Molecular structure of 1,2,4,5-tetracyanobenzene from gas-phase electron diffraction and theoretical calculations

The molecular structure of 1,2,4,5-tetracyanobenzene has been determined by gas-phase electron diffraction and by ab initio calculations at several levels of theory. The electron diffraction study indicates an elongation of the aromatic ring along the (H)C ... C(H) axis, characterized by angular deformation of the benzene ring and lengthening of the (NC)C-C(CN) bonds. The following bond lengths (r(g)) and bond angles were obtained by electron diffraction: (C-C)(ring,mean) 1.406 +/- 0.003 Angstrom, C-C(N) 1.429 +/- 0.003 Angstrom, C drop N 1.161 +/- 0.002 Angstrom, angle C-ipso - C-ortho - C-ipso 118.0 +/- 0.4 degrees, C-ipso - C-ipso - C(N) 120.8 +/- 0.3 degrees.