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NQR spectroscopy and X-ray crystallography have been jointly applied to the study of the small guest molecules CH2C12, CHCI3, CC14, CBr2CI2, C(CH3)2C12 etc. in the Werner host complex Ni(SCN)2(3-methylpyridine)4. Specific host-guest dipole-dipole interactions play an important role in order disorder effects for guest molecules in the cavities of orthorhombic system, Fddd. Thus a weakly polar molecule such as CBr2C12 exhibits a disordered alternation, both the bromine and the chlorine atoms occupying the two possible sites in the 6"2 cavity, whereas for the polar molecule C(CH3)2C12, an ordered structure is observed. In addition, two new types of crystal structures, C2/c and Pi, are reported here for dichloromethane and chloroform clathrates.

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A molecular-graphics study has been performed in order to build and visualize the shape of cavities within different clathrates from X-ray diffraction data [e.g. Dianin's compound, Werner complexes Ni(SCN)2(3-methylpyridine)4, Fe(acetylacetonate)3 and Ni(ethylxanthate)2(4,4'-dimethyl-2,2'-bipyridyl) complexes]. The algorithm of the solvent-accessible surfaces representation has been applied to a part of the whole crystal structure rather than to isolated host molecules, by using the MOLCAD molecular modeling package. This type of modelization has been found very efficient both to study the shape properties of the host cavities (cage or channel types) and to approach the structural features of the host/guest interactions.