The molecular and crystal structure of hydrogen cyanide tetramer (diaminomaleonitrile)

A three-dimensional crystal structure analysis of hydrogen cyanide tetramer has led to a location of all atoms with average standard deviations of 0.0025 A for carbon and nitrogen atoms and 0.04 A for hydrogens. The diaminomaleonitrile structure is proved. In its crystal setting the molecule has no symmetry. The two amino groups have different configurations, one being planar and one tetrahedral while both being involved in intermolecular N H • • • 1W hydrogen bonds. An analysis is made of the anisotropic nature of the atomic thermal vibrations. Molecular orbital calculations have been made for this molecule and for tetracyanoethylene leading to z bond orders for all bonds. Order/length relationships for the carbon-carbon bonds are discussed in some detail.