Lindsay P. Harding

Self-Assembly of a 3-D Triply Interlocked Chiral [2]Catenane

A tripodal cyclotriveratrylene-based ligand with chelating 2,2‘-bipyridine arms self-assembles with either Zn(NO3)2 or Co(NO3)2 to give 3-D trigonal bipyramidal [M3L2] cage assemblies. These cages triply interlock forming [2]catenane species that have been characterized by mass spectrometry and, in the case of the Zn(II) complex, by X-ray crystallography.

Stellated polyhedral assembly of a topologically complicated Pd4L4 'Solomon cube'

Metallosupramolecular chemistry relies on self-assembly processes in which complicated species form through labile dative-covalent interactions. Two remarkable areas of this chemistry are the synthesis of topologically complicated threaded assemblies and of three-dimensional (3D) polyhedral assemblies. Very few polyhedral 3D metallosupramolecular assemblies show threaded motifs within them. Here we report an example of a new type of threaded 3D metallosupramolecular assembly built from four organic ligands and four palladium ions, a Pd4L4 so-called ‘Solomons cube’ in which interweaving and twisting of the ligands form both Solomons links and figure-of-eight ring motifs. In the solid state, six of these Pd4L4 tetramers assemble into a hollow spheroid that closely resembles a stellated truncated hexahedron. A topologically non-trivial metallosupramolecular structure is formed by a Pd4L4 complex in which interweaving and twisting of the ligands results in both Solomons Link and figure-of-eight ring motifs. In the solid state, six of these complexes assemble into a hollow spheroid that closely resembles a stellated truncated hexahedron.

Mixed-Ligand Molecular Paneling: Dodecanuclear Cuboctahedral Coordination Cages Based on a Combination of Edge-Bridging and Face-Capping Ligands

Reaction of a tris-bidentate ligand L(1) (which can cap one triangular face of a metal polyhedron), a bis-bidentate ligand L(2) (which can span one edge of a metal polyhedron), and a range of M(2+) ions (M = Co, Cu, Cd), which all have a preference for six coordination geometry, results in assembly of the mixed-ligand polyhedral cages [M12(mu(3)-L(1))4(mu-L(2))12](24+). When the components are combined in the correct proportions [M(2+):L(1):L(2) = 3:1:3] in MeNO2, this is the sole product. The array of 12 M(2+) cations has a cuboctahedral geometry, containing six square and eight triangular faces around a substantial central cavity; four of the eight M3 triangular faces (every alternate one) are capped by a ligand L(1), with the remaining four M3 faces having a bridging ligand L(2) along each edge in a cyclic helical array. Thus, four homochiral triangular {M3(L(2))3}(6+) helical units are connected by four additional L(1) ligands to give the mixed-ligand cuboctahedral array, a topology which could not be formed in any homoleptic complex of this type but requires the cooperation of two different types of ligand. The complex [Cd3(L(2))3(ClO4)4(MeCN)2(H2O)2](ClO4)2, a trinuclear triple helicate in which two sites at each Cd(II) are occupied by monodentate ligands (solvent or counterions), was also characterized and constitutes an incomplete fragment of the dodecanuclear cage comprising one triangular {M3(L(2))3}(6+) face which has not yet reacted with the ligands L(1). (1)H NMR and electrospray mass spectrometric studies show that the dodecanuclear cages remain intact in solution; the NMR studies show that the Cd 12 cage has four-fold (D2) symmetry, such that there are three independent Cd(II) environments, as confirmed by a (113)Cd NMR spectrum. These mixed-ligand cuboctahedral complexes reveal the potential of using combinations of face-capping and edge-bridging ligands to extend the range of accessible topologies of polyhedral coordination cages.

Octapi Interactions: Self-Assembly of a Pd-Based [2]Catenane Driven by Eightfold π Interactions

An unprecedented 2.5 nm array of pi interactions between eight aromatic rings drives the formation of a [2]catenane. Disruption of this array through the use of longer ligands results in the formation of only single, uncatenated rings. The catenated complex is shown to persist in solution alongside its constituent metallomacrocycles.

Homo- and heteropolynuclear helicates with a ‘2 + 3 + 2’-dentate compartmental ligand

An octadentate ligand L has been prepared which contains a sequence of bidentate (pyrazolyl-pyridine), terdentate [bis(pyrazolyl)pyridine] and bidentate (pyrazolyl-pyridine) binding sites separated by p-xylyl spacers. This forms a range of double helical complexes in which the two ligands define 4-, 6-, and 4-coordinate binding sites, and there is substantial π-stacking between overlapping parallel areas of the ligands. In [Cu3L2][PF6]4 the sequence of oxidation states for the copper ions is +1, +2, +1 with the Cu(I) ions being four-coordinate at the terminal sites and Cu(II) being in the central six-coordinate site. In [Cu3(OAc)2L2][PF6]4 all copper centres are in oxidation state +2, with the terminal ions having an additional monodentate acetate ligand giving them a five-coordinate geometry. The 4 + 6 + 4 arrangement of coordination numbers means that reaction of L with a mixture of Fe(II) and Ag(I) results in high yield formation of [Ag2FeL2][BF4]4 in which Ag(I) ions occupy the terminal 4-coordinate sites and Fe(II) occupies the central pseudo-octahedral site. Reaction of L with Ag(I) produced a mixture of [Ag3L2][BF4]3 (major product) and [Ag4L2][BF4]4 (minor product). In [Ag3L2][BF4]3 the central Ag(I) ion is, unusually, in a pseudo-octahedral coordination environment from the two meridional, terdentate bis(pyrazolyl)pyridine donors. In [Ag4L2][BF4]4 in contrast the central 6-coordinate cavity is occupied by two Ag(I) ions separated by 2.85 A. The terdentate chelating bis(pyrazolyl)pyridine units at the centre of the helicate are now substantially twisted such that each donates a bidentate pyrazolyl-pyridine to one Ag(I) centre and a monodentate pyrazole unit to the other. In solution, 1H NMR and mass spectroscopic evidence indicates that the fourth Ag(I) ion is lost and [Ag3L2][BF4]3 forms, unless a large excess of Ag(I) is present in which case traces of [Ag4L2][BF4]4 can be detected by mass spectrometry.

Tripodal 4-pyridyl-derived host ligands and their metallo-supramolecular chemistry: stella octangula and bowl-shaped assemblies

The synthesis of five new cyclotriveratrylene derivatives with 4-pyridyl side arms is reported, along with the crystal structures of three of these. Three ligands with extended 4-pyridylphenyl side arms and a ligand derived from cyclotriphenolene have been shown to form [Pd(6)L(8)](12+) stella octangula assemblies using diffusion-ordered spectroscopy NMR and electrospray MS techniques. This confirms the generality of the stella octagula assembly, providing that the ligand arms show a degree of rigidity. The more flexible ether-linked ligand tris(4-pyridylmethyl)cyclotriguaiacylene forms a smaller [Pd(3)L(4)](6+) bowl-shaped assembly in the solid state and in solution. The previously reported ligand tris(4-pyridylmethylamino)cyclotriguaiacylene forms a similar assembly in solution.

Ag(I) Organometallic Coordination Polymers and Capsule with Tris-Allyl Cyclotriveratrylene Derivatives

Tris-allyl-cyclotriguaiacylene combines with silver salts to give a range of crystalline network structures and one discrete complex. A number of different coordination modes are found within the complexes including η(2)-allyl, aryl, and OR groups binding to Ag(I). AgSbF(6) gives two types of three-dimensional (3-D) coordination polymer with unusual topologies, along with a discrete Ag(2)L(2) capsule dependent on reaction stoichiometry and reaction conditions. Isostructural coordination chain structures are found with AgBF(4) and AgClO(4), while use of Ag(CF(3)SO(3)) gives two-dimensional (2-D) and 3-D coordination polymers through bridging triflate anions.

A wavelength and lifetime responsive cryptate-containing fluorescent probe for zinc ions in water

A diamino-functionalised cryptate can react irreversibly with butanal in water, in the presence of an excess of a metal ion, to form a cyclised bis-aminal complex, which displays metal-dependent luminescence properties.

Head‐To‐Tail and Heteroleptic Pentanuclear Circular Helicates

Everybody form a circle: Careful design of ligand strands and their reaction with Cu2+ ions leads to the formation of the title helicates. Incorporation of differing numbers of N-donor units within a ligand strand containing a phenyl spacer results in a pentanuclear head-to-tail circular helicate, whereas reaction of two different ligands results in a heteroleptic pentanuclear circular helicate (see picture; green: Cu, red and blue: ligands).

Structural characterisation of a perdeuteriomethylated exopolysaccharide by NMR spectroscopy: characterisation of the novel exopolysaccharide produced by Lactobacillus delbrueckii subsp. bulgaricus EU23

The exopolysaccharide (EPS) from Lactobacillus delbrueckii subsp. bulgaricus EU23 was perdeuteriomethylated and the perdeuteriomethylated EPS (pdm-EPS) purified by elution from a C(18) Sep-Pak cartridge. Both 1D and 2D NMR spectra were recorded for the pdm-EPS and these were interpreted to provide assignments for the individual 1H and 13C resonances of the sugar residues of the repeating unit. Using a combination of the results from monomer analysis and linkage analysis of the native EPS and the ROESY and HMBC NMR spectra of the pdm-EPS the following structure has been determined for the repeating unit:A process for characterising polysaccharides having low solubility in aqueous solution is reported.