Unexpected proline coordination in the copper chain polymer [Cu(μ‐Cl)2(μ‐DL‐proline‐κ2O:O′)]1∞

In catena‐poly[copper(II)‐di‐μ‐chlorido‐μ‐proline‐κ²O:O′], [CuCl₂(C₅H₉NO₂)]_n, two symmetry‐independent metal cations adopt distorted octahedral coordination, typical for d⁹ Jahn–Teller systems. Each chloride bridge is involved in both a short and a very long interaction with a Cu^II centre. The centrosymmetric crystal structure contains homochiral chains of opposite handedness which extend along the shortest lattice parameter (i.e. a). The O:O′‐bridging coordination mode of proline, although a common motif for such complexes in general, is remarkable for Cu^II; the vast majority of amino acid derivatives of this cation are characterized by N,O‐chelation.     

A New Chain Polymer via Thermolysis: [Hg(μ‐Br)2(3,5‐Br2py)]∞

The new ligand‐deficient chain polymer [Hg(μ‐Br)₂(3,5‐Br₂py)]_∞ has been obtained in form of single crystals by thermolysis of the ligand‐rich [Hg(μ‐Br)₂(3,5‐Br₂py)₂]_∞ at 180 °C at ambient pressure. From this reaction, high quality crystals of the product are directly accessible. The title compound features Hg^II cations in a distorted square‐pyramidal coordination; their metal centers aggregate via edge‐sharing with asymmetric halide bridges to chains in which all apical N donor ligands are oriented to the same side of the [Hg(μ‐Br)₂]_∞ backbone. The new polymer cannot be prepared by stoichiometric reaction in solution.     

Exfoliation of hexa-peri-hexabenzocoronene in water

Unsubstituted hexa-peri-hexabenzocoronene (HBC)-a small and well defined model system for graphite/graphene-was exfoliated and dissolved in water and the resulting individualized nano graphene sheets were characterized spectroscopically for the first time.     

Synthesis of chromium(0) and molybdenum(0) bis (eta(6)-arene) derivatives and their monoelectronic oxidation to [M(eta(6)-arene)(2)](+) cations

M(eta(6)-arene)(2) species (M = Cr, arene = 1,3,5-Me(3)C(6)H(3); M = Mo, arene = 1,3,5-Me(3)C(6)H(3), 1,3,5-(i)Pr(3)C(6)H(3)), have been prepared by a modified Fischer-Hafner synthesis or by metal vapour techniques. The reaction of Cr(eta(6)-1,3,5-Me(3)C(6)H(3))(2) with the fulvene derivatives pentacarbomethoxycyclopentadiene (pcmcpH), 1-benzoyl-6-hydroxy-6-phenylfulvene (dbcpH), or 1-benzoyl-3-nitro-6-hydroxy-6-phenylfulvene (dbncpH) proceeds with evolution of dihydrogen and formation of the ionic derivatives [Cr(eta(6)-1,3,5-Me(3)C(6)H(3))(2)][E], where E = pcmcp, dbcp, or dbncp. Mo(eta(6)-arene)(2) derivatives (arene = toluene, 1,3,5-Me(3)C(6)H(3), 1,3,5-(i)Pr(3)C(6)H(3)) are oxidized to [Mo(eta(6)-arene)(2)](+) by pcmcpH. The crystal and molecular structures of [M(eta(6)-1,3,5-R(3)C(6)H(3))(2)][pcmcp] (M = Cr, R = Me; M = Mo, R = Me, (i)Pr) have been solved by X-ray single crystal diffraction.     

Equilibrium, 1H and 13C NMR spectroscopy,and X-ray diffraction studies on the complexes Bi(DOTA)- and Bi(DO3A-Bu)

Several Bi(III) complexes are used in medicine as drugs. Bi(DO3A-Bu) has recently been proposed as a nonionic contrast agent in X-ray imaging (H(3)DO3A-Bu = 10-[2,3-dihydroxy-(1-hydroxymethyl)propyl]-1,4,7,10-tetraazacyclododecane-1,4,7,-triacetic acid). The solution equilibria and NMR structure and dynamics of Bi(DO3A-Bu) and of the similar Bi(DOTA)(-) have been investigated (H(4)DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid). The stability constants were determined with the study of the competition equilibria between Br(-) ions and the ligands DOTA or DO3A-Bu for the Bi(III) by spectrophotometry. The stability constants, obtained for Bi(DOTA)(-) and Bi(DO3A-Bu), are very high, log K = 30.3 and 26.8, respectively. Potentiometric titrations indicated the dissociation of one of the protons among the three alcoholic OH groups in Bi(DO3A-Bu). The dissociation constant is log K = 7.53 (0.09) indicating that at physiological pH about 50% of the species possess -1 charge. It was shown by (1)H and (13)C NMR spectroscopy that the OH group attached to the middle carbon atom of the "butriol" side chain is coordinated to the Bi(III) and starts to deprotonate at pH > 5.5. The crystal structure of NaBi(DOTA).H(2)O shows an octacoordinated arrangement of the donor atoms around the Bi(III), with no water in the inner sphere. The crystals belong to the centrosymmetric space group C2/c. The temperature dependent (1)H and (13)C NMR spectra indicate that both Bi(DOTA)(-) and Bi(DO3A-Bu)(-) complexes are fluxional. For Bi(DOTA), the Delta(deltadeltadeltadelta) right harpoon over left harpoon Lambda(lambdalambdalambdalambda) fluxionality was identified, and on the basis of the activation parameters, a synchronous motion was suggested for the fluxional motion resulting in the change of ring conformation and of the helicity of the complex. The transition state is supposed to be more symmetrical than the initial state. The deprotonated Bi(DO3A-Bu) has a highly asymmetric NMR structure in solution, and its fluxional motion is slower than that of Bi(DOTA)(-).     

Novel Cr-PNP complexes as catalysts for the trimerisation of ethylene

Cr(III) complexes of tridentate PNP ligands have been prepared and evaluated as catalysts for ethylene trimerisation, with several giving high activity and excellent selectivity towards 1-hexene when activated with methylaluminoxane.     

Isolation and structural elucidation of the geometrical isomers of lutein and zeaxanthin in extracts from human plasma.

All-E-(3R,3'R,6'R)-lutein, all-E-(3R,3'R)-zeaxanthin, all-E-(3R,3'S,6'R)-3'-epilutein and some geometrical isomers of the former two dihydroxycarotenoids have been separated from an extract of human plasma by semipreparative high-performance liquid chromatography on a silica-based nitrile-bonded column. In the order of chromatographic elution, the isolated fractions were identified as all-E-lutein, all-E-zeaxanthin, all-E-3'-epilutein, 9Z-lutein, 9'Z-lutein, a mixture of 13Z-lutein and 13'Z-lutein, 9Z-zeaxanthin, 13Z-zeaxanthin and 15Z-zeaxanthin. The structures of all compounds, including the relative configuration at C(3') and C(6') of the luteins and the position of the stereomutated double bonds in the geometrical isomers, were unambiguously established by 1H nuclear magnetic resonance spectroscopy. The absolute configuration of the three all-E compounds was derived by circular dichroism and is also assumed to be valid for the geometrical isomers. The ultraviolet-visible absorption and mass spectra of each of the individually isolated compounds were also in agreement with the proposed structures.     

The causal universe

Creation of matter is possible in the cosmological context, without cost of energy. This creation is regulated by the laws of quantum mechanics and general relativity. These elements are used to conceive a singularity-free causal open homogeneous isotropic cosmology. The history of the universe unfolds in two stages: the fireball production stage, which occurs as the response to a spontaneous local disturbance, is followed by free expansion. The latter extrapolates back to the former to avoid the initial big-bang singularity.This essay was awarded the first prize for 1978 by the Gravity Research Foundation. (Ed.)