# Nanocrystal [Ti_{14}C_{13}] to Metallocarbohedrene [Ti_{8}C_{13}]:
Structural Principles and Mechanism

journal contribution

posted on 20.03.1996, 00:00 by Ian DanceGradient-corrected density functional calculations have
characterized the geometric and electronic structures
of the metal-carbon clusters
[Ti

_{14}C_{13}]^{0,+}and [Ti_{8}C_{13}]^{0,+}and the intermediates Ti*C*_{x}_{13}in the sequence of photoextrusions of Ti atoms from [Ti_{14}C_{13}]^{+}to [Ti_{8}C_{13}]^{+}. Ti_{14}C_{13}is a vertex-contracted “nanocrystal” fragment of the face-centered cubic TiC lattice, with low-lying spin states, while Ti_{8}C_{13}is a C^{c}-centered tetra-Ti^{o}-capped Ti^{i}_{4}tetrahedron with C_{2}groups cradled in six Ti^{i}_{2}Ti^{o}_{2}butterflies and has a large HOMO-LUMO gap. This sequence of six photodissociations of Ti atoms is significant because it involves the transformation of a fragment of a non-molecular lattice structure to a molecular cluster structure and the formation of six C−C bonds on the surface. The transformation is most endergonic in the first stage to [Ti_{13}C_{13}]^{+}, and decreasingly endergonic to [Ti_{12}C_{13}]^{+}and [Ti_{11}C_{13}]^{+}. The geometry changes are concerted, with each intermediate partly prepared for the next extrusion of Ti, and the central C^{c}atom plays a significant role in the substantial structural rearrangements. The high symmetry (*O**) of [Ti*_{h}_{14}C_{13}]^{+}is completely lost at [Ti_{12}C_{13}]^{+}, but there is recovery of*C*_{3}*symmetry at the intermediate [Ti*_{v}_{11}C_{13}]^{+}which already has in place the four C^{c}−Ti^{i}bonds and the Ti^{i}(C_{2})_{3}(Ti^{o})_{3}face characteristic of [Ti_{8}C_{13}]^{+}. Energy changes follow the geometry changes.