title: Selected AB4(2-/-) (A = C, Si, Ge; B = Al, Ga, In) ions: a battle between covalency and aromaticity, and prediction of square planar Si in SiIn4(2-/-).
abstract: CAl(4)(2-/-) (D(4h), (1)A(1g)) is a cluster ion that has been established to be planar, aromatic, and contain a tetracoordinate planar C atom. Valence isoelectronic substitution of C with Si and Ge in this cluster leads to a radical change of structure toward distorted pentagonal species. We find that this structural change goes together with the cluster acquiring partial covalency of bonding between Si/Ge and Al(4), facilitated by hybridization of the atomic orbitals (AOs). Counter intuitively, for the AAl(4)(2-/-) (A = C, Si, Ge) clusters, hybridization in the dopant atom is strengthened from C, to Si, and to Ge, even though typically AOs are more likely to hybridize if they are closer in energy (i.e. in earlier elements in the Periodic Table). The trend is explained by the better overlap of the hybrids of the heavier dopants with the orbitals of Al(4). From the thus understood trend, it is inferred that covalency in such clusters can be switched off, by varying the relative sizes of the AOs of the main element and the dopant. Using this mechanism, we then successfully killed covalency in Si, and predicted a new aromatic cluster ion containing a tetracoordinate square planar Si, SiIn(4)(2-/-).
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095-1569, USA. ana@chem.ucla.edu
authors.forename: Anastassia N
authors.initials: AN
authors.lastname: Alexandrova
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Nayhouse
authors.forename: Mioy T
authors.initials: MT
authors.lastname: Huynh
authors.forename: Jonathan L
authors.initials: JL
authors.lastname: Kuo
authors.forename: Arek V
authors.initials: AV
authors.lastname: Melkonian
authors.forename: Gerardo
authors.initials: G
authors.lastname: Chavez
authors.forename: Nina M
authors.initials: NM
authors.lastname: Hernando
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Kowal
authors.forename: Chi-Ping
authors.initials: CP
authors.lastname: Liu
mesh_terms: D000535:Aluminum / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D005708:Gallium / Q000737:chemistry*; D005857:Germanium / Q000737:chemistry*; D007204:Indium / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry; D011789:Quantum Theory; D012825:Silicon / Q000737:chemistry*
chemical_list: D007477:Ions; D005857:Germanium; D007204:Indium; D002244:Carbon; D005708:Gallium; D000535:Aluminum; D012825:Silicon