Showing papers by "Guillermo Mínguez Espallargas published in 2009"

Rational Modification of the Hierarchy of Intermolecular Interactions in Molecular Crystal Structures by Using Tunable Halogen Bonds

Abstract: A family of 16 isomolecular salts (3-XpyH)(2)[MX'(4)] (3-XpyH=3-halopyridinium; M=Co, Zn; X=(F), Cl, Br, (I); X'=Cl, Br, I) each containing rigid organic cations and tetrahedral halometallate anions has been prepared and characterized by X-ray single crystal and/or powder diffraction. Their crystal structures reflect the competition and cooperation between non-covalent interactions: N-H center dot center dot center dot X'-M hydrogen bonds, C-X center dot center dot center dot X'-M halogen bonds and pi-pi stacking. The latter are essentially unchanged in strength across the series, but both halogen bonds and hydrogen bonds are modified in strength upon changing the halogens involved. Changing the organic halogen (X) from F to I strengthens the C-X center dot center dot center dot X'-M halogen bonds, whereas an analogous change of the inorganic halogen (X') weakens both halogen bonds and N-H center dot center dot center dot X'-M hydrogen bonds. By so tuning the strength of the putative halogen bonds from repulsive to weak to moderately strong attractive interactions, the hierarchy of the interactions has been modified rationally leading to systematic changes in crystal packing. Three classes of crystal structure are obtained. In type A (C-F center dot center dot center dot X'-M) halogen bonds are absent. The structure is directed by N-H center dot center dot center dot X'-M hydrogen bonds and pi-stacking interactions. In type B structures, involving small organic halogens (X) and large inorganic halogens (X'), long (weak) C-X center dot center dot center dot X'-M interactions are observed with type I halogen-halogen interaction geometries (C-X center dot center dot center dot X' approximate to X center dot center dot center dot X'-M approximate to 155 degrees), but hydrogen bonds still dominate. Thus, minor but quite significant perturbations from the type A structure arise. In type C, involving larger organic halogens (X) and smaller inorganic halogens (X'), stronger halogen bonds are formed with a type II halogen-halogen interaction geometry (C-X center dot center dot center dot X' approximate to 180 degrees; X center dot center dot center dot X'-M approximate to 110 degrees) that is electrostatically attractive. The halogen bonds play a major role alongside hydrogen bonds in directing the type C structures, which as a result are quite different from type A and B.

Combining Metals with Halogen Bonds

Abstract: Halogen bonds in the solid state have been investigated for many years, with a major resurgence in activity occurring in the past decade. The emphasis of most studies has been on organic components. This Highlight focusses on inorganic components, or at least metal-containing components, and explores their propensity to form halogen bonds. The use of C–X⋯X′–M halogen bonds in forming networks is briefly reviewed and their utility in investigating the nature of halogen bonds is explored since their strength can be tuned by changing either the organic (donor) halogen (C–X) or the inorganic (acceptor) halogen (M–X′). A survey has been performed of crystal structures in which interactions are of suitable geometry to be considered as halogen bonds. In particular the role of simple monatomic (e.g.oxo, nitrido) and diatomic (e.g.carbonyl, cyanide) ligands as halogen bond acceptors in transition metal complexes is examined. Main group metals are also considered in a further section that considers D–X⋯A–M halogen bonds, where D = halogen bond donor, A = halogen bond acceptor and M = main group metal or metalloid. Many examples presented herein were not identified as halogen bonds in the original articles. The aim of this survey is to examine the breadth of elements that can be involved in halogen bonding involving at least one inorganic (metal-containing) component and consider this range of interactions as a basis for future research in halogen bonding with applications in crystal engineering and allied areas.