Decap

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Under drastic conditions, that is, using high concentration of methanolic potassium hydroxide, Os6(CO)18 is decapped to give the dianion [Os5(CO)15]2 in high yields.9 Under milder conditions (high dilution and a weaker base such as iodide), [Os6(CO)18]2 (Ref. 10) is the product of the reaction. 

When the number of metal atoms in a cluster increases, the geometries of the clusters become more complex, and some are often structurally better described in terms of capped or decapped polyhedra and condensed polyhedra. For example, the first and second clusters listed in Table 19.4.3 are a capped octahedron and a bicapped octahedron, respectively. Consequently, capping or decapping with a transition-metal fragment to a deltapolyhedral cluster leads to an increase or decrease in the cluster valence electron count of 12. When a transition-metal atom caps a triangular face of the cluster, it forms three M-M bonds with the vertex atoms, so according to the 18-electron rule, the cluster needs an additional 18 - 6 = 12 electrons. The parent octahedron of [Os6(CO)is]2- has g = 86, the monocapped octahedron Osy(CO)2i has g = 98, and the bicapped octahedron [Oss(CO)22]2- hasg = 110. 

Generally, capped or decapped deltapolyhedral clusters are characterized by the number of skeletal valence electrons g... 

A classical example of correlation of structure with valence electron count of transition-metal clusters is shown in Fig. 19.4.2. There the structures of a series of osmium clusters are systematized by applying the capping and decapping procedures. 

A set of spectra, recorded during stepwise deposition of ZnO onto a decapped Cu(In,Ga)Se2 surface is shown in Fig. 4.26. The ZnO film has been sputtered from an undoped ZnO target using 15 W dc power but otherwise the same standard deposition conditions, which have been used for investigation of the CdS/ZnO interface. On a first inspection no changes in the shape of the peaks is observed during deposition. A chemical reaction between Cu(In,Ga)Se2 and ZnO is, therefore, not evident. 

Fig. 4.26. Core levels, Zn LMM Auger level and valence bands recorded using monochromatic A1 Ka radiation during sputter deposition of undoped ZnO onto a decapped Cu(In,Ga)Se2 sample. The deposition times are indicated in seconds...

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