Effects of Heterogeneity in Small ;r-Type Dimers: Homogeneous and Mixed Dimers of Diacetylene and Cyanogen

摘要

The homo- and heterogeneous dimers of diacetylene (H-C≡C-C≡C-H) and cyanogen (N≡C—C≡N) were studied using ab initio electronic structure computations to probe the effects of heterogeneity on,,noncovalent interactions between systems with delocalized n electron networks. Full geometry optimizations and harmonic vibrational frequencies were performed using the robust coupled-cluster with single and double and perturbative triple excitations (CCSD(T)) method with the triple-ζ plus 2 sets of polarization functions TZ2P(f,d)++ basis set. Seven basic configurations were examined for each dimer (cross, stacked, parallel-slipped, parallel-tipped, linear, T-shaped and Y-shaped), but only four stationary points were identified on the potential energy surfaces (PESs) of the homogeneous cyanogen dimer and the mixed diacetylene/cyanogen dimer. Six previously characterized stationary points on the diacetylene dimer PES were re-examined with the CCSD(T) method and the TZ2P(f,d)++ basis set for consistency. Second-order Moller-Plesset perturbation theory (MP2) and CCSD(T) complete basis set (CBS) limit interaction energies were estimated using the explicitly correlated MP2-F12 and CCSD(T)-F12 methods in conjunction with the VQZ-F12 basis set. On the cyanogen dimer PES, the C_(2v) T-shaped structure is the only minimum, with an average electronic interaction energy, E_(int), of -1.96 kcal mol~(-1) at the CCSD(T) CBS limit. The C_s Y-shaped structure (in agreement with previous results) is the global minimum on the diacetylene dimer PES, having a mean CCSD(T) CBS limit E_(int) of —1.75 kcal mol~(-1). Three low-lying minima have been identified on the diacetylene/cyanogen dimer PES, a C_(∞v), linear, a C_(2v) cross, and a C_s parallel-slipped structure with average CCSD(T) CBS limit interaction energies of -2.00, -2.16, and -2.45 kcal mol~(-1), respectively.