Bridging the Molecule-Solid State Interface

Recently three discrete transition metal borides have been prepared and structurally characterized. These metal-rich metallaboranes con- 

We have seen how bonding principles carry over from discrete species to related fragments in the solid state. An interesting question then is whether the same discrete species can serve as precursors for the efficient production of specific solid state materials containing the cluster cores of the discrete compounds as building blocks of the solid. 

Metal organic chemical vapor deposition (MOCVD) is a well-established, practical technique for forming simple as well as complex solid state films (130). For binary systems the conventional approach is to use mixtures of the most readily available molecules containing the elements of interest. This approach has been employed to prepare borides of several types. For example, iron-boron alloys have been pre- 

In recent years a number of groups have developed compounds that serve as single precursors for specific binary materials 133, 134, 135,136,137,138,139,140,141,142). In this approach, the objective is to synthesize precursor molecules that are easy to handle with low toxicity and that intrinsically contain not only the desired stoichiometry of the material but also a low energy decomposition pathway. When successful these rational precursors have the desired properties of convenience and safety but, as important, create opportunities for preparing films of presently known stoichiometry with new properties as well as for exploring systems of unknown stoichiometry and properties. 

From the discussion in Section II,C it should be clear that there is a relationship between the structures of borides and boranes as far as the boron networks are concerned. A comparison of the literature shows that the known structural diversity of the boranes is much greater than that of the borides. This may well be due to the rigorous conditions required for boride preparation that is, only the most stable boron networks are formed. TTie low-temperature routes illustrated in the foregoing work suggest an approach to presently unknown compounds with novel boride networks. Hence, the multitude of known metalla-boranes constitute a stockpile of potential precursors to metal borides with new and perhaps useful properties. 

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