Ab initio study of weakly bound halogen complexes: RXa⟨-PH3

Ab initio calculations were employed to study the role of ipso carbon hybridization in halogenated compounds RX (R = methyl, phenyl, acetyl, H and X = F, Cl, Br and I) and its interaction with a phosphorus atom, as occurs in the halogen bonded complex type RXa <-PH3. The analysis was performed using ab initio MP2, MP4 and CCSD(T) methods. Systematic energy analysis found that the interaction energies are in the range -4.14 to -11.92 kJ mol(-1) (at MP2 level without ZPE correction). Effects of electronic correlation levels were evaluated at MP4 and CCSD(T) levels and a reduction of up to 27 % in interaction energy obtained in MP2 was observed. Analysis of the electrostatic maps confirms that the PhCla <-PH3 and all MeXa <-PH3 complexes are unstable. NBO analysis suggested that the charge transfer between the moieties is bigger when using iodine than bromine and chlorine. The electrical properties of these complexes (dipole and polarizability) were determined and the most important observed aspect was the systematic increase at the dipole polarizability, given by the interaction polarizability. This increase is in the range of 0.7-6.7 u.a. (about 3-7 %).