Generalizations about Structure and Bonding

The results summarized here support the following generalizations about structure and bonding of metal complexes bonded to metal oxide and zeolite supports  

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In previous chapters, we have presented a great deal of information about structure and bonding in coordination compounds. This chapter will be devoted to describing some of the important chemistry in the broad areas of organometallic complexes and those in which there are metal-metal bonds. The body of literature on each of these topics is enormous, so the coverage here will include basic concepts and a general survey. 

As underlined by Miller el al. (2002) in a comprehensive review about structure and bonding around the Zintl border of the Periodic Table, the Nesper criteria imply that Zintl phases (as valence compounds) are generally point compounds and may have a semi-metallic behaviour. 

X-ray studies of stable siienes had been published and much of the information about structure and bonding in siienes came from ab initio molecular orbital calculatious. These data are well summarized in several review articles by Brook and Brook and by Michl and Raabe . The important role which ab initio calculations play in this field is outlined in the comprehensive review by Apeloig and by Kami and Apeloig. We will therefore emphasize in this paragraph the new important findings and we will outline the general trends of structural silene chemistry. Some stmctural data and original references are summarized in Table 12. 

In view of a renewed interest in the structural chemistry of organic derivatives of antimony(V) during the last decade, a brief account of the same is presented highlighting points of special importance and future growth. Attention is focussed on the structural and bonding aspects. Details about their synthesis are only included when they are applicable in general. 

Unfortunately the transient carbonium ions presumably formed in catalytic cracking cannot be easily observed. Furthermore, there remain many questions about degrees of adsorption bonding involved with these intermediates, as well as need of information about structures and possible alternative reaction paths. In general, however, this lack of exact knowledge is characteristic of almost all reaction kinetics, catalytic or otherwise. 

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