Heterometal atoms

The increasing number of metal clusters containing heterometal atoms and/or organic fragments suggest that skeletal isomerism will develop considerably in the near future. 

The electrochemical behavior of heterometallic clusters has been reviewed clsewbcre."" The interest in examining clusters stems from their potential to act as "electron sinks " in principle, an aggregate of several metal atoms may be capable of multiple redox state changes. The incorporation of heterometals provides the opportunity to tune the electrochemical response, effects which should be maximized in very mixed"-metal clusters. Few very mixed -metal clusters have been subjected to detailed electrochemical studies the majority of reports deal with cyclic voltammetry only. Table XII contains a summary of electrochemical investigations of "very mixed"-metal clusters. 

Figure 3.5 The heterometal lie cluster [NaMg NPr 2 2(OBu")]2 with sodium, magnesium and nitrogen atoms shown as black spheres and carbon and oxygen atoms are white...

The other way to introduce heterometals is their isomorphous substitution for Si in the framework, in a similar manner to the isomorphous substitution of Al. The heteroatoms should be tetrahedral (T) atoms. In hydrothermal synthesis, the type and amount of T atom, other than Si, that may be incorporated into the zeolite framework are restricted due to solubility and specific chemical behavior of the T-atom precursors in the synthesis mixture. Breck has reviewed the early literature where Ga, P and Ge ions were potentially incorporated into a few zeolite structures via a primary synthesis route [9]. However, until the late 1970s, exchangeable cations and other extraframework species had been the primary focus of researchers. 

Finally, the time-dependent DFT calculations agreed with the experimental results, showing that the transition responsible for the luminescent behavior is that from an antibonding occupied orbital, mainly centered in the gold interacting atoms with a contribution from the heterometals, to a bonding virtual orbital located between the gold and the silver (or copper) centers. 

In contrast, those cluster compounds with an 18-electron environment at the central heterometal do not undergo nucleophilic addition reactions. Ligand substitution reactions at both the central heterometal and the peripheral gold atoms are observed to occur for both 16- and 18-electron cluster compounds, as in the reactions shown below ... 

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