secl has often been used as an example for teaching vsepr rules of hypervalent molecules. as such, one would predict four bonds but five electron groups giving rise to a seesaw geometry. this clearly is not the case in the crystal structure. others have suggested that the crystal structure can be represented as secl and cl. this formulation would predict a pyramidal geometry for the secl cation with a cl-se-cl bond angle of approximately 109°. however, this molecule is an excellent example of a situation where maximal bonding cannot be achieved with the simplest molecular formula. the formation of the tetramer (secl), with delocalized sigma bonding of the bridging chloride is clearly preferred over a "hypervalent" small molecule.