Collect. Czech. Chem. Commun. 1998, 63, 1245-1263

Bare Molecular Anions of Unsaturated Hydrocarbons: Density Functional Charge and Spin Distributions Based on Their Single Crystal Structures

Zdeněk Havlasa and Hans Bockb

a Institute of Organic Chemistry and Biochemistry Academy of Sciences of the Czech Republic, 116 10 Prague 6, Czech Republic
b Chemistry Department, University of Frankfurt, Marie-Curie-Str. 11, D-60439 Frankfurt/Main, Germany


Bare π-hydrocarbon radical anions M, dianions M as well as even a radical trianion M can be crystallized as alkali metal salts, [M(•)−n][Me+solv]n if the solvent-shared contact ion multiples, [M(•)−n..(Me+)n]solv, present in aprotic solution after the reduction at an alkali metal mirror can be separated by advantageous cation solvation. Altogether 22 π-hydrocarbon anions M(•)−n comprising polycyclic cata- as well as peri-annelated six-membered ring compounds, polyphenyls, those with nonalternant polycyclic skeletal topology, open chain and organosilicon derivatives have been characterized by low-temperature X-ray crystallographic analyses. Based on the structural data determined, their charge and spin populations have been approximated by density functional calculations including natural bond orbital analyses (DFT/NBO). Although in general the total (σ + π) charges at individual C centers of the hydrocarbon skeletons cannot be correlated neither with the structural data nor with the spin distribution, numerous interesting details as well as some useful rules are provided. They concern, for instance, central C-C bond elongation and peripheral C-C bond shortening, preferred charge localization patterns, effects of conformational changes in the π-radical anions crystallized or Jahn-Teller distortions of formally degenerate molecular radical anion states.

Keywords: Hydrocarbon radical anions; Radical ions; Density functional theory; X-Ray diffraction; Ab initio calculations.