Lee Brammer

Tables of bond lengths determined by X-ray and neutron diffraction. Part 1. Bond lengths in organic compounds

The average lengths of bonds involving the elements H, B, C, N, O, F, Si, P, S, Cl, As, Se, Br, Te, and l in organic compounds are reported.

Developments in inorganic crystal engineering

The design and synthesis of crystalline materials through the self-assembly of molecular building blocks and the pursuit of functional materials based upon this approach are usually classified under the banner Crystal Engineering. The field is interdisciplinary in nature involving synthetic, materials, structural and theoretical chemists. There are strong ties to modern crystallography which can offer rapid and accurate structure determination and, in particular, insight into molecular and intermolecular geometries. Illustrative examples that chart the development field and provide an assessment of the current state of the art will be reviewed with an emphasis on inorganic chemistry. Broadly speaking, two classes of compounds will be discussed: those based upon molecules or ions linked into networks via noncovalent interactions and those (coordination polymers) in which metal centres are linked using coordination bonds through bridging ligands into extended networks.

New trends in crystal engineering

The articles and highlights presented at the second CrystEngComm meeting, held in Nottingham in September 2004 are reviewed. The discussion has highlighted the current development of crystal engineering and allowed to emerge some of its future potentials. In particular, the papers described in this highlight focus on four fundamental aspects: (i) intermolecular interactions: evaluation and application to crystal design; (ii) networks: design and applications; (iii) approaches to crystal synthesis; (iv) polymorphism, solvates and chiral crystal resolution.

Combining metals with halogen bonds

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.

Supplement. Tables of bond lengths determined by X-ray and neutron diffraction. Part 2. Organometallic compounds and co-ordination complexes of the d- and f-block metals

Average lengths for metal–ligand bonds are reported, together with some intraligand distances, for complexes of the d- and f-block metals. Mean values are presented for 325 different bond types involving metal atoms bonded to H, B, C, N, O, F, Si, P, S, Cl, As, Se, Br, Te, or I atoms of the ligands.

Hydrogen bonding in substituted-ammonium salts of the tetracarbonylcobaltate(−I) anion: some insights into potential roles for transition metals in organometallic crystal engineering

Abstract This review examines the supramolecular structures of substituted-ammonium salts of the tetracarbonylcobaltate(−I) anion, Co(CO) 4 − . The salts discussed contain cations of increasing complexity, ranging from simple tertiary ammonium cations, through cations consisting of dimeric or trimeric units, to a protonated tetraamine. Across the series distinct changes in the supramolecular structure are apparent. For the simplest cations the principal cation–anion interaction is a short (strong) direct N–H⋯Co hydrogen bond, which is augmented by longer (weaker) C–H⋯O hydrogen bonds. The availability of amine acceptor sites results in competition with the metal center for the available N–H donors and leads to the formation of dimeric, trimeric, and even polymeric N–H + ⋯N hydrogen-bonded ammonium/amine cations. Such cations typically utilize all N–H donors, leaving cation–anion links to be formed solely through C–H⋯O hydrogen bonds. In the extreme case of the protonated tetraamine, a strong N–H + ⋯N hydrogen bonded cation network is formed, the anions reside in channels and few cation–anion links are present. The Co(CO) 4 − anion is revealed as a rich source of hydrogen bond acceptor sites. Three types are identified and discussed in detail, namely the metal center (Co), the carbonyl oxygens, and the carbonyl π -system. Further, in determining the overall supramolecular arrangement, it is clear that a balance exists between the effect of hydrogen bonds of different types (strengths) depending upon their relative populations. The observations presented in the review are discussed in the context of organometallic crystal engineering, and the potential roles for metal-mediated hydrogen bonding are illustrated.

Metal Fluorides Form Strong Hydrogen Bonds and Halogen Bonds : Measuring Interaction Enthalpies and Entropies in Solution

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.

Hydrogen bonding and perhalometallate ions: A supramolecular synthetic strategy for new inorganic materials

A synthetic strategy for constructing ionic hydrogen-bonded materials by combining perhalometallate anions with cations able to serve as hydrogen bond donors is presented. The approach is based on identification of well defined hydrogen bond acceptor sites on the anions by a combination of experimental and theoretical approaches. Selective population of these sites by hydrogen bond donors has the potential to afford organized crystalline arrays in one, two, or three dimensions. The approach is applicable to a wide range of metal centers.

Typical interatomic distances: organic compounds

Mean bond lengths for organic compounds, derived from the Cambridge Structural Database, are tabulated for 625 different bond types involving the elements C, H, N, O, B, F, P, S, Cl, As, Se, Br, Te and I. Associated statistical information characterizes each of the distributions, which are derived from both X-ray and neutron diffraction data.

Involving metals in halogen–halogen interactions: second-sphere Lewis acid ligands for perhalometallate ions (M–X⋯X′–C)

Lewis-acidic halocarbon groups (X–C) serve as effective second-sphere ligands for perhalometallate ions and provide an alternative means to hydrogen bonds for developing the supramolecular chemistry of such ions, exemplified here by short directional M–X⋯X′–C halogen bond linkages used in conjunction with hydrogen bonds for crystal synthesis.