Geminal Charge-Assisted Tetrel Bonds in Bis-Pyridinium Methylene Salts.

C(sp3) atoms are known to act as electrophilic sites in self-assembly processes, and in all cases reported till now, they form only one interaction with nucleophiles; that is, they function as monodentate tetrel bond donors. This manuscript reports experimental (X-ray structural analysis) and theoretical evidence (DFT calculations), proving that the methylene carbon in bis-pyridinium methylene salts establishes two short and directional C(sp3)···anion interactions; that is, they function as bidentate tetrel bond donors.

Anion⋠⋠⋠Anion Coinage Bonds: The Case of Tetrachloridoaurate.

Interactions in crystalline tetrachloridoaurates of acetylcholine and dimethylpropiothetine are characterized by Au⋅⋅⋅Cl and Au⋅⋅⋅O short contacts. The former interactions assemble the AuCl4 - units into supramolecular anionic polymers, while the latter interactions append the acetylcholine and propiothetine units to the polymer. The distorted octahedral geometry of the bonding pattern around the gold center is rationalized on the basis of the anisotropic distribution of the electron density, which enables gold to behave as an electrophile (π-hole coinage-bond donor). Computational studies prove that gold atoms in negatively charged species can function as acceptors of electron density. The attractive nature of the Au⋅⋅⋅Cl/O interactions described here complement the known aurophilic bonds involved in gold-centered interactions.

The diiodomethyl-sulfonyl moiety: an unexplored halogen bond-donor motif.

Herein, we report the crystal structures of the antimicrobial agent diiodomethyl-p-tolylsulfone and of three halogen bonded co-crystals demonstrating that the bioactive moiety -SO2CHI2 can function as a quite effective halogen bond based motif in the solid state and in solution, namely demonstrating that α-iodosulfones may become a new entry in the quite small group of alkyl-iodides functioning as reliable halogen bond-donors.

Close contacts involving germanium and tin in crystal structures: experimental evidence of tetrel bonds.

Modeling indicates the presence of a region of low electronic density (a "σ-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. Graphical abstract Intra- and intermolecular tetrel bonds involving organogermanium and -tin derivatives in crystalline solids.

Halogen bonding in hypervalent iodine and bromine derivatives: halonium salts.

Halogen bonds have been identified in a series of ionic compounds involving bromonium and iodonium cations and several different anions, some also containing hypervalent atoms. The hypervalent bromine and iodine atoms in the examined compounds are found to have positive σ-holes on the extensions of their covalent bonds, while the hypervalent atoms in the anions have negative σ-holes. The positive σ-holes on the halogens of the studied halonium salts determine the linearity of the short contacts between the halogen and neutral or anionic electron donors, as usual in halogen bonds.

(4,7,13,16,21,24-Hexaoxa-1,10-di-aza-bicyclo-[8.8.8]hexa-cosa-ne)sodium iodide-1,1,2,2,tetra-fluoro-1,2-diiodo-ethane (2/3).

The title complex (CX1), [Na(C18H36N2O6)]I·1.5C2F4I2, is a three-component adduct containing a [2.2.2]-cryptand, sodium iodide and 1,1,2,2-tetra-fluoro-1,2-di-iodo-ethane. The di-iodo-ethane works as a bidentate halogen-bonding (XB) donor, the [2.2.2]-cryptand chelates the sodium cation, and the iodide counter-ion acts as a tridentate XB acceptor. A (6,3) network is formed in which iodide anions are the nodes and halocarbons the sides. The network symmetry is C 3i and the I⋯I(-) XB distance is 3.4492 (5) Å. This network is strongly deformed and wrinkled. It forms a layer 9.6686 (18) Šhigh and the inter-layer distance is 4.4889 (10) Å. The cations, inter-acting with each other via weak O⋯H hydrogen bonds, are confined between two anionic layers and also form a (6,3) net. The structure of CX1 is closely related to that of the KI homologue (CX2). The 1,1,2,2,-tetrafluoro-1,2-diiodoethane molecule is rotationally disordered around the I⋯I axis, resulting in an 1:1 disorder of the C2F4 moiety.

1,3-Bis(2,3,5,6-tetra-fluoro-4-iodo-phen-oxy)-2,2-bis-[(2,3,5,6-tetra-fluoro-4-iodo-phen-oxy)meth-yl]propane.

In the crystal structure of the title compound, C29H8F16I4O4, short I⋯I and I⋯F contacts, which can be understood as halogen bonds (XBs), represent the strongest inter-molecular inter-actions, consistent with the presence of I and F atoms, and the absence of H atoms, at the periphery of the mol-ecule. In addition, π-π stacking inter-actions between tetra-fluoro-iodo-phenyl (TFIP) groups and five short F⋯F inter-actions are present.