Solid-state studies on c60 solvates
- Autores: Jin Ye
- Directores de la Tesis: Maria Del Barrio Casado (dir. tes.), Josep Lluís Tamarit Mur (codir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2017
- Idioma: español
- Tribunal Calificador de la Tesis: Roberto Macovez (presid.), Maria Teresa Calvet Pallàs (secret.), Denise Mondieig (voc.)
- Programa de doctorado: Programa de Doctorado en Física Computacional y Aplicada por la Universidad Politécnica de Catalunya
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
This thesis focuses on the thermodynamic and crystallographic characterization of C60 solvates formed with small organic molecules (CBr2(CH3)2, CBr2Cl2, CBr2H2, CBrCl2H and CBrClH2) Chapter I provides an introduction concerning the physical and chemical properties of fullerene C60 as well as the state of the art for solvates or co-crystals formed between C60 and organic materials. Chapter II provides information about experimental techniques and models used for the acquisition and analyses of experimental data. The analysis and discussion of the obtained results are presented in the following five chapters, one for each organic solvent under scrutiny. The last chapter is devoted to overall conclusions concerning the structural and thermodynamic common properties of the studied solvates.
In Chapter III, the stable monoclinic solvate C60·2CBr2H2, has been structurally and thermodynamically characterized. It exhibits overall orientational order due to strong interactions between C60 and solvent host molecule. The orientational order is consistent with the stability found as well as with the high negative excess volume and a high desolvation enthalpy.
Chapter IV deals with cubic co-crystals of C60·12CBr2(CH3)2, with C2v molecular symmetry. The cubic co-crystals are found to be unstable in air and transform spontaneously into hexagonal co-crystals C60·2CBr2(CH3)2, in which solvent molecules (orientationally disordered) are located close to the prismatic hexagonal voids of the structure.
Chapter V describes the cubic co-crystals of C60·12CCl2Br2, also unstable in air. Co-crystals transform spontaneously into the hexagonal co-crystals C60·2CCl2Br2 (formed with negative excess volume) in which the solvent molecules (C2v symmetry) are orientationally disordered and are located close to the prismatic hexagonal voids.
In Chapter VI, the in air stable solvate C60·2CBrCl2H is described. The solvent molecules, with C3v pseudo-symmetry (if one consider the halogen Br and Cl being interchangeable). The hexagonal solvate undergoes a transformation on heating to another solvate of lower stoichiometry C60·CBrCl2H with a monoclinic structure. Paradoxically, the measured desolvation enthalpies for both C60·2CBrCl2H and C60·CBrCl2H do not exceed the sublimation enthalpy of pure CBrCl2H.
Chapter VII is devoted to the characterization of the monoclinic solvate C60·2CBrClH2. This low-temperature solvate transforms reversibly on heating to an hexagonal structure with the same stoichiometry. Both co-crystal structures form with a negative excess volume indicating strong intermolecular interactions between the C60 and CBrCl2H. This result is in clear contradiction to the determined desolvation enthalpy, clearly smaller than the sublimation enthalpies of the involved solvent.
The last chapter VIII, put together overall experimental results in order to derive common properties for the different studied solvates. To do so, the results of this thesis are analyzed in combination with previous reported results for molecular solvates for which the solvent molecules have strong similarities to those studied in this work. Thus, we present a tentative overview of crystallographic and thermodynamic results obtained in the frame of a systematic investigation on C60:Solvent solvates. The results of this thesis represent an step forward in the direction of extending the current experimental knowledge of co-crystals of C60:Solvents. Moreover, the work makes a proposal in order to rationalize the structural properties of these solvates, which mainly consists of a prediction of the solvate volumes according to the van der Waals volumes of the involved chemical species.
