Abstract

Two new prototypes delocalized π⋯π complexes are introduced: the dimers of cyanogen, (N≡C-C≡N)2, and diacetylene, (HC≡C-C≡CH)2. These dimers have properties similar to larger delocalized π⋯π systems such as benzene dimer but are small enough that they can be probed in far greater detail with high accuracy electronic structure methods. Parallel-slipped and T-shaped structures of both cyanogen dimer and diacetylene dimer have been optimized with 15 different procedures. The effects of basis set size, theoretical method, counterpoise correction, and the rigid monomer approximation on the structure and energetics of each dimer have been examined. MP2 and CCSD(T) optimized geometries for all four dimer structures are reported, as well as estimates of the CCSD(T) complete basis set (CBS) interaction energy for every optimized geometry. The data reported here suggest that future optimizations of delocalized π⋯π clusters should be carried out with basis sets of triple-ζ quality. Larger basis sets and the expensive counterpoise correction to the molecular geometry are not necessary. The rigid monomer approximation has very little effect on structure and energetics of these dimers and may be used without consequence. Due to a consistent cancellation of errors, optimization with the MP2 method leads to CCSD(T)/CBS interaction energies that are within 0.2 kcal mol-1 of those for structures optimized with the CCSD(T) method. Future studies that aim to resolve structures separated by a few tenths of a kcal mol-1 should consider the effects of optimization with the CCSD(T) method. © the Owner Societies.

Department(s)

Chemistry

International Standard Serial Number (ISSN)

1463-9076

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2024 Royal Society of Chemistry, All rights reserved.

Publication Date

19 Apr 2007

Download

Full Text Link

Included in

Chemistry Commons

Share

 
COinS