CLATHRATE COMPOUNDS OF CADMIUM CYANIDE AND RELATED HOSTS WITH CRISTOBALITE-LIKE LATTICE STRUCTURES

The crystal structures of three series of clathrate compounds with organic guest molecules G have been determined, Cd(CN)2.G, [CdM(CN)4].2G (M = Hg or Zn) and [NMe4.G][CuM(CN)4] (M = Cd or Zn). The cubic Fd3mBAR unit-cell parameter for the first series (Z = 8) ranges from 12.647(6) angstrom for G = CHCl3 to 12.767(2) angstrom for CCl3CF3, depending on the molecular size and orientation of the guest in the cavity. In the second series the space group Fd3mBAR is unchanged upon 50% substitution of Cd in the first with Hg or Zn owing to the random distribution of the tetrahedral centres; the lattice parameter varies little when M = Hg, but when M = Zn a = 12.243(2) angstrom, a decrease of 0.5 angstrom from the value for Cd(CN)2.CCl4. The anionic host in the third series accommodates the NMe4+ guest together with neutral CCl4; the lattice parameter of the cubic F43mBAR unit cell decreases by ca. 0.6 angstrom in comparison with the values in the first two series. The X-ray data for 24 single crystals are discussed in terms of the crystallographic discrimination between C and N of the linking CN groups and the orientation of the guest molecules, in particular of the tetrahedral and pseudo-tetrahedral guest molecules, in the cavity approximating to a tetrahedron.