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The interaction of Cu(II) with three β-diketone ligands of type R1C(O)CH2C(O)R2(where R1= 2-, 3-, or 4-pyridyl and R2= C6H5, respectively), HL1−HL3, along with the X-ray structures and the pKavalues of each ligand, are reported. HL1yields a dimeric complex of type [Cu(L1)2]2. In this structure, two deprotonated HL1ligands coordinate in a transplanar fashion around each Cu(II) center, one oxygen from each CuL2unit bridges to an axial site of the second complex unit such that both Cu(II) centers attain equivalent five-coordinate square pyramidal geometries. The two-substituted pyridyl groups in this complex do not coordinate, perhaps reflecting steric factors associated with the closeness of the pyridyl nitrogen to the attached (conjugated) β-diketonato backbone of each ligand. The remaining two Cu(II) species, derived from HL2and HL3, are both coordination polymers of type [Cu(L)2]nin which the terminal pyridine group of each ligand is intermolecularly linked to an adjacent copper center to generate the respective infinite structures. HL2was also demonstrated to form a fibrous metallogel when reacted with CuCl2in an acetonitrile/water mixture under defined conditions. [ABSTRACT FROM AUTHOR]

Complexes between Cu(ii) or Ni(ii) and O- or N-containing ligands, pyridine-2,6-dicarboxylic acid (H2L1), 4-pyranone-2,6-dicarboxylic acid (H2L2), 4H-pyran-2,6-dicarboxylic acid (H2L3), (S)-tetrahydro-2-furoic acid (S-HL4), 2,2′-bipyridine (L5), 1,10-phenanthroline (L6) or bis(2-pyridylmethyl)amine (L7), have been synthesised and characterised by X-ray crystallography. In the ionic complex [Cu(H2L1)(L5)(OH2)]·[Cu(L1)2]·3H2O (1), one L1group and L5are close to parallel, which is not the case for the dimeric complex [Cu2(HL1)2(L1)(L6)]·5.5H2O (2), in which the HL1groups on each Cu(ii) centre are bent inwards at an angle of 11°. The complex {[Cu(HL3)(L3)0.5(OH2)]·1.75H2O}n(3) shows a paddle-wheel arrangement. In {[Cu(S-L4)(L7)]ClO4}n(S-4), coordination occurs viathe endocyclic O atom and the pendant carboxylic acid group and supports binding modes posited previously for complexes formed in solution between Cu(ii) and N-acetylneuraminic acid (sialic acid). The CD spectrum of S-4(670 nm, −4.8 mdeg; 550 nm, +1.4 mdeg) is equal and opposite to its enantiomer {[Cu(R-L4)(L7)]ClO4}n(R-4). Complexes between Cu(ii) or Ni(ii) and H2L2show a 1-dimensional coordination polymer in [Cu(L2)(OH2)4]n(5) and a discrete complex in [Ni(HL2)2(OH2)4] (6). Complexes 1–6exhibited a range of coordination geometries, nuclearities, chiralities and polymeric architectures, which suggest that the interactions between Cu(ii) or Ni(ii) and endocyclic O- or N-containing bioligands in chemical biology settings will be varied. [ABSTRACT FROM AUTHOR]

Following molecular modelling employing molecular mechanics and semi-empirical (PM3) calculations as an aid to ligand design, a new copper(i)-containing [2]-catenane has been prepared by the reaction of 6,6′-bis[(4″-formylphenoxy)methyl]-2,2′-bipyridyl with 1,6-hexanediamine in the presence of a copper(i) template, followed by in situ sodium borohydride reduction of the tetra-imine species generated. The corresponding [2]-catenane was obtained as a deep orange crystalline solid. The X-ray structure of this product along with that of the corresponding bis-dialdehyde precursor copper(i) complex have been determined. In the latter case, the structure is pre-organized for catenane formation. The new catenane appears to be the first example of a tetrahedral metal template product incorporating a bis-bipyridyl derivative core. Isolation of the metal-free [2]-catenane has also been achieved following treatment of the copper(i) catenane complex in dimethylsulfoxide with tetrabutylammonium cyanide. [ABSTRACT FROM AUTHOR]

The conformations of 14 threonine-derived pseudoproline-containing dipeptides (including four d-allo-Thr derivatives) have been investigated by NMR. In solution, the major conformer observed for all dipeptides is that in which the amide bond between the pseudoproline and the preceding amino acid is cis. For dipeptides in which the N-terminus is protected, the ratio of cis- to trans-conformers does not depend significantly on the side chain of the N-terminal amino acid, or the stereochemistry of the Thr residue. However, for dipeptides bearing a free N-terminus, there are significant differences in the ratios of cis- to trans-conformers depending on the side chain present. Three dipeptides were crystallized and their X-ray structures determined. In two cases, (benzyloxycarbonyl (Cbz)-Val-Thr(ΨMe,Mepro)-OMe and Cbz-Val-Thr(ΨMe,Mepro)-OH), the dipeptides adopt a trans-conformation in the solid state, in contrast to the structures observed in solution. In the third case, (9-fluorenylmethoxycarbonyl (Fmoc)-Val-d-allo-Thr(ΨMe,Mepro)-OH), a cis-amide geometry is observed. These structural differences are attributed to crystal-packing interactions. [ABSTRACT FROM AUTHOR]

Uncharged complexes, formulated as trimeric metallocycles of type [M3(L1)3(Py)6] (where M = cobalt(ii), nickel(ii) and zinc(ii) and L1 is the doubly deprotonated form of a 1,4-phenylene linked bis-β-diketone ligand of type 1,4-bis(RC(O)CH2C(O))C6H4 (R = t-Bu)) have been synthesised, adding to related, previously reported complexes of these metals with L1 (R = Ph) and copper(ii) with L1 (R = Me, Et, Pr, t-Bu, Ph). New lipophilic ligand derivatives with R = hexyl, octyl or nonyl were also prepared for use in solvent extraction experiments. The X-ray structures of H2L1 (R = t-Bu) and of its trinuclear (triangular) nickel(ii) complex [Ni3(L1)3(Py)6]·3.5Py (R = t-Bu) are also presented. Electrochemical studies of H2L1, [Co3(L1)3(Py)6], [Ni3(L1)3(Py)6], [Cu3(L1)3], [Zn3(L1)3(Py)6] and [Fe4(L1)6] (all with R = t-Bu) show that oxidative processes for the complexes are predominantly irreversible, but several examples of quasireversible behaviour also occur and support the assignment of an anodic process, seen between +1.0 and +1.6 V, as involving metal-centred oxidations. The reduction behaviour for the respective metal complexes is not simple, being irreversible in most cases. Solvent extraction studies (water/chloroform) involving the systematic variation of the metal, bis-β-diketone and heterocyclic base concentrations have been performed for cobalt(ii) and zinc(ii) using a radiotracer technique in order to probe the stoichiometries of the respective extracted species. Significant extraction synergism was observed when 4-ethylpyridine was also present with the bis-β-diketone ligand in the chloroform phase. Competitive extraction studies demonstrated a clear uptake preference for copper(ii) over cobalt(ii), nickel(ii), zinc(ii) and cadmium(ii). [ABSTRACT FROM AUTHOR]

A series of platinum(ii) complexes of the type [Pt(NN)(pyB)2](NO3)2 (NN = bipy, phen; pyB = 3- or 4-pyridineboronic acid) were successfully prepared and fully characterised by 1D- and 2D-multinuclear NMR spectroscopy and ESI-MS. Using VT 1H NMR spectroscopy, rotational isomers for [Pt(NN)(3-pyB)2](NO3)2 were identified and the free energies of activation for rotation of 3-pyB about the Pt–N bond were determined to be ΔG‡310 = 69.2 ± 0.1 kJ mol−1 and ΔG‡305 = 66.0 ± 0.1 kJ mol−1 for [Pt(bipy)(3-pyB)2](NO3)2 and [Pt(phen)(3-pyB)2](NO3)2, respectively. The 3- and 4-pyB ligands readily deboronate in boiling H2O to afford [Pt(NN)(py)2](NO3)2; the structure of [Pt(phen)(py)2]2+ (as its PF6− salt) was confirmed by X-ray crystallography. Preliminary thermal denaturation studies revealed only minimal interactions between [Pt(NN)(pyB)2](NO3)2 and calf-thymus DNA and is attributed to hydroxylation of the boronic acid groups at pH 7.4 to afford the corresponding zwitterionic boronate species. This was confirmed by means of variable pH 1H and 11B{1H} NMR spectroscopy. [ABSTRACT FROM AUTHOR]

The synthesis of two new bifuctional ligand sytems incorporating two different “classical” coordination units connected by a bent (but flexible) thioether linkage is reported. The new systems are the -diketone-pyridyl derivative, 3-(pyridin-4-ylthio)pentane-2,4-dione (L1), and its hydrazine condensation product, the pyridyl-pyrazole species 4-(3,5-dimethyl-1H-pyrazol-4-ylthio)pyridine (L2). Both systems were designed for use in metal−organic framework studies. With L1, four metal-containing products were crystallized, Cu(L1−H)2n(1), Cu(L1−H)2·0.5H2O·CHCl3n(2), Zn(L1−H)2·2H2On(3), and Zn(L1−H)2·2MeOHn(4); these display three different array types. Compound 1incorporates 5-coordinate Cu(II) ions with square pyramidal stereochemistry. The -diketonato groups from two ligands coordinate in the basal plane with the apical position occupied by a pyridyl nitrogen from a third ligand that bridges to an adjacent copper center. Propagation of this coordination motif produces a 1D chain. In 2, which is a pseudo-polymorphic phase of 1, each Cu(II) ion is 6-coordinate with each metal center being bound by two bidentate -diketonato groups and two pyridyl donors from four different ligands in a cis configuration. The ligand arrangement bridges each metal to four others producing an infinite 2D rhombic grid (4,4) net. The grids stack to form channels containing disordered water and chloroform molecules; the solvent-accessible space is 33% of the crystal volume. Crystals of 3are isostructural with 2, except that they incorporate water as the only solvate in the channels. The solvent-accessible voids constitute 22% of the crystal volume, reflecting closer packing of adjacent grids. A TGA study showed that the water molecules are removed by 375 K and that the resulting desolvated complex is stable up to 573 K. Compound 4is a pseudo-polymorph of 3in which the 6-coordinate Zn(II) coordination is similar to that in 3but with polymeric connectivity producing a chiral 8,4 type 3D network (space group P41212). Helical channels corresponding to 25% of the crystal volume run parallel to the 4-fold axes and are occupied by methanol guests. With 4-(3,5-dimethyl-1H-pyrazol-4-ylthio)pyridine (L2), an extended array consisting of zwitterionic Co(L2H)Cl3n(5) units linked by hydrogen bonds and the metal-linked molecular framework speciesZn(L2)Cl2·0.5H2On(6) were obtained. The cobalt center in 5is tetrahedrally coordinated by three chloride ions and a pyrazole nitrogen from (L2H); the protonation is present at the pyridyl nitrogen atom. This protonated pyridyl nitrogen forms a charge-assisted hydrogen bond of type N−H···Cl with a coordinated chloride from an adjacent complex to yield a hydrogen-bonded chainlike array. Intermolecular N−H···Cl hydrogen bonds also exist between the non-deprotonated pyrazole nitrogen and adjacent chloro ligands. Each tetrahedral Zn(II) center in 6is coordinated to two chloride ions, a pyridyl nitrogen from one L2ligand and a pyrazole nitrogen from another. Each L2thus bridges adjacent Zn(II) centers, forming 1D polymeric chains that aggregate in the crystal to produce narrow channels occupied by water molecules. [ABSTRACT FROM AUTHOR]

A new metallo-capsule has been synthesised that consists of three copper(ii) ions and two molecules of a tris-deprotonated tripodal ligand in which three 2,4-pentanedione groups are linked via their γ-carbons through thioether spacers to the 1,3,5-positions of a triazine core. [ABSTRACT FROM AUTHOR]

A rigid linear bis-bidentate quaterpyridine undergoes metal directed self-assembly with iron(ii) salts yielding M4L6 host–guest complexes; selective anion binding for PF6− over BF4− is observed. [ABSTRACT FROM AUTHOR]

Five new silver(I) coordination polymers of types [Ag2L1(NO3)2]n(1), [Ag2L2(NO3)2]n(2), [Ag2L3(NO3)2]n(3), [Ag2L4(NO3)2]n(4), and [AgL5(NO3)]n(5) have been synthesized, where L1–L5are the Schiff base ligands formed from 2:1 condensation of acetylacetone with the symmetrical diamines H2N(CH2)nNH2, with n= 2 and 6 to give L1and L2, 1,2-bis(2-aminophenoxy)ethane to give L3, 1,4-bis(2-aminophenoxy)butane to give L4, and 1,6-bis(4-aminophenoxy)butane to give L5. The single crystal X-ray structures of the Ag(I) complexes 1–5have been determined. Both 1and 2adopt three-dimensional polymeric network structures, while 3–5adopt two-dimensional-layered framework structures. In 1and 2, the terminal O and γ-C atoms of two acacH-imine domains of the same ligand bind to different silver ions, while in each of 3–5a γ-C from one or both acacH-imine domains binds to a silver ion, with the remaining coordination sites occupied by bridging monodentate or bidentate nitrato groups and/or a Schiff base ligand oxygen donor. [ABSTRACT FROM AUTHOR]

In the present study the interaction of Fe(ii) and Ni(ii) with the related expanded quaterpyridines, 1,2-, 1,3- and 1,4-bis-(5′-methyl-[2,2′]bipyridinyl-5-ylmethoxy)benzene ligands (4–6respectively), incorporating flexible, bis-aryl/methylene ether linkages in the bridges between the dipyridyl domains, was shown to predominantly result in the assembly of [M2L3]4+complexes; although with 4and 6there was also evidence for the (minor) formation of the corresponding [M4L6]8+species. Overall, this result contrasts with the behaviour of the essentially rigid ‘parent’ quaterpyridine 1for which only tetrahedral [M4L6]8+cage species were observed when reacted with various Fe(ii) salts. It also contrasts with that observed for 2and 3incorporating essentially rigid substituted phenylene and biphenylene bridges between the dipyridyl domains where reaction with Fe(ii) and Ni(ii) yielded both [M2L3]4+and [M4L6]8+complex types, but in this case it was the latter species that was assigned as the thermodynamically favoured product type. The X-ray structures of the triple helicate complexes [H2O⊂Ni2(4)3](PF6)4·THF·2.2H2O, [Ni2(6)3](PF6)4·1.95MeCN·1.2THF·1.8H2O, and the very unusual triple helicate PF6−inclusion complex, [(PF6)⊂Ni2(5)3](PF6)3·1.75MeCN·5.25THF·0.25H2O are reported. [ABSTRACT FROM AUTHOR]

As an extension of prior studies involving the linear quaterpyridine ligand, 5,5′′′-dimethyl-2,2′:5′,5′′:2′′,2′′′-quaterpyridine 1, the synthesis of the related expanded quaterpyridine derivatives 2and 3incorporating dimethoxy-substituted 1,4-phenylene and tetramethoxy-substituted 4,4′-biphenylene bridges between pairs of 2,2′-bipyridyl groups has been carried out viadouble-Suzuki coupling reactions between 5-bromo-5′-methyl-2′-bipyridine and the appropriate di-pinacol-diboronic esters using microwave heating. Reaction of 2and 3with selected Fe(ii) or Ni(ii) salts yields a mixture of both [M2L3]4+triple helicates and [M4L6]8+tetrahedra, in particular cases the ratio of the products formed was shown to be dependent on the reaction conditions; the respective products are all sufficiently inert to allow their chromatographic separation and isolation. Longer reaction times and higher concentrations were found to favour tetrahedron formation. The X-ray structures of solvated [Ni2(2)3](PF6)4, [(PF6) ⊂ Fe4(2)6](PF6)7, [Fe4(3)6](PF6)8and [Ni4(3)6](PF6)8have been determined, while the structure of the parent Fe(ii) cage in the series, [(PF6) ⊂ Fe4(1)6](PF6)7, was reported previously. The internal volumes of the Fe(ii) tetrahedral cages have been calculated and increase from 102 Å3for [Fe4(1)6]8+to 227 Å3for [Fe4(2)6]8+to 417 Å3for [Fe4(3)6]8+and to an impressive 839 Å3for [Ni4(3)6]8+. The corresponding void volume in the triple helicate [Ni2(2)3]4+is 29 Å3. [ABSTRACT FROM AUTHOR]

The formation of 3D fused 10-membered “bracelet” frameworks derived from the alkyl-substituted curcurbit[5]urils (SQ[5]s), 1,2,4-hexamethylcucurbit[5]uril (1,2,4-HMeQ[5]), and pentacyclopentanocucurbit[5]uril (PCyHQ[5]) and K誉 is described. These remarkable catenated structures feature trigonal-planar branching units involving three SQ[5]s connected via their bound K誉 in a triangular manner in which the coordination of each K誉 to the five portal carbonyl oxygen atoms of one SQ[5] as well as to a bridging portal carbonyl oxygen from an adjacent SQ[5] draws the edges of three portals into close proximity. The corresponding offset angle at each junction provides the basis for the 3D assembly of the observed fused 10-membered SQ[5] bracelet frameworks. [ABSTRACT FROM AUTHOR]

Cyclic tetrapeptides have generated great interest because of their broad-ranging biological properties. In order to synthesize these highly strained 12-membered cyclic compounds, a cyclization strategy using pseudoprolines as removable turn inducers has been developed. The pseudoproline derivatives induce a cisoidamide bond in the linear peptide backbone which facilitates cyclization. After cyclization, the turn inducers can be readily removed to afford cyclic tetrapeptides containing serine or threonine residues. [ABSTRACT FROM AUTHOR]

Diastereopure (1R,2R)-N,N′-bis(acetylacetone)cyclohexanedi-imine L1and its corresponding (1R,2R)L1/(1S,2S)L2enantiomeric mixture react with AgNO3to yield the unusual coordination polymer [Ag2(L1)(L2)(NO3)2]n(1) and the unique trimetallic discrete species {[Ag3(L1)3(μ3-O,O,O-NO3)(H2O)3]2(NO3)}(NO3)3·8.5H2O (2) which incorporates a symmetrical μ3-bridging nitrato group that gives rise to a C3-symmetric triskelion motif; both species also feature γ-carbon η1aryl-like coordination of neutral bridging acetylacetone-imine units to the respective Ag(I) centres. [ABSTRACT FROM AUTHOR]

The synthesis and crystal structure of a new 34-membered N6O4-donor macrocycle 2 is reported. Solvent extraction experiments (water/chloroform) indicated that 2 acts as an efficient extractant towards silver(i) and zinc(ii) at pH values beyond 6 while the extraction of iodide and chromate occurs below this pH. A competitive metal extraction experiment at pH 7.2 in which the perchlorate salts of cobalt(ii), nickel(ii), copper(ii), zinc(ii) and cadmium(ii) were present together in the aqueous phase led to the following order of increasing extraction efficiency: cobalt(ii) < nickel(ii) < zinc(ii) < copper(ii) ∼ cadmium(ii). A substantial synergistic enhancement of zinc(ii) salt extraction was observed for a dual-host extraction system using the macrocycle 2 as cation binder and the tripodal thiourea ligand 3 as anion receptor; in particular, a notable extraction of zinc(ii) sulfate was obtained. [ABSTRACT FROM AUTHOR]