The host complexes M(Cyclopentylamine)(2)Ni(CN)(4) (M=Co or Cd) have been prepared in powder form. The spectral data suggest that the structures of these compounds are similar to those of the Hofmann-dma-type hosts. The absorption and the liberation processes of the aromatic guests (benzene, toluene, 1,2-, 1,3-, 1,4-dichlorobenzene, 1,4-dibromobenzene o-, m-, p-xylene, naphthalene) in these hosts have been examined at room temperature by gravimetric and spectroscopic measurements. The desorption of the benzene guest against time has been measured. The host structures do not change on inclusion and liberation of the guests. The host compounds have been suggested as sorbents for isomeric separations.