ABSTRACT
Although devoted to the rationalization of different aromaticity indexes in explaining the aromatic behavior in metal clusters, this chapter begins with a brief description about aromaticity.
Aromaticity is a qualitative phenomenon, which is of utmost importance in the wide realm of chemistry [1]. Prior to the discovery of benzene by Michael Faraday as early as 1825 [2], the compounds with a distinctive smell or “aroma” were found to be quite stable and were usually known by the name “aromatic” compounds. Soon after the discovery of benzene, this phenomenon has gained a tremendous impetus. With the discovery of new molecules exhibiting aromatic or antiaromatic behavior, the impetus has gained a further momentum in research [3]. The concept of aromaticity has earlier been conned to hydrocarbon systems only; however, the modern era has also witnessed its importance among the heteroatomic systems as well [4]. Several such systems with σ-electronic framework have attracted much attention. Moreover, innovation of metal clusters with d-orbital aromaticity is also very
15.1 What is Aromaticity? ....................................................................................297 15.2 Different Indexes of Aromaticity .................................................................. 298 15.3 Why Metal Clusters are so Important? ......................................................... 301 15.4 Review of the Works on Metal Clusters and Clusters involving Metal Atoms ................................................................... 301 15.5 Rationalization of Different Aromaticity Indexes ........................................308 15.6 Summary and Future Prospects ................................................................... 314 References .............................................................................................................. 314
important, particularly in the context of describing transition-metal complexes [5]. The concept of three-dimensional aromaticity is quite amazing and this theory helps us in elucidating the stability of various apparently unstable molecular complexes and organometallic compounds [6].
