Structure
Compounds with seesaw geometry have two types of ligands, one pair related by 180° often called axial ligands. A separate pair of ligands is situated orthogonal to the axial ligands. Typically the bond distance to the apical ligands is longer than to the equatorial ligands. The angle between the axial liglands and the equatorial liglands is 90°; whereas the angle between the two equatorial liglands themselves is 120°.
Seesaw molecules, like trigonal bipyramidal ones, are subject to Berry pseudorotation. Thus, the 19F NMR spectrum of SF4 (like that of PF5) consists of single resonance near room temperature. The four atoms in motion act as a lever about the central atom; for example, the four fluorine atoms of sulfur tetrafluoride rotate around the sulfur atom.
Read more about this topic: Seesaw Molecular Geometry
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