Dichlorosilane, SiH2Cl2, forms two different kinds of coordination compounds with pyridine and 3-picoline : the simple adduct trans-SiH2Cl2(L)(2) and the ionic complex [SiH2(L)(4)]Cl-2. 4CHCl(3) (L = pyridine, 3-picoline). The adducts trans-SiH2Cl2(py)(2), 1, and trans-SiH2Cl2(3pic)(2), 2, form directly from the reaction of bis(dichlorosilyl)methylamine, NMe(SiHCl2)(2) with pyridine (py), and 3-picoline (3pic). Reaction of 1 with an excess of pyridine in chloroform yielded [SiH2(py)(4)]Cl-2. 4CHCl(3), 3. The molecular and crystal structures of 1-3 were investigated by single-crystal X-ray diffraction. The Si atoms of all three compounds are hexacoordinated and lie on centers of inversion. The basic structural parameters are the following : 1 (monoclinic, C2/c) : Si-N 196.9(1) pm, Si-Cl 228.8(1) pm; N-Si-Cl 90.0(1)degrees, C-N-C 119.0(2)degrees; Cl-Si-N-C 102.4(1)degrees. 2 (triclinic, P (1) over bar) : Si-N 197:5(1) pm, Si-Cl 229.2(1) pm; N-Si-Cl 90.3(1)degrees, C-N-C 118.8(1)degrees; Cl-Si-N-C 101.2(1)degrees. 3 (monoclinic, C2/m) : Si-N 196.2(4) and 197.0(4) pm, Si ... Cl 419.9 pm; N-Si-N 90.0 degrees. All three complexes, neutral and cationic, exhibit very similar lengths of the dative Si-N bond. Hartree-Fock calculations with 3-21G(d) and 6-31G(d) basis sets and density functional calculations with the B3LYP functional and a 6-31G(d) basis set were employed for geometry optimizations of trans-SiH2Cl2(py)(2) and [SiH2(py)(4)](2+). The optimized structures revealed similar Si-N bond lengths and geometric parameters of the pyridine moieties for both types of complexes as well. Single point energy calculations [B3LYP/6-311+G(2d,p)//B3LYP/6-31G(d)], including corrections for the basis set superposition error, showed that the formation of 1 from SiH2Cl2 and pyridine in the gas phase is slightly endothermic (Delta H-298 = 17.2 kJ mol(-1)) and endergonic (Delta G(298) = 113.6 kJ mol(-1)). The significance of the Lewis acidity of SiH2Cl2 is thus questioned and intermolecular interactions (e.g. hydrogen bonds) are held responsible for the existence of 1 in the solid state.