Effects of the Aromatic Substitution Pattern in Cation−π Sandwich Complexes

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2013-03, Vol.117 (12), p.2598-2604
• Main Authors: Wireduaah, Selina, Parker, Trent M, Lewis, Michael
• Format: Article
• Language: English
• Subjects: Atomic and molecular physics; Benzene - chemistry; Binding; Binding energy; Calculations and mathematical techniques in atomic and molecular physics (excluding electron correlation calculations); Cations; Computation; Constants; Correlation; Density-functional theory; Electronic structure of atoms, molecules and their ions: theory; Electrons; Exact sciences and technology; Mathematical analysis; Metals, Alkaline Earth - chemistry; Models, Chemical; Physical chemistry; Physics; Static Electricity; Thermodynamics
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp309740r

A computational study investigating the effects of the aromatic substitution pattern on the structure and binding energies of cation−π sandwich complexes is reported. The correlation between the binding energies (E bind) and Hammett substituent constants is approximately the same as what is observed for cation−π half-sandwich complexes. For cation−π sandwich complexes where both aromatics contain substituents the issue of relative conformation is a possible factor in the strength of the binding; however, the work presented here shows the E bind values are approximately the same regardless of the relative conformation of the two substituted aromatics. Finally, recent computational work has shown conflicting results on whether cation−π sandwich E bind values (E bind,S) are approximately equal to twice the respective half-sandwich E bind values (E bind,HS), or if cation−π sandwich E bind,S values are less than double the respective half-sandwich E bind,HS values. The work presented here shows that for cation−π sandwich complexes involving substituted aromatics the E bind,S values are less than twice the respective half-sandwich E bind,HS values, and this is termed nonadditive. The extent to which the cation−π sandwich complexes investigated here are nonadditive is greater for B3LYP calculated values than for MP2 calculated values and for sandwich complexes with electron-donating substituents than those with electron-withdrawing groups.