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Abstract: Differential scanning calorimetry and IR-spectroscopy have been used to study the depolymerization of the 2D tetragonal (T) polymerized phase of C60 at p =1atm. The depolymerization enthalpy obtained was 17.7±1.7kJ per mole of C60. Experimental enthalpies of depolymerization along with the lattice energies calculated by the atom–atom potential method were combined into the thermochemical cycles to account for the trends in the relative stability of the polymerized phases of C60. Surprisingly low depolymerization enthalpy of 2D rhombohedral (R) phase compared to 1D orthorhombic (O) and 2D T-phases was explained by the unfavorable packing energy of the isolated rhombohedral layers into R-crystal lattice, though the averaged C60 =C60 bond energy was also lower for R- than for O- and T- phases, being 31, 42 and 43kJ/mol, respectively. Results of DFT quantum chemical calculations of the energetics of C60 polymers were in qualitative agreement with this trend. The mechanism of depolymerization appeared to be significantly different for R-phase compared to other polymers. While decomposition of O- and T-phases occurred in one step without any IR-detectable intermediate species, depolymerization of R-phase was found to be at least a two-step process. Comparison of experimental and DFT simulated IR-spectra suggested that intermediate species were cyclic trimers or similar oligomers. [Copyright &y& Elsevier]

Differential Scanning Calorimetry and infra-red spectroscopy have been used to study the depolymerization of the two pressure polymerized phases of C60, i.e., rhombohedral (R) and orthorhombic (O) into monomeric C60 at p=1 atm. The depolymerization enthalpies obtained were 10.3 ± 0.5 and 20.1 ± 0.6 kJ/mol for R-, O-phases, respectively. The R-phase, prepared at 1025–1050 K and 6 GPa (‘magnetic carbon’) demonstrated the depolymerization behaviour, similar to the typical R-phase. Part of the p–T-phase diagram of C60 was sketched in, using experimental and literature data. [Copyright &y& Elsevier]

By adiabatic vacuum calorimetry the temperature dependence of heat capacity for crystalline dimer of fullerene C60 has been determined in the range 6–340 K at standard pressure. Between 46 and 56 K, a glass-like transition of the dimer, the nature of which is, probably, similar to that described for C60, has been found. The results were used to calculate the thermodynamic functions of the dimer: the heat capacity Cp∘(T), enthalpy H°(T)−H°(0), entropy S°(T)−S°(0) and Gibbs function G°(T)−H°(0) over the range from T→0 to 340 K. For T<60 K the fractal dimension D in the heat capacity function of the multifractal variant of the Debye’s theory of heat capacity was estimated and in the 20–45 K range D was found to be 1. That indicates a chain structure of the dimer. The heat capacities of the dimer have been compared to those of the initial fullerite C60. The standard entropy of formation of the crystalline dimer from graphite, at T=298.15 K and at standard pressure, and the entropies of transition of the initial fullerite C60 to the crystalline dimer have been calculated. [Copyright &y& Elsevier]