Equilibrium geometries and associated energetic properties of mixed metal-silicon clusters from global optimization

4d and 5d bimetal doped tubular silicon clusters Si12M2 with M = Nb, Ta, Mo and W: a bimetallic configuration model

M₂Si₁₂ clusters are found in a bimetallic tubular structure where one metal atom is located in the central region of a (6/6) tube, and the other is capped outside to a hexagonal face. A bimetallic configuration containing 11 MOs, partially or fully occupied by up to 22 electrons, was established to interpret their stability.

Electronic structure and redox properties of metal nitride endohedral fullerenes M(3)N@C(2n) (M=Sc, Y, La, and Gd; 2n=80, 84, 88, 92, 96)

An extensive study of the redox properties of metal nitride endohedral fullerenes (MNEFs) based on DFT computational calculations has been performed. The electronic structure of the singly oxidized and reduced MNEFs has been thoroughly analyzed and the first anodic and cathodic potentials, as well as the electrochemical gaps, have been predicted for a large number of M(3)N@C(2n) systems (M=Sc, Y, La, and Gd; 2n=80, 84, 88, 92, and 96). In particular, calculations that include thermal and entropic effects correctly predict the different anodic behavior of the two isomers (I(h) and D(5h)) of Sc(3)N@C(80), which is the basis for their electrochemical separation. Important differences were found in the electronic structure of reduced M(3)N@C(80) when M=Sc or when M is a more electropositive metal, such as Y or Gd. Moreover, the changes in the electrochemical gaps within the Gd(3)N@C(2n) series (2n=80, 84, and 88) have been rationalized and the use of Y-based computational models to study the Gd-based systems has been justified. The redox properties of the largest MNEFs characterized so far, La(3)N@C(2n) (2n=92 and 96), were also correctly predicted. Finally, the quality of these predictions and their usefulness in distinguishing the carbon cages for MNEFs with unknown structures is discussed.

Photodissociation of Metal−Silicon Clusters: Encapsulated versus Surface-Bound Metal

Metal-silicon cluster cations of the form MSi(n)+ (M = Cu, Ag, Cr) are produced in a molecular beam with pulsed laser vaporization. These species are mass-selected in a reflectron time-of-flight spectrometer and studied with laser photodissociation at 532 and 355 nm. For the noble metals copper and silver, photodissociation of the n = 7 and 10 clusters proceeds primarily by the loss of metal atoms, indicating that the metal is not located within the interior of silicon cages, and that metal-silicon bonding is weaker than silicon-silicon bonding. Chromium-silicon clusters for n = 7 also lose primarily the metal atom, but at n = 15 and 16 these dissociate via the loss of silicon, producing smaller metal-silicon species. This behavior is consistent with stronger metal-silicon bonding and encapsulated metal structures, as suggested previously by theory. MSi6(+) cations are produced efficiently in all of these photodissociation processes, indicating that these species have enhanced stability compared to other small clusters. Improved values are obtained for the ionization potentials of Si7 and Si10.