Nitrogen pyramidal geometry

This nitrogen atom has three bonds and one lone pair, so it is sp hybridized, just as we would expect. The lone pair occupies an sp hybridized orbital, and the nitrogen atom has trigonal pyramidal geometry, just as we saw in the previous section. But now consider the nitrogen atom in the following compound ... 

Macrocycles attached to redox responsive groups such as ferrocene (78) can give selective transition metal ion receptors. The X-ray structure reveals a five-coordinate zinc with distorted square-pyramidal geometry bound to the four macrocycle nitrogens and an iodide. In the solid state the two ferrocenyl groups are positioned on the same side of the ligand with distances to the metal center of 5.347(7) and 6.120(8) A and these distances can be related to the redox behavior.689... 

Reaction of Cl3SiC6H2-2,4,6-Ph3 with ammonia affords the tris(amino)-silane compound (H2N)3SiC6H2-2,4,6-Ph3 in 71% yield [Eq. 9]." The X-ray crystal structure was the first for a species in which three NH2 groups were bound to one silicon atom. There is pyramidal geometry at the nitrogen atoms. The structural characterization of a series of such Si-NH2 compounds led to the conclusion that N — Si p-d 77-overlap was not significant in the Si-N bonding.99... 

The problem with the calculation is that s and p functions centered on the atoms do not provide sufficient mathematical flexibility to adequately describe the wave function for the pyramidal geometry. This is true even though the atoms nitrogen and hydrogen can individually be reasonably well described entirely by s and p functions. The molecular orbitals, which are eigenfunctions of a Schrodinger equation involving multiple nuclei at various positions in space, require more mathematical flexibility than do the atoms. 

---