Quantifying Host–Guest Interaction Energies in Clathrates of Dianin’s Compound

The subtle intermolecular host–guest interaction energies have been quantified for 17 different clathrates of the Dianin’s compound. Energy framework analysis of the host structure reveals that, in addition to strong electrostatic forces due to H-bonding, the framework is stabilized by very strong dispersion interactions, resulting in a three-dimensional energy framework. Compared to the host framework, the host–guest interactions are rather weak, and the enclathration only perturbs the host energy framework. Larger guest molecules result in more attractive host–guest interactions, although the shape of the guest molecule is also found to be important. Easy rotation about the <i>c</i>-axis was found for the hexane guest molecule, while the rotation is hindered in the cases of CCl₄, CCl₃CN, and C­(CH₃)₃­CN. For the Dianin clathrates containing the C­(CH₃)₃­CN or the acetone guest species, attractive interaction energies between guest molecules in adjacent cavities suggest short-range ordering of the guest molecules. For the clathrates containing multiple guest molecules per cavity, intermolecular interaction energies were used to determine probable guest molecule configurations. In the same way, simple energy calculations like the ones presented here can help crystallographers solve disordered molecular structures by discarding unstable configurations

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, 575−58710.1107/S205225251700848X.] We conclude that they compare very well with available benchmark estimates derived from sublimation enthalpies, and in many cases they are comparable with, and sometimes better than, more computationally demanding approaches, such as those based on periodic DFT plus dispersion methodologies. The performance over the complete set of 110 crystals indicates a mean absolute deviation from benchmark energies of only 6.6 kJ mol^–1. Applications to polymorphic crystals and larger molecules are also presented and critically discussed. The results highlight the importance of recognizing the consequences of different sets of crystal/molecule geometries when different methodologies are compared, as well as the need for more extensive benchmark sets of crystal structures and associated lattice energies

Accurate and Efficient Model Energies for Exploring Intermolecular Interactions in Molecular Crystals

The energy of interaction between molecules is commonly expressed in terms of four key components: electrostatic, polarization, dispersion, and exchange-repulsion. Using monomer wave functions to obtain accurate estimates of electrostatic, polarization, and repulsion energies along with Grimme’s dispersion corrections, a series of energy models are derived by fitting to dispersion-corrected DFT energies for a large number of molecular pairs extracted from organic and inorganic molecular crystals. The best performing model reproduces B3LYP-D2/6-31G­(d,p) counterpoise-corrected energies with a mean absolute deviation (MAD) of just over 1 kJ mol^–1 but in considerably less computation time. It also performs surprisingly well against benchmark CCSD­(T)/CBS energies, with a MAD of 2.5 kJ mol^–1 for a combined data set including Hobza’s X40, S22, A24, and S66 dimers. Two of these energy models, the most accurate and the fastest, are expected to find widespread application in investigations of molecular crystals

Supramolecular Recognition and Energy Frameworks in Host–Guest Complexes of 18-Crown‑6 and Sulfonamides

Crystalline molecular complexes of 18-crown-6 with three sulfonamide analogues (methane, benzene, and toluene sulfonamides) have been synthesized and characterized. Among these, the 18-crown-6:benzenesulfonamide complex exhibits three crystal forms, including a polymorphic pair. Interaction energy calculations show that the host–guest binding energies in these complexes are very high (∼92–104 kJ·mol^–1). Energy framework analysis identifies the hierarchy of intermolecular interactions and their topology; a trimeric motif formed by two guest molecules and a crown host is found to be a salient structural feature in these complexes. This study establishes the “sulfonamide-crown motif” as a very robust and predictable supramolecular recognition unit

Molecular Imprisonment: Host Response to Guest Location, Orientation, and Dynamics in Clathrates of Dianin’s Compound

Single crystal X-ray diffraction data measured at 100 K for Dianin’s compound (DC) and 18 of its clathrates formed with a wide range of guest molecules provide considerable insight into the way the host adjusts to accommodate guest molecules. Detailed information is also obtained regarding the location, orientation, and dynamics of the guests in the host cavity. Although all unit cells are closely similar in size, the host undergoes significant change in response to the imprisonment of its various guests. Enclathration typically results in a larger cell and cavity volume, but for the small molecules methanol, ethanol, and nitromethane the host actually shrinks significantly around the guests in the cavity. In most clathrates, there is evidence of close contacts between atoms in the guest and the phenol −OH group and/or ring of the DC host. The series of clathrates formed by benzene, toluene, and the halobenzenes show the orientation of the benzene ring to be progressively modifed by the increasing size of the substituent atom or group on the ring in a systematic manner that reflects functional group contributions to van der Waals volumes