D. Sundholm et al., INTERMOLECULAR INTERACTIONS IN P-CHLOROBENZOIC ACID DIMERS, The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory, 102(36), 1998, pp. 7137-7142
The molecular structure of the parallel orientation of the p-chloroben
zoic acid dimer has been studied at the second-order Moller-Plesset le
vel using split-valence-quality basis sets augmented by polarization f
unctions. In the obtained dimer structure, the Cl atoms are located be
hind the carboxyl groups of the neighboring monomer, while in crystall
ine copper and nickel p-chlorobenzoate complexes, the Cl atoms and the
benzene nuclei form a parallel displaced umbrella structure with the
Cl atoms mutually above the center of the respective benzene ring. The
interaction energy for the parallel p-chlorobenzoic acid dimer comple
x is calculated at the second-order Moller-Plesset level to be 5.1 kca
l mol(-1). The intermolecular attraction is mainly due to dispersion e
ffects between the aromatic rings. The obtained distance between the b
enzene nuclei of 343 pm is in agreement with the experimental values o
f 341.6 and 366.6 pm measured for nickel and copper p-chlorobenzoate c
omplexes, respectively. At the second-order Moller-Plesset level, the
umbrella structure is found to be bound by 2.6 kcal mol(-1), as compar
ed to infinite separations, with a chlorine-ring distance of 364 pm. H
owever, at the second-order Moller-Plesset level, the umbrella structu
re is not a local minimum.