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

The crystal structures of three series of clathrate compounds with org anic 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 Fd3mBA R 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% substi tution of Cd in the first with Hg or Zn owing to the random distributi on of the tetrahedral centres; the lattice parameter varies little whe n M = Hg, but when M = Zn a = 12.243(2) angstrom, a decrease of 0.5 an gstrom from the value for Cd(CN)2.CCl4. The anionic host in the third series accommodates the NMe4+ guest together with neutral CCl4; the la ttice parameter of the cubic F43mBAR unit cell decreases by ca. 0.6 an gstrom in comparison with the values in the first two series. The X-ra y data for 24 single crystals are discussed in terms of the crystallog raphic 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.