The halogen bonded complexes between six carbonyl bases and molecular chlorine are investigated theoretically. The interaction energies calculated at the CCSD(T)/aug-cc-pVTZ level range between -1.61 and -3.50 kcal mol(-1). These energies are related to the ionization potential, proton affinity, and also to the most negative values (V(s,min)) on the electrostatic potential surface of the carbonyl bases. A symmetry adapted perturbation theory decomposition of the energies has been performed. The interaction results in an elongation of the Cl-Cl bond and a contraction of the CF and CH bonds accompanied by a blue shift of the ν(CH) vibrations. The properties of the Cl2 molecules are discussed as a function of the σ*(Cl-Cl) occupation, the hybridization, and the occupation of the Rydberg orbitals of the two chlorine atoms. Our calculations predict a large enhancement of the infrared and Raman intensities of the ν(Cl-Cl) vibration on going from isolated to complexed Cl2.
Keywords: DFT; MP2; carbonyl compounds; halogen bond; molecular chlorine.
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