Metal-oxo-surface model

The chemistry associated with the metal-oxo-surfaces modeled by the metalla-calix[4]arene at the molecular level will be reviewed according to subdivisions in the following sections. 

The quasi-planar array of oxygen atoms at the lower rim of the calix[4]arene has inspired studies of calix[4]arene-metal complexes as models for metal-oxo surfaces of heterogeneous catalysts. ... 

For further similar metaUa derivatives and their chemistry see C. Floriani and R. Floriani-Moro, Metal Reactivity on Oxo Surfaces Modeled by Calix[4]arenes, in Reference lb, p. 536. 

Gustafsson and coworkers (Khai et al. 2008) applied a similar approach in a study of metal binding in selected Vietnamese soils. The multisurface models considered metal binding to three types of surfaces iron (oxo)hydroxides (modeled using the DLM, Section 12.2.2), organic matter (using either the Stockholm Humic model or... 

In Fig. 5.5a a simple scheme of reaction steps is proposed. Some of the assumptions of our model are summarized in Table 5.1. The short-hand representation of a surface site is a simplification that does not take into account either detailed structural aspects of the oxide surface or the oxidation state of the metal ion and its coordination number. It implies (model assumption 2 in Table 5.1) that all functional surface groups, such as those in a cross-linked polyhydroxo-oxo acid, are treated as if they were identical. 

An octahedral model of the 101 plane of anatase shown in Figure 4 of [89] indicates the locations of different types of surface oxo and hydroxo groups and a possible binding mechanism of metal cations. 

In a model study [34], nitrobenzene has been observed to react with an heterogeneous rhodium catalyst to afford surface oxo and imido species. Reduction with CO gives a surface carbonyl complex, with the metal in a low oxidation state and this is supposed to favour the CO insertion into the Rh=NR bond, which is considered to be the rate determining step. However, rhodium metals requires pyridine [34] (a base) or FeCb [146] (an acid) in order to be active (an induction period is also observed at least with the pyridine-promoted system) and these characteristics are not explained by the mechanism above reported. 

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