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Dynamics of Dianin's clathrates
This Dissertation investigates the structures of the 1,5-pentanediol, 1,6-hexanediol, and 1-heptanol clathrates of 4-p-hydroxyphenyl-2,2,4-trimethyl chroman (Dianin's compound) and the solid state dynamics of the carbon tetrachloride, chloroform, and 1,6-hexanediol Dianin's clathrates. ^ The structures of two previously undetermined Dianin's clathrates, 1,5-pentanediol and 1-6,hexanediol, and the structure of the 1-heptanol clathrate for which the guest's location and structure had been assumed but not refined were determined by X-ray crystallography. The clathrates belong to the R3¯ trigonal space group. All three guests passed through the waist of the hourglass-shaped cage along the three-fold axis. In all three clathrates, rotational and inversion disorder were present. ^ Full elastic constant tensors for the carbon tetrachloride, chloroform, and hexanediol clathrates were measured by Brillouin spectroscopy. The remeasured c33 elastic constant for the heptanol clathrate was 9.8% lower than previously reported. In general, there was a decrease in stiffness for guest inclusion. The carbon tetrachloride, chloroform, hexanediol, and heptanol clathrates showed a 30.6%, 29.9%, 31.6%, and 32.2% decrease in stiffness compared to the previously reported clathrand, respectively, along c33. Neither the c33 nor the c44 elastic constants were singularly dependent on the density or the guest-host, hydrogen bond. ^ The differences in the shape of the guests between the more spherical carbon tetrachloride and quasi-spherical chloroform guests to the more rod-like heptanol and hexanediol guests affects the c44, c11, and c12 elastic constants. The rod-like guests show greater resistance to shear motion in the crystallographic ab plane. The larger waist centered volume of the carbon tetrachloride guest compared to the chloroform guest causes an increase in stiffness in the c44, c11, and c12 elastic constants. ^ The optical modes from .5 cm–1 to 500 cm –1 are reported The previously observed supramolecular optical mode (∼0.5 cm–l) was observed for the clathrates studied in this work. Its frequency is on the order of the heat carrying acoustic modes and it is posited to arise from optic-acoustic coupling. As such, it is likely responsible for the low thermal conductivity of the clathrand and carbon tetrachloride clathrates. ^
Selbo, Jon Gordon, "Dynamics of Dianin's clathrates" (2000). ETD collection for University of Nebraska - Lincoln. AAI9997019.