Triplet germylenes with separable minima at ab initio and DFT levels

Substitution effects on novel bicyclo[2.2.1]hepta-7-silylenes by DFT

Substitution effects on stability (ΔΕ_s-t) of novel singlet and triplet forms of bicyclo[2.2.1]hepta-7-silylenes are compared and contrasted, at B3LYP/6-311++G** level of theory. All species appear as ground state minima on their energy surface, for showing no negative force constant. Singlets (1_s-24_s) are ground state and more stable than their corresponding triplets (1_t-24_t). The most stable scrutinized silylenes appear to be 2,3-disilabicyclo[2.2.1]hepta-7-silylene (9) for showing the highest value of ΔE_s-t. This stability can be related to our imposed topology and β-silicon effect. The band gaps (ΔΕ_HOMO-LUMO) show the same trend as ΔE_s-t and the lowest unoccupied molecular orbital energies. Also, the electrophilicity appears inverse correlation with our results of ΔΕ_s-t. The purpose of the present work was to assess the influence of 1 to 6 silicon substitutions on the stability, band gaps, nucleophilicity, electrophilicity, and proton affinity. Finally, our investigation introduces novel silylenes with possible applications in chemistry such as semiconductors, cumulated multidentate ligands, etc. Synopsis Substitution effects on stability (ΔΕ_s-t) of novel singlet (s) and triplet (t) forms of bicyclo[2.2.1]hepta-7-silylenes are compared and contrasted, at B3LYP/6-311++G** level of theory. All species appear as ground state minima on their energy surface, for showing no negative force constant. Singlets (1_s-24_s) are ground state and more stable than their corresponding triplets (1_t-24_t). The most stable scrutinized silylenes appear to be 2,3-disilabicyclo[2.2.1]hepta-7-silylene (9) for showing the highest value of ΔE_s-t. This stability can be related to our imposed topology and β-silicon effect. The purpose of the present work was to assess the influence of 1 to 6 silicon substitutions on stability (ΔΕ_s-t), band gaps (ΔΕ_HOMO-LUMO), nucleophilicity (N), electrophilicity (ω), and proton affinity (ΔΕ_PA). Finally, this new generation has the intrinsic potential to form accumulated multidentate ligands.

Novel triplet germylenes in focus: normal vs. abnormal triplet exocyclic tetrazol-5-vinylidene germylenes at DFT

Substituent effects on stability (assumed as the singlet and triplet energy gaps, ΔΕ_S-T) of novel 1,4-disubstituted-tetrazole-5-vinylidene germylenes (normal, 1_R) and their corresponding 1,3-disubstituted-tetrazole-5-vinylidene germylenes (abnormal, 2_R) are computed and compared, at B3LYP/6-311++G** and M06/6-311++G**, where R = H, CN, CF₃, F, SH, C₆H₆, OMe, and OH. Interestingly, every triplet vinylidene germylene shows more stability than its corresponding singlet. Also, every triplet abnormal isomer (2_R) emerges to be more stable than its corresponding normal (1_R). All abnormal 2_R isomers show broader band gaps (ΔE_HOMO-LUMO) and higher nucleophilicity (N), but less electrophilicity (ω) than their corresponding normal 1_R isomers. The NICS (nuclear-independent chemical shift) results indicate that every 1_R (except singlet 2_Ph) emerges more aromatic than its corresponding 2_R. Our Hammet studies indicate that 1_R is more sensitive to the electronic effects of substituents, R, than 2_R. Electron-donating species increase N in both 1_R and 2_R, while electron-withdrawing groups increase stability.

Tuning Hydrogenated Silicon, Germanium, and SiGe Nanocluster Properties Using Theoretical Calculations and a Machine Learning Approach

There are limited studies available that predict the properties of hydrogenated silicon-germanium (SiGe) clusters. For this purpose, we conducted a computational study of 46 hydrogenated SiGe clusters (Si _xGe _yH _z, 1 < X + Y ≤ 6) to predict the structural, thermochemical, and electronic properties. The optimized geometries of the Si _xGe _yH _z clusters were investigated using quantum chemical calculations and statistical thermodynamics. The clusters contained 6 to 9 fused Si-Si, Ge-Ge, or Si-Ge bonds, i.e., bonds participating in more than one 3- to 4-membered rings, and different degrees of hydrogenation, i.e., the ratio of hydrogen to Si/Ge atoms varied depending on cluster size and degree of multifunctionality. Our studies have established trends in standard enthalpy of formation, standard entropy, and constant pressure heat capacity as a function of cluster composition and structure. A novel bond additivity correction model for SiGe chemistry was regressed from experimental data on seven acyclic Si/Ge/SiGe species to improve the accuracy of the standard enthalpy of formation predictions. Electronic properties were investigated by analysis of the HOMO-LUMO energy gap to study the effect of elemental composition on the electronic stability of Si _xGe _yH _z clusters. These properties will be discussed in the context of tailored nanomaterials design and generalized using a machine learning approach.