Order-disorder effects of small guests in clathrates studied by nuclear quadrupole resonance and crystallography. Part I. Carbon tetrachloride and related molecules in Ni(SCN)2(3-methylpyridine)4

NQR spectroscopy and X-ray crystallography have been jointly applied to the study of the small guest molecules CHCl, CHCl, CCl, CBrCl, C(CH)2Cl etc. in the Werner host complex Ni(SCN)(3-methylpyridine). Specific host-guest dipole-dipole interactions play an important role in order-disorder effects for guest molecules in the cavities of orthorhombic system,. Thus a weakly polar molecule such as CBrCl exhibits a disordered alternation, both the bromine and the chlorine atoms occupying the two possible sites in the cavity, whereas for the polar molecule C(CH)Cl, an ordered structure is observed. In addition, two new types of crystal structures,2/ and, are reported here for dichloromethane and chloroform clathrates.