Interactions In Molecular Crystals Research Articles

Mechanoresponsive Flexible Crystals.

Flexible crystals have gained significant attention owing to their remarkable pliability, plasticity, and adaptability, making them highly popular in various research and application fields. The main challenges in developing flexible crystals lie in the rational design, preparation, and performance optimization of such crystals. Therefore, a comprehensive understanding of the fundamental origins of crystal flexibility is crucial for establishing evaluation criteria and design principles. This Perspective offers a retrospective analysis of the development of flexible crystals over the past two decades. It summarizes the elastic standards and possible plastic bending mechanisms tailored to diverse flexible crystals and analyzes the assessment of their theoretical basis and applicability. Meanwhile, the compatibility between crystal elasticity and plasticity has been discussed, unveiling the immense prospects of elastic/plastic crystals for applications in biomedicine, flexible electronic devices, and flexible optics. Furthermore, this Perspective presents state-of-the-art experimental avenues and analysis methods for investigating molecular interactions in molecular crystals, which is vital for the future exploration of the mechanisms of crystal flexibility.

Quantification of the thermodynamic effects of the low-spin - high-spin interaction in molecular crystals of a mononuclear iron(II) spin crossover complex.

A method is proposed to estimate the energetic and entropic effects of spins of neighbouring molecules on the spin transition of a mononuclear spin crossover (SCO) complex in a molecular crystal. Density functional theory (DFT) methods have been used to model the SCO material [FeII(Lnpdtz)2(NCS)2] (Lnpdtz = 2-naphthyl-5-pyridyl-1,2,4-thiadiazole) exhibiting numerous π-π interactions using a 2D arrangement of 15 molecules. The modelling considers only the effects in the crystallographical ac plane with a particularly pronounced stacking but paves the way for future work with 3D arrangements which are computational much more costly. It involves the optimisation and normal mode calculation of the molecules in a rigid matrix of both low-spin (LS) and high-spin (HS) neighbours. This procedure has been used to calculate the previously defined cooperativity parameter Hcoop (S. Rackwitz, W. Klopper, V. Schünemann and J. A. Wolny, Phys. Chem. Chem. Phys., 2013, 15, 15450). For [FeII(Lnpdtz)2(NCS)] we obtain Hcoop = 11 kJ mol-1, a value which is comparable to those found for 3D polynuclear spin crossover materials. A normal mode analysis of the optimised centrally located molecule indicates that the vibrational entropy of the spin transition is somewhat higher (5 J K-1 mol-1) for the LS to HS transition in the LS matrix than in the HS one. The calculations show that the interactions with the neighbours influence the low-frequency modes with wave numbers <65-70 cm-1. These cause the main difference in the vibrational entropy of the spin transition for the vicinity of high- and low-spin molecules. Furthermore, a deformation of the coordination sphere of the central molecule is observed when the spins of the surrounding centres are switched. This deformation is accompanied by a change in the equatorial Fe-N bond lengths.

A transferable quantum mechanical energy model for intermolecular interactions using a single empirical parameter.

The calculation of intermolecular interactions in molecular crystals using model energies provides a unified route to understanding the complex interplay of driving forces in crystallization, elastic properties and more. Presented here is a new single-parameter interaction energy model (CE-1p), extending the previous CrystalExplorer energy model and calibrated using density functional theory (DFT) calculations at the ωB97M-V/def2-QZVP level over 1157 intermolecular interactions from 147 crystal structures. The new model incorporates an improved treatment of dispersion interactions and polarizabilities using the exchange-hole dipole model (XDM), along with the use of effective core potentials (ECPs), facilitating application to molecules containing elements across the periodic table (from H to Rn). This new model is validated against high-level reference data with outstanding performance, comparable to state-of-the-art DFT methods for molecular crystal lattice energies over the X23 set (mean absolute deviation 3.6 kJ mol-1) and for intermolecular interactions in the S66x8 benchmark set (root mean-square deviation 3.3 kJ mol-1). The performance of this model is further examined compared to the GFN2-xTB tight-binding model, providing recommendations for the evaluation of intermolecular interactions in molecular crystal systems.

Structural and computational insights into two trimethylenedipyridine co-crystals: Inputs from X-ray diffraction, Hirshfeld surface, PIXEL, QTAIM and NCI plots

Two trimethylenedipyridine co-crystals, [(TMDP)·(H2OBA)] (1) and [(TMDP)·(SUC)] (2) [TMDP = 4, 4′-trimethylenedipyridine, H2OBA = 4,4′-oxybis(benzoic acid), and SUC = succinic acid) were designed, synthesized and their single crystals were grown by slow evaporation technique. The grown crystals were characterized by elemental analysis and UV–Vis spectroscopic technique, and the structures of the grown crystals were elucidated using single-crystal X-ray diffraction analysis. Supramolecular assemblies of co-crystal (1) are stabilized through several intermolecular hydrogen bonds such as O‒H···N, C‒H···O, C‒H···π, as well as π···π interactions whereas for co-crystal (2) only intramolecular hydrogen bonding interaction, O‒H···N is responsible for stabilization of supramolecular network. Hirshfeld surfaces were used to gain additional insight into non-covalent interactions in molecular crystals, and 2D fingerprint plots provided a quantitative analysis of different non-covalent interactions in the crystal structures. The interaction energies of the molecular pairs, as well as the lattice energies of the crystal structures, have been studied using the PIXEL method. The nature and strength of the non-covalent interactions at their (3, –1) bond critical points (BCPs) have been explored using Bader's quantum theory of “Atoms in Molecules” (QTAIM). The non-covalent interactions were further characterized through the NCI plots.

Concerning virial-based estimations of strength of bonding intermolecular interactions in molecular crystals and supramolecular complexes

It is shown that the electronic virial-based correlation should be used to estimate bonding contributions to the rigidity of molecular vibrations in crystals.

Ferroelectricity and Phase Change Memory of Bis(tetradecylamide)-Substituted Benzene Derivatives

Interplay between intermolecular interactions including hydrogen bonding, halogen–halogen, and van der Waals interactions in molecular crystals leads to diverse phase transition behaviors and physical properties. Bis(tetradecylamide)-substituted benzene derivatives, terephthalamide (C14-TPA), isophthalamide (C14-IPA), and phthalamide (C14-PA), were examined, and the electric field–polarization curves of the former two crystals indicated ferroelectric hysteresis behavior in high-temperature solid phases. C14-XIPA derivatives where X = CH3, Cl, Br, or I at the 5-position of the IPA molecule were synthesized, and the effects of substituent X on the molecular assembly structure and physical properties were investigated. H- and CH3-substituted C14-IPA and C14-MeIPA formed a crystalline phase in which intermolecular amide-type N–H···O═ hydrogen-bonding interactions were dominant, whereas halogen-substituted C14-XIPAs formed a metastable glass phase upon cooling from the isotropic liquid. The formation of the glass phase is associated with energy competition between hydrogen bonding, halogen–halogen, and van der Waals interactions among the −CONH–, −X, and −CnH2n+1 units. The glass-crystal phase transition of C14-XIPAs (X = Cl, Br, or I) changes the refractive index under polarized optical microscopic observation, which can be utilized for phase-change memory.

Structural Elucidation, Hirshfeld Surface, FMO, Molecular electrostatic potential (MEP) and Fukui function analyses of Quinoline based Schiff base Compound

A quinoline-derived Schiff base ligand, namely 2,5-Dimethyl-N1,N4-bis((quinoline-4-yl)-methylene)benzene-1,4-diamine 1 was characterized by single crystal X-ray structural studies that included a thorough examination of visualizing and investigating intermolecular interactions in molecular crystals via the Hirshfeld surface. The crystal packing of 1 displays intermolecular π∙∙∙π stacking interactions, resulting in a one-dimensional array. The major role of π∙∙∙π stacking interactions in stabilizing the crystal is also supported by the pre-eminence of dispersion energy over the other components in interaction energy calculation and energy framework analysis. The electronic structure of the ligand computed at B3LYP/6-311++G(d,p) level shows a good correlation with the experimentally obtained structure. Additionally, the Fukui function is calculated to identify the electrophilic and nucleophilic active sites in the molecule.

Boosting ultralong organic phosphorescence performance by synergistic heavy-atom effect and multiple intermolecular interactions in molecular crystal

A feasible strategy through synergistic heavy-atom effect and methylation approach to suppress non-radiative pathway and accelerate ISC processes is demonstrated. As a result, efficient and long-lived phosphorescence is realized.

Liquid Phase Exfoliation of Rubrene Single Crystals into Nanorods and Nanobelts.

Liquid phase exfoliation (LPE) is a popular method to create dispersions of two-dimensional nanosheets from layered inorganic van der Waals crystals. Here, it is applied to orthorhombic and triclinic single crystals of the organic semiconductor rubrene with only noncovalent interactions (mainly π-π) between the molecules. Distinct nanorods and nanobelts of rubrene are formed, stabilized against aggregation in aqueous sodium cholate solution, and isolated by liquid cascade centrifugation. Selected-area electron diffraction and Raman spectroscopy confirm the crystallinity of the rubrene nanorods and nanobelts while the optical properties (absorbance, photoluminescence) of the dispersions are similar to rubrene solutions due to their randomized orientations. The formation of these stable crystalline rubrene nanostructures with only a few molecular layers by LPE confirms that noncovalent interactions in molecular crystals can be strong enough to enable mechanical exfoliation similar to inorganic layered materials.

Ruthenium (II) β-diketimine as hydroamination catalyst, crystal structure and DFT computations

A new half-sandwich ruthenium (II) complex containing β-diketiminate ligand has been synthesized and used for hydroamination of acrylonitrile with aromatic and aliphatic amines. The catalytic activity of prepared complex was compared with a series of ruthenium complexes of β-diketiminate ligands, and the effect of electronic and steric properties of these ligands on catalytic activity of their complexes was investigated. Replacement of H atom in α position of β-diketiminate with (CF3) as an electron-withdrawing group leads to decreasing the reaction yield, and on the other hand, electron-donating group (CH3) has the opposite effect. In addition, crystal structure of [Ru(p-cymen)Cl(LH,Cl)] was determined by single X-ray crystallography. Hirshfeld surface analysis has been performed to determine the dominate interactions in molecular crystal. Furthermore, density functional, QTAIM and energy calculations have been carried out, to get the detailed insight into electronic and bonding characteristics of titled compound.

Supramolecular architectures sustained by delocalised C–I⋯π(arene) interactions in molecular crystals and the propensity of their formation

A survey of delocalised C–I⋯π(chelate ring) interactions is presented.

Non-Covalent Interactions in Molecular Crystals: Exploring the Accuracy of the Exchange-Hole Dipole Moment Model with Local Orbitals.

We present the first implementation of the exchange-hole dipole moment (XDM) model in combination with a numerical finite-support local orbital method (the SIESTA method) for the modeling of non-covalent interactions in periodic solids. The XDM model is parametrized for both the B86bPBE and PBE functionals using double-ζ- and triple-ζ-quality basis sets (DZP and TZP). The use of finite-support local orbitals is shown to have minimal impact on the computed dispersion coefficients for van der Waals molecular dimers and small molecular solids. However, the quality of the basis set affects the accuracy of calculated dimer binding energies and molecular-crystal lattice energies quite significantly; the size of the counterpoise correction indicates that this is caused by basis-set incompleteness error. In the case of the DZP basis set, its performance for weakly bound gas-phase dimers is similar to that of a double-ζ Gaussian basis set without diffuse functions. The new XDM implementation was tested on graphite and phosphorene exfoliation, and on the X23 benchmark set of molecular-crystal lattice energies. Our results indicate that lattice energies similar to plane-wave calculations can be obtained only if the counterpoise correction is applied. Alternatively, the calculated equilibrium geometries are reasonably close to the plane-wave equivalents, and composite approaches in which a single-point plane-wave calculation is used at the XDM/DZP equilibrium geometry yield good accuracy at a significantly lower computational cost.

Diaquabis(5-methoxyindole-2-carboxylato)bis(3-picoline)nickel(II) Complex: Synthesis, Characterization, XRD, TGA, DFT and HSA

A new complex of diaquabis(5-methoxyindole-2-carboxylato)bis(3-picoline)nickel(II) (Ni(5-MeOI2CA)2(3-pic)2(H2O)2), was synthesized for the first time and characterized by elemental analysis, FT-IR and electronic spectroscopy (UV-Vis) and single-crystal X-ray diffraction (XRD) techniques. The thermal degradation of the Ni(II) complex was investigated using thermogravimetric and differential thermal analyses techniques in oxygen atmosphere. The molecular structure of the complex was determined by single crystal X-ray diffraction technique. Hirshfeld surface analysis (HSA) investigated the packing modes and intermolecular interactions in molecular crystals, as they provide a visual picture of intermolecular interactions. In addition, all computational studies at B3LYP/6-311++G(d,p) were carried out for theoretical characterization of Ni(II) complex. The optimized geometry results, which were well represented the X-ray data, were shown that the chosen of DFT/B3LYP/6-311++G(d,p) was a successful choice for title compound. After a successful optimization, FMOs, chemical activity, non-linear optical properties (NLO), molecular electrostatic potential (MEP), Mulliken population (MPA), natural population analyses (NPA), Fukui function analysis (FFA) and natural bond orbital analysis (NBO), which could not obtained by experimental ways, were calculated and investigated. The computed of net charges and chemical activity studies which helped to identifying the electrophilic/nucleophilic nature.

Correlation of Intermolecular Acyl Transfer Reactivity with Noncovalent Lattice Interactions in Molecular Crystals: Toward Prediction of Reactivity of Organic Molecules in the Solid State.

Intermolecular acyl transfer reactivity in several molecular crystals was studied, and the outcome of the reactivity was analyzed in the light of structural information obtained from the crystals of the reactants. Minor changes in the molecular structure resulted in significant variations in the noncovalent interactions and packing of molecules in the crystal lattice, which drastically affected the facility of the intermolecular acyl transfer reactivity in these crystals. Analysis of the reactivity vs crystal structure data revealed dependence of the reactivity on electrophile···nucleophile interactions and C-H···π interactions between the reacting molecules. The presence of these noncovalent interactions augmented the acyl transfer reactivity, while their absence hindered the reactivity of the molecules in the crystal. The validity of these correlations allows the prediction of intermolecular acyl transfer reactivity in crystals and co-crystals of unknown reactivity. This crystal structure-reactivity correlation parallels the molecular structure-reactivity correlation in solution-state reactions, widely accepted as organic functional group transformations, and sets the stage for the development of a similar approach for reactions in the solid state.

Intermolecular interactions in molecular crystals and their effect on thermally activated delayed fluorescence of helicene-based emitters

In crystals of donor–acceptor helicene molecules, thermally activated delayed fluorescence (TADF) is strongly enhanced by the presence of occluded hexane molecules.

Synthesis, Hirshfeld surface analysis, laser damage threshold, third-order nonlinear optical property and DFT computation studies of Dichlorobis(DL-valine)zinc(II): A spectroscopic approach

The organometallic crystal of Dichlorobis(DL-valine)zinc(II) was grown by solution growth method. The computed structural geometry, vibrational wavenumbers and UV–visible spectra were compared with experimental results. Hirshfeld surface map was used to locate electron density and the fingerprint plots percentages are responsible for the stabilization of intermolecular interactions in molecular crystal. The second-order hyperpolarizability value of the molecule was also calculated at density functional theory method. The surface resistance and third-order nonlinear optical property of the crystal were studied by laser induced surface damage threshold and Z-scan techniques, respectively using Nd:YAG laser with wavelength 532 nm. The open aperture result exhibits the reverse saturation absorption, which indicate that this material has potential candidate for optical limiting and optoelectronic applications.

Intermolecular vibrational modes and H-bond interactions in crystalline urea investigated by terahertz spectroscopy and theoretical calculation

The characteristic absorption spectra of crystalline urea in 0.6–1.8 THz region have been measured by terahertz time-domain spectroscopy at room temperature experimentally. Five broad absorption peaks were observed at 0.69, 1.08, 1.27, 1.47 and 1.64 THz respectively. Moreover, density functional theory (DFT) calculation has been performed for the isolated urea molecule, and there is no infrared intensity in the region below 1.8 THz. This means that single molecule calculations are failure to predict the experimental spectra of urea crystals. To simulate these spectra, calculations on a cluster of seven urea molecules using M06-2X and B3LYP-D3 are performed, and we found that M06-2X perform better. The observed THz vibrational modes are assigned to bending and torsional modes related to the intermolecular H-bond interactions with the help of potential energy distribution (PED) method. Using the reduced-density-gradient (RDG) analysis, the positions and types of intermolecular H-bond interactions in urea crystals are visualized. Therefore, we can confirm that terahertz spectroscopy can be used as an effective means to detect intermolecular H-bond interactions in molecular crystals.

CrystalExplorer model energies and energy frameworks: extension to metal coordination compounds, organic salts, solvates and open-shell systems.

The application domain of accurate and efficient CE-B3LYP and CE-HF model energies for intermolecular interactions in molecular crystals is extended by calibration against density functional results for 1794 molecule/ion pairs extracted from 171 crystal structures. The mean absolute deviation of CE-B3LYP model energies from DFT values is a modest 2.4 kJ mol-1 for pairwise energies that span a range of 3.75 MJ mol-1. The new sets of scale factors determined by fitting to counterpoise-corrected DFT calculations result in minimal changes from previous energy values. Coupled with the use of separate polarizabilities for interactions involving monatomic ions, these model energies can now be applied with confidence to a vast number of molecular crystals. Energy frameworks have been enhanced to represent the destabilizing interactions that are important for molecules with large dipole moments and organic salts. Applications to a variety of molecular crystals are presented in detail to highlight the utility and promise of these tools.

Intermolecular interactions in molecular crystals: what's in a name?

Structure-property relationships are the key to modern crystal engineering, and for molecular crystals this requires both a thorough understanding of intermolecular interactions, and the subsequent use of this to create solids with desired properties. There has been a rapid increase in publications aimed at furthering this understanding, especially the importance of non-canonical interactions such as halogen, chalcogen, pnicogen, and tetrel bonds. Here we show how all of these interactions - and hydrogen bonds - can be readily understood through their common origin in the redistribution of electron density that results from chemical bonding. This redistribution is directly linked to the molecular electrostatic potential, to qualitative concepts such as electrostatic complementarity, and to the calculation of quantitative intermolecular interaction energies. Visualization of these energies, along with their electrostatic and dispersion components, sheds light on the architecture of molecular crystals, in turn providing a link to actual crystal properties.

Nonlinear Electromagnetic Interactions in Energetic Materials

We study the scattering of electromagnetic waves in anisotropic energetic materials. Nonlinear light-matter interactions in molecular crystals result in frequency-conversion and polarization changes. Applied electromagnetic fields of moderate intensity can induce these nonlinear effects without triggering chemical decomposition, offering a mechanism for non-ionizing identification of explosives. We use molecular dynamics simulations to compute such two-dimensional Raman spectra in the terahertz range for planar slabs made of PETN and ammonium nitrate. We discuss third-harmonic generation and polarization-conversion processes in such materials. These observed far-field spectral features of the reflected or transmitted light may serve as an alternative tool for stand-off explosive detection.