Host-guest interactions and stability of Hofmann-type benzene and aniline clathrates studied by i.r. spectroscopy
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The results are presented for an i.r. spectroscopic study of thirteen Hofmann-type benzene and aniline clathrates, M(NH3)2Ni(CN)4, 2G (M = Mn, Fe, Ni, Cu, Zn, Cd: G = benzene or aniline: and M = Co with aniline). A detailed analysis of the infrared spectra indicates the presence of hydrogen bonding between the ammonia molecules of the host lattices and pi electrons of the aromatic guest molecules. Further hydrogen bonding appears to be present between the amine group of the aniline guest molecules and the cyanide bonds of the host lattices. This bonding may account, in part, for the greater stability of the aniline compared to the benzene clathrates. Analysis of bands in the cyanide stretching region is used to interpret differences in the crystal structures of the clathrates and the nature of the decomposition of the benzene clathrates under grinding or evacuation. The large breadth of the perpendicular compared to the parallel ammonia vibrations indicates that the ammonia molecules are not fixed but undergo rather free internal rotation.