Isolobal character

F.G.A. Stone I had thought that the answer to your question had been embodied in the lecture. However, perhaps I failed to stress that the isolobal approach in our work has been predictive rather than a mere correlation of apparently unrelated results. I would highlight two experiments which emphasize the predictive character of the research. 

The axially symmetric metal carbonyl fragments M(CO)n (n = 1, 3, 4) have three outpointing hybrid orbitals with a high proportion of s and p orbital character, which are suitable for forming cluster skeletal molecular orbitals (77, 78, 238). The number and radial characteristics of these frontier molecular orbitals, which are illustrated schematically in Fig. 26a, are reminiscent of the frontier orbitals of a main group diatomic hydride fragment E—H, where E = C or B (Fig. 26b). To describe this similarity the term isolobal has been introduced (77). Molecular orbital... 

The existence of mixed metal-boron clusters constitutes one example of the validity of the isolobal principles when applied to a class of compounds. The stoichiometric and structural diversity of metallaboranes is truly striking, and the idea of isolobal fragments combined with the electron counting rules is sufficient to rationalize this diversity—this fact is impressive (67,68,69, 70, 71, 72, 73, 74). We have explored the mixing of boron and metal characters in cluster MOs in the Bs nHg-nlFeCCOla) ] nido cluster series (Fig. 5). Examples of the first four members of this series (a, b, c, and d) have been well characterized (75, 76, 77), and suggestive evidence has been published for a B2H6RU3-... 

What is flie electronic structure of the Fe2(CO)g molecule This is not easy to say with no background. Could there be some multiple bonds between iron atoms of the a, n, or 8 character Well, flie isolobal analogy will allow us to say the following in fact. Fe2(CO)g is an ethylene-like molecule, with all consequences concerning the iron-iron bond (double), the planarity of (CO)2Fe=Fe(CO)2 fiagment, etc. Also, we will be able to predict that the Fe(CO)4 moiety resembles ( is isolobal with") the CH2, that it will hind to CH2, forming the H2C=Fe(CO)4, and can just replace CH2 in many other instances in organic chemistry. 

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