Gold clusters anionic

Furche, F., Ahlrichs, R., Weis, P., Jacob, C., Gilb, S., Bierweiler, T. and Kappes, M.M. (2002) The structures of small gold cluster anions as determined by a combination of ion mobility measurements and density functional calculations. Journal of Chemical Physics, 117, 6982-6990. 

Wallace, W.T., Wyrwas, R.B., Whetten, R.L., Mitric, R. and Bonadc-Kouteck, V. (2003) Oxygen adsorption on hydrated gold cluster anions experiment and theory. Journal of the American Chemical Society, 125, 8408-8414. 

Bernhardt TM, Socaciu-Siebert LD, Hagen J, Woste L (2005) Size and composition dependence in CO oxidation reaction on small free gold, silver, and binary silver-gold cluster anions. Appl Catal A Gen 291 170... 

Koyasu K, Mitsui M, Nakajima A, Kaya K (2002) Photoelectron spectroscopy of paUadium-doped gold cluster anions AunPd n= - ). Chem Phys Lett 358 224... 

Adsorption of two O2 molecules as observed in this experiment for Ag had been predicted before for the gold cluster anions [356] however, it was never observed experimentally which lead to further discussion in the literature [357,358]. In combination with a systematic theoretical study performed by the group of Bonacic-Koutecky [351] an understanding of the measured rate constant evolution with cluster size depicted in Fig. 1.58a emerges and reasons for the distinct behavior of silver cluster anions can be given [351]. 

Fig. 1.61. Compilation of experimentai resuits from the iiterature on the reiative reactivity of gold cluster anions in the adsorption reaction of one O2 or one CO molecule, respectively, as a function of the ciuster size n. (a) Reactions of Aun with O2 filled squares) data from [370], open triangles) data from [372], open circles) data from [160]. (b) Reactions of An with CO filled squares) data from [372], open circles) data from [352]. For comparison, all data are normalized to the reactivity of Aue toward O2...

Cooperative Coadsorption Effects on Small Gold Clusters. Two examples of cooperative adsorption effects on small gold cluster anions identified in temperature dependent rf-ion trap experiments (see Chemical and Catal3dic Properties of Gas-Phase Clusters for experimental details) will be presented in the following. Au3 does not react with O2 in the ion trap experiment at any reaction temperature [34]. It, however, adsorbs a maximum of two CO molecules at reaction temperatures below 250 K [185]. If the gold trimer is exposed simultaneously to CO and O2 inside the octopole ion trap, still no reaction products are observed at reaction temperatures above 250 K as can be seen... 

Catalytic CO Oxidation by Free Au2. The potential catal3dic activity of Au2 in the CO combustion reaction was first predicted by Hakkinen and Land-man [382]. The subsequent experimental investigation employing an rf-ion trap indeed revealed the catalytic reaction of the gold dimer and, in conjunction with theory, a detailed reaction cycle could be formulated [33]. Also for particular larger gold cluster anions evidence for catalytic CO2 formation has... 

To focus on the influence of water on the chemical activity of gold in nanocatal3dic reactions, quantum mechanical ab initio calculations were performed [396] for model systems that do not exhibit charging effects originating from excess electrons bound to free An clusters (i.e., gold cluster anions) [33,382,397] or from defects at the metal-oxide surface [209,368] that have been shown, as described in the previous subsections, to promote the... 

Johansson MP, Lechtken A, Schooss Kappes MM, Furche F (2008) 2D-3D transition of gold cluster anions resolved. Phys Rev A 77 053202-053208... 

In the families of heptanuclear clusters, two geometries are found the capped octahedron that is typical for 98-valence electrons, and the vertex-sharing open tetrahedral (butterfly) stmctures typical for 106-valence electrons. An example of the former is Osy(CO)22 (51) an example of the latter is [H2AuOsg(CO)2Q] (52). In the AuOs cluster anion, the gold atom is at the vertex-sharing position. 

Hakkinen, H. and Landman, U. (2000) Gold clusters (Aun, 2 < N < 10) and their anions. Physical Review B - Condensed Matter, 62, R2287-R2290. 

The reactions of the gold anion Au- and of the di- and triatomic gold cluster monoanions Au2- and Au3- with CO were studied in a radio-frequency octopole ion trap experiment at cryogenic temperatures. Au- shows no affinity for CO, but the two cluster anions absorb up to two CO molecules. Particular stability has been ascribed to [Au3(CO)2]-, for which the binding energy has been estimated from thermolysis rate coefficients.292... 

DF calculations were carried out on CO complexes of small neutral, cationic, and anionic gold clusters Au with n= 1-6. The -coordination mode (terminal C-coordination) was found to be the most favorable one irrespective of the charge of the cluster, and cluster planarity is more stable for the bare clusters and their carbonyls. As expected, adsorption energies are greatest for the cationic clusters, and decrease with size. Instead, the adsorption energies of... 

The oxidation of CO to CO2 by metal-oxide clusters has received quite some attention, in part due to its relevance for the catalytic converters in automobiles, in part also because carbon monoxide is often used as a probe molecule in surface science and the reasonable simplicity of the system may still permit adequate theoretical treatments. In addition to the various systems involving PtmO cations as well as PtmO anions (see above), considerable efforts have been devoted to cluster anions of silver and gold, as reviewed recently [87]. A particular highlight is a conceptual catalytic cycle for the Au2 -mediated oxidation of CO with molecular oxygen, for which... 

The reactivity of Au O clusters to oxygen as a function of n was measured by Salisbury and coworkers using time of flight mass spectroscopy. It was found that odd-n (even-n) clusters have negligible (significant) reactivity, which is explained by the fact that the O2 molecule, acting as a one-electron aceptor, binds to anionic gold clusters, which have an unpaired electron. 

Gold is one of the least reactive metals in bulk form. However, in recent years a considerable amount of theoretical and experimental works have studied the reactivity of small neutral and charged Au clusters towards different molecules, like H2, O2, CO, and organic radicals " . The reactivity depends on the size and charge state of the cluster. In the previous section we have studied the reactivity towards oxygen adsorption of anionic silver and gold clusters. In this section we study the reactivity of neutral gold clusters towards molecular O2 (subsection 6.1) and CO (subsection 6.2). 

The synthetic methods used involve reaction of a cluster anion with [AuCIL], elimination of methane between a cluster hydride and [AuMeL] or addition of LAu+ units to metal-metal bonds. The emphasis here will be on structure and reactions of the complexes. Some examples of mixed gold clusters are given in Table 15, where it can be seen that most work has been on derivatives of clusters of iron, ruthenium and osmium. 

---