Involvement of Arsenic Atom of AsF3 in Five Pnicogen Bonds: Differences between X-ray Structure and Theoretical Models

Bonding within the AsF3 crystal is analyzed via quantum chemical methods so as to identify and quantify the pnicogen bonds that are present. The structure of a finite crystal segment containing nine molecules is compared with that of a fully optimized cluster of the same size. The geometries are qualitatively different, with a much larger binding energy within the optimized nonamer. Although the total interaction energy of a central unit with the remaining peripheral molecules is comparable for the two structures, the binding of the peripherals with one another is far larger in the optimized cluster. This distinction of much stronger total binding within the optimized cluster is not limited to the nonamer but repeats itself for smaller aggregates as well. The average binding energy of the cluster rises quickly with size, asymptotically approaching a value nearly triple that of the dimer.

The Effects of Electronegativity of X and Hybridization of C on the X-C⋅⋅⋅O Interactions: A Statistical Analysis on Tetrel Bonding

Cone and distance-cone corrected statistical analyses have been performed on X-C⋅⋅⋅O (X=H, B, C, N, O and F; the C atom is sp² and sp³ hybridized) tetrel bonds. The sp³ -C and sp² -C prefer to form the interactions through σ-hole (∠XCO≈180°) and π-hole (∠XCO≈90°), respectively. With the increase in electronegativity of X, the preference for the particular angles of the respective geometries increases and the C⋅⋅⋅O distance becomes shorter. The angular preference is found to be more prominent in the cases of π-hole interactions than that in the σ-hole interactions. A similar distance-cone corrected statistical analysis on O=C⋅⋅⋅O interaction also suggests that the preferred ∠OCO angle is ∼90° and the preferred C⋅⋅⋅O distance is around the sum of van der Waals radii (3.22 Å) of the C and O atoms. However, a cone-corrected statistical analysis on X-Si⋅⋅⋅O interactions suggests that the preference for linearity in this case is much higher than that for the X-C⋅⋅⋅O σ-hole interactions.