Molecular Crystal Structure and Electron Density Distribution in the Crystal of Pentaethyl-1,5-dicarba-closo-pentaborane [C₂B₃(Et)₅] at 120 K

Abstract

The molecular and crystal structure and electron density distribution were studied for a single crystal of pentaethyl-1,5-dicarba-closo-pentaborane C 2 B 3 (Et) 5 by the high-resolution X-ray diffraction method at 120 K (5696 observed reflections, R ) 0.056). The single crystal was grown by in situ crystallization with an IR-laser beam producing a molten zone in a Lindeman capillary. In crystal the molecule of the title compound has local C 1 -symmetry with different orientations of the Et-groups with respect to the central trigonal-bipyramidal C 2 B 3 fragment, mean B-C and B-B distances are 1.571 and 1.876 Å, respectively, the axial C...C distance is 2.277 Å. An ab initio calculations of the molecular structure indicated that rotation barriers of the Et groups with respect to the central frame are very small, that may be the reason of the low molecular symmetry and diffrerent orientation of the Et groups in molecule due to the crystal packing effects. Deformation electron density (DED) maps obtained via a conventional "X-X" method, and using a multipole refinement procedure, showed charge accumulation in the B-C bonds of the central frame, and these bonds were found to be essentially bent outward of the C 2 B 3 cage. On the contrary, no charge accumulation was detected in the B-B bonds, thus indicating the absence of the direct B-B interactions. Positive and delocalized DED was also found in all B-C-B triangle faces of the central cage, that indicates the contribution of the multicenter bonding in the electronic structure of this formally electron-precise molecule. Topological analysis of the experimental charge density distribution has been performed including an analysis of the Laplacian maps, and these data confirmed all important features of the DED maps.

A new look at the structure and reactivity of 10-vertex nido-dicarbaboranes

“…The topology of EDD for nido-5,6-C 2 B 8 H 12 has something in common with that reported for closo-and nido-clusters earlier [8][9][10][11][12][13][14][15][16]. Firstly, the bonding in the cage is realized both via multicenter and two-center bonds of reduced order.…”

“…The works using AIM were reported only for a limited number of boranes and carboranes and concerned mainly closo species [8][9][10][11][12][13][14][15]. For these types of clusters it was shown that stabilization of electron-deficient systems is achieved both by accumulation of electronic charge along the bond paths and by its delocalization over the polyhedron surface.…”

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

“…For all distances and bonding angles, no significant differences from those in similar compounds [12] are observed. (2) (9) To obtain information on its reactivity, 1a was treated with six equivalents of dimethylamine to form 1c as a colorless, viscous liquid in 88% yield (Scheme 1). Its 11 B NMR spectrum showed a signal at δ ϭ 38.5, confirming that each boryl group had one dimethylamino and one chlorine substituent.…”

“…The compositions of the products followed from analytical data and X-ray structure analyses of 1b, 4b, 5b, 6a, and 6f. ( Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002) pentaborane(5), [6,9] by electron density distribution, [9] and by ab initio computations. [10] We report here on the synthesis and the characterization of 1,1,1-tris(dichloroboryl)-3,3-dimethylbutane and its transformation into 2,3,4-trichloro-1,5-dicarba-closo-pentaborane(5) (6a).…”

Cages and Clusters of Indium: Spherical Aromaticity?

“…Thus, based on geometric, energetic, and magnetic criteria, the closo-cluster compounds [E 5 H 5 ] 2À (E ¼ B, Al, Ga, In) are nonaromatic, and this offers a possible explanation for why clusters of this type have not yet been synthesized. Currently, only derivatives [12,[59][60][61], such as carbaboranes and a silagallanate [Me 3 SiSi (GaR) 3 GaSiMe 3 ] À (R ¼ Si(SiMe 3 ) 3 ) [62], have been reported.…”