3-Methylpiperidinium ionic liquids.

A wide range of room temperature ionic liquids based on the 3-methylpiperdinium cation core were produced from 3-methylpiperidine, which is a derivative of DYTEK® A amine. First, reaction with 1-bromoalkanes or 1-bromoalkoxyalkanes generated the corresponding tertiary amines (Rmßpip, R = alkyl or alkoxyalkyl); further quaternisation reactions with the appropriate methylating agents yielded the quaternary [Rmmßpip]X salts (X(-) = I(-), [CF3CO2](-) or [OTf](-); Tf = -SO2CF3), and [Rmmßpip][NTf2] were prepared by anion metathesis from the corresponding iodides. All [NTf2](-) salts are liquids at room temperature. [Rmmßpip]X (X(-) = I(-), [CF3CO2](-) or [OTf](-)) are low-melting solids when R = alkyl, but room temperature liquids upon introduction of ether functionalities on R. Neither of the 3-methylpiperdinium ionic liquids showed any signs of crystallisation, even well below 0 °C. Some related non-C-substituted piperidinium and pyrrolidinium analogues were prepared and studied for comparison. Crystal structures of 1-hexyl-1,3-dimethylpiperidinium tetraphenylborate, 1-butyl-3-methylpiperidinium bromide, 1-(2-methoxyethyl)-1-methylpiperidinium chloride and 1-(2-methoxyethyl)-1-methylpyrrolidinium bromide are reported. Extensive structural and physical data are collected and compared to literature data, with special emphasis on the systematic study of the cation ring size and/or asymmetry effects on density, viscosity and ionic conductivity, allowing general trends to be outlined. Cyclic voltammetry shows that 3-methylpiperidinium ionic liquids, similarly to azepanium, piperidinium or pyrrolidinium counterparts, are extremely electrochemically stable; the portfolio of useful alternatives for safe and high-performing electrolytes is thus greatly extended.

Alkyltributylphosphonium chloride ionic liquids: synthesis, physicochemical properties and crystal structure.

A series of alkyltributylphosphonium chloride ionic liquids, prepared from tributylphosphine and the respective 1-chloroalkane, C(n)H(2n+1)Cl (where n = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12 or 14), is reported. This work is a continuation of an extended series of tetraalkylphosphonium ionic liquids, where the focus is on the variability of n and its impact on the physical properties, such as melting points/glass transitions, thermal stability, density and viscosity. Experimental density and viscosity data were interpreted using QPSR and group contribution methods and the crystal structure of propyl(tributyl)phosphonium chloride is detailed.

Mercuric ionic liquids: [C(n)mim][HgX3], where n = 3, 4 and X = Cl, Br.

A series of mercury(II) ionic liquids, [C(n)mim][HgX(3)], where [C(n)mim] = n-alkyl-3-methylimidazolium with n = 3, 4 and X = Cl, Br, have been synthesized following two different synthetic approaches, and structurally characterized by means of single-crystal X-ray structure analysis ([C(3)mim][HgCl(3)] (1), Cc (No. 9), Z = 4, a = 16.831(4) Å, b = 10.7496(15) Å, c = 7.4661(14) Å, ß = 105.97(2)°, V = 1298.7(4) Å(3) at 298 K; [C(4)mim][HgCl(3)] (2), Cc (No. 9), Z = 4, a = 17.3178(28) Å, b = 10.7410(15) Å, c = 7.4706(14) Å, ß = 105.590(13)°, V = 1338.5(4) Å(3) at 170 K; [C(3)mim][HgBr(3)] (3), P2(1)/c (No. 14), Z = 4, a = 10.2041(10) Å, b = 10.7332(13) Å, c = 14.5796(16) Å, ß = 122.47(2)°, V = 1347.2(3) Å(3) at 170 K; [C(4)mim][HgBr(3)] (4), Cc (No. 9), Z = 4, a = 17.093(3) Å, b = 11.0498(14) Å, c = 7.8656(12) Å, ß = 106.953(13)°, V = 1421.1(4) Å(3) at 170 K). Compounds 1, 2, and 4 are isostructural and are characterized by strongly elongated trigonal [HgX(5)] bipyramids, which are connected via common edges in chains. In contrast, 3 contains [Hg(2)Br(6)] units formed by two edge-sharing tetrahedra. With melting points of 69.3 °C (1), 93.9 °C (2), 39.5 °C (3), and 58.3 °C (4), all compounds qualify as ionic liquids. 1, 2, and 4 solidify upon fast cooling as glasses, whereas 3 crystallizes. Cyclic voltammetry shows two separate, quasi-reversible redox processes, which can be associated with the 2Hg(2+)/Hg(2)(2+) and Hg(2)(2+)/2Hg redox couples.

Solid and liquid charge-transfer complex formation between 1-methylnaphthalene and 1-alkyl-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide ionic liquids.

Liquid charge-transfer (CT) complexes were observed to form on contacting electron-rich aromatics with electron withdrawing group appended 1-alkyl-4-cyanopyridinium ionic liquids (ILs). Cooling below the melting point of the ionic liquid resulted in crystallisation of ionic liquid from the complex for 2-cyano and 3-cyano pyridinium isomers and in the formation of a 1 : 1 IL : aromatic crystalline CT-complex with the 4-cyanopyridinium isomer. The liquid structure of a 1 : 1 mixture of 1-methyl-4-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide with 1-methylnaphthalene has been probed by neutron diffraction experiments and molecular dynamics simulations. A high degree of correlation between the experimental data and the simulations was found with a significant displacement of the anions from around the cation by the aromatic species and the resulting structure having pi-pi stacks between the cations and the aromatic.

In search of pure liquid salt forms of aspirin: ionic liquid approaches with acetylsalicylic acid and salicylic acid.

We present an ionic liquid (IL) approach towards a dual functional liquid salt form of aspirin using different pharmaceutically active cations composed of antibacterials, analgesics, local anesthetics, and antiarrhythmic drugs in combination with acetylsalicylic acid or its metabolite salicylic acid and discuss stability of these ILs in comparison to solid salts. Several low-melting or liquid salts of salicylic acid with dual functionality and promising properties were isolated and characterized; however, although such ILs with aspirin could be prepared, they suffer from limited stability and slowly decompose into the corresponding salicylate ILs when exposed to moisture.

Ionic liquids containing boron cluster anions.

The combination of different boron cluster anions and some of the cations typically found in the composition of ionic liquids has been possible by straightforward metathetic reactions, producing new low melting point salts; the imidazolium cations have been systematically studied, [C(n)mim]+ (when [C(n)mim]+ = 1-alkyl-3-methylimidazolium; n = 2, 4, 6, 8, 10, 12, 14, 16, or 18). Melting points increase in the anionic order [Co(C2B9H11)2]- < [C2B9H12]- < [B10Cl10]2- < [B12Cl12]2-. Nevertheless, alkyl chain length dramatically influences the thermal behavior, suggesting that packing inefficiency is the main cause of the existence of room temperature ionic liquids. The salts [C(n)mim][Co(C2B9H11)2] (n = 4, 6, 8, 10, 12 or 14) are liquids at room temperature, presenting strikingly low glass transition temperatures (> or = -34 degrees C). The salts [C(n)mim]2[X] ([X]2- = [B10Cl10]2- or [B12Cl12]2-, n = 16 or 18) show liquid crystal phases between the solid and liquid states. Tetraalkylphosphonium salts of [B10Cl10]2- have also been prepared. Physical properties, such as thermal stability, density, or viscosity, have been measured for some selected samples. The presence of the perhalogenated dianion [B12Cl12]2- in the composition of the imidazolium salts renders highly thermally stable compounds. For example, [C2mim]2[B12Cl12] starts to decompose above 480 degrees C in a dynamic TGA analysis under a dinitrogen atmosphere. Crystal structures of [C2mim][Co(C2B9H11)2] and [C2mim]2[B12Cl12] have been determined. 1H NMR spectra of selected imidazolium-boron cluster anion salts have been recorded from solutions as a function of the concentration, showing trends related to the cation-anion interactions.

The cyclic "silver-diphos" motif [Ag2(mu-diphosphine)2]2+ as a synthon for building up larger structures.

The dinuclear, cyclic structural motif [Ag2(diphosphine)2](2+), here termed the "silver-diphos" motif, previously observed in many diphosphine-silver complexes, has been investigated as a synthon for building up larger structures such as coordination cages and polymers. A series of ligands containing one to four meta-substituted diphosphine groups, attached via a central core, has been synthesized from the corresponding fluoroarenes by reaction with KPPh2. Upon reaction with silver salts, the target synthon is adopted by meta-substituted diphosphines 1,3-bis(diphenylphosphino)benzene (L1), 2,6-bis(diphenylphosphino)benzonitrile (L2), and 3,5-bis(diphenylphosphino)benzamide (L3), each of which gives a single species in solution consistent with the expected dimeric complexes [Ag2L2(anion)2]. X-ray crystal structures of [Ag2(L1)2(OTf)2] and [Ag2(L2)2(SbF6)2] confirm the adoption of the silver-diphos motif in the solid state. Amide-functionalized diphosphine L3 forms a hydrogen-bonded chain structure in the solid state via the amide group. A discrete boxlike cage [Ag4(L4)2][SbF6]4 based on two silver-diphos synthons is formed when the tetraphosphine Ph2Sn{3,5-bis(diphenylphosphino)benzene}2 (L4) reacts with silver(I). Its single-crystal X-ray structure reveals a central cavity of minimum diameter, ca. 5.0 A, which contains a single SbF6(-) counterion disordered over two sites. In contrast to the highly selective behavior of the di- and tetra-phosphines L1-L4, the heptaphosphine P{3,5-bis(diphenylphosphino)benzene}3 L5 and the hexaphosphine PhSn{3,5-bis(diphenylphosphino)benzene}3 L6 give dynamic mixtures upon reaction with silver salts in solution. This nonspecific behavior is rationalized by the fact that their diphosphine groups are not appropriately disposed to form stable discrete structures based on the silver-diphos synthon. By contrast, the octaphosphine Sn{3,5-bis(diphenylphosphino)benzene}4 L7 does selectively form a single, discrete, highly symmetrical product in solution, [Ag4(L7)(OTf)4]. In this case, the ligand unexpectedly adopts an interarm tetra-chelating coordination mode, resulting in a continuous 24-membered ring around the periphery of the molecule. To understand the adoption of this unusual coordination mode, the alternative diphosphine Ph2Sn(3-diphenylphosphinobenzene)2 L8, which models a single interarm chelating site of L7, was also investigated. By contrast to L7, its coordination was nonspecific, giving mixtures of silver complexes upon reaction with AgOTf. The selective interarm chelation by L7 may therefore be stabilized by the continuous coordination ring in [Ag4(L7)(OTf)4]; that is, the four chelating sites can be thought of as acting in a cooperative manner. Alternatively, interarm steric repulsions between phenyl groups may favor interarm chelation. Overall, we conclude that, if the diphosphine groups are appropriately articulated to act independently (i. e., they are adequately separated and oriented), the silver-diphos synthon can be a useful tool for the coordination-based self-assembly of larger structures.

A new approach for the detection of ethylene using silica-supported palladium complexes.

The coordination of olefins to square-planar Pd(II) and Pt(II) complexes containing 2,9-dimethylphenanthroline ( L1) often involves a change of color associated with a change of geometry at the metal center. In order to obtain suitable colorimetric detectors for ethylene gas, a series of new Pd(II) and Pt(II) compounds with a range of 2,9-disubstituted phenanthroline ligands [2,9-di- n-butyl-1,10-phenanthroline ( L2), 2,9-di- s-butyl-1,10-phenanthroline ( L3), 2,9-diphenyl-1,10-phenanthroline ( L4), and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (bathocuproine, L5)] have been prepared and their reactivity toward ethylene investigated both in solution and after depositing the detector compounds on a variety of solid supports. The Pd(II) complex [PdCl 2( L2)] supported on silica undergoes a clear color change upon exposure to ethylene, while remaining stable toward air and water, and forms the basis for new simple colorimetric detectors with potential applications in ethylene pipe-leak detection and the monitoring of fruit ripening. Encouragingly, the detector is able to discriminate between fruit at different stages of ripening. The response of the detector to other volatiles was also examined, and specific color changes were also observed upon exposure to aromatic acetylenes. The crystal structures of four new derivatives, including the ethylene-Pt(II) complex [PtCl 2(C 2H 4)( L2)], are also described.

Liquid structure of the ionic liquid, 1-methyl-4-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide determined from neutron scattering and molecular dynamics simulations.

The liquid structure of 1-methyl-4-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide, a prototypical ionic liquid containing an electron-withdrawing group on the cation, has been investigated at 368 K. Experimental neutron scattering combined with empirical potential structure refinement analysis of the data and classical molecular dynamics simulations have been used to probe the liquid structure in detail. Both techniques generated highly consistent results that provide valuable validation of the force fields and refinement approaches. A significant degree of apparent charge ordering is found in the liquid structure, although the nonspherical shape of the ions results in interpenetration of cations into the first shell of adjacent cations, with much shorter closest contact distances than the averaged center-of-mass cation-cation and cation-anion separations.

Metamorphosis of a butterfly: synthesis, structural, thermal, magnetic and DFT characterisation of a ferromagnetically coupled tetranuclear copper(II) complex.

The reaction in water of Cu(OH)(2) with 2,2'-bipyridine (bipy) and (NH(4))(2)HPO(4) in a 4 : 4 : 2 molar ratio under an inert atmosphere leads to the formation of a tetranuclear copper(II) complex of formula {[(H(2)O)(2)Cu(4)(bipy)(4)(mu(4)-PO(4))(2)(mu(2)-OH)] x 0.5 HPO(4) x 15.5 H(2)O}, 1, with butterfly topology. The structure of the tetranuclear core in 1 consists of four crystallographically unique copper(II) ions in approximate square-pyramidal geometry with each coordinated to a bipy ligand and interacting through two mu(4)-O,O',O''-phosphate bridges. Additional bridging between Cu(3) and Cu(4) is provided by a hydroxide ligand, whereas two water molecules cap the Cu(1) and Cu(2) square pyramids to yield a N(2)O(3) chromophore at each copper atom. Adjacent tetranuclear units align in anti-parallel fashion where proximate metal-bound water molecules interact with each other through both intra- and inter-molecular H-bonding to link two such clusters. These pairs then further associate through pi[...]pi interactions between bipy ligands to form a 2D sheet with neighbouring sheets separated by H-bonded lattice water molecules, which form a 2D H-bonded network. Variable-temperature magnetic susceptibility measurements performed upon 1 reveal net intramolecular ferromagnetic coupling between the copper(II) ions and this is supported and rationalized by a DFT study.

Synthesis and structural and magnetic characterization of {[(phen)(2)Ni](2)(micro-P(2)O(7))} . 27H(2)O and {[(phen)(2)Mn](2)(micro-P(2)O(7))} . 13H(2)O: rare examples of coordination complexes with the pyrophosphate ligand.

The reaction in water of M(II) [M = Ni or Mn] with 1,10-phenanthroline (phen) and sodium pyrophosphate (Na4P2O7) in a 2:4:1 stoichiometry resulted in the crystallization of dinuclear complexes featuring the heretofore rare bridging pyrophosphate. Single-crystal X-ray diffraction studies revealed the complexes to be {[(phen)2Ni]2(micro-P2O7)} . 27H2O (1) and {[(phen)2Mn]2(micro-P2O7)} . 13H2O (2) where the asymmetric M(phen)2 units are bridged by bis-bidentate pyrophosphate, each metal ion exhibiting a distorted octahedral geometry. The bridging pyrophosphate places adjacent metal centers at 5.031 A in 1 and 4.700 A in 2, and its conformation also gives rise to an intramolecular pi-pi interaction between two adjacent phen ligands. Intermolecular pi-pi interactions between phen ligands from adjacent dinuclear complexes create an ornate 3D network in 1, whereas a 2D sheet results in 2. The hydrophilic nature of the pyrophosphate ligand leads to heavy hydration with the potential solvent-accessible area for 1 and 2 accounting for 45.7% and 26.4% of their unit cell volumes, respectively. Variable-temperature magnetic susceptibility measurements on polycrystalline samples of 1 and 2 revealed net weak intramolecular antiferromagnetic coupling between metal centers in both compounds with J = -3.77 cm(-1) in 1 and J = -0.88 cm(-1) in 2, the Hamiltonian being defined as H = -JSA.SB. The ability of the bis-bidentate pyrophosphate to mediate magnetic interactions between divalent first row transition metal ions is discussed bearing in mind the number and nature of the interacting magnetic orbitals.

Structure and solvation in ionic liquids.

This Account describes experimental data used to understand the structure of ionic liquids and solute-solvent interactions of both molecular solutes and dissolved metal complexes. In general, the structures of the ionic liquids determined from experimental data show good agreement with both simulated structures and solid-state structures. For all ionic liquids studied, strong charge ordering is found leading to long-range order even in the presence of a solute. For dissolved metal complexes, the ionic liquid is not innocent and a clear dependence on the speciation is observed with variations in both the cation and anion.

Rational design of a dual-mode optical and chemical prodrug.

PURPOSE: The purpose of this study is to demonstrate the rational design and behaviour of the first dual-mode optical and chemical prodrug, exemplified by an acetyl salicylic acid-based system. METHODS: A cyclic 1,4-benzodioxinone prodrug was synthesised by reaction of 3,5-dimethoxybenzoin and acetyl salicoyl chloride with pyridine. After purification by column chromatography and recrystallization, characterization was achieved using infrared and NMR spectroscopies, mass spectrometry, elemental analysis and single crystal X-ray diffraction. Light-triggered drug liberation was characterised via UV-visible spectroscopy following low-power 365 nm irradiation for controlled times. Chemical drug liberation was characterised via UV-visible spectroscopy in pH 5.5 solution. RESULTS: The synthetic method yielded pure prodrug, with full supporting characterisation. Light-triggered drug liberation proceeded at a rate of 8.30x10(-2) s-1, while chemical, hydrolytic liberation proceeded independently at 1.89x10(-3) s-1. The photochemical and hydrolytic reactions were both quantitative. CONCLUSIONS: This study demonstrates the first rational dual-mode optical and chemical prodrug, using acetyl salicylic acid as a model, acting as a paradigm for future dual-mode systems. Photochemical drug liberation proceeds 44 times faster than chemical liberation, suggesting potential use in drug-eluting medical devices where an additional burst of drug is required at the onset of infection.

Thermodynamics, structure, and dynamics in room temperature ionic liquids: the case of 1-butyl-3-methyl imidazolium hexafluorophosphate ([bmim][PF6]).

A detailed investigation of the phase diagram of 1-butyl-3-methyl imidazolium hexafluorophosphate ([bmim][PF(6)]) is presented on the basis of a wide set of experimental data accessing thermodynamic, structural, and dynamical properties of this important room temperature ionic liquid (RTIL). The combination of quasi adiabatic, continuous calorimetry, wide angle neutron and X-ray diffraction, and quasi elastic neutron scattering allows the exploration of many novel features of this material. Thermodynamic and microscopic structural information is derived on both glassy and crystalline states and compared with results that recently appeared in the literature allowing direct information to be obtained on the existence of two crystalline phases that were not previously characterized and confirming the view that RTILs show a substantial degree of order (even in their amorphous states), which resembles the crystalline order. We highlight a strong connection between structure and dynamics, showing the existence of three temperature ranges in the glassy state across which both the spatial correlation and the dynamics change. The complex crystalline polymorphism in [bmim][PF(6)] also is investigated; we compare our findings with the corresponding findings for similar RTILs. These results provide a strong experimental basis for the exploration of the features of the phase diagram of RTILs and for the further study of longer alkyl chain salts.

Liquid structure of the ionic liquid 1,3-dimethylimidazolium bis[(trifluoromethyl)sulfonyl]amide.

Neutron diffraction has been used to determine the liquid structure of 1,3-dimethylimidazolium bis[(trifluoromethyl)sulfonyl]amide ([dmim][NTf2]). Significantly smaller charge ordering is found in this liquid compared with analogous chloride and hexafluorophosphate salts due to the diffuse charge density and size of the [NTf2]- anion. This is manifested in a much larger cation-cation and cation-anion separation and an overlap of the cation-cation and cation-anion shells. Comparison of the liquid structure with the crystal structure reported by Holbrey et al. (Dalton Trans. 2004, 2267) indicates little correlation, for example, the [NTf2]- anion adopts a trans orientation predominantly in the liquid whereas a cis orientation is found in the solid phase.

Hydrogen-bond tuning of ferromagnetic interactions: synthesis, structure and magnetic properties of polynuclear copper(II) complexes incorporating p-block oxo-anions.

The reaction of copper(II) hydroxide with 2,2'-bipyridine (bipy) (1 : 1) in alkaline aqueous solution (pH 14) at room temperature affords the alternating carbonate/hydroxo-bridged copper(II) polymeric chain compound {[Cu3(bipy)3(mu-OH)2(mu-CO3)2].11H2O}n, 1, as determined by single-crystal X-ray diffraction. The structure of 1 is built up from two similar centro-symmetric dinuclear [(bipy)Cu(mu-OH)]2 cores which link together via bridging carbonate groups to mononuclear [(bipy)Cu] fragments to form the chain. Interdigitation of adjacent chains through pi-pi interactions, which involve each bipy ligand, forms sheets that are separated by the water molecules of crystallisation. Variable-temperature magnetic susceptibility measurements have shown that 1 behaves as an isolated spin doublet with two non-interacting spin triplets with the magnetic coupling through the bis-mu-hydroxo bridges being strongly ferromagnetic in nature. The hydrothermal reaction of copper(II) hydroxide, bipy and ammonium hydrogenphosphate (pH 8) yields a dinuclear copper(II) complex of formula {[Cu2(bipy)2(mu-OH)2(HPO4)(H2O)].4H2O}, 2, as determined by single-crystal X-ray diffraction. The structure of consists of an asymmetric dinuclear bis-mu-hydroxo copper(II) core with a monodentate hydrogenphosphate dianion coordinating to one copper(II) atom (above) and a water molecule to the other (below). Intra- and inter-molecular hydrogen bond interactions involving the hydrogenphosphate, water molecules and bis-mu-hydroxo groups link adjacent dinuclear fragments into chains, which interdigitate to form sheets that are separated by the water molecules of crystallisation. The investigation of the magnetic properties of 2 showed that the strength of the ferromagnetic interaction through the bis-mu-hydroxo bridges is influenced by the significant out-of-plane displacement of the hydrogen atom of the hydroxo groups, brought about through hydrogen bonding to the hydrogenphosphate ligand, and yielded the strongest ferromagnetic coupling yet reported for the bis-mu-hydroxo copper(II) core.

Polar self-assembly: steric effects leading to polar mixed-ligand coordination cages.

We present a highly unusual example of self-assembly, specifically a polar, mixed-ligand cage which forms in preference to symmetrical homo-ligand products, and which suggests that steric effects can be exploited to obtain novel non-uniform polyhedral cages. In particular, reaction between the bulky tripodal triphosphine 2,4,6-tris(diphenylphosphino)triazine, L1, the non-bulky tripodal trinitrile 2,4,6-tris(cyanomethyl)trimethylbenzene, L2 and silver hexafluoroantimonate, AgSbF6, in a 3:1:4 ratio gives the mixed-ligand aggregate [Ag4(L1)3(L2)(SbF6)]3+, 1-SbF6, instantly as the only product in quantitative yield. The X-ray crystal structure of complex 1-SbF6 is consistent with the suspected solution-state structure. The cage derives from trigonal-pyramidal geometry, the basal vertices of which are defined by three bulky triphosphines, L1, and the apical vertex by the non-bulky trinitrile, L2. There is apical elongation amounting to 19% in comparison to the ideal uniform tetrahedron. The cage also encapsulates an SbF6 anion. 19F NMR spectra in solution for the analogous PF6 complex [Ag4(L1)3(L2)(PF6)]3+, 1-PF6, confirm that one anion is also encapsulated in solution. The synthesis of the analogous CF3SO3(-) complex, [Ag4(L1)3(L2)(OTf)]3+, 1-OTf, in solution is also described, although 1-PF6 and 1-OTf could not be isolated due to slow decomposition in solution. The selective formation of these mixed-ligand cages is discussed in terms of ligand-ligand and ligand-included anion steric repulsions, which we propose prevent the formation of the competing hypothetical homo-ligand tetrahedral structure [Ag4(L1)4(SbF6)]3+, and thus favour the mixed ligand cage. "Cage cone angles" for L1 and L2 are estimated at 115 degrees and 101 degrees, respectively. Variable-temperature 31P NMR spectroscopy shows that complex 1-SbF6 and the related previously reported partial tetrahedral complex [Ag4(L1)3(anion)]3+ undergo dynamic twisting processes in solution between enantiomeric C3-symmetry conformations.

A new approach to combretastatin D2.

A concise and convergent route to combretastatin D2 is described together with some preliminary biological data.

First EXAFS studies on aurophilic interactions in solution.

EXAFS has been used to directly show the existence of Au...Au interactions in dissolved Au(I) complexes for the first time; the information has been used to understand the optical properties of these materials.