ISSN:
1573-1111
Keywords:
Thiourea inclusion compound
;
phase transition
;
entropy of transition
;
orientational disorder
;
guest-guest interaction
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract Heat capacities of the inclusion compound (thiourea)3.00CCl4 have been measured in the temperature range 15–300 K. A first-order phase transition was found at 41.3 K and a second-order transition at 67.17 K. The enthalpy and entropy of the transition are 149 J mol−1 and 3.7 J K−1 mol−1 for the former, and 241 J mol−1 and 3.9 J K−1 mol−1 for the latter. A divergent expression ΔC = A{(T c −T)/T c} −α was fitted to the excess heat capacity of the upper phase transition. The best-fit parameters wereA = 7.4 J K−1 mol−1,T c = 67.166 K and α = 0.31. Possible types of molecular disorder in the high temperature phase are discussed in relation to the transition entropy and the molecular and site symmetries of the guest molecule. The heat capacity of the lowest temperature phase was unusually large and may indicate the existence of very low frequency vibrational modes or labile configurational excitation of the guest molecule. Standard thermodynamic functions were calculated from the heat capacity data and are tabulated in the appendix.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01053122
Permalink
