D. Hnyk et al., MOLECULAR-STRUCTURE OF 1,2-DICARBA-CLOSO-DECABORANE(10) AS STUDIED BYTHE CONCERTED USE OF ELECTRON-DIFFRACTION AND AB-INITIO CALCULATIONS, Inorganic chemistry, 33(21), 1994, pp. 4781-4786
An electron diffraction study of 1,2-dicarba-closo-decaborane (10), 1,
2C(2)B(8)H(10), constrained by ab initio calculations has been underta
ken. A satisfactory refinement (R(G) = 0.052) was obtained with a bica
pped ''square'' antiprismatic model assuming C-s symmetry. In this str
ucture one carbon atom occupies one of the two capping positions, whil
e the other is adjacent, in a basal position of a ''square'' pyramid.
The experimental molecular dimensions (r(a)) are consistent with the r
(e) structure as derived by the MP2(fc)/6-31G optimization. The C-C e
dge [r(a) = 153.8(8) pm, r(e) = 153 pm] leads to distortion from the r
egular square pyramidal. shape. The compression of the carbon atoms to
ward the center of the cluster results in a substantial opening of the
B(3)C(2)B(5) bond angle [both electron diffraction and MP2(fc)/6-31G
calculations give 95 degrees] from the parent 90 degrees. As a conseq
uence, the C(2)B(3) distance is the longest CB nearest-neighbor separa
tion so far observed in the gas phase, r(a) = 179.4(4) pm [cf. r(e) =
177.7 pm, MP2(fc)/6-31G)]. The reliability of the experimental struct
ure is assessed both by IGLO (individual gauge for localized orbitals)
calculations of B-11 chemical shifts and by MP2(fc)/6-31G single-poi
nt energy calculations.