The nickel cyanide-ammonia complex forms clathrate compounds with aniline, benzene, pyridine, pyrrole, and thiophene. The structure is tetragonal and the unit cell contains atoms corresponding to twice the formula when benzene is enclosed in nickel complex. Each benzene molecule is comparatively remote from nickel atoms. It is contained in a cavity where it makes contacts at van der Waals distances with other benzene molecules and with atoms of cyanide and ammonia groups. It is not linked by chemical bonds to the nickel complex. The clathrated molecules in this system are easily evolved when the compound is ground or heated to high temperatures. These clathrates are not particularly stable systems. The stability and decomposition of nickel cyanide-ammonia clathrates are described.