How the H‑Bond Layout Determines Mechanical Properties of Crystalline Amino Acid Hydrogen Maleates

The stiffness tensor and elastic anisotropy characteristics for the crystalline hydrogen maleates of l-isoleucinium, l-leucinium, and l-norvalinium with l-norvaline have been calculated using the periodic DFT calculations and atom-centered basis sets. The H-bond orientations have been compared with spatial directions of the minimum and maximum values of Young’s modulus, shear modulus, and linear compressibility. In spite of the similar layered structures, l-isoleucinium and l-leucinium hydrogen maleates show significant difference in elastic moduli anisotropy. The flexibility of l-leucinium hydrogen maleate is explained by the relatively high universal elastic anisotropy index and the large anisotropy ratios of elastic moduli. In its turn, this index is determined by the almost coincidental Young’s modulus maximum direction and the orientation of the strongest H-bonds

Cl···Cl Interactions in Molecular Crystals: Insights from the Theoretical Charge Density Analysis

The structure, IR harmonic frequencies and intensities of normal vibrations of 20 molecular crystals with the X–Cl···Cl–X contacts of different types, where X = C, Cl, and F and the Cl···Cl distance varying from ∼3.0 to ∼4.0 Å, are computed using the solid-state DFT method. The obtained crystalline wave functions have been further used to define and describe quantitatively the Cl···Cl interactions via the electron-density features at the Cl···Cl bond critical points. We found that the electron-density at the bond critical point is almost independent of the particular type of the contact or hybridization of the ipso carbon atom. The energy of Cl···Cl interactions, <i>E</i>_int, is evaluated from the linking <i>E</i>_int and local electronic kinetic energy density at the Cl···Cl bond critical points. <i>E</i>_int varies from 2 to 12 kJ/mol. The applicability of the geometrical criterion for the detection of the Cl···Cl interactions in crystals with two or more intermolecular Cl···Cl contacts for the unique chlorine atom is not straightforward. The detection of these interactions in such crystals may be done by the quantum-topological analysis of the periodic electron density

Halogen Bonding and Other Iodine Interactions in Crystals of Dihydrothiazolo(oxazino)quinolinium Oligoiodides from the Electron-Density Viewpoint

The spatial organization of electron density in dihydrothiazolo­(oxazino)­quinolinium crystals with oligoiodide anions of various structures has been studied on the basis of 3D periodic Kohn–Sham calculations. The combination of QTAIMC and the analysis of one-electron potential and electrostatic potential has revealed the significant differences between halogen bonds (Type II interactions) and van der Waals (Type I) interactions for iodine atoms in crystalline environment. The traces of σ-holes in electrostatic potential on the zero-flux interatomic surfaces of iodine moieties are the distinctive feature of halogen bonding; they do not appear in the weak van der Waals I···I interactions at all. The analysis of superposition of the gradient fields of the electron density and electrostatic potential has allowed detection of the strong electron redistribution along the oligoiodide chain [I₃^–···II···I₃^–]; the electron density is shifted from I₃^– moiety to the cation via iodine molecule I₂ as a mediator. The quantitative relationship between the experimentally measured dissociation energy <i>D</i>_e(II/I···I) and the kinetic energy density at the bond critical point in the whole range of observed iodine interactions has been established

Noncovalent Interactions in Crystalline Picolinic Acid N‑Oxide: Insights from Experimental and Theoretical Charge Density Analysis

This study provides a detailed description of noncovalent interactions of different types and strengths in the title crystal using a combined experimental and theoretical study of the charge density distribution. The nature of the noncovalent interactions is visualized using information theory and through the superposition of the gradient fields in the electron density and electrostatic potential. The energy of the intramolecular O–H···O bond, intermolecular C–H···O bonds, and π-stacking interactions, <i>E</i>_int, are evaluated from empirical correlations between <i>E</i>_int and geometrical and electron-density bond critical point parameters. The complete set of noncovalent interactions including the strong intramolecular O–H···O (<i>E</i>_int > 90 kJ/mol) and weak C–H···O (<i>E</i>_int < 10 kJ/mol) hydrogen bonds, and π-stacking interactions (<i>E</i>_int < 4 kJ/mol) is quantitatively described. The results from the experimental charge density analysis are compared with periodic quantum calculations using density functional theory with the Grimme dispersion correction. It was found that the Grimme dispersion correction did not provide a good simultaneous description of both weak and strong noncovalent interactions in the studied crystal. It is shown that the obtained energies of noncovalent interactions lead to a reasonable value of the lattice energy. The latter is treated as the total intermolecular interaction energy

Noncovalent Interactions in Crystalline Picolinic Acid N‑Oxide: Insights from Experimental and Theoretical Charge Density Analysis

This study provides a detailed description of noncovalent interactions of different types and strengths in the title crystal using a combined experimental and theoretical study of the charge density distribution. The nature of the noncovalent interactions is visualized using information theory and through the superposition of the gradient fields in the electron density and electrostatic potential. The energy of the intramolecular O–H···O bond, intermolecular C–H···O bonds, and π-stacking interactions, <i>E</i>_int, are evaluated from empirical correlations between <i>E</i>_int and geometrical and electron-density bond critical point parameters. The complete set of noncovalent interactions including the strong intramolecular O–H···O (<i>E</i>_int > 90 kJ/mol) and weak C–H···O (<i>E</i>_int < 10 kJ/mol) hydrogen bonds, and π-stacking interactions (<i>E</i>_int < 4 kJ/mol) is quantitatively described. The results from the experimental charge density analysis are compared with periodic quantum calculations using density functional theory with the Grimme dispersion correction. It was found that the Grimme dispersion correction did not provide a good simultaneous description of both weak and strong noncovalent interactions in the studied crystal. It is shown that the obtained energies of noncovalent interactions lead to a reasonable value of the lattice energy. The latter is treated as the total intermolecular interaction energy

Evaluation of the Lattice Energy of the Two-Component Molecular Crystals Using Solid-State Density Functional Theory

The lattice energy <i>E</i>_latt of the two-component crystals (three co-crystals, a salt, and a hydrate) is evaluated using two schemes. The first one is based on the total energy of the crystal and its components computed using the solid-state density functional theory method with the plane-wave basis set. The second approach explores intermolecular energies estimated using the bond critical point parameters obtained from the Bader analysis of crystalline electron density or the pairwise potentials. The <i>E</i>_latt values of two-component crystals are found to be lower or equal to the sum of the absolute sublimation enthalpies of the pure components. The computed energies of the supramolecular synthons vary from ∼80 to ∼30 kJ/mol and decrease in the following order: acid–amide > acid–pyridine > hydroxyl–acid > amide–amide > hydroxyl–pyridine. The contributions from different types of noncovalent interactions to the <i>E</i>_latt value are analyzed. We found that at least 50% of the lattice energy comes from the heterosynthon and a few relatively strong H-bonds between the heterodimer and the adjacent molecules