Can simple 'molecular' corrections outperform projector augmented-wave density functional theory in the prediction of 35 Cl electric field gradient tensor parameters for chlorine-containing crystalline systems?

Many-body expansion (MBE) fragment approaches have been applied to accurately compute nuclear magnetic resonance (NMR) parameters in crystalline systems. Recent examples demonstrate that electric field gradient (EFG) tensor parameters can be accurately calculated for 14 N and 17 O. A key additional development is the simple molecular correction (SMC) approach, which uses two one-body fragment (i.e., isolated molecule) calculations to adjust NMR parameter values established using 'benchmark' projector augmented-wave (PAW) density functional theory (DFT) values. Here, we apply a SMC using the hybrid PBE0 exchange-correlation (XC) functional to see if this can improve the accuracy of calculated 35 Cl EFG tensor parameters. We selected eight organic and two inorganic crystal structures and considered 15 chlorine sites. We find that this SMC improves the accuracy of computed values for both the 35 Cl quadrupolar coupling constant (CQ ) and the asymmetry parameter ( η Q ) by approximately 30% compared with benchmark PAW DFT values. We also assessed a SMC that offers local improvements not only in terms of the quality of the XC functional but simultaneously in the quality of the description of relativistic effects via the inclusion of spin-orbit effects. As the inorganic systems considered contain heavy atoms bonded to the chlorine atoms, we find further improvements in the accuracy of calculated 35 Cl EFG tensor parameters when both a hybrid functional and spin-orbit effects are included in the SMC. On the contrary, for chlorine-containing organics, the inclusion of spin-orbit relativistic effects using a SMC does not improve the accuracy of computed 35 Cl EFG tensor parameters.

An unexpected tautomer: synthesis and crystal structure of N-[6-amino-4-(methyl-sulfan-yl)-1,2-di-hydro-1,3,5-triazin-2-yl-idene]benzenesulfonamide

The title compound, C10H11N5O2S2, consists of an unexpected tautomer with a protonated nitro-gen atom in the triazine ring and a formal exocyclic double bond C=N to the sulfonamide moiety. The ring angles at the unsubstituted nitro-gen atoms are narrow, at 115.57 (12) and 115.19 (12)°, respectively, whereas the angle at the carbon atom between these N atoms is very wide, 127.97 (13)°. The inter-planar angle between the two rings is 79.56 (5)°. The mol-ecules are linked by three classical hydrogen bonds, forming a ribbon structure. There are also unusual linkages involving three short contacts (< 3 Å) from a sulfonamide oxygen atom to the C-NH-C part of a triazine ring.

Review of Applications of Density Functional Theory (DFT) Quantum Mechanical Calculations to Study the High-Pressure Polymorphs of Organic Crystalline Materials

Since its inception, chemistry has been predominated by the use of temperature to generate or change materials, but applications of pressure of more than a few tens of atmospheres for such purposes have been rarely observed. However, pressure is a very effective thermodynamic variable that is increasingly used to generate new materials or alter the properties of existing ones. As computational approaches designed to simulate the solid state are normally tuned using structural data at ambient pressure, applying them to high-pressure issues is a highly challenging test of their validity from a computational standpoint. However, the use of quantum chemical calculations, typically at the level of density functional theory (DFT), has repeatedly been shown to be a great tool that can be used to both predict properties that can be later confirmed by experimenters and to explain, at the molecular level, the observations of high-pressure experiments. This article's main goal is to compile, analyze, and synthesize the findings of works addressing the use of DFT in the context of molecular crystals subjected to high-pressure conditions in order to give a general overview of the possibilities offered by these state-of-the-art calculations.

Can We Predict the Isosymmetric Phase Transition? Application of DFT Calculations to Study the Pressure Induced Transformation of Chlorothiazide

Isosymmetric structural phase transition (IPT, type 0), in which there are no changes in the occupation of Wyckoff positions, the number of atoms in the unit cell, and the space group symmetry, is relatively uncommon. Chlorothiazide, a diuretic agent with a secondary function as an antihypertensive, has been proven to undergo pressure-induced IPT of Form I to Form II at 4.2 GPa. For that reason, it has been chosen as a model compound in this study to determine if IPT can be predicted in silico using periodic DFT calculations. The transformation of Form II into Form I, occurring under decompression, was observed in geometry optimization calculations. However, the reverse transition was not detected, although the calculated differences in the DFT energies and thermodynamic parameters indicated that Form II should be more stable at increased pressure. Finally, the IPT was successfully simulated using ab initio molecular dynamics calculations.

Mechanical study of a copper dietary supplement, copper glycinate hydrate

Here, the mechanical properties of a copper-based dietary supplement were systematically investigated via a combined theoretical–experimental approach.

Effect of Chirality on the Compression of 2-(2-Oxo-1-pyrrolidinyl)butyramide: A Tale of Two Crystals

Understanding polymorphism in chiral systems for drug manufacturing is essential to avoid undesired therapeutic effects. Generally, polymorphism is studied through changes in temperature and solution concentration. A less common approach is the application of pressure. The goal of this work is to investigate the effect of pressure on levetiracetam (pure enantiomer) and etiracetam (racemic compound). Anisotropic compressions of levetiracetam and etiracetam are observed to 5.26 and 6.29 GPa, respectively. The most compressible direction for both was identified to be perpendicular to the layers of the structure. Raman spectroscopy and an analysis of intermolecular interactions suggest subtle phase transitions in levetiracetam (∼2 GPa) and etiracetam (∼1.5 GPa). The stability of etiracetam increases with respect to levetiracetam on compression; hence, the chiral resolution of this system is unfavorable using pressure. This work contributes to the ongoing efforts in understanding the stability of chiral systems.

High-pressure preference for reduced water content in porous zinc aspartate hydrates

The zinc aspartate (ZnAsp2) complex, a common dietary supplement, preferentially crystallizes as the dihydrate (ZnAsp2·2H2O) from aqueous solution. Under normal conditions the dihydrate easily transforms into the sesquihydrate (ZnAsp2·1.5H2O). The dihydrate crystal structure is triclinic, space group P1, and the sesquihydrate is monoclinic, space group C2/c. However, their structures are closely related and similarly consist of zinc aspartate ribbons parallel to pores accommodating water molecules. These porous structures can breathe water molecules in and out depending on the temperature and air humidity. High pressure above 50 MPa favours the sesquihydrate, as shown by recrystallizations under pressure and compressibility measured by single-crystal X-ray diffraction up to 4 GPa. This preference is explained by the reduced volume of the sesquihydrate and water compressed separately, compared with the dihydrate. The sesquihydrate undergoes an isostructural phase transition when the voids collapse at 0.8 GPa, whereas no phase transitions occur in the dihydrate, because its pores are supported by increased water content.

Elastic and hydrostatic behaviour of a zinc dietary supplement, zinc glycinate hydrate

Coordination polymer based dietary supplement tablets are commonly consumed in our daily life and play an important role in the pharmaceutical industry. To fully understand their tableting process, their mechanical properties need to be comprehensively studied. In this work, the elastic and hydrostatic behaviour of a zinc supplement, zinc glycinate hydrate (Zn[O2CCH2NH2]2·H2O), have been studied via density functional theory (DFT) calculations and high-pressure synchrotron powder X-ray diffraction. This material has a pseudo-layered structure and can be successfully exfoliated into nanosheets. The DFT calculated elastic moduli along the principal axes (13.84-36.11 GPa) indicate a significant elastic anisotropy of ZnG as expected for a layered system, and the directional dependent elastic modulus can be corroborated with the underlying atomic structure. In addition, the calculated B/G ratios (1.30-3.83) according to Pugh's criterion reveal that ZnG could be brittle under uniaxial stress (B and G are bulk modulus and shear modulus, respectively). Furthermore, the measured B is ∼31 GPa, which lies in the middle of the values between inorganic dietary supplements and small organic drug crystals. These results provide some quantitative information about the tableting process of the hybrid dietary supplement which could be different from their inorganic and organic pharmaceutical counterparts.

Discovery and recovery of delta p-aminobenzoic acid

A new high-pressure recoverable form has been observed in the model system, p-aminobenzoic acid.

Structural investigation and compression of a co-crystal of indomethacin and saccharin

Indomethacin : saccharin cocrystal has been studied under high pressure conditions and the amide interactions compared with previous high pressure studies.

Investigation of acrylic acid at high pressure using neutron diffraction

This article details the exploration of perdeuterated acrylic acid at high pressure using neutron diffraction. The structural changes that occur in acrylic acid-d₄ are followed via diffraction and rationalized using the Pixel method. Acrylic acid undergoes a reconstructive phase transition to a new phase at ∼0.8 GPa and remains molecular to 7.2 GPa before polymerizing on decompression to ambient pressure. The resulting product is analyzed via Raman and FT-IR spectroscopy and differential scanning calorimetry and found to possess a different molecular structure compared with polymers produced via traditional routes.