Species containing interstitial transition-metal atoms

3 Species containing interstitial transition-metal atoms 

Several hexacapped eubic clusters containing a transition metal atom lodged at the center of the cubic core have been structurally characterized. These compounds of formula M9( 4-E)6Ls, listed in Table 1, are known for M = Ni or Pd. A typical example of this new class of electron-rich compound is the 124-MVE compound Ni9(/ 4-GeEt)6(CO)8 (3) characterized by Dahl and coworkers.With MVE counts varying from 121 to 130, they are more electron-rich that their non-centered Mg(/ 4-E)6L8 parents, which contain a maximum of 120 MVEs vide supra). 

This family of compounds has been extensively studied in recent years. Wheeler has analyzed the electronic structure of Ni9(//4-Te)6(PEt3)8 with EH calculations. Hoffmann and coworkers have also used EH calculations to examine the electronic structure of this molecular cubic cluster to draw relationships with nickel-tellurium extended structures. More recently, we have performed EH and Xa calculations to rationalize the bonding in these clusters, as a function of different parameters such as the electron count or the nature and the size of the different elements constituting the cluster cage. For symmetry reasons, a localized two-center-two-electron 

It turns out that most of the metal-centered cubic species listed in Table 1 do not fit with these four hypothetical closed-shell configurations. Only the 124-MVE compound 3 has an electronic structure which agrees with one of these situations. Both EH and Xa calculations on the 124-electron model Ni9(/i4-GeH)6(CO)s indicate a closed-shell electron configuration 120 (eg). Examination of the EH bond overlap populations shows that neither the M-M nor the M-E bonding contacts 

---

The centered 10-vertex polyhedra are of particular interest since the shapes of the outer 10-vertex polyhedron depends on the interstitial atom and the electron count. In fact, four very different 10-vertex polyhedra (Fig. 7) have all been shown to form stable isolable species containing interstitial transition or post-transition metal atoms. These polyhedra include structures with three-, four-, or fivefold symmetry. Thus for the ions M Inio ° (M = Ni, Pd, Pt) found in the intermetal-lics KioInioM, the Injo polyhedron is a Cgv tetracapped trigonal prism [91]. 

---