Organic anions. Part 12. Hard sphere electrostatic calculations on group 1 organometallic compounds: ion pairs of dianions and radical anions

Abstract

Hard Sphere Electrostatic (HSE) calculations on the structure of the dilithium salts of the dianions of benzene, naphthalene, anthracene, phenanthrene, acenaphthalene, stilbene, and hexatriene (R^2–, 2Li⁺) are compared with known crystal structures and the results of MO calculations. The HSE method is then used to predict the structures of other species for which no structural data are available, i.e. R^2–, Li⁺; R^2–, Cs^–; R^2–, SS⁺; R^2–, 2Cs⁺; R^2–, 2SS⁺; R^2–, Li⁺, Cs⁺; and R^2–, Li⁺, SS⁺ where R^2– represents the same series of dianions and SS⁺ is the abbreviation used for the counterion in a solvent-separated ion pair. Whereas the sites adopted by the lithium cations in R^–, 2Li⁺ rarely correspond to those found in R^–, Li⁺ the main minima for R^2–, 2Li⁺ are mostly combinations of those found in the single counterion case R^2–, Li⁺. This is a reflection of the greater importance of anion/cation attraction and lesser importance of cation/cation repulsion in these dianions. Calculations are also reported for the structures of ion pairs (M⁺= Li⁺, Cs⁺, SS⁺) of the radical anions of benzene, naphthalene, anthracene, phenanthrene, stilbene, and hexatriene, and for some ion pairs of dications R²⁺, X^–; R²⁺, 2X^– and radical cations R^+., X^–.