RESUMEN
The infrared gas-phase absorption spectrum of methane was used to determine its Clapeyron solid-gas equilibrium curve in the 40-77 K temperature range. For comparative purposes and to obtain more reliable results, two different optical experimental setups were used. At higher temperatures (53-77 K), a single pass cryogenically cooled cell was coupled to a standard low-resolution Fourier transform infrared spectrometer. The second system was a state-of-the-art vertical-external-cavity surface-emitting laser tunable source operating at around 2.3 µm, combined with a 7 m path Herriott cell, to record methane absorption features down to 40 K. From the measurements, the vapor pressure curve ln( p/Pa) = -(1191.92 ± 8.92)/( T/K) + (22.49 ± 0.16) was derived in the range 40-77 K. This corresponds to a value of 9910 ± 75 J mol-1 for the sublimation enthalpy. The relation was validated down to 40 K, increasing our knowledge of the saturation pressure by 2 orders of magnitude. Data were compared with available pressure measurements from the literature, obtained by manometric or mass spectrometry techniques, and the sublimation enthalpy was compared with a thermodynamic approach based on heat capacity measurements in the solid and gas phases.
RESUMEN
The dinitroxide biradical crystallizes forming hexagonal open frameworks with one-dimensional corrugated channels filled with crystallization solvent. The large pockets constitutive of the channels allowed the inclusion of C(60) in the paramagnetic network. The rapidity and high fidelity of crystal growth were used to prepare isostructural multilayer host-guest crystals successively stained with C(60).