14. Solute–solvent interactions mediated by main group element(lone-pair)···π(aryl) interactions

Abstract

Since the disclosure of tellurium(II, IV)···π(aryl) interactions in their crystal structures [1], there has been increasing interest in ascertaining the importance of this type of supramolecular synthon, i.e. main group element(lp)···π(arene), in the structural chemistry of main group element chemistry [2][3][4][5][6][7][8][9][10]. It is noted in passing that analogous interactions have been revealed in structural biology and are known to provide important stabilising contacts [11,12]. In molecular structural chemistry, the emphasis thus far has been upon seeking "stand-alone" element(lp)···π(arene) contacts and determining the supramolecular architectures they sustain [2][3][4][5][6][7][8][9][10]. Usually these architectures are zero-and one-dimensional; however, examples of two-and even three-dimensional aggregation patterns are known [9,10]. With the restriction that the element(lp)···π(arene) interaction operates in a given dimension within a crystal, in isolation from other supramolecular synthons, these interactions occur in a maximum of 14% of thallium(I) structures. This is reduced to 9% in bismuth(III) structures and down to a minimum of 2-3% for tin(II) and lead(II) compounds [9,10]. In terms of bonding, it is likely that the lone-pair···π interaction has similar features to halogen bonding [13] in that there is an asymmetric distribution of electron density in the lone-pair of electrons. This leaves an electropositive region at the tip of the lone-pair that interacts with the π electrons of the ring. This electron-deficient region is termed variously a σ-hole or polar cap, and the energy of stabilisation imparted by these interactions is in the region of 10 kJ mol −1 , i.e. similar to that imparted by C-H···π(aryl) interactions. In keeping with the theme of the present volume, "Aspects of Multi-Component Crystals: Synthesis, Concepts and Function", a description herein of the supramolecular architectures sustained by main group element(lp)···π(aryl) interactions is given where the π system is a solvent molecule such as benzene. ProceduresStandard protocols were utilised to identify structures for the current survey [10]. The Cambridge Structural Database (CSD: version 5.37 + 2 updates) [14] was searched using CONQUEST (version 1.18) [15]. There were two key geometric restraints, as illustrated in Figure 14.1a. The first restraint is the distance d, between the metal centre and the ring centroid, labelled Cg, which was set at 4.0 Å. This distance is shown to be suffihttps://doi

Virtual Multicomponent Crystal Screening: Hydrogen Bonding Revisited

“…The physicochemical properties of the majority of existing or newly discovered active pharmaceutical ingredients (APIs) limit the drug development process, primarily due to poor solubility and bioavailability . A crystal engineer aims to design a solid form that is stable under different temperatures and humidity conditions, meets the required solubility, dissolution rate, bioavailability criteria, and also shows proper compressibility and flowability …”