D3h point group can be explained by giving an example of --------------
Answers
Group Theory
Narayan S. Hosmane, in Advanced Inorganic Chemistry, 2017
Molecular orbital correlation diagram for triangular planar structure (BF₃)
1. BF₃h is a planar triangular molecule belonging to the D₃h point group.
a. Group theory can allow one to choose the B and F atomic orbitals that are symmetry matched to form molecular orbitals. These were derived earlier.
b. The extent to which they will interact and the composition of the MOs in terms of the SALC orbitals will depend on the relative energy of the B and F orbitals involved.
c. Recall that only orbitals of comparable energies can form molecular orbitals. This usually means that only valence orbitals are delocalized. That is, even though the F's and the B have 1s orbitals, we may consider them as core electrons that remain on the individual atoms. This is an approximation, and in ab initio calculations they are considered. However, for qualitative bonding descriptions, only valence electrons need be considered.
d. From symmetry considerations, only one-dimensional irreducible representations and two-dimensional irreducible representations are found. Also note that the B has no atomic orbitals with or symmetries.
e. Also recall that the bonding MOs will have more of the character of the low-energy atomic orbitals, whereas the antibonding will be more similar to the higher energy input orbitals.
2. Correlation Diagram for BF3.
a. BF3 has 24 valence electrons and 16 valence orbitals. Instead of solving a 16 × 16 determinate, the use of group theory has simplified it to just several pairwise combinations.
b. Note that the 2s fluorine orbitals are so stable compared with the B orbitals that they interact very little and can be considered as essentially nonbonding; only the p orbitals interact.
c. Also note that from symmetry, the A'₂ and E" F orbitals are nonbonding, as is the e’ fluorine SALC arising from their py orbitals.