Low-Temperature Heat Capacity and Standard Thermodynamic Functions of Li12C60(THF)1.4Fulleride

Abstract

Low-temperature heat capacities of the crystalline coordination compound Li12C60(THF)1.4 have been measured by a precision adiabatic calorimeter over the temperature range T = 6 K to T = 350 K and by a differential scanning calorimeter over the temperature range T = 330 K to T = 520 K for the first time. Using the obtained data, the temperature of the onset of Li12C60(THF)1.4 destruction was determined to be 468 K. The experimental results have been used to calculate the standard (po = 0.1 MPa) thermodynamic functions: molar heat capacities Cp,mo, enthalpy Ho(T) − Ho(0), entropy So(T), and Gibbs energy Go(T) − Ho(0) of Li12C60(THF)1.4 (cr) over the range from T → 0 K to T = 468 K. The low-temperature (T < 50 K) dependence of the heat capacity was analyzed based on Debye’s heat capacity theory of solids and its fractal variant. As results, the characteristic temperatures as well as the fractal dimension were determined, and some conclusions about structure topology are given. The standard entropy of formation at T = 298.15 K of Li12C60(THF)1.4 (cr) was calculated. The standard thermodynamic properties of tested fulleride and previously studied C60 fullerite and hydrofullerene C60H36 were compared.