The Geometric and Electronic Structures of Niobium Carbon Clusters

Abstract

More than 50 [Nb x C y ] + clusters have been observed in the gas phase. We report a density functional investigation of 100 isomers of 28 of the most prominent of these clusters, ranging in size from [Nb 2 C 2 ] to [Nb 12 C 20 ] and [Nb 14 C 16 ], calculated as both neutral and monocation species. Vertical ionization energies and normalized binding energies are provided for all isomers, and the most probable structures of the 28 [Nb x C y ] clusters are assigned. The species [Nb 8 C 12 ] and [Nb 14 C 13 ] have the same structures (T d and O h , respectively) as the Ti analogues. The calculations and interpretations generate a broad picture of the geometric structures, electronic structures, and observed reactivities of Nb x C y clusters. The relevant structural principles and the key substructural components have been defined. At the local level, Nb-C bonding is the principal source of stability, together with C-C bonding where it occurs, whereas Nb-Nb bonding energy is less important but still significant. Cradle-motif Nb 4 C 2 moieties are important, but not if they are strongly distorted. The 3-fold wheel substructure and the spire (3-fold or 4-fold) are key substructures involving C 2 . Fused cubanoid units as occur in the nanocrystallites are the main containers of isolated C atoms and are usually slightly distorted. Substitution of C 2 in place of C in a nanocrystallite occurs in some Nb x C y clusters that are slightly C-rich. Fusion of wheels or spires onto nanocrystallite sections occurs with increasing C content, and the most C-rich clusters contain C 2 units only, but not longer C n chains.

Threshold photoionization and density functional theory studies of bimetallic-carbide nanocrystals and fragments: Ta3ZrCy (y=–4)

“…4,8,33 It is therefore reasonable to expect that Ta 3 ZrC 4 also possesses these properties and, as such, warrants further investigation. The electronic structure and the frontier MOs of the isoelectronic Ta 4 C 4 + are shown in Fig.…”

Predicted infrared and Raman spectra for neutralTi8C12isomers

“…Shortly thereafter, Dance 8,9 proposed a tetracapped tetrahedron of T d symmetry and later showed that the T h dodecahedron was higher in energy by 15 eV. Other geometries have also been proposed including structures belonging to the C 3v point group 10,11,12,13 . Comparison of the drift time of mass selected Ti 8 C + 12 with calculated mobilities for various structures reinforces the proposed hollow cage structures instead of more closely packed cubic structures 14,15 .…”

Towards Rational Syntheses of the Elusive Metallocarbohedrenes: Density Functional Prescriptions for Electronic and Geometric Structures

“…A possible reaction is given in Equation (35): It is interesting to compare this reaction with the one leading to 64 B [Eq. (21)] in which the Cr(CO) 3 fragments are located on the inner positions. In the present case, the high oxidation state of chromium prevents initial formation of carbonyl species and mechanistically it is likely that CO will only be adsorbed once the CrÀC s bonds have been formed.…”

“…In 3 each C 2 group forms two s bonds to the two o M atoms, and the two p-bonding orbitals of C 2 are directed towards i M. The local coordination of each o M is o M(s-C 2 ) 3 in a spire motif (3 s, Figure 1), [21,24] while the local coordination of each i M is i M(p-C 2 ) 3 in a wheel motif (3 w). The i MÀ i M and i MÀ o M distances are variable under the T d symmetry of 3.…”