Weak noncovalent interactions in two positional isomers of acrylonitrile derivatives: inputs from PIXEL energy, Hirshfeld surface and QTAIM analyses

A single crystal X-ray diffraction analysis was performed on two positional isomers (m-tolyl and p-tolyl) of acrylonitrile derivatives, namely, (Z)-3-(4-(pyridin-2-yl) phenyl)-2-(m-tolyl) acrylonitrile (1) and (Z)-3-(4-(pyridin-2-yl)phenyl)-2-(p-tolyl) acrylonitrile (2). Compound 1 crystallized in the monoclinic P2₁/n space group with two crystallographically independent molecules. Compound 2 also possesses two crystallographically independent molecules and crystallized in the triclinic P-1 space group. The Hirshfeld surface analysis revealed that, in both isomers, intermolecular H⋅⋅⋅H/C/N contacts contribute significantly to the crystal packing. More than 40% of the contribution arises from intermolecular C-H⋅⋅⋅C(π) contacts. In both compounds, the relative contribution of these contacts is comparable, indicating that the positional isomeric effects are marginal. The structures in which these isomers are arranged in the solid state are very similar, and the lattice energies are also comparable between the isomers. The Coulomb-London-Pauli-PIXEL (CLP-PIXEL) energy analysis identified the energetically significant dimers. The strength of the intra- and intermolecular interactions was evaluated using the quantum theory of atoms in molecules approach. The UV-Vis absorbance in three different solvents (chloroform, ethanol, and ethyl acetate) for isomers 1 and 2 are very similar. This result is in good agreement with the time-dependent density-functional theory (TD-DFT) calculations.

Thermodynamic and Computational (DFT) Study of Non-Covalent Interaction Mechanisms of Charge Transfer Complex of Linagliptin with 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and Chloranilic acid (CHA)

This study describes the non-covalent interactions of the charge transfer complex (CT), which was responsible for the synthesis of Linagliptin (LNG) with 2,3-Dichloro-5,6-Dicyano-1,4-benzoquinone (DDQ), or with Chloranilic acid (CHA) complexes in acetonitrile (MeCN) at temperatures of (25 ± 2 °C). Then, a UV–Vis spectrophotometer was utilized to identify Linagliptin (LNG) from these complexes. For the quantitative measurement of Linagliptin in bulk form, UV–Vis techniques have been developed and validated in accordance with ICH criteria for several aspects, including selectivity, linearity, accuracy, precision, LOD, LOQ, and robustness. The optimization of the complex synthesis was based on solvent polarization; the ratio of molecules in complexes; the association constant; and Gibbs energy (ΔG°). The experimental work is supported by the computational investigation of the complexes utilizing density functional theory as well as (QTAIM); (NCI) index; and (RDG). According to the optimized conditions, Beer’s law was observed between 2.5–100 and 5–100 µM with correlation coefficients of 1.9997 and 1.9998 for LGN-DDQ and LGN-CHA complexes, respectively. For LGN-DDQ and LGN-CHA complexes, the LOD and LOQ were (1.0844 and 1.4406 μM) and (3.2861 and 4.3655 μM), respectively. The approach was successfully used to measure LGN in its bulk form with high precision and accuracy.

Solution and Solid-State Photophysical Properties of Positional Isomeric Acrylonitrile Derivatives with Core Pyridine and Phenyl Moieties: Experimental and DFT Studies

The compounds I (Z)-2-(phenyl)-3-(2,4,5-trimethoxyphenyl)acrylonitrile with one side (2,4,5-MeO-), one symmetrical (2Z,2'Z)-2,2'-(1,4-phenylene)bis(3-(2,4,5-trimethoxyphenyl)acrylonitrile), II (both sides with (2,4,5-MeO-), and three positional isomers with pyridine (Z)-2-(pyridin-2- 3, or 4-yl)-3-(2,4,5-trimethoxyphenyl)acrylonitrile, III-V were synthetized and characterized by UV-Vis, fluorescence, IR, H1-NMR, and EI mass spectrometry as well as single crystal X-ray diffraction (SCXRD). The optical properties were strongly influenced by the solvent (hyperchromic and hypochromic shift), which were compared with the solid state. According to the solvatochromism theory, the excited-state (μe) and ground-state (μg) dipole moments were calculated based on the variation of Stokes shift with the solvent's relative permittivity, refractive index, and polarity parameters. SCXRD analyses revealed that the compounds I and II crystallized in the monoclinic system with the space group, P21/n and P21/c, respectively, and with Z = 4 and 2. III, IV, and V crystallized in space groups: orthorhombic, Pbca; triclinic, P-1; and monoclinic, P21 with Z = 1, 2, and 2, respectively. The intermolecular interactions for compounds I-V were investigated using the CCDC Mercury software and their energies were quantified using PIXEL. The density of states (DOS), molecular electrostatic potential surfaces (MEPS), and natural bond orbitals (NBO) of the compounds were determined to evaluate the photophysical properties.

Role of hydrogen bonds and weak non-covalent interactions in the supramolecular assembly of 9-hydroxyeucaliptol: crystal structure, Hirshfeld surface analysis, and DFT calculations

The compound 1,3,3-trimethyl-2-oxabicyclo[2.2.2]octan-9-ol (9-hydroxyeucaliptol) has been prepared and characterized by single-crystal X-ray diffraction analysis, infrared, Raman, and UV-visible spectroscopies. The molecular geometry of the title compound was also investigated theoretically by density functional theory (DFT) calculations to compare with the experimental data. The substance crystallizes in the trigonal crystal system, space group P3₂ with Z = 9 molecules per unit cell. There are three independent molecules in the crystal asymmetric unit having the same chirality and showing some differences in the orientation of the H-atom of the hydroxyl group. The crystal structure of 9-hydroxyeucaliptol shows that the hydroxyl group presents an anti-conformation with respect to the O-atom of the ether group. The crystal packing of 9-hydroxyeucaliptol is stabilized by intermolecular O-H···O hydrogen bonds involving the hydroxyl groups of different molecules, which play a decisive role in the preferred conformation adopted in solid state. The intermolecular interactions observed in solid state were also studied through the Hirshfeld surface analysis and quantum theory of atoms in molecules (QTAIM) approaches. Energy framework calculations have also been carried out to analyze and visualize the topology of the supramolecular assembly, and the results indicate a significant contribution from electrostatic energy over the dispersion.

Quantitative analysis of hydrogen and chalcogen bonds in two pyrimidine-5-carbonitrile derivatives, potential DHFR inhibitors: an integrated crystallographic and theoretical study

Two potential bioactive pyrimidine-5-carbonitrile derivatives have been synthesized and characterized by spectroscopic techniques (1H and 13C-NMR) and the three dimensional structures were elucidated by single crystal X-ray diffraction at low temperature (160 K). In both structures, the molecular conformation is locked by an intramolecular C-H⋯C interaction involving the cyano and CH of the thiophene and phenyl rings. The intermolecular interactions were analyzed in a qualitative manner based on the Hirshfeld surface and 2D-fingerprint plots. The results suggest that the phenyl and thiophene moieties have an effect on the crystal packing. For instance, the chalcogen bonds are only preferred in the thiophene derivative. However, both structures uses a common N-H⋯O hydrogen bond motif. Moreover, the structures of 1 and 2 display 1D isostructurality and molecular chains stabilize by intermolecular N-H⋯O and N-H⋯N hydrogen bonds. The nature and extent of different non-covalent interactions were further characterized by the topological parameters derived from the quantum theory of atoms-in-molecules approach. This analysis indicates that apart from N-H⋯O hydrogen bonds, other non-covalent interactions are closed-shell in nature. A strong and linear N-H⋯O hydrogen bond shows intermediate bonding character between shared and closed-shell interactions. The molecular docking analysis suggests that both compounds display potential inhibitory effect against the dihydrofolate reductase (DHFR) enzyme from humans and Staphylococcus aureus.

Quantitative analysis of intermolecular interactions in cocrystals and a pair of polymorphous cocrystal hydrates from 1,4-dihydroquinoxaline-2,3-dione and 1H-benzo[d]imidazol-2(3H)-one with 2,5-dihydroxy-1,4-benzoquinones: a combined X-ray structural and theoretical analysis

Study and quantification of intermolecular interactions in five cocrystals and cocrystals hydrates by PIXEL, DFT, Hirshfeld surface and QTAIM calculations.

Qualitative as well as quantitative analysis of interactions present in chlorine and bromine substituted aromatic organic crystals: A DFT linked Crystal Explorer study

The effect of noncovalent interactions in shaping a crystal structure is explored qualitatively as well as quantitatively in a DFT linked Crystal Explorer (CE) study of nine different Chlorine and Bromine substituted benzene derivatives. The qualitative approach to analyze interactions is based on Hirshfeld surface that locates electronic charge distribution on the surface, quantitative estimation is obtained by linking DFT computations withCE.In the halogen substituted benzene derivatives considered here, in addition to conventional hydrogen and halogen bonding other interactions such as those between Chlorine-Hydrogen, Bromine-Hydrogen, Bromine-Oxygen have been deciphered. The molecular crystal structure of a variety of halogen substituted aromatic molecules has been rationalized and attributed to specific interactions.

Solvatochromism and pH effect on the emission of a triphenylimidazole-phenylacrylonitrile derivative: experimental and DFT studies

In this work, a study of the photophysical properties in different solvents and at different pH values of a luminogenic compound with a donor-π-acceptor (D-π-A) structure was carried out. The compound (Z)-3-(4-(4,5-diphenyl-1H-imidazol-2-yl)phenyl)-2-phenylacrylonitrile (2) was synthesized and characterized by SCXRD, FT-IR, 1H NMR, 13C NMR, EIMS, UV-Vis absorption and fluorescence. The SCXRD characterization reveals a monoclinic system, P21/c, with Z = 4 and an imidazole core having hydrogen bonding with respect to water molecules present in the asymmetric unit. It leads to a strong π-π-interaction in the solid state. The fluorescence λ max emission of the powder and thin film was observed at 563 nm and 540 nm respectively. Several degrees of positive solvatochromic fluorescence were observed due to different molecular conformations in various solvents. When the pH of the compound was changed with HCl or NaOH, a shift in the wavelength of emission was observed in a reversible manner. At pH 2, the λ max of emission was at 541 nm whereas at pH 14 there were two emissions at 561 nm and 671 nm. Due to their good emission in the solid state, compound 2 was tested as an emitting layer in OLEDs; the devices showed an acceptable performance with a luminance average of 450 cd m-2. The band gap was analyzed by optical absorption, cyclic voltammetry measurement and DFT calculations.

Qu-anti-tative analysis of weak non-covalent inter-actions in (Z)-3-(4-chloro-phen-yl)-2-phenyl-acrylo-nitrile: insights from PIXEL and Hirshfeld surface analysis

In the solid state, the title compound, C15H10ClN, is disordered over two orientations with a refined occupancy ratio of 0.86 (2):0.14 (2). The crystal structure is mainly stabilized by inter-molecular C-H⋯N and C-H⋯Cl hydrogen bonds, and C-H⋯π inter-actions. The mol-ecules pack in columns and adjacent columns are linked by weak C-H⋯Cl inter-actions. The PIXEL energy analysis suggests that the inter-molecular C-H⋯π inter-actions form a strong dimer in the major component. Hirshfeld analysis reveals that H⋯C, H⋯H, H⋯Cl and H⋯N contacts are the most important contributors to the crystal packing.

Experimental and Theoretical Insights into the Optical Properties and Intermolecular Interactions in Push-Pull Bromide Salts

Experimental and theoretical insights into the nature of intermolecular interactions and their effect on optical properties of 1-allyl-4-(1-cyano-2-(4-dialkylaminophenyl)vinyl)pyridin-1-ium bromide salts (I and II) are reported. A comparison of optical properties in solution and in the solid-state of the salts (I and II) with their precursors (Ia and IIa) is made. The experimental absorption maxima (λmax) in CHCl3 is at 528 nm for I and at 542 nm for II, and a strong bathochromic shift of ∼110 nm is observed for salts I and II compared with their precursors. The absorption bands in solid-state at ∼627 nm for I and at ∼615 nm for II that are assigned to charge transfer (CT) effect. The optical properties and single crystal structural features of I and II are explored by experimental and computational tools. The calculated λmax and the CT are in good agreement with the experimental results. The intermolecular interactions existing in the crystal structures and their energies are quantified for various dimers by PIXEL, QTAIM and DFT approaches. Three types of interactions, (i) the cation⋅⋅⋅cation interactions, (ii) cation⋅⋅⋅anion interactions and (iii) anion⋅⋅⋅anion interactions are observed. The cationic moiety is mainly destabilized by C-H⋅⋅⋅N/π and π⋅⋅⋅π interactions whereas the cation and anion moiety is predominantly stabilized by strong C-H⋅⋅⋅Br- interactions in both structures. The existence of charge transfer between cation and anion moieties in these structures is established through NBO analysis.

Film morphology of acrylonitrile materials deposited by a solution process and vacuum evaporation. Supramolecular interactions, optoelectronic properties and an approximation by computational calculations

α,β-Unsaturated acrylonitrile compounds with a pyridine scaffold are fluorescent materials with efficient solid-state emission and electroluminescence properties.

On the influence of small chemical changes upon the supramolecular association in substituted 2-(phenoxy)-1,4-naphthoquinones

X-ray crystallography reveals the common feature of the title compounds is a 1,4-naphthoquinone ring system with a substituted phenoxy residue adjacent to an oxo-group to give 1 (H), 2 (3-Br), 3 (3-CF3), 4 (4-CN) and 5 (4-NO2). To a first approximation the fused ring system along with the two oxo substituents is planar with the major difference between the molecules relating to the relative orientations of the pendant phenoxy residues: dihedral angles range from 56.56(4)° (3) to 87.52(10)° (2). The presence of intermolecular C–H···O interactions is the common feature of the supramolecular association in the crystals of 1–5. In each of 1 and 5, these extend in three-dimensions but, only to supramolecular dimers in 4, chains in 2 and layers in 3. Each crystal also features C=O···π interactions, pointing to the importance of these points of contact in this series di-oxocompounds. In 2, these, along with C–Br···π interactions lead to a three-dimensional architecture. For 3, the C=O···π and π···π interactions occur within the layers which stack without directional interactions between them. In 4, C–H···O and C=O···π interactions combine to give a supramolecular layer, which also stack without directional interactions in the inter-layer region. Further analysis of the molecular packing was conducted by a Hirshfeld surface analysis (HSA). This points to the significant role of H···H, C···H/H···C and O···H/H···O contacts in the packing of 1. Notably different roles for these contacts are found in the other crystals correlating with the participation of the respective substituents in the molecular packing. The HSA suggests the association between layers in 3 (weak F···F and H···F interactions) and 4 (weak H···N interactions) is contributed by the phenoxy-substituents.