Why are the axial bond lengths greater than those of the equatorial bonds in a pentagonal bi-pyramid (PBP) geometry molecule; but the opposite is true for trigonal bi-pyramid (TBP) geometry molecules? I think that it might have something to do with the angles between the bonds, so I thought of a possible explanation.

In a TBP molecule, the equatorial bonds are spaced apart from each other by 120 degrees, resulting in lesser repulsion; compared to the axial bonds at 90 degrees. The reduced repulsion leads to greater stability of the equatorial bonds.

In contrast, the equatorial bonds in a PBP molecule are separated by 72 degrees which results in them being less stable when compared to the axial bonds.

To what extent is this reasoning correct? And please provide a more detailed and accurate explanation, if there is one. Thanks!!