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Crystallisation of the tetrahaloaryl host 2,4,10,12-tetrabromo-6,7,14,15-tetrahydro-6,14-thiacycloocta[1,2-b:5,6-b′]diquinoline 7 from benzene, chloroform, 3-methylpyridine, 4-methylpyridine, 2-methylpyridine, or tert-butylcyclohexane, yields a series of closely related inclusion compounds (7)2·(guest) in space group P. Two host molecules surround a single guest to form a penannular repeat unit in each of these crystal structures. Structural variation arises from the differing guest sizes, shapes and interactions. The corners of four molecular pens are linked by utilising novel S/Br clusters as supramolecular synthons: S2Br4 for the first four compounds, and S2Br6 for the latter two cases. The aromatic faces of the repeat units associate through offset π⋯π interactions. Aromatic edge–edge linkage occurs in the former group of compounds by means of N2Br2 and N2Br4 clusters, but these are absent in the final two structures. Mesitylene (1,3,5-trimethylbenzene) is too wide for penannular inclusion. It yields an alternative layer structure, (7)·(mesitylene), also in P. This compound is stabilised by means of host–guest C–H⋯π associations, plus host–host aromatic and S⋯Br⋯Br⋯N interactions.

As part of a program aimed at introducing functionality onto the Troger’s base framework post-synthesis, we investigated the formylation reaction of Troger’s base analogues with Vilsmeier reagents. We found that rather than the anticipated reaction at the aryl rings, these compounds react with Vilsmeier reagents to afford compounds with a modified strap, whereby the apical methylene group is replaced by a methylene strap bearing an N,N-disubstituted amine.

The sulfur-bridged compound 7α,15α-dibromo-6,7,14,15-tetrahydro-6α,14α-thiacycloocta[1,2-b:5,6-b′]diquinoline (10) yields an apohost crystal form plus a series of six lattice inclusion compounds. The diverse range of their X-ray crystal forms is described, and the structures are compared in crystal engineering terms. Compound 10 exhibits none of the anomalous properties shown earlier by its oxygen-bridged and nor-bromo cousins. Further, it demonstrates inclusion capabilities considerably superior to its methano-bridged analogue. Although the sulfur atom does not appear to be actively driving inclusion host behavior, closer analysis reveals that it is always involved. Multiple sulfur interactions are present in all these clathrate structures, most commonly involving bifurcated H···S···H motifs.

Troger’s base analogues were prepared bearing methoxy groups in the 1,7-, 2,8-, 3,9- or 4,10-positions. These compounds were converted to their dihydroxy analogues in excellent yields upon treatment with boron tribromide and the 4,10-dihydroxy analogue could be prepared by directly from 4-hydroxyaniline. The synthetic utility of the dihydroxy-functionalised compounds as building blocks was demonstrated by the synthesis of a dialkoxy and a diester Troger’s base analogue.

Four novel imidazolium salts, precursors to N-heterocyclic carbene (NHC) ligands, with 2,5-dimethoxybenzyl or 2,5-dihydroxybenzyl (i.e., p-hydroquinone) substituents have been prepared. The crystal structure of the hydroquinone-substituted imidazolium salt H3L3Br reveals Br−⋯H–O bridged chiral chains of alternating [H3L3]+ cations and Br− counter-ions parallel to the x-axis. Palladium(II) complexes were accessible from reactions of the dimethoxyphenyl-substituted imidazolium precursors with palladium(II) acetate, but not from reactions of imidazolium cations with hydroquinonyl substituents. The crystal structure of the bis(dimethoxybenzyl)-substituted bis(NHC)Pd complex, cis-[PdBr2(L2)] (2), is described. Puckering of the bis(NHC) ligand leads to a cleft in which an included molecule of dimethylformamide is situated. The cleft is closed by one of the dimethoxybenzyl groups which π-stacks with the dimethylformamide; the other dimethoxybenzyl group points away from the cleft and Pd(II) centre. Reaction of complex 2 with BBr3 afforded the targeted bis(hydroquinone)-substituted bis(NHC)Pd(II) complex 3 (97% yield) which, in turn, was oxidised by 2,3-dichloro-5,6-dicyano-benzoquinone to the corresponding p-benzoquinone-substituted bis(NHC)Pd(II) complex 4 (98% yield). The cyclic voltammograms of the Pd(II) complexes 2–4 reveal waves that are attributed to an admix of the anticipated ligand-centred and [Pd(C-NHC)2Br2]-centred processes.

The V-shaped racemic compound 4,12-dinitro-6,7,14,15-tetrahydro-6,14- methanocycloocta[1,2-b:5,6-b']diquinoline 2 crystallises from solvents of differing water content as a centrosymmetric spheroidal hexamer in the form of a series of isostructural clusters (2) 6•(water) x X-ray structures of these crystals in space group R3̄ show that they can exhibit an extent of hydration anywhere throughout the composition range x = 0 to 1. © 2011 Springer Science+Business Media B.V.

The very simple alicyclic compounds 3,7-dimethylbicyclo[3.3.0]octane-endo-3,endo-7-diol 3 and 2,6-dimethylbicyclo[3.3.0]octane-endo-2,endo-6-diol 5 were selected for study in the knowledge that these are awkwardly shaped molecules that are likely to pack in the solid state with some difficulty. The design philosophy behind the choice of these particular test molecules is explained. We expected that these isomeric diols would probably yield more than one crystal form if crystallized from a range of different solvents. Dialcohol 3 was found to give three (benzene clathrate, hemihydrate, and hydrate), and dialcohol 5 to give two (racemic and kryptoracemate/false conglomerate), crystal forms. The X-ray structures of these five very different crystalline solids (formed by two very similar model compounds) are described and contrasted. Our findings demonstrate that awkward molecules can be identified and indicate that the formation of alternative crystal forms is likely to be a comparatively frequent occurrence...

The first example of a heteropolyoxomolybdate containing palladium(IV) was isolated and characterized by X ray crystallography The palladium(IV) hexamolybdate, K0 75Na3 75[PdMo6O24H3 (5)] 17H(2)O, ...

The sulfur-bridged compound 6,7,14,15-tetrahydro-6,14-thiacycloocta[1,2-b:5,6-b′]diquinoline (11) yields a solvent-free crystal form but also produces lattice inclusion compounds containing chloroform, water, and methanol. This latter behavior is in marked contrast to the noninclusion characteristics shown by its corresponding oxygen- and methano-bridged analogues. X-ray structures of the three different crystal types formed by 11 reveal that all contain a two-molecule repeat unit in which the S atom of the first is located within the V-shaped cleft of the second. This assembly is reminiscent of a ball and socket joint, and the adoption of this motif is the root cause of the unexpected solid-state inclusion properties shown by 11.

The one-step synthesis of a series of hybrid dibenzo Troger's base analogues bearing at least one halogen atom is described. The strategy involves a reaction between two different anilines and affords hybrid compounds in yields as high as 46 %, together with the symmetric Troger's base products. This straightforward approach requires only one chromatographic step and has the potential to replace multi-step approaches to hybrid Troger's base compounds. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The dibromodiquinoline derivative 2 yields crystalline lattice inclusion compounds with a wide range of guest molecules. The solvent-free crystal structure is also formed. In all these, pairs of dibromodiquinoline molecules form centrosymmetric brick-like dimers by means of three different aromatic edge−face (EF) interactions. The resultant (EF)6 building blocks, which are virtually identical across the series of 13 crystal structures described, act as tectons that pack into layers. Guest molecules occupy interlayer spaces near the corners of the tectons, with the host−guest attractions acting as molecular mortar and allowing variation of the inclusion structures dependent on guest size, shape, and functionality. The apohost crystal structure demonstrates that guest-free packing of these molecular bricks (analogous to the dry stone construction method) is also favorable. The molecular substitution of a dibromodiquinoline unit required to ensure dimeric (EF)6 tecton formation is explained.

Three new ligands with an indole substituent tethered to a pyridylalkylamine or imidazolylalkylamine metal-binding domain have been prepared from tryptamine. Copper(II) complexes have been prepared and characterized, three by X-ray crystallography. Electrochemistry has been used to ascertain the mutual effects of the copper and indole redox centres upon each other.

A protocol for the introduction of spiro[4.5] lactone straps onto the Troger's base scaffold has been developed. The conversion was found to be most efficient when an appropriate carboxylic acid derivative reacted with 5,6,11,12-tetrahydrodibenzo[b,f][1,5]diazocines. Whilst phthaloyl dichloride was the main strap-forming precursor used, other 1,2-unsaturated dicarboxylic acids could be used in the presence of N,N'-dicyclohexylcarbodiimide.

Reaction of the dipyridyl-substituted tetrapropoxycalix[4]arene 1 with palladium(II) chloride yields the unusual metallomacrocycle 2. The calixarene substituents of 1 and 2 show major conformational differences from X-ray determinations, and molecule 2 crystallizes as the inclusion compound (2).(CHCl3)x (x ∼ 7) in space group R3. Three repeating layers stack to form parallel tubes that contain the disordered guests. Intruding host propoxy groups constrict these tubes at every third layer, and the formation of this tubulate structure is explained in terms of the host wheel and axle topology.

A new series of (diisopropylcarbamato)(oxido)zinc complexes were obtained by innovative synthetic approaches. The (carbamato)zinc clusters [Zn4(μ4-O)(O2CNiPr2)6] (1) and [Zn8(μ4-O)2(O2CNiPr2)12] (2) were synthesised by an identical reaction procedure involving protolysis of ZnEt2 with iPr2NH/CO2 and followed by stoichiometric hydrolysis. Recrystallisation of the reaction product from nitrile solvents yielded the tetrazinc complex 1. Conversely, recrystallisation from alkane solvents yielded crystals of the octazinc complex 2. The two structural isomers were readily interconverted simply by recrystallisation from the appropriate solvent. Both complexes were structurally characterised by X-ray crystallography. The tetrazinc complex 1 has the quintessential basic zinc acetate type structure. Its dimer, the octazinc complex 2 is a new derivative of the [M8(μ4-O)2(O2CNiPr2)12] class, examples of which are known for all other first-row transition metals. The solution chemistry was investigated using variable-temperature NMR spectroscopy and ESI-MS. The new synthetic approach offers a route to other similar complexes. Thus, using Et2NH in place of iPr2NH yielded the known complex [Zn4(μ4-O)(O2CNEt2)6] (3).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

The crystal structures of the methylene-bridged diquinolines 1,2 are compared to those of their newly synthesised thia-substituted analogues 9,10. As expected from our molecular design, neither non-brominated compound 1 nor 9 shows inclusion properties, but the dibrominated structures 2 and 10 act as versatile lattice inclusion host molecules. All our crystal structures of the methylene-bridged compounds 1,2 contain an (EF)6 centrosymmetric dimeric building block, built from three different types of aryl edge-face (EF) interactions. The crystal structures of the thia-compounds 9,10 also involve (EF)6 dimers, but fall into two distinct types. In one group, the sulfur atom effectively mimics the methylene group and isostructural compounds result across the two series. The second group is comprised of structures that are markedly dissimilar between the two series, even though the sulfur substituent does not play an overt role in the molecular packing. These similarities and differences are examined in crystal engineering terms.

The Weber multi-ring aryl hydrocarbons 1–4, dihalo diheteroaryl 6,8, and tetrahalo aryl 10,12 compounds are examples of host molecules from well-known families of lattice inclusion systems. Despite these three systems having a number of features in common, no attempt has been made previously to establish their inter-relationship. In this work, the diheteroaryl ring system of 5 has been substituted with two and four pendant phenyl groups to give the non-halogenated compounds 15 and 17, respectively. In common with typical unsubstituted diheteroaryl compounds (such as 5 and 7), compound 15 shows no host properties. On the other hand, 17 can include several different guests and therefore its behaviour represents a cross-over into the Weber system. Crystal engineering aspects of the X-ray structures of 15, (17)·(chloroform) and (17)·(toluene) are analysed in this light.

New tetrabromo calix[4]arene derivatives 2 and 5a/5b have been synthesised and found to function as inclusion hosts for nitrile guests. The X-ray structures of (2)2 · (pivalonitrile)3 and (5a) · (acetonitrile)3 · (water) show that, in each compound, molecular inclusion occurs by a combination of complexation within the calixarene bowl and lattice inclusion outside the bowl. Racemic 5a/5b crystallises as a conglomerate, with chiral discrimination between these enantiomers being assisted by the propeller-shaped molecular conformation they adopt in the solid state.

Chloro-substituted diquinoline dibromide 6 is a versatile host molecule that includes guest molecules of different functionality in several different ways. The crystal structures of 6 and its lattice inclusion compounds with carbon disulfide, dichloromethane, acetone, chloroform, benzene, and toluene are reported and analyzed in crystal engineering terms. Also described is the quinolinium inclusion compound (11)·(acetophenone). The inclusion properties of 6, and the ways that it achieves these, are very different from those of its non-chlorinated parent, 4. Different types of aromatic interfacial packing are discussed. There is far greater dependence on these types of interactions and a complete absence of the aromatic edge−edge C−H···N dimer motif in the crystal structures of 6.

The major component (35-65%) of the volatile oil obtained by steam distillation of the leaves of Melaleuca triumphalis has been identified as (rel)-1beta-pentyl-1alpha,6alpha-dihydroxy-3,3,5,5-tetramethylcyclohexa-2,4-dione (trivial name triumphalone). Relative stereochemistry was established by nuclear Overhauser experiments and X-ray studies on the 2-(3,5-dinitrobenzoic acid) derivative. The remainder of the oil was composed of mono- and sesquiterpene hydrocarbons and alcohols. On prolonged standing the presence of a rearrangement product of triumphalone was observed which was characterized as (rel)-1beta-pentyl-1alpha,3alpha-dihydroxy-4,4,6,6-tetramethylcyclohexa-2,5-dione (trivial name isotriumphalone), presumably arising from an acid catalyzed shift of the pentyl group from C-1 to C-2.

Copper complexes of a new resorcinol-substituted trimethylethylenediamine ligand have been isolated and characterised. The results reveal limitations to the use chiral ligands with hydrogen bond donor groups located for intermolecular hydrogen bonding for the self-assembly of helical coordination polymers and include the X-ray crystal structure of an unusual mixed-valent Cu(II)2Cu(I) trimer in which CuBr 3 2 - anion acts as a bridging ligand between the two Cu(II) centres.

Three 5,17-diacetylcalix[4]arene derivatives 3–5 have been prepared, evaluated for inclusion properties, and their single crystal X-ray structures determined. The diacetyl calixarenes 3 and 4 were obtained by acetylation of their parent dimethoxy 1 or dipropoxy 2 compounds, respectively, whereas 5,17-diacetyl-25,26,27,28-tetrapropoxycalix[4]arene 5 was prepared by alkylation of 4. Crystallisation of 3 resulted in no inclusion from chloroform, but yielded lattice inclusion compounds from acetonitrile or acetone. The calixarene 3 maintains its cone conformation in these crystals, but displays degrees of distortion depending upon the included solvent. Crystal structures of solvent-free 4 and 5 are also described. A new preparation of the monomethoxy derivative 6 is described, and its X-ray structure with chloroform guest is analysed.

Two new meso-indanyl-substituted calix[4]pyrrole receptors, 2 and 3 , have been synthesized. A range of calix[4]pyrrole host-neutral molecule complexes crystallise from solutions of 2 in a variety of solvents and the structures of four have been elucidated by X-ray crystallography. The F− and Cl− anion affinities of 2 have been measured in acetonitrile, and are significantly different from the corresponding affinities of the prototypical calix[4]pyrrole, the octamethyl-derivative, 1 . ESI-FTICR-MS has been used to determine the relative F− and Cl− anion affinities of receptors 1 and 2 in methanol–acetonitrile solution. Deprotonation of 1 and 2 by fluoride is observed (under the conditions of the MS experiment).

Treatment of 3-(4-chlorophenyl)-7-hydroxymethyl-4,6-dimethoxyindole with 3-(4-chlorophenyl)-4,6-dimethoxyindole results in the generation of two geometrically isomeric diindolylmethanes in addition to a novel triindolyl oligomer, which has been structurally characterised. The 2,7′-diindolylmethanes were found to be unstable under Vilsmeier formylation conditions, thus hampering macrocyle precursor construction. In an alternate approach, the 3-(4-chlorophenyl)-4,6-dimethoxyindole-7-carbaldehyde was converted into the indolyl-pyrrolyl macrocycle precursor 5-(3-(4-chlorophenyl)-4,6-dimethoxyindole-2-ylmethyl)-4-ethyl-3-methylpyrrole-2,7-dicarbaldehyde, which was used to generate an unsymmetrical pentaaza macrocycle.

A range of secondary 2-amidophenylglyoxylamides self-assemble by intermolecular hydrogen bonding between the secondary amide proton and the 2-amidophenyl carbonyl oxygen atom.

The pi – halogen dimer (PHD) interaction is a new type of intermolecular packing motif discovered in certain crystalline diquinoline compounds. It consists of a combination of one aromatic offset face-face (OFF) interaction, and four aromatic pi – halogen interactions, and provides a compact building block for the self-assembly of lattice inclusion compounds. This article reviews the current state of knowledge about this new solid-state construction motif.

The diquinoline derivative 12 was found to yield the diquinolinium dibromide 13 trihydrate on crystallisation from 2-bromoethanol. X-Ray crystallography revealed that the diquinolinium dications pack as parallel (and anti-parallel) stacks, with the bromide ions and water molecules occupying inter-stack channels. The interplay of aromatic offset face-face, N+-H ⋅s O, bromide ⋅s H-O, C-H ⋅s bromide and bromine ⋅s bromide interactions determines this solid-state structure.

The crystal structures of tris(2-methyl-1,10-phenanthroline)ruthenium(II) iodide, tris(6-methyl-2,2′-bipyridine)ruthenium(II) tetrafluoroborate and tris(6,6′-dimethyl-2,2′-bipyridine)ruthenium(II) tetrafluoroborate 0.75 hydrate are described. The average Ru–N distances in the complex cations are 2.063, 2.089, and 2.119 A, severally. The substituents in the ligands exert a strong influence on the geometry of the coordination core, which deviates significantly from regular octahedral. The deviation is most marked for the dimethyl-substituted system where pronounced inter-ligand forces result in gross angular distortion of the relative orientations of the three ligand molecules.

The new pentapyridyldiamine ligand, L1, which incorporates two bis(2-pyridylethyl)amine donor domains held together by a 2,6-dimethylenepyridine linker, is readily prepared. In the presence of metal salts, L1 is unstable due to facile elimination of vinyl pyridine. Complexes of L1 are therefore difficult to isolate. Nonetheless, a novel copper dimer [Cu2(L1)(μ-OH)(CH3CN)](ClO4)3 has been isolated in small quantities along with the interesting monomer [Cu(L2)](ClO4)2, in which L2 is the tetrapyridyldiamine ligand derived from the decomposition of L1 by loss of one pyridylethyl `arm'. The crystal structures of the two complexes are reported: the [Cu2(L1)(μ-OH)(CH3CN)]2+ cation exhibits a μ-hydroxo-bridged dicopper(II) core and a coordinated acetonitrile molecule, akin to a putative intermediate in nitrile hydrolysis, and the chiral [Cu(L2)]2+ cation is revealed to have a five-coordinate copper(II) centre that is stabilised by an intramolecular hydrogen-bond between the 2° amine group and a pendant pyridylethyl `arm'.

Dibromodiquinoline 8 forms lattice inclusion compounds when crystallized from solvents such as dichloromethane, tetrahydrofuran, chloroform, and benzene. The crystal structures of these compounds are described in crystal engineering terms, and are also compared with the solvent-free crystal structures of 8 and its nonbrominated precursor 6. Aromatic edge−edge double C−H···N interactions play a crucial role in all six solids. These comprise both cyclic hydrogen-bonded dimer and bifurcated C−H···N···H−C types. A diverse range of structurally different double C−H···N motifs is encountered in these, and closely related, compounds.

7,15-Dibromo-8,16-diphenyl-6,7,14,15-tetrahydro-6,14-methanocycloocta[1,2-b : 5,6-b′]diquinoline 4 has been synthesised and found to form lattice inclusion compounds with a wide range of guests. The host molecules associate into centrosymmetric brick-like dimers by means of multiple aromatic edge–face (EF) interactions. These (EF)6 units then pack as layers with the guests occupying inter-brick spaces. Differences in tilt and/or translation of the dimers, along with changes in host–guest association, permit accommodation of guest molecules with differing sizes and shapes. The X-ray structures of the 1 : 1 compounds of 4 with chloroform and p-xylene are contrasted.

Reaction of calix[4]arene with alkaline earth metals (Ca/Sr/Ba) in methanol followed by the addition of various titanium(IV) sources afforded novel dimeric 1:1 alkaline earth/titanium(IV) calix[4]arene complexes. In each complex the central core of the crystallographically imposed centrosymmetric dimer consists of a rhombus of alternating alkaline earth metals and μ3-oxo-centres. Five terminal methanol ligands form seven-coordinate calcium and strontium centres, while the barium centres are bridged by two additional methanol ligands, making them nine-coordinate. Each oxo centre is the apical ligand of a square-pyramidal titanium(IV) centre, whose basal plane ligands are the four phenolate oxygens from a calix[4]arene in the symmetrical cone-conformation. Deprotonation of calix[4]arene with potassium metal, followed by the addition of a titanium(IV) source containing at least one acetylacetonate ligand, formed a mixed potassium/titanium complex based on one calix[4]arene. The potassium cation in this complex binds within the π-basic calix[4]arene cavity, whilst titanium is octahedrally complexed in the exo-position, by four phenolates and one acetylacetonate. The alkaline earth titanium dimers and potassium/titanium monomers could be interconverted merely by changing the solvent, with the appropriate cations and ligands present in solution. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The crystallisation and crystal structures of three new crystal forms of MePh3P+I3− are described, bringing to four the number of polymorphs of this compound. Crystallisations were from alcohols, mixed alcohols, and dichloromethane, and are reproducible. There are strong similarities between all four of the crystal packing arrangements, which are solvent-free. In all structures the MePh3P+ cations associate in two-dimensional nets using edge-to-face, offset-face-to-face, and methyl-to-face motifs, and the I3− ions lie between these nets, with subtle variations in structure caused by sliding displacements of relatively constant cation-anion assemblies. The related compound EtPh3P+I3− has very similar crystal packing. The interactions between the I3− and MePh3P+ are mainly C–H⋯I, with some phenyl faces parallel to I3−. The major electrostatic component of the lattice energy is associated with the occurrence of I3− ions against the faces of nets of cations, consistent with this structural feature being the most invariant aspect of the crystal packing, while the structural variability is associated with the less stabilising cation⋯cation motifs. It appears that these crystals provide a good example of a system where shape is not a dominant feature in crystal packing, and that the tetramorphs represent almost equi-ergic local minima in a relatively deep section of the lattice energy hypersurface. The crystal packing of (MePh3P+)2I82− is similar.

A proposal for a redox-linked conformational gate to proton translocation--a proton pump gate--based upon a transition-metal redox-switchable hemilabile ligand (RHL) system is made. Consideration of the requirements for such a system reveals copper(II) to be the ideal metal centre. To test the proposal and, thereby, to provide an artificial proton pump gate, the copper coordination chemistry of three tris(pyridylmethyl)amine (tpa) ligands with one "leg" (PY*) substituted at the 6-position of the pyridine ring by a dimethoxyphenyl (L(1)), a hydroquinone (H(2)L(2)) or a quinone (L(3)) substituent has been investigated. Crystal structures of sp-[Cu(kappa(4)N-L(1))Cl]Cl.3 H(2)O (sp=square pyramidal), sp-[Cu(kappa(3)N-H(2)L(2))Cl(2)] and tbp-[Cu(kappa(4)N,kappaO-HL(2))][PF(6)] (tbp=trigonal bipyramidal) have been determined. The Cu(I) complexes [Cu(L)(MeCN)(n)](+) (L=L(1), H(2)L(2)) display physicochemical properties consistent with a "dangling" PY* leg; from the NMR spectra, the barriers to inversion of the ligand amine donor for the Cu(I) complexes are estimated to be within the range of about 30-45 kJ mol(-1). In the Cu(II) complexes, coordination of the PY* leg is finely balanced and critically depends on the nature of the PY* substituent and the availability of potential co-ligand(s). For example, tbp-[Cu(kappa(4)N-L(1))Cl](+) reacts cleanly with Cl(-) ions to afford sp-[Cu(kappa(3)N-L(1))Cl(2)]; Vis/NIR spectrophotometric titrations suggest the affinity of tbp-[Cu(kappa(4)N-L(1))Cl](+) for Cl(-) ion in dichloromethane is 9.7 x 10(2) and is at least 10(4)-fold greater than that of tbp-[Cu(kappa(4)N-L(3))Cl](+). The complex sp-[Cu(kappa(3)N-H(2)L(2))Cl(2)] has a "dangling" PY* leg, in which an intramolecular OH(hydroquinone).N(pyridine) hydrogen bond "ties-up" the pyridyl nitrogen atom, and reacts with Brønsted bases to give tbp-[Cu(kappa(4)N,kappaO-HL(2))](+). Two-electron oxidation of sp-[Cu(kappa(3)N-H(2)L(2))Cl(2)] is linked to loss of two protons and a conformational change, and affords tbp-[Cu(kappa(4)N-L(3))Cl](+). The [Cu(kappa(3)N-H(2)L(2))Cl(2)]-[Cu(kappa(4)N-L(3))Cl](+) system provides a first demonstration of the critical step in the proposed proton pumping cycle, namely a redox-driven and proton-linked conformational change. The possible biological relevance of this work to proton pumping in cytochrome c oxidase is mentioned.

A convenient synthetic procedure has been developed for the preparation of a series of new C 2 -symmetric clathrate hosts each containing three key structural components: two planar aromatic wings, two protruding sensor groups, and a central linker unit. The dibromo compound 4 described here is built around the flexible bicyclo [3.3.0]octane ring system and has quinoline-based wings. Two molecules of the host wrap around a guest trapping it within a cyclophane-like molecular pen. The aromatic wings function like the fences enclosing an animal in a stockyard. With differing guests the wings slip relative to each other to give the best host-guest combination using a quadrilateral pen. The structures of the 2:1 inclusion compounds formed between 4 with 1,1,1-trichloroethane (methyl chloroform) and 1,1,2,2-tetrachloroethane are discussed.