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Published year: 20224
Marchettiite, (NH 4 )C 5 H 3 N 4 O 3 , a new organic mineral from Mount Cervandone, Devero Valley, Western–Central Alps, Italy

Abstract (Expand)

The new mineral marchettiite (IMA2017-066) is the natural equivalent of ammonium hydrogen urate. It has a simple molecular formula C5H7N5O3 and can be alternatively written as (NH4)C5H3N4O3. Marchettiite … was found in a cleft at Mount Cervandone, Devero Valley, Piedmont, Italy, where it occurs as aggregates of opaque pale pink to white, platy prismatic crystals. This mineral has a white streak, dull and opaque lustre, it is not fluorescent and has a hardness of 2–2.5 (Mohs’ scale). The tenacity is brittle and crystals have a good cleavage parallel to {001}. The calculated density is 1.69 g/cm3. Marchettiite is biaxial (–) with 2V of 47.24°; the optical properties of marchettiite were determined by periodic-DFT methods providing the following values: α = 1.372, β = 1.681 and γ = 1.768. No twinning was observed. Electron microprobe analyses gave the following chemical formula: C4.99H6.97N4.91O3.00. Although the small crystal size did not allow refinement of structural data by single-crystal diffraction, we were able to refine the structure by powder micro X-ray diffraction. Marchettiite has space group P and the following unit-cell parameters: a = 3.6533(2) Å, b = 10.2046(7) Å, c = 10.5837(7) Å, α = 113.809(5)°, β = 91.313(8)°, γ = 92.44(1)° and V = 360.312 Å3. The strongest lines in the powder diffraction pattern [d in Å (I)(hkl)] are: 9.784(50)(001); 8.663(80)(01); 5.659(100)(011); 3.443(100)(10); 3.241(70)(003) and 3.158(100)(1. Marchettiite is named after Gianfranco Marchetti, the mineral collector who found this mineral.

Authors: Alessandro Guastoni, Fabrizio Nestola, Federico Zorzi, Arianna Lanza, Michelle Ernst, Paolo Gentile, Sergio Andò, Alessandra Lorenzetti

Date Published: 1st Dec 2022

Publication Type: Journal

Pitfalls in the location of guest molecules in metal-organic frameworks

Abstract

Not specified

Authors: Tomasz Poręba, Piero Macchi, Michelle Ernst

Date Published: 1st Dec 2022

Publication Type: Journal

Premelting Anomalies in Pyromellitic Dianhydride: Negative Thermal Expansion, Accelerated Radiation Damage, and Polymorphic Phase Transition

Abstract (Expand)

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.

Authors: Tomasz Porȩba, Marcin Świa̧tkowski, Michelle Ernst, Giorgia Confalonieri

Date Published: 5th May 2022

Publication Type: Journal

Strength and Nature of Host‐Guest Interactions in Metal‐Organic Frameworks from a Quantum‐Chemical Perspective

Abstract (Expand)

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.

Authors: Michelle Ernst, Ganna Gryn'ova

Date Published: 20th Apr 2022

Publication Type: Journal

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