Maurizio Ursini

Dimensional caging of polyiodides: cation-templated synthesis using bipyridinium salts

The potential of bipyridinium derivatives in the cation templated synthesis of polyiodides has been explored by applying the strategy of size-matching between cations and anions. Bipyridinium cations 1–4, bearing benzyl and functionalized benzyl pendants at nitrogen atoms, are able to template the selective formation of I42− and I3− species. Thanks to the supramolecular space compartmentation induced by the benzyl pendants, the formation of I42−and I3− is independent of the stoichiometry adopted in the crystallization procedure. Bipyridinium cation 5, bearing methyl pendants, is unable to induce space compartmentation and different polyiodides are obtained depending on the stoichiometry used in the crystallization process as the cation–anion size-matching alone does not control the polyiodide formation.

Halogen bonding in hypervalent iodine and bromine derivatives: halonium salts

The presence of halogen bonds in some hypervalent iodine and bromine derivatives is demonstrated. Hypervalent atoms in polyatomic cations and anions do have σ-holes on the extensions of their covalent bonds and the cation holes are influential on the crystal lattice structures of halonium salts.

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

AbstractModeling 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 abstractIntra- and intermolecular tetrel bonds involving organogermanium and -tin derivatives in crystalline solids

(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-tetrafluoro-1,2-diiodoethane. The diiodoethane 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) Å high and the inter-layer distance is 4.4889 (10) Å. The cations, interacting 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-tetra­fluoro-4-iodo­phen­oxy)-2,2-bis­[(2,3,5,6-tetra­fluoro-4-iodo­phen­oxy)meth­yl]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 intermolecular interactions, consistent with the presence of I and F atoms, and the absence of H atoms, at the periphery of the molecule. In addition, π–π stacking interactions between tetrafluoroiodophenyl (TFIP) groups and five short F⋯F interactions are present.