Despite an absence of conventional porosity, the 1D coordination polymer [Ag-4(O2C(CF2)(2)CF3)(4)(TMP)(3)] (1; TMP=tetramethylpyrazine) can absorb small alcohols from the vapour phase, which insert into AgO bonds to yield coordination polymers [Ag-4(O2C(CF2)(2)CF3)(4)(TMP)(3)(ROH)(2)] (1-ROH; R=Me, Et, iPr). The reactions are reversible single-crystal-to-single-crystal transformations. Vapour-solid equilibria have been examined by gas-phase IR spectroscopy (K=5.68(9)x10(-5) (MeOH), 9.5(3)x10(-6) (EtOH), 6.14(5)x10(-5) (iPrOH) at 295K, 1bar). Thermal analyses (TGA, DSC) have enabled quantitative comparison of two-step reactions 1-ROH12, in which 2 is the 2D coordination polymer [Ag-4(O2C(CF2)(2)CF3)(4)(TMP)(2)] formed by loss of TMP ligands exclusively from singly-bridging sites. Four polymorphic forms of 1 (1-A(LT), 1-A(HT), 1-B-LT and 1-B-HT; HT=high temperature, LT=low temperature) have been identified crystallographically. In situ powder X-ray diffraction (PXRD) studies of the 1-ROH12 transformations indicate the role of the HT polymorphs in these reactions. The structural relationship between polymorphs, involving changes in conformation of perfluoroalkyl chains and a change in orientation of entire polymers (A versus B forms), suggests a mechanism for the observed reactions and a pathway for guest transport within the fluorous layers. Consistent with this pathway, optical microscopy and AFM studies on single crystals of 1-MeOH/1-A(HT) show that cracks parallel to the layers of interdigitated perfluoroalkyl chains develop during the MeOH release/uptake process.

Bifurcated C–H⋯(F–C)2 hydrogen bonds are most commonly close to being symmetric and are clearly evident in structures of two new fluoronaphthalenes.

Halogen bonds have been applied for the supramolecular organization of organic free radicals in the solid state and their role in the propagation of the magnetic exchange has been studied.

Diiodoacetylene, C2I2, is the smallest ditopic halogen bond donor other than I-2 or other dihalogens. A convenient synthesis of diiodoacetylene from the common Sonagashira coupling reagent Me3SiC CH, is described. The halogen-bonded adducts of C2I2 with dimethylformamide (DMF), pyrazine (pyz) and 1,4-diazabicyclooctane (dabco) have been characterised by X-ray crystallography. All adopt 1D halogen-bonded chains linked via short C-I center dot center dot center dot O [I center dot center dot center dot O 2.834(4)-2.888(4) angstrom; C-I center dot center dot center dot O > 170 degrees] or C-I center dot center dot center dot N [I center dot center dot center dot N 2.715(3)-2.832(7) angstrom; C-I center dot center dot center dot N > 175 degrees] interactions. Attempts to synthesise the adduct of C2I2 with hexamethylenetetramine (hmta) resulted in isolation and crystallographic characterisation of the adduct of C2I4. hmta, indicating decomposition of C2I2 to yield C2I4 in solution. The adduct comprises two independent C2I4 molecules that act, respectively, as tetratopic and ditopic halogen bond donors forming C-I center dot center dot center dot N interactions [I center dot center dot center dot N 2.948(7)-2.999(8) angstrom; C-I center dot center dot center dot N > 165 degrees], occupying three of the four nitrogen sites on htma. The remaining nitrogen sites engage in N center dot center dot center dot C(pi) interactions directed orthogonal to the plane of the ditopic C2I4 molecules. Separate surveys of halogen bonds formed by diiodo(poly)alkynes I(C C)(n)I (n = 1-3) and by C2I4 molecules indicate that C-I center dot center dot center dot N halogen bonds are shorter, when normalised for van der Waals radii, and, by inference, stronger than halogen bonds involving other acceptor groups, and demonstrates that C-sp-I center dot center dot center dot N halogen bonds are generally shorter C-sp2-I center dot center dot center dot N halogen bonds.

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The solution x-ray scattering technique permits studies of biological macromolecules in near physiological conditions, which are not always compatible with high-resolution structural studies.Timeresolved solution scattering studies have been used to examine a number of different conformational changes as a function of time primarily at the tertiary and/or quaternary structure level.There exist a number of macromolecular systems which simply can not be contained within the crystallographic lattice structure.All virus and bacteriophage systems undergo complex assembly and maturation processes.Solution x-ray scattering and their time-resolved studies cover small proteins of several thousands of Da to multimega Da virus/phage particles, allowing structural studies of initial assembly processes as well as the late maturation processes.This talk will highlight the time-resolved study on the scaffolding protein-mediated assembly of P22 bacteriophage capsid and the maturation structural kinetics of HK97 bacteriophage capsid to illustrate how timeresolved solution scattering studies can complement crystallography and cryoelectron microscopy in structural virology.It will be shown that the scaffolding protein monomer-dimer assembly equilibrium controls the entire P22 capsid assembly process.In the case of HK97 maturation, the highly cooperative all-or-nothing structural transitions of 420 capsid proteins preveil in all steps so far been examined.

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.

How does it fit? The one-dimensional coordination polymer [Ag4L3{O2C(CF2)3CF3}4(EtOH)2]n (1; L=tetramethylpyrazine, see scheme) eliminates coordinated ethanol in an intramolecular substitution reaction. The reaction occurs in a single-crystal-to-single-crystal transformation and leads to extrusion of ethanol from the nonporous crystals. The reverse reaction involving uptake of ethanol vapor has been verified using X-ray powder diffraction. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2008/z703194_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

The organometallic compound trans-(tetrafluoropyrid-2-yl)bis(triethylphosphine)-fluoronickel(II) (NiF) is shown to serve as a strong hydrogen bond and halogen bond acceptor in solution via intermolecular interactions with the fluoride ligand. The nature of the interactions has been confirmed by multinuclear NMR spectroscopy. Experimental binding constants, enthalpies, and entropies of interaction with hydrogen-bond-donor indole and halogen-bond-donor iodopentafluorobenzene have been determined by 19F NMR titration. In toluene-d8 solution indole forms a 1:1 and 2:1 complex with NiF (K1 = 57.9(3), K2 = 0.58(4)). Interaction enthalpies and entropies are -23.4(2) kJ mol-1 and -44.5(8) J mol-1 K-1, respectively, for the 1:1 complex; -14.8(8) kJ mol-1 and -53(3) J mol-1 K-1, respectively, for the 2:1 complex. In toluene-d8 solution iodopentafluorobenzene forms only a 1:1 complex (K1 = 3.41(9)) with enthalpy and entropy of interaction of -16(1) kJ mol-1 and -42(4) J mol-1 K-1, respectively. A marked solvent effect was observed for the halogen bond interaction. NMR titrations in heptane solution indicated formation of both 1:1 and 2:1 complexes of iodopentafluorobenzene with NiF (K1 = 21.8(2), K2 = 0.22(4)). Interaction enthalpies and entropies are -26(1) kJ mol-1 and -63(4) J mol-1 K-1, respectively, for the 1:1 complex; -21(1) kJ mol-1 and -83(5) J mol-1 K-1, respectively, for the 2:1 complex. There is a paucity of such experimental energetic data particularly for halogen bonds despite substantial structural data. These measurements demonstrate that halogen bonds are competitive with hydrogen bonds as intermolecular interactions and provide a suitable benchmark for theoretical calculations and quantitative input into design efforts in supramolecular chemistry and crystal engineering.

EtCN partially displaces coordinated carbon monoxide from cis-PtCl2(CO)(2) giving an equilibrium mixture of the two geometrical isomers Of PtCl2(CO)(NCEt), together with unreacted cis-PtCl2(CO)(2), as monitored by IR and NMR measurements. The equilibrium has also been studied starting from PtCl2(NCEt)(2), through displacement of coordinated EtCN by CO. The equilibrium constant of the reaction between PtCl2(CO)(NCEt) [cis + trans] and CO to produce cis-PtCl2(CO)(2) (48 +/- 6, corresponding to Delta G(0) = -9.5 +/- 0.3 kJ mol(-1)) has been measured at 23.4 degrees C, in the presence of SnCl2 as catalyst, the uncatalysed reaction being exceedingly slow. With an appropriate control of the CO partial pressure, PtCl2(CO)(NCEt) was obtained in a nearly quantitative yield either from cis-PtCl2(CO)(2) + EtCN or from PtCl2(NCEt)(2) + CO. The molecular and crystal structure Of cis-PtCl2(CO)(NCEt) has been solved by X-ray diffractometry. (C) 2007 Elsevier B.V. All rights reserved.