The nitroxide C9H16NO2 (tano) forms channel inclusion compounds with a large range of linear chains or slightly branched molecules. All of them present disorder phenomena of the guest species in the channels of the structure, but also in those of the host matrix molecules from one chiral form to another. The evolution of this disorder as a function of the temperature is accompanied by one-or two-phase transitions above 100 K. Using the incoherent quasi-elastic neutron scattering technique (IQNS), we have studied the motions of the chains and of the tano molecules for the tano/heptane, tano/octane, tano/1-bromohexadecane and tano/l-bromodecane systems in their low-, intermediate-and high-temperature phases. The experiments were carried out on polycrystalline samples using several neutron spectrometers at the Institut Laue-Langevin in Grenoble, at the Laboratoire Leon Brillouin in Saclay and at the Rutherford-Appleton Laboratory (UK}, at temperatures ranging from 103 to 300 K. The results are examined in terms of the general model proposed in the earlier IQNS study of the tano/alkane compounds with short included chains and the original features associated with the chain length are discussed. An extensive inelastic neutron scattering study of a series of systems with various guest chains, together with Raman light scattering experiments on the same compounds provided information about the conformational behaviour of the included chains. Molecular mechanics calculations evaluated the heights of the potential barriers associated with the ring inversion of the tano molecules and those with the rotation of the methyl groups about their threefold axis. * Corresponding author.
clusion compounds [4,5]. However, the percentage of alkane to tano is only 5% in weight.
At room temperature, X-ray analyses show that all the alkane inclusion compounds are isomorphous: space group Cz/~, Z = 4 and their crystallographic parameters differ by less than 1%. Typically, for tano-heptane at T =233 K a=36.0,~, b=5.95•, c=35.5~, /3=120 ~' . The guest molecules are enclosed end-to-end into parallel channels, 18/~ apart, with a diameter of 5,~ [1,2]. X-ray rotation photographs show