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Neil R Champness

Publications and source records attributed to Neil R Champness.

8 recordsLinked to original sources

Controlling molecular deposition and layer structure with supramolecular surface assemblies.

Selective non-covalent interactions have been widely exploited in solution-based chemistry to direct the assembly of molecules into nanometre-sized functional structures such as capsules, switches and prototype machines. More recently, the concepts of supramolecular organization have also been applied to two-dimensional assemblies on surfaces stabilized by hydrogen bonding, dipolar coupling or metal co-ordination. Structures realized to date include isolated rows, clusters and extended networks, as well as more complex multi-component arrangements. Another approach to controlling surface structures uses adsorbed molecular monolayers to create preferential binding sites that accommodate individual target molecules. Here we combine these approaches, by using hydrogen bonding to guide the assembly of two types of molecules into a two-dimensional open honeycomb network that then controls and templates new surface phases formed by subsequently deposited fullerene molecules. We find that the open network acts as a two-dimensional array of large pores of sufficient capacity to accommodate several large guest molecules, with the network itself also serving as a template for the formation of a fullerene layer.

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Stereoselective association of binuclear metallacycles in coordination polymers.

A series of structurally related binuclear metallacycles [Cd(NO(3))(2)L](2), where L is an angular exo-bidentate ligand, have been synthesized. Each metallacycle contains two coordinatively unsaturated, chiral metal centers within a single molecule, and the assembly of these metallacycles into polymeric framework structures has been studied systematically for the first time. Stereoselective homochiral association of [Cd(NO(3))(2)L](2) leads to the formation of helical coordination polymers, whereas meso type association results in nonhelical chain structures. The type of stereoselective aggregation depends on the conditions of self-assembly as well as on ligand functionality. Both helical and nonhelical polymeric complexes have been isolated for the metallacycle [Cd(NO(3))(2)(2,4'-pyacph)](2) (2,4'-pyacph = 2,4'-(4-ethynylphenyl)bipyridyl). Homochiral association results in the formation of helical [Cd(NO(3))]( infinity ) chains which link the binuclear [Cd(NO(3))(2)(2,4'-pyacph)](2) metallacycles into racemic two-dimensional sheets which contain both P and M [Cd(NO(3))]( infinity ) helices. In contrast, meso-association leads to the formation of nonhelical one-dimensional chains. It is shown that the product of homochiral association is predominately formed at room temperature and that of meso-association is generated at elevated temperatures. Thus, it may be concluded that the homochiral association appears to be energetically less favorable than the meso-association, a conclusion that has been confirmed by theoretical calculations of the crystal lattice energy. Several high-yield syntheses of bipyridyl-type ligands used for metallacyclic assembly are also reported.

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Helical templating of polyiodide networks at a binuclear metallo complex.

A homobimetallic supramolecular helicate has been prepared from a new multimodal ligand, and used to template the formation of two polyiodide networks, one containing an unprecedented figure-of-eight polyiodide helix, the other dominated by peripheral C-H...I polyiodide chain interactions.

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Structural isomerism in CuSCN coordination polymers.

CuSCN reacts with the angular ligand 2,4-bis(4-pyridyl)-1,3,5-triazine (dpt) to afford rare examples of coordination polymer structural isomers including a non-centrosymmetric three-dimensional framework with Cd(SO4) topology constructed from tetrahedral metal cations.

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Constructing terbium co-ordination polymers of 4,4'-bipyridine-N,N'-dioxide by means of diffusion solvent mixtures.

Five different co-ordination polymers of terbium(III) and the bidentate ligand 4,4'-bipyridine-N,N'-dioxide (L), [Tb(L)(CH(3)OH)(NO(3))(3)](infinity) (1), ([Tb(L)(1.5)(NO(3))(3)].CH(2)Cl(2))(infinity) (2), ([Tb(L)(1.5)(NO(3))(3)].CH(3)OH.0.8H(2)O)(infinity) (3), ([Tb(L)(1.5)(NO(3))(3)].0.4C(2)Cl(4).0.8CH(3)OH)(infinity) (4), and [Tb(L)(2)(NO(3))(3)](infinity) (5) have been synthesised by the use of different "diffusion solvent mixtures", and structurally characterised by X-ray crystallography. Compound 1, with a Tb:L stoichiometry of 1:1, adopts a zig-zag chain structure, which forms three-fold interpenetrating diamondoid frameworks through interchain hydrogen bonding between co-ordinated methanol and a nitrate group on an adjacent chain. Polymers 2, 3, and 4 all have a Tb:L stoichiometry of 1:1.5, but adopt different topologies. For 2, a ladder arrangement is found and large channels which accommodate solvent CH(2)Cl(2) molecules are formed by superposition of the ladders. For 3 and 4 4.8(2) net structures are observed. The superposition of the 4.8(2) nets in 3 and 4, by disposing adjacent layers such that every octagon is positioned below a tetragon from the neighbouring layer, allows the formation of two kinds of channel, with that inside the tetragons accommodating methanol molecules. The other kind of channel, between tetragons, accommodates water molecules in the case of 3 and tetrachloroethylene molecules in the case of 4. Compound 5, with a Tb:L stoichiometry of 1:2, has a linear polymeric structure with one bridging and one terminal ligand, and forms (6,3) plane nets by means of intermolecular electrostatic interactions between N-oxide moieties. X-ray powder diffraction studies show that upon desolvation, compound 2 maintains its original ladder framework.

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Using multimodal ligands to influence network topology in silver(I) coordination polymers.

A range of Ag(I) one- and two-dimensional coordination frameworks has been prepared and structurally characterized by using the multimodal ligand 3,6-di-pyrazin-2-yl-(1,2,4,5)-tetrazine, which offers both monodentate and chelating binding sites. It is demonstrated that multimodal ligands can be used to prepare coordination frameworks with novel and unusual topologies and to influence the precise geometrical arrangement of both ligands and metal centers within such supramolecular arrays.

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