title: Nonspherical Deltahedra in Low-Energy Dicarbalane Structures Testing the Wade-Mingos Rules: The Regular Icosahedron Is Not Favored for the 12-Vertex Dicarbalane.
abstract: Theoretical studies on the dicarbalanes C2Al(n-2)Men (n = 7-14; Me = methyl) predict both carbon atoms to be located at degree 4 vertices of a central C2Al(n-2) deltahedron in the lowest energy structures. As a consequence, deltahedra having two degree 4 vertices, two degree 6 vertices, and eight degree 5 vertices rather than the regular icosahedron having exclusively degree 5 vertices are found for the 12-vertex dicarbalane C2Al10Me12. However, the lowest energy C2Al(n-2)Men (n = 7-11) structures are based on the same most spherical (closo) deltahedra as the corresponding deltahedral boranes. The lowest energy structures for the 13- and 14-vertex systems C2Al(n-2)Men (n = 13 and 14) are also deltahedra having exactly two degree 4 vertices for the carbon atoms. The six-vertex C2Al4Me6 system is exceptional since bicapped tetrahedral and capped square pyramidal structures with degree 3 vertices for the carbon atoms are energetically preferred over the octahedral structure suggested by the Wade-Mingos rules.
authors.affiliation: Department of Chemistry, Faculty of Chemistry and Chemical Engineering, Babeş-Bolyai University , RO-400028 Cluj-Napoca, Romania.
authors.forename: Amr A A
authors.initials: AA
authors.lastname: Attia
authors.affiliation: Department of Chemistry, Faculty of Chemistry and Chemical Engineering, Babeş-Bolyai University , RO-400028 Cluj-Napoca, Romania.
authors.forename: Alexandru
authors.initials: A
authors.lastname: Lupan
authors.affiliation: Department of Chemistry and Center for Computational Quantum Chemistry, University of Georgia , Athens, Georgia 30602, United States.
authors.forename: R Bruce
authors.initials: RB
authors.lastname: King