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

Abstract

Bare π-hydrocarbon radical anions M •r − , dianions M r − r − as well as even a radical trianion M •r −r −r − can be crystallized as alkali metal salts,, 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 (•)r − 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.

Single crystals of an ionic anthracene aggregate with a triplet ground state

“…For both the rather large aggregates [(anthracene) 4− 3 (K + 2 THF 3 ) +2 2 ] and [(anthracene) 2− 2 (K + 2 THF 3 ) +2 ], the singlet-and triplet-state computations have been performed at the UB3LYP/6-31G* level, using the NEC SX4 supercomputer of the Höchstleistungs-Rechenzentrum Stuttgart, Germany using the Gaussian 94 program package 9 . The singlet-state calculations were started from the broken symmetry orbital.…”