The interplay between hydrogen bonds and stacking/T-type interactions in molecular cocrystals.

Supramolecular synthon and hydrogen bond pairing approaches have influenced the understanding of cocrystal formation for decades, but are hydrogen bonds really the dominant interaction in cocrystals? To investigate this, an extensive analysis of 1:1 two-component cocrystals in the Cambridge Structural Database was undertaken, revealing that stacking and T-type interactions are just as, if not more important than hydrogen bonds in molecular cocrystals. A total of 84% of the most common coformers in the dataset are aromatic. When analysing cocrystal dimers, only 20% consist of solely strong hydrogen bonds, with over 50% of contacts involving stacking and T-type interactions.

A solid solution to computational challenges presented by crystal structures exhibiting disorder.

Crystal structues exhibiting disorder still present a barrier for many computational methods. Dittrich et al. [(2024).

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).

Functionalised organometallic photoswitches containing dihydropyrene units.

Functionalising organic molecular photoswitches with metal complexes has been shown to alter and enhance their switching states. These organometallic photoswitches provide a promising basis for novel smart molecular materials and molecular electronic devices. We have detailed the synthesis and characterisation of mono- and bimetallic half-sandwich ruthenium and iron complexes functionalised with alkynyl dihydropyrenes (DHP).

Multistate Switching of Some Ruthenium Alkynyl and Vinyl Spiropyran Complexes.

To study the switching properties of photochromes, we undertook the synthesis and characterization of several ruthenium organometallic complexes of the type [Ru(Cp*)(dppe)(C≡C-SP)] or [Ru(CO)(dppe)(PPh)Cl(CH═CH-SP)], where SP = spiropyran. The spectroscopic and electrochemical properties of the complexes were determined by careful cyclic voltammetric and spectroelectrochemical experiments. Whereas the mononuclear alkynyl ruthenium complexes undergo one-electron oxidations localized over the metal alkynyl moiety, the oxidation of the mononuclear vinyl ruthenium complexes is centered on the indoline moiety of the spiropyran.

CrystalClear: an open, modular protocol for predicting molecular crystal growth from solution.

We present a new protocol for the prediction of free energies that determine the growth of sites in molecular crystals for subsequent use in Monte Carlo simulations using tools such as CrystalGrower [Hill , , 2021, , 1126-1146]. Key features of the proposed approach are that it requires minimal input, namely the crystal structure and solvent only, and provides automated, rapid generation of the interaction energies. The constituent components of this protocol, namely interactions between molecules (growth units) in the crystal, solvation contributions and treatment of long-range interactions are described in detail.

2,7- and 4,9-Dialkynyldihydropyrene Molecular Switches: Syntheses, Properties, and Charge Transport in Single-Molecule Junctions.

This paper describes the syntheses of several functionalized dihydropyrene (DHP) molecular switches with different substitution patterns. Regioselective nucleophilic alkylation of a 5-substituted dimethyl isophthalate allowed the development of a workable synthetic protocol for the preparation of 2,7-alkyne-functionalized DHPs. Synthesis of DHPs with surface-anchoring groups in the 2,7- and 4,9-positions is described.

Global Analysis of the Mechanical Properties of Organic Crystals.

Organic crystals, although widely studied, have not been considered nascent candidate materials in engineering design. Here we summarize the mechanical properties of organic crystals that have been reported over the past three decades, and we establish a global mechanical property profile that can be used to predict and identify mechanically robust organic crystals. Being composed of light elements, organic crystals populate a narrow region in the mechanical property-density space between soft, disordered organic materials and stiff, ordered materials.

A Universal Force Field for Materials, Periodic GFN-FF: Implementation and Examination.

In this study, the adaption of the recently published molecular GFN-FF for periodic boundary conditions (pGFN-FF) is described through the use of neighbor lists combined with appropriate charge sums to handle any dimensionality from 1D polymers to 2D surfaces and 3D solids. Numerical integration over the Brillouin zone for the calculation of π bond orders of periodic fragments is also included. Aside from adapting the GFN-FF method to handle periodicity, improvements to the method are proposed in regard to the calculation of topological charges through the inclusion of a screened Coulomb term that leads to more physical charges and avoids a number of pathological cases.

: a program for Hirshfeld surface analysis, visualization and quantitative analysis of molecular crystals.

is a native cross-platform program supported on Windows, MacOS and Linux with the primary function of visualization and investigation of molecular crystal structures, especially through the decorated Hirshfeld surface and its corresponding two-dimensional fingerprint, and through the visualization of void spaces in the crystal via isosurfaces of the promolecule electron density. Over the past decade, significant changes and enhancements have been incorporated into the program, such as the capacity to accurately and quickly calculate and visualize quantitative intermolecular interactions and, perhaps most importantly, the ability to interface with the and programs to calculate quantum-mechanical properties of molecules. The current version, , incorporates these and other changes, and the software can be downloaded and used free of charge for academic research.

Evaluation of density functional theory for a large and diverse set of organic and inorganic equilibrium structures.

Density functional theory (DFT) has been extensively benchmarked for energetic properties; however, less attention has been given to equilibrium structures and the effect of using a certain DFT geometry on subsequent energetic properties. We evaluate the performance of 52 contemporary DFT methods for obtaining the structures of 122 species in the W4-11-GEOM database. This dataset includes a total of 246 unique bonds: 117 H─X, 65 X─Y, 49 X═Y, and 15 XY bonds (where X and Y are first- and second-row atoms) and 133 key bond angles: 96 X-Y-H, 22 X-Y-Z, and 15 H-X-H angles.

An Expandable Hydrogen-Bonded Organic Framework Characterized by Three-Dimensional Electron Diffraction.

A molecular crystal of a 2-D hydrogen-bonded organic framework (HOF) undergoes an unusual structural transformation after solvent removal from the crystal pores during activation. The conformationally flexible host molecule, , adapts its molecular conformation during activation to initiate a framework expansion. The microcrystalline activated phase was characterized by three-dimensional electron diffraction (3D ED), which revealed that uses out-of-plane anthracene units as adaptive structural anchors.

Mining predicted crystal structure landscapes with high throughput crystallisation: old molecules, new insights.

Organic molecules tend to close pack to form dense structures when they are crystallised from organic solvents. Porous molecular crystals defy this rule: they contain open space, which is typically stabilised by inclusion of solvent in the interconnected pores during crystallisation. The design and discovery of such structures is often challenging and time consuming, in part because it is difficult to predict solvent effects on crystal form stability.

Bridging Crystal Engineering and Drug Discovery by Utilizing Intermolecular Interactions and Molecular Shapes in Crystals.

Most structure-based drug discovery methods utilize crystal structures of receptor proteins. Crystal engineering, on the other hand, utilizes the wealth of chemical information inherent in small-molecule crystal structures in the Cambridge Structural Database (CSD). We show that the interaction surfaces and shapes of molecules in experimentally determined small-molecule crystal structures can serve as effective tools in drug discovery.

Accurate Lattice Energies for Molecular Crystals from Experimental Crystal Structures.

Using four different benchmark sets of molecular crystals, we establish the level of confidence for lattice energies estimated using CE-B3LYP model energies and experimental crystal structures. [ IUCrJ 2017 , 4 , 575 - 587 10.1107/S205225251700848X .

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 for pairwise energies that span a range of 3.

Basis set convergence of CCSD(T) equilibrium geometries using a large and diverse set of molecular structures.

We examine the basis set convergence of the CCSD(T) method for obtaining the structures of the 108 neutral first- and second-row species in the W4-11 database (with up to five non-hydrogen atoms). This set includes a total of 181 unique bonds: 75 H-X, 49 X-Y, 43 X=Y, and 14 X≡Y bonds (where X and Y are first- and second-row atoms). As reference values, geometries optimized at the CCSD(T)/aug'-cc-pV(6+d)Z level of theory are used.

High Throughput Profiling of Molecular Shapes in Crystals.

Molecular shape is important in both crystallisation and supramolecular assembly, yet its role is not completely understood. We present a computationally efficient scheme to describe and classify the molecular shapes in crystals. The method involves rotation invariant description of Hirshfeld surfaces in terms of of spherical harmonic functions.