Square pyramidal geometry describes the shape of certain chemical compounds with the formula  where L is a ligand. If the ligand atoms were connected, the resulting shape would be that of a pyramid with a square base. The point group symmetry involved is of type C.  The geometry is common for certain main group compounds that have a stereochemically-active lone pair, as described by VSEPR theory.  Certain compounds crystallize in both the trigonal bipyramidal and the square pyramidal structures, notably .