Thermodynamic properties of 1,1′-biadamantane

A comprehensive study of thermodynamic properties of 1,1′-biadamantane in different phase states has been carried out. The heat capacity of the compound in the condensed state was measured in two adiabatic calorimeters in the temperature range from 5 to 370 K and in a single-cup scanning calorimeter from 315 to 610 K. Two solid-to-solid phase transitions at 336.3 ± 0.3 K with ΔtrsHm° = 1.154 ± 0.019 kJ mol−1 and 509.6 ± 0.5 K with ΔtrsHm° = 1.30 ± 0.03 kJ mol−1, and fusion at Tfus ∼ 561 K were revealed in this temperature interval. It was found that 1,1′-biadamantane did not form plastic crystals. The thermodynamic functions of the compound in the crystalline state were derived. The saturated vapour pressure of 1,1′-biadamantane from 393 to 443 K was determined by the Knudsen effusion method:lnpPa=(32.82±0.37)−(13126±153)KT.The sublimation enthalpy was obtained from the results of the effusion measurements: ΔsubHm° (417.8 K) = 109.1 ± 1.3 kJ mol−1, ΔsubHm° (298.15 K) = 113.8 ± 1.4 kJ mol−1. The complete set of fundamentals was compiled from experimental spectral data and results of calculations in terms of the density functional theory (B3LYP/6-31G*). The combustion enthalpy of C20H30, ΔcHm° (298.15 K, cr) = −(11801.3 ± 7.3) kJ mol−1, was determined by the bomb-calorimetry method and the enthalpy of formation, ΔfHm° (298.15 K, cr) = −(356.4 ± 7.8) kJ mol−1, was obtained. The thermodynamic properties of 1,1′-biadamantane in the ideal-gas state were calculated.