Publications

We have established a comprehensive approach to evaluate the structure–property relationships in solid pyromellitic dianhydride (PMDA) at high temperature. Synchrotron single-crystal X-ray diffraction … experiments have yielded structural models for this volatile compound up to 250 °C. PMDA exhibits negative thermal expansion around 145 °C, which is correlated to geometrical changes in the intermolecular carbonyl–carbonyl interactions. A reversible phase transition above ca. 210 °C was detected by differential scanning calorimetry and is associated with the lowering of the molecular symmetry, as indicated by Raman spectroscopy. X-ray powder and single-crystal diffraction data confirm the formation of a new high-temperature monoclinic phase, with two symmetry-independent anhydride groups in the asymmetric unit. The influence of pyromellitic acid impurities on the formation temperature of the new phase has been investigated, and thermodynamic parameters of pure pyromellitic dianhydride have been revaluated. Additionally, the analysis of the temperature- and time-dependent variations in the diffraction patterns allowed us to track the augmented radiation-driven decarboxylation upon heating. Significantly, the formation of a high-temperature low-symmetry phase in PMDA may challenge the solid-state polymerization that aims for highly oriented materials.

Metal-organic frameworks (MOFs) offer a convenient means for capturing, transporting, and releasing small molecules. Their rational design requires an in-depth understanding of the underlying non-covalent … host-guest interactions, and the ability to easily and rapidly pre-screen candidate architectures in silico. In this work, we devised a recipe for computing the strength and analysing the nature of the host-guest interactions in MOFs. By assessing a range of density functional theory methods across periodic and finite supramolecular cluster scale we find that appropriately constructed clusters readily reproduce the key interactions occurring in periodic models at a fraction of the computational cost. Host-guest interaction energies can be reliably computed with dispersion-corrected density functional theory methods; however, decoding their precise nature demands insights from energy decomposition schemes and quantum-chemical tools for bonding analysis such as the quantum theory of atoms in molecules, the non-covalent interactions index or the density overlap regions indicator.