Surface coordination chemistry

Sulzberger, B. (1990), "Photoredox Reactions at Hydrous Metal Oxide Surfaces a Surface Coordination Chemistry Approach", in W. Stumm, Ed., Aquatic Chemical Kinetics, Wiley-lnterscience, New York, pp. 401-429. 

Iron has a rich surface coordination chemistry that forms the basis of its important catalytic properties. There are many catalytic applications in which metallic iron or its oxides play a vital part, and the best known are associated with the synthesis of ammonia from hydrogen and nitrogen at high pressure (Haber-Bosch Process), and in hydrocarbon synthesis from CO/C02/hydrogen mixtures (Fischer-Tropsch synthesis). The surface species present in the former includes hydrides and nitrides as well as NH, NH2, and coordinated NH3 itself. Many intermediates have been proposed for hydrogenation of carbon oxides during Fischer-Tropsch synthesis that include growing hydrocarbon chains. 

A number of attempts have been made to understand the mechanism of the adsorption of chelates on oxide minerals. For instance, IR spectroscopic studies10 have indicated the presence of a basic monosalicylaldoximate copper complex as well as the bis-salicylaldoximate complex on the surface of malachite (basic copper carbonate) treated with salicylaldoxime. However, other workers4 have shown that the copper chelate is partitioned between the surface and dispersed within the solution, and that a dissolution-precipitation process is responsible for the formation of the chelate. Research into the chemistry of the interaction of chelating collectors with mineral surfaces is still in its infancy, and it can be expected that future developments will depend on a better understanding of the surface coordination chemistry involved. 

See, for example, the reviews by B. Sulzberger, Photoredox reactions at hydrous metal oxide surfaces A surface coordination chemistry approach, Chap. 14 in W. Stumm, op. cit.,3 and T. D. Waite, op. cit.27... 

Surface Crystallography and Composition. Platinum (11) and nickel (8,9,12) have been the metal surfaces examined in our surface science studies to date. The surface coordination chemistry has been examined as a function of surface crystallography and surface composition. Surfaces specifically chosen for an assay of metal coordination number and of geometric effects were the three low Miller index planes (111), (110) and (100) as well as the stepped 9(lll)x(lll) and stepped-kinked 7(lll)x(310) surfaces (both platinum and nickel are face centered cubic). 

Toluene surface coordination chemistry was quite different from that of benzene. Toluene chemisorption on all the clean surfaces was thermally irreversible. In addition, toluene was not displaced from these surfaces by trimethylphosphine nor by any other potentially strong field ligand examined to date, e.g., carbon monoxide or methyl isocyanide. In the thermal decomposition of toluene on these surfaces (attempted thermal desorption experiments), there were two thermal desorption maxima for H2 (or D2 from perdeuterotoluene) with the exception of the Ni(110) surface. This is illustrated in Figure 6 for Ni(lll)-C7Dg. 

Hydrocarbon Fragments - Modeling by Molecular Orbital and Cluster Chemistry. A basic guideline for metal surface coordination chemistry with respect to hydrocarbon or hydrocarbon derivatives may be formulated as follows If the stereochemistry of the chemisorption state allows C-H hydrogen atoms to closely approach surface metal atoms then the chemisorption state should be further stabilized by the formation of a three-center two-electron C-H-metal bond. This effect should be more pronounced the more electron deficient the metal surface. There should be an activation of the C-H bond and the hydrogen atom should become more protonic in character. If the C-H bond is sufficiently weakened by this interaction then C-H bond cleavage should result. 

Surface chemistry of the oxide-water interface is emphasized here, not only because the oxides are of great importance at the mineral-water (including the clay-water) interface but also because its coordination chemistry is much better understood than that of other surfaces. Experimental studies on the surface interactions of carbonates, sulfides, disulfides, phosphates, and biological materials are only now emerging. The concepts of surface coordination chemistry can also be applied to these interfaces. This chapter is designed... 

Combining concepts of surface coordination chemistry with established models of lattice statistics and activated complex theory, Wieland et al. (8) proposed a general rate expression for the proton-catalyzed dissolution of oxide minerals ... 

PHOTOREDOX REACTIONS AT HYDROUS METAL OXIDE SURFACES A SURFACE COORDINATION CHEMISTRY APPROACH... 

The dependence of mineral weathering on hydrogen ion activity in solution can be demonstrated using surface coordination chemistry as in... 

J2.23 Surface coordination chemistry of monometallic and bimetallic electrocatalysts... 

The mechanisms of surface chemical reactions represent a problem in coordination chemistry, which is the study of complexes, molecular units comprising a central group surrounded by other atoms in close association. This book is principally an introduction to the interpretation of surface phenomena in soils from the point of view of coordination chemistry. Therefore the basic concept to be discussed is the surface functional group, the central moiety in surface complexes, whose formation provides the most important mechanism of adsorption by the solid phases in soils. No detailed consideration of adsorption isotherm equations or the thermodynamic theory of ion exchange is presented, except insofar as their tenuous relation with surface coordination chemistry is to be illustrated. The discussion in this book is intended to be self-contained, but a previous exposure to soil physical chemistry, soil mineralogy, and the fundamentals of inorganic chemistry will prove helpful. 

Zhang JJ, Anson FC (1993) Complexes of Cu(II) with electroactive chelating ligands adsorbed on graphite-electrodes - Surface coordination chemistry and electrocatalysis. J Electroanal Chem 348(l-2) 81-97... 

SER effects have been observed for a number of adsorbates on copper hydro-sols. Triphenylphosphine, diphenyl sulfide, and benzotriazole all partially displace adsorbed pyridine from colloidal copper and result in SER spectra which contain both pyridine bands and those of the coadsorbate. Diphenyl sulfide and thio-phenol were found to displace pyridine. [207] A similar displacement of pyridine by thiophenol was observed with copper organosols. [218] Tliese results exemplify the potential of this technique for investigating the surface coordination chemistry of colloidal metals. SER spectra of cytosine and of guanine and their derivatives on copper and on silver have been reported. [219, 220]... 

Summary. Self-assembled monolayers of alkanethiolates on surfaces of gold, silver, and copper have helped to illustrate differences in the chemistry of these surfaces and have clarified the relationship between the structure of a monolayer and its wetting properties (75,25). We are presently examining other ligands and substrates to identify surface coordination chemistries that will lead to new self-assembling systems (36). One of the goals of this project is to apply the differences between the coordination... 

Hence, surface chemistry of oxides at a molecular level considered as surface coordination chemistry of oxides. 

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