 3 Et 5 reported by Köster et al [6] [1.876(4) Å ].…”

“…Nevertheless, the BϪB bond in 6a is long and the BϪC bond short in comparison with data relating to octahedral carboranes [BϪB: 1.72 Å , CϪB: 1.62 Å in 1,6-C 2 B 4 H 6 ]. [17] The C 2 B 3 carborane may be described as a classically bonded structure in which the trigonal bipyramid is bonded through 2c,2e CϪB bonds, but involves no strong BϪB overlap. [17,18] This was confirmed by measurements of the electron density distribution of the closo-cluster C 2 B 3 Et 5 , which gave no electron density in the BϪBϪB plane of the molecule; [9] electron density was, however, found above each triangular CB 2 face.…”

1,1,1-Trisborylalkanes as Precursors for Dicarbapentaboranes(5) − Synthesis, Reactivity, and Structures of closo-1,5-Bis(neopentyl)-2,3,4-trichloro-1,5-dicarbapentaborane and Its Derivatives

“…Colorless crystals of 6a were grown from a solution in pentane at 4°C; its molecular structure is shown in Figure 4. [17] The BϪB bond lengths are substantially shorter than the structure data [1.965(8) Å ] published by Meller et al, [7,8] who classified their molecules as bicycles. [17] The BϪB bond lengths are substantially shorter than the structure data [1.965(8) Å ] published by Meller et al, [7,8] who classified their molecules as bicycles.…”

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

“…1 Representative examples for the five-and the six-vertex cages include 1,5-C 2 B 3 H 5 (trigonal bipyramid, TBP) and 1,6-C 2 B 4 H 6 (square bipyramid). 2,3 Seven-vertex cages (B 7 H 7 2-and 2,4-C 2 B 5 H 7 ) have a pentagonal-bipyramidal skeleton. 4 However, a hexagonal bipyramidal (HBP) structure was not observed for the eightvertex cage.…”