Group 16 chalcogens potentially provide Lewis‐acidic σ‐holes, which are able to form attractive supramolecular interactions with electron rich partners through chalcogen bonds. Here, a multifaceted experimental and computational study of a large series of novel chalcogen‐bonded cocrystals, prepared using the principles of crystal engineering, is presented. Single‐crystal X‐ray diffraction studies reveal that dicyanoselenadiazole and dicyanotelluradiazole derivatives work as promising supramolecular synthons with the ability to form double chalcogen bonds with a wide range of electron donors including halides and oxygen‐ and nitrogen‐containing heterocycles. Extensive 77Se and 125Te solid‐state nuclear magnetic resonance spectroscopic investigations of cocrystals establish correlations between the NMR parameters of selenium and tellurium and the local chalcogen bonding geometry. The relationships between the electronic environment of the chalcogen bond and the 77Se and 125Te chemical shift tensors were elucidated through a natural localized molecular orbital density functional theory analysis. This systematic study of chalcogen‐bond‐based crystal engineering lays the foundations for the preparation of the various multicomponent systems and establishes solid‐state NMR protocols to detect these interactions in powdered materials.

Flurorine promotes the electrophilicity of sulfur to the point that chalcogen bond formation affects the crystal packing in the solid.

Modeling indicates the presence of a region of low electronic density (a Bσ-hole^) on group 14 elements, and this offers an explanation for the ability of these elements to act as electrophilic sites and to form attractive interactions with nucleophiles. While many papers have described theoretical investigations of interactions involving carbon and silicon, such investigations of the heavier group 14 elements are relatively scarce. The purpose of this review is to rectify, to some extent, the current lack of experimental data on interactions formed by germanium and tin with nucleophiles. A survey of crystal structures in the Cambridge Structural Database is reported. This survey reveals that close contacts between Ge or Sn and lone-pair-possessing atoms are quite common, they can be either intra-or intermolecular contacts, and they are usually oriented along the extension of the covalent bond formed by the tetrel with the most electron-withdrawing substituent. Several examples are discussed in which germanium and tin atoms bear four carbon residues or in which halogen, oxygen, sulfur, or nitrogen substituents replace one, two, or three of those carbon residues. These close contacts are assumed to be the result of attractive interactions between the involved atoms and afford experimental evidence of the ability of germanium and tin to act as electrophilic sites, namely tetrel bond (TB) donors. This ability can govern the conformations and the packing of organic derivatives in the solid state. TBs can therefore be considered a promising and robust tool for crystal engineering.

Benzylic selenocyanates are versatile anion receptors which operate in solution and in the solid state via chalcogen bonding interactions.

We report a multifaceted experimental and computational study of three self-complementary chalcogen-bond donors as well as a series of seven chalcogen bonded cocrystals.

We introduce methyl, methoxy, and phenyl substituents at the para-, meta-, and ortho-positions of pyridine N-oxide to investigate the effect of chemical substitution on the resulting nine chalcogen-bonded structures formed upon cocrystallization with 3,4dicyano-1,2,5-selenodiazole and 3,4-dicyano-1,2,5-telluradiazole. Single-crystal X-ray diffraction studies reveal the presence of double chalcogen bonding interactions in the cocrystals and demonstrate the impact of the substitution on the geometric features of the chalcogen bonds. 77 Se and 125 Te solid-state NMR spectroscopy is employed to measure selenium and tellurium chemical shift tensors of the products, and various trends are described. The smallest component of the 77 Se chemical shift tensor (δ 33 ) provides the strongest correlation with the chalcogen bond distance. Solution NMR provides qualitative evidence for the persistence of the chalcogen bonds in solution. Finally, 1 J( 77 Se, 14 N) coupling constants in 3,4-dicyano-1,2,5-selenodiazole and its chalcogen-bonded cocrystals are measured after accounting for residual dipolar coupling between 77 Se and 14 N; however, changes in 1 J( 77 Se, 14 N) attributable to chalcogen bonding upon cocrystallization are comparable to the experimental uncertainties. This systematic study of chalcogenbonded cocrystals demonstrates the potential utility of the substitution effect for applications of chalcogen bonds in crystal engineering and demonstrates the value of solid-state NMR in characterizing such systems.

Experimental and theoretical studies of fluoro-, chloro-, and bromo-substituted derivatives of barbituric acid and indandione show that imide protons form short hydrogen bonds and bromine or, to a lesser extent, chlorine atoms form halogen bonds. The imide nitrogen atoms act as effective pnictogen bond donors, while C(sp 2 ) and C(sp 3 ) atoms act as tetrel bond donors; the resulting N•••O and C•••O close interactions are a distinctive feature of crystal lattices in all compounds. Importantly, halogen atoms promote the electrophilicity of C(sp 3 ) sites and favor the formation of C(sp 3 )•••O close contacts. Oxygen atoms of carbonyl groups of barbituric and indandione units or of water molecules function as the interaction acceptor sites: namely, they donate electron density to hydrogen, halogen, nitrogen, and carbon atoms. Modeling of various barbituric acid derivatives indicates that the positive electrostatic potentials of π-holes orthogonal to the C(sp 2 ) carbons and σ-holes on the elongation of quasi-axial F/Cl/Br−C(sp 3 ) bonds merge to produce a single well-defined point of the most positive electrostatic potential on one face of the barbituric acids. This single local maximum of the potential on the molecular face is close to the site occupied by the oxygen forming the C(sp 3 )•••O, and C(sp 2 )•••O, short contacts observed in crystals.

Classical examples of supramolecular recognition units or synthons are the ones formed by hydrogen bonds. Here, we report the ubiquity of a S⋅⋅⋅O chalcogen bonded synthon observed in a series of supramolecular complexes of the amyotrophic lateral sclerosis drug riluzole. Although the potential of higher chalcogens such as Se and Te to form robust and directional chalcogen bonded motifs is known, intermolecular sulfur chalcogen bonding is considered to be weak owing to the lower polarizability of S atoms. Here, the robustness and electronic nature of a S⋅⋅⋅O chalcogen bonding non‐classical synthon, and the origin of its exceptional directionality have been explored. Bond orders of the drug–coformer chalcogen bonding are found to be as high as one third of a single bond, and they are largely ionic in nature. The contribution of the S⋅⋅⋅O chalcogen bonded motifs to the lattice energies of a series of crystals from the Cambridge Structural Database has been analyzed, showing they can be indeed significant, especially in molecules devoid of strong hydrogen bond donor groups.