The Motion of the Benzene Molecules in the Host Lattices of M(NH3)2M’(CN)4·2C6H6 Clathrates

In our previous report1 we discussed host-guest interactions in a series of Hofmann-type clathrates of the general formula: M(NH3)2M’(CN)4-2C6H6, where M is Ni, Fe, Co, Zn, Mn and Cd and M’ is Ni. It was found that the splitting of the band due to CH out-of-plane vibration in benzene, at liquid nitrogen temperature, (at around 985 cm-1), increases as the volume of the tetragonal unit cell decreases. A similar behaviour we recorded in a series of benzene clathrate compounds (isostructural with Hofmann-type clathrates) in which the M’ metal was replaced by Pt or Pd, and it was interpreted as a consequence of a »free« rotation in the benzene molecules at room temperature but hindered at low temperatures. The magnitude of the splitting of this band, at liquid nitrogen temperatures, for all the clathrates studied was correlated with the volume of the tetragonal unit cell and with the effective ionic radii of the octahedrally coordinated metal M and the square- planar coordinated metal M’. The slope of Ai< vs, V(Unitcell) is =-100 cm"1 nm-3

A RE-CORRELATION OF THE VIBRATIONAL SPECTRA AND CRYSTALLOGRAPHIC DATA FOR THE VARIOUS ICE POLYMORPHS

Nous avons obtenu des spectres Raman de bonne qualité sur les glaces Ih, II, III, V, VI et IX dans leur domaine de stabilité thermodynamique à l'aide de cellule Raman, sous pression et température variables. Nous discutons des relations entre les spectres Raman dans la région dynamique du réseau, en essayant de l'interpréter par sa structure cristallographique.We have obtained good quality Raman spectra of ices Ih, II, III, V, VI and IX in their regions of thermodynamic stability with a variable pressure, variable temperature Raman cell. We discuss the relationships between the Raman spectra in the lattice region and attempt to interpret them in tems of the available crystal structure data