The heat capacities of the clathrate compounds formed by inclusion of p-C6H4(CH3)(2) and p-C6D4(CD3)(2) in tetrakis(4-methylpyridine) nickel(II) thiocyanate, and the empty host compound have been measured at temperatures between (12 and 300) K. Two temperature regions of anomalous heat capacity were found for leach of the clathrate compounds. The molar heat capacity divided by the temperature (C-p,C-m/T) plotted against the temperature gave clear representation of the anomalies, making it possible to estimate the temperature, enthalpy, and entropy associated with the heat capacity peaks. Standard thermodynamic functions were calculated and tabulated for rounded temperatures. These data were combined with those of p-xylene to give the entropy of clathrate formation. Experimental evidence is presented that helium is captured into the empty host cavity to form a clathrate compound at low temperatures.