Geometry of simple molecules. 2. Modeling the geometry of AX3E and AX2E2 molecules through the nonbonded interaction (NBI) model.
A new conceptual model of molecular geometry is presented, called the nonbonded interaction (NBI) model. This model is applied to the geometries of the AX3E and AX2E2 (A = N, O, P, S, As, Se, or Te; X = H, F, Cl, Br, I, CH(3), tBu, CF3, SiH3, Sn(tBu)3, or SnPh3) molecule types. For these molecules, the NBI model can be quantified on the basis of a balance between terminal atom-terminal atom (X-X) interactions and lone pair-terminal atom (E-X) interactions. The empirically observed X-A-X angles range from 91.0 degrees (SeH2) to 180 degrees (O(Sn(tBu)3)2), and the NBI model predicts the X-A-X angle with a mean unsigned error of 1.0 degrees using the empirical A-X distance, 1.5 degrees using the LMP2/6-31G** A-X distance, and 1.1 degrees using the MMFF94 A-X distance. This level of precision compares well to the LMP2/6-31G**-predicted X-A-X angles and is significantly better than the MMFF94-predicted X-A-X angles. Terminal groups that are not sufficiently spherical (CF3, SiH3, and SnPh3) can still be addressed qualitatively by the NBI model, as can molecules with a mixture of terminal groups. The NBI model is able to explain, often quantitatively, the geometry of all of the molecules studied, without any additional postulates or extensive parametrization.
Department of Chemistry, Indiana University of Pennsylvania, Indiana, Pennsylvania 15705, USA. rfsee@grove.iup.edu
Ronald F
RF
See
Thomas A
TA
Baker
Pamela
P
Kahler