The increase in atmospheric carbon dioxide is linked to climate changes; hence there is an urgent need to reduce the accumulation of CO2 in the atmosphere. The utilization of CO2 as a raw material in the synthesis of chemicals and liquid energy carriers offers a way to mitigate the increasing CO2 buildup. This review covers six important CO2 transformations namely: chemical transformations, photochemical reductions, chemical and electrochemical reductions, biological conversions, reforming and inorganic transformations. Furthermore, the vast research area of carbon capture and storage is reviewed briefly. This review is intended as an introduction to CO2, its synthetic reactions and their possible role in future CO2 mitigation schemes that has to match the scale of man-made CO2 in the atmosphere, which rapidly approaches 1 teraton.

The teraton challenge. A review of fixation and transformation of carbon dioxide

The need to reduce the accumulation of CO2 into the atmosphere requires new technologies able to reduce the CO2 emission. The utilization of CO2 as a building block may represent an interesting approach to synthetic methodologies less intensive in carbon and energy. In this paper the general properties of carbon dioxide and its interaction with metal centres is first considered. The potential of carbon dioxide as a raw material in the synthesis of chemicals such as carboxylates, carbonates, carbamates is then discussed. The utilization of CO2 as source of carbon for the synthesis of fuels or other C1 molecules such as formic acid and methanol is also described and the conditions for its implementation are outlined. A comparison of chemical and biotechnological conversion routes of CO2 is made and the barriers to their exploitation are highlighted.

Utilisation of CO2 as a chemical feedstock: opportunities and challenges

Infrared spectroscopic identification of species arising from reactive adsorption of carbon oxides on metal oxide surfaces

The possibility of recycling CO{sub 2} from industrial emissions and of removing some of this greenhouse gas, an environmental pollutant, is receiving increased attention. Also, the possibility of using CO{sub 2} as the starting material for the synthesis of fine chemicals provides an attractive alternative to compounds presently derived from petroleum. Efforts to convert CO{sub 2} to useful chemicals will inevitably center on transition metal catalysts. Furthermore, efforts to enhance the yield of hydrogen in water gas shift reactions are also centered on carbon dioxide interactions with transition metal catalysts. For all these reasons, a broader understanding of the organometallic chemistry of CO{sub 2} is being sought. In this article, only those compounds that can be clearly identified as having carbon dioxide bound to metal centers through carbon will be considered. Thus the discussions will not include metal formate complexes whose chemistry has been reviewed recently. Also, the discussions will not include metallocarboxylic acids or metallocarboxylate esters except where these compounds have been used as reagents for the synthesis of CO{sub 2} complexes or result from reactions of these compounds. 111 refs.

The Organometallic Chemistry of Carbon Dioxide.

Chemists today are increasingly fascinated by gold’s unique position in the family of elements. In this review, the author looks at important new results emerging from recent research in gold chemistry.

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The fascinating implications of new results in gold chemistry

The preparation and isolation of (I)[Au(pip)Cl], (II)[AuCl(pip)2], and (III)[Au(pip)2][PF6](where pip = piper-idine) are described. The X-ray structure of (I) is reported : it consists of linear [(pip)AuCl] molecules arranged in tetramers, the gold atoms forming a loose square cluster. The structure was determined by the heavy-atom method from 1089 unique reflections measured by diffractomer and refined by least-squares techniques to R 0.064. Crystals are tetragonal, a= 12.474(20), c= 9.694(10)A, Z= 8.

Some piperidine derivatives of gold(I): crystal and molecular structure of chloro(piperidine)gold(I)

The reaction of [Os6(CO)18] with [Os3(CO)11H]– gives the anion [HOs3(CO)10·O2C·Os6(CO)17]– which has been fully characterized by a single crystal X-ray diffraction study on the [(Ph3P)2N]+ salt.

Synthesis and X-ray structure of an osmium carbonyl anion [HOs3(CO)10·O2C·Os6(CO)17]–

Crystals of the polar conformer of the quinoxaline antibiotic triostin A are orthorhombic, space group P212121, with a= 20.940(5), b= 18.528(4), and c= 18.795(4)A. There are two molecules of isoamyl acetate solvent per triostin A molecule. The cyclic octadepsipeptide has approximate two-fold symmetry. The quinoxaline chromophores and the disulphide cross-bridge project from opposite sides of the peptide ring. The conformation is compared with that found for the synthetic analogue TANDEM, and with the results of n.m.r. investigation. The observed structure accounts for the higher binding constants of the natural antibiotic, as well as its capacity to bind at GC-rich sequences in DNAs.

Crystal and molecular structure of the DNA-binding antitumour antibiotic triostin A

The complex [Os6(CO)13] reacts with methanolic potassium hydroxide to produce [Os5(CO)15]2– which, upon acidification, gives [HOs5(CO)15]– and [H2Os5(CO)15]; single crystal X-ray diffraction and 13C n.m.r. studies show the presence, within the anionic pentaosmium clusters, of trigonal bipyramidal metal arrangements.

Synthesis of [Os5(CO)15]2–, [HOs5(CO)15]–, and [H2Os5(CO)15]; X-ray crystal structure of [(Ph3P)2N]+[HOs5(CO)15]–

The crystal structures of potassium tetrafluorochromate(III), K[CrF4](1), and dipotassium dichlorohexafluorotrichromate(II), K2[Cr3Cl2F6](2), are reported. The structure of (1) consists of infinite triangular anionic columns comprising approximately planar Cr3F9 units linked above and below by fluoride bridges, the columns being separated by K+ ions. Each CrIII atom is octahedrally co-ordinated by six F atoms. The structure of (2) contains two crystallographically independent CrII atoms which have distorted octahedral co-ordination by four equatorial F atoms and two axial Cl atoms. The Cr atoms are linked together by single Cr–F–Cr bridges and also by a novel chloride fluoride double bridge. The structure can also be thought of as comprising two-dimensional CrF2 sheets, held together by Cl atom bridges. Charge balance is maintained by K+ ions. Crystal data for (1) are: a= 15.76(1), b= 7.43(1), c= 18.38(1)A, Z= 24, orthorhombic, space group Pnma, final R= 0.041 for 1 975 diffractometer data with Io > 3σ(Io). Crystal data for (2) are: a= 6.726(1), b= 11.157(5), c= 7.391(3)A, β= 125.31(4)°, Z= 2, monoclinic, space group P21/c, final R= 0.041 for 1 044 diffractometer data with Io > 2σ(Io).

Structural studies of potassium tetrafluorochromate(III), K[CrF4], and the novel mixed chloride fluoride, dipotassium dichlorohexafluorotrichromate(II), K2[Cr3Cl2F6]

John J. Guy

Papers

Some piperidine derivatives of gold(I): crystal and molecular structure of chloro(piperidine)gold(I)

Synthesis and X-ray structure of an osmium carbonyl anion [HOs3(CO)10·O2C·Os6(CO)17]–

Crystal and molecular structure of the DNA-binding antitumour antibiotic triostin A

Synthesis of [Os5(CO)15]2–, [HOs5(CO)15]–, and [H2Os5(CO)15]; X-ray crystal structure of [(Ph3P)2N]+[HOs5(CO)15]–

Structural studies of potassium tetrafluorochromate(III), K[CrF4], and the novel mixed chloride fluoride, dipotassium dichlorohexafluorotrichromate(II), K2[Cr3Cl2F6]