In chemistry, the molecular geometry of a compound refers to the three-dimensional arrangement of atoms within that molecule. One common type of molecular geometry is disphenoidal or seesaw (also known as sawhorse) geometry, which occurs when a central atom is bonded to four other atoms and one lone pair of electrons.

The ideal angles between the different ligands in a disphenoidal molecule are critical in determining its overall shape and properties. The angle between the axial ligands and the equatorial ligands is typically 90°, while the angle between the two equatorial ligands themselves is 120°. These angles result in similar time-averaged environments for the two types of ligands.

One of the key features of disphenoidal molecules is that they are subject to Berry pseudorotation, a process in which the axial ligands move to equatorial positions and vice versa. This movement can occur due to repulsion between the bonding pairs at 120° angles. The bond distance to the axial ligands is typically longer than to the equatorial ligands.

In disphenoidal molecules, the equatorial pair of ligands is situated in a plane orthogonal to the axis of the axial pair. The axial pair lies along a common bond axis, resulting in a bond angle of 180° between them.

The seesaw geometry gets its name from the observation that it resembles a playground seesaw, with two types of ligands - axial and equatorial - arranged in a way that is reminiscent of the balance point on a seesaw. This geometry occurs when a molecule has a steric number of 5, meaning that the central atom is bonded to four other atoms and one lone pair of electrons.

In contrast to molecules with trigonal bipyramidal geometry, which have two axial and three equatorial positions, disphenoidal molecules have one equatorial lone pair in place of one of the atoms. This results in a different arrangement of bonds and angles, leading to unique properties and behaviors for these molecules.

Overall, understanding the angles of a seesaw molecular geometry is important for chemists who want to predict the behavior and properties of disphenoidal compounds. By considering the ideal angles between the different ligands, researchers can better understand the molecular structure and its implications for chemical reactions and interactions.

Angles of a seesaw molecular geometry