Gas-phase equilibrium molecular structures and ab initio thermochemistry of anthracene and rubrene

Otlyotov A, Kurochkin IY, Minenkov Y, et al. Gas-phase equilibrium molecular structures and ab initio thermochemistry of anthracene and rubrene. Physical Chemistry Chemical Physics. 2022.Semi-experimental gas-phase structures of anthracene and rubrene (5,6,11,12-tetraphenyltetracene) were determined by means of gas electron diffraction (GED). The use of the flexible restraints in the refinement of the GED data successfully resolves non-equivalent C–C bond lengths. The tetracene core of an isolated rubrene molecule was found to exhibit twist distortion of about 18°; this is less than DFT calculations predict (30–40°). The modified Feller-Peterson-Dixon method in conjunction with high-level DLPNO-CCSD(T) calculations was employed to resolve the discrepancy between the available experimental gas-phase enthalpies of formation for rubrene. The theoretical value of ΔfHmo(g, 298 K) = 759.4 ± 5.9 kJ mol−1 meets its recent experimental counterpart (765.6 ± 8.4 kJ mol−1) and is in strong disagreement with the previous estimation (882 kJ mol−1)