Neil S Oxtoby | PubMed Health

PubMed2005

Water superstructures within organic arrays; hydrogen-bonded water sheets, chains and clusters.

A strategy for encouraging the formation of extended water arrays is presented, in which molecules that contain a 1,4-dihydroquinoxaline-2,3-dione core are used as supramolecular hosts for the accommodation of guest water molecules and arrays. These molecules were selected as they contain a hydrophilic oxalamide-based "terminus" that allows water molecules to hydrogen-bond to the host organic molecules as well as to each other. The host molecules also contain a hydrophobic "end" based upon an aromatic ring, which serves to encourage the formation of discrete water clusters in preference to three-dimensional networks, as the water molecules cannot form strong hydrogen bonds with this part of the molecule. A systematic study of several hydrated structures of four organic molecules based on 1,4-dihydroquinoxaline-2,3-dione (qd) is discussed. The organic molecules, qd, 6-methyl-1,4-dihydroquinoxaline-2,3-dione (mqd), 6,7-dimethyl-1,4-dihydroquinoxaline-2,3-dione (dmqd) and 1,4-dihydrobenzo[g]quinoxaline-2,3-dione (Phqd), act as supramolecular crystal hosts for the clusters of water, with zero-, one- and two-dimensional arrays of water being observed. The hydrogen bonding in the structures, both within the water clusters and between the clusters and organic molecules, is examined. In particular, the structure of dmqd6 H2O contains a two-dimensional water sheet composed of pentagonal and octagonal units. Phqd3 H2O forms a hydrophilic extended structure encouraging the formation of one-dimensional chains consisting entirely of water. Both qd2 H2O and dmqd2 H2O can be considered to form one-dimensional chains, but only by utilising bridging carbonyl groups of the oxalamide moieties to form the extended array; if only the water is considered, zero-dimensional water tetramers are observed. The remaining hydrated structures, [Na+dmqd-]dmqdH2O, dmqd1/3H2O and mqd1/2H2O, all contain discrete water molecules but do not form extended water structures.

Crystallography, X-Ray↗

PubMed2003

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.

Journal Article↗

PubMed2002

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.

Binding Sites↗