Molecular structures of various alkyldichlorosilanes in the solid state.

A series of organodichlorosilanes RR'SiCl2 (R,R' = (CH2 )3 ; (CH2 )4 ; (CH2 )5 ; Me,Me; Me,H; Me,Cl) was studied by single-crystal X-ray diffraction analyses. At ambient temperature liquid chlorosilanes (melting points in the range of 180-220 K) were transferred into glass capillaries and crystallized in situ on a diffractometer. In the solid state structure these chlorosilanes are monomeric, even in the case of the sterically less demanding 1,1-dichlorosilacyclobutane (CH2 )3 SiCl2 . Interestingly, regardless the steric demand of the alkyl substituents, the dialkyldichlorosilanes exhibit essentially the same Cl-Si-Cl angle (for (CH2 )3 SiCl2 , (CH2 )4 SiCl2 , (CH2 )5 SiCl2 , Me2 SiCl2 : 106.08(3)°, 106.07(4)°/105.86(4)°, 106.91(2)° and 105.59(6)°, respectively). Replacement of one alkyl group by hydrogen has only a marginal influence on the Cl-Si-Cl angle (MeHSiCl2 106.31(3)°), whereas in MeSiCl3 slightly wider Cl-Si-Cl angles are found (ranging between 107.04(11)° and 107.86(11)°), in accordance with VSEPR. Computational analyses, i.e., potential energy surface scans of the Cl-Si-Cl angle variation, of (CH2 )3 SiCl2 , Me2 SiCl2 , MeHSiCl2 and H2 SiCl2 reveal essentially identical energy profiles for the Cl-Si-Cl deformation in these four dichlorosilanes with basically superimposed curves for (CH2 )3 SiCl2 and Me2 SiCl2 , whereas with increasing H-substitution the energetic minimum is shifted to a slightly wider Cl-Si-Cl angle. In the crystal packing only MeHSiCl2 exhibits weak intermolecular SiCl van der Waals contacts, whereas the Si-Cl moieties of the other five chlorosilanes engage in intermolecular ClH and (for (CH2 )3 SiCl2 , (CH2 )4 SiCl2 and MeSiCl3 ) ClCl contacts.