Both dilithiosilanes (SiH2Li2) and disodiosilanes (SiH2Na2) favor unusual structures. The lowest singlet and lowest triplet potential energy surfaces (PES) were searched with the 3-21G and 3-21G(*) basis sets, and a number of stationary points were located. The “normal” tetrahedral-based singlet, 3s (C2v), was the lowest energy structure at HF but not at correlated levels of theory. The most interesting singlet SiH2Li2structures were reoptimized at HF/6-31G, and the final energies were calculated at MP4SDTQ/6-31G and corrected for the zero-point vibrational energy. in the global minimum structure (1s), the lithiums are unsymmetrically placed in the Csplane orthogonal to the SiH2moiety. This form is 6.3 kcal mol-1lower in energy than the conventional tetrahedral singlet (3s) and 3.9 kcal mol-1lower than the inverted tetrahedral singlet (2s). The3B2state with a conventional tetrahedral geometry, lying only 14.1 kcal mol-1above 1s at UMP2/6-31G*//3-21G(*) + ZPVE, is the lowest triplet 1t. Other local triplet minima include 2t (3A“, Cs) with all atoms in the same plane, 3t (3B2) with an inverted tetrahedral structure, 4t (3A') with a structure similar to 1s, and 5t (3B1C2v) with collinear SiLiLi. The triplets 2t, 3t, 4t, and 5t are 15.0, 18.0, 20.8, and 25.8 kcal mol-1, respectively, above the global singlet minimum. Some of the corresponding energy minima were calculated for disodiosilanes at 3-21G. The ionicity of the SiLi and SiNa bonds is compared to that of the CLi and CNa bonds by means of NPA and integrated projected electron population analyses.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry