TY - JOUR
T1 - Unusual Structures of Dilithiosilanes and Disodiosilanes
T2 - Ionicity of the Silicon-Alkali-Metal Bond
AU - Rajca, Andrzej
AU - Wang, Peng
AU - Streitwieser, Andrew
AU - Von Schleyer, Paul
PY - 1989/7/1
Y1 - 1989/7/1
N2 - 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.
AB - 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.
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U2 - 10.1021/ic00314a040
DO - 10.1021/ic00314a040
M3 - Article
AN - SCOPUS:26344431797
VL - 28
SP - 3064
EP - 3070
JO - Inorganic Chemistry
JF - Inorganic Chemistry
SN - 0020-1669
IS - 15
ER -