Main-group clusters bond energy

Figure 10 Schematic energy-level spectrum for a radially bonded cluster with a main group interstitial atom...

The Group 14 metallocenes are the most widely known series of isolated main group sandwich compounds. Schleyer calculated the model compounds T -CpC and T -CpSi and found that the pentahapto carbon compound is less stable than the single-bonded fulvenyl cation or the phenyl cation (36). On the other hand, Tj -CpSi has been predicted to be the most stable one among possible isomers. A mass spectrometry study of Group 14 half-sandwich metallocenes has been made and their atomization energies were calculated (57). It was concluded that nido-cluster is the most stable stmcture and that the stability of these metallocenes increases from CpPb to CpC+. 

Figure 4 Molecular orbitals for [(ZreZlClig], derived from an empty cluster, [(ZrsDlClig], and an main-group atom, Z. The energy gap between the bonding and the antibonding ti orbitals is indicated.

---