Clathrate compounds of cadmium cyanide and related hosts with cristobalite-like lattice structures

Abstract

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 Fdmunit-cell parameter for the first series (Z= 8) ranges from 12.647(6)Å for G = CHCl₃ to 12.767(2)Å for CCl₃CF₃, depending on the molecular size and orientation of the guest in the cavity. In the second series the space group Fdm 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)Å, a decrease of 0.5 Å 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 F3munit cell decreases by ca. 0.6 Å 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.