π-Bond energies in doubly bonded silicon species, H 2 SidX (X ) E 14 H 2 , E 15 H, E 16 ), were determined using G2 and G3 procedures. In addition, the distribution of electron density in the internuclear area between silicon and the element in H 2 SidX and H 3 Si-XH was estimated using quantum-topological approaches AIM (MP2/6-311++G(2d,p)) and ELF (HF/6-311++G(2d,p)). Both parameters, an increase of electron density at the critical point of the silicon-element bond and π-bond energy, appeared to correlate linearly, increasing on going from group 14 to group 16 elements. The contribution of the ion-component to the SidE π-bond energy increases as the negative inductive effect of the element grows, attaining the maximum for silanone.

Silatranes XSi(OCH2CH2)3N exhibit a good linear relationship between their experimental and calculated (IGLO and GIAO) values of the NMR chemical shifts of (15)N, δN, and the lengths of dative bonds Si←N, dSiN, determined in the gas phase (ED, CCSD), solutions (COSMO PBE0, B3PW91), and crystals (X-ray). An aggregate of the obtained data provides strong evidence that the gas-phase value of dSiN in MeSi(OCH2CH2)3N should be greater by ∼0.05 Å than that determined in the electron diffraction (ED) experiment (2.45 Å). Given this condition, a long-standing contradiction between the data of the structural (X-ray, ED) and NMR (15)N experiments for the molecules of 1-methyl- and 1-fluorosilatrane regarding the sensitivity of their coordination contact Si←N to the medium effect is resolved.

Dipole-bound molecular anions are often envisioned as unperturbed neutral, polar molecules with single excess electrons. We report the observation of intramolecular structural distortions within silatrane molecules due to the formation of their dipole-bound anions. The combination of Rydberg electron transfer-anion photoelectron spectroscopy (RET-PES) and ab initio computational methodologies (CCSD and MP2) was used to study 1-hydro- (HS) and 1-fluoro- (FS) silatranes and their dipole bound anions, HS and FS. The vertical detachment energies (VDEs) of HS and FS were measured to be 48 and 93 meV, respectively. Ab initio calculations accurately reproduced these VDE values as well as their photoelectron spectral profiles. This work revealed significant shortening (by ∼0.1 Å) of dative Si ← N bond lengths when HS and FS formed dipole-bound anions, HS and FS. Detailed computational (Franck-Condon) analyses explained the absence of vibrational features in the photoelectron spectra of HS and FS.