Stacking interaction in pyrazine dimer

Abstract

The structure and stability of pyrazine dimer in different orientations have been investigated using second- and fourth-order Møller-Plesset perturbation theory (MP2, MP4) and coupled-cluster singles and doubles with non-iterative perturbative triples method [CCSD(T)] with various basis sets (6-31G^∗∗, 6-311G^∗∗, 6-311++G^∗∗, cc-pVDZ, aug-cc-pVDZ, cc-pVTZ, and aug-cc-pVTZ). With the largest basis set (aug-cc-pVTZ) at the MP2 level of theory, the calculated binding energies (basis set superposition error corrected) for the sandwich, N–N axial-displaced, lateral-displaced, cross-displaced, T-shaped (T_N-ring and T_H-ring), and wedge-shaped (W_N-C and W_C-C) geometries are found to be 3.01, 4.18, 4.63, 5.92, 4.54, 2.78, 2.89, and 3.23 kcal/mol, respectively. Although MP2 calculations predict the cross-displaced geometry to be the most stable one, MP4 and CCSD(T) calculations show the most stable geometry to be T-shaped (T_N-ring), with a center-of-mass separation of 4.2 Å. Dispersion interaction seems to be the major source of attraction in all the geometries considered, while the nature of electrostatic interaction depends on the mutual orientation of the two rings.