Theoretical Study of the O•••Cl Interaction in Fluorinated Dimethyl Ethers Complexed with a Cl Atom: Is It through a Two-Center-Three-Electron Bond?

Theoretical investigations are carried out on the interaction between fluorinated dimethyl ethers (FDME, n(F) = 0-4) and the Cl atom. Short intermolecular O center dot center dot center dot Cl distances between 2.401 and 2.938 angstrom reveal the formation of a new class of complexes. The interaction energies calculated with the G2(MP2) method range between -9.1 (n(F) = 4) and -26.0 (n(F) = 0) kJ/mol. The charge transfer occurring from the ethers to atomic Cl is moderate and ranges between 0.012 e (n(F) = 4) to 0.188 e (n(F) = 0). The binding energies are linearly related to the proton affinity, to the charge transfer (CT) occurring in the molecular system and inversely proportional to the ionization potential and electron affinity (IP-EA) values. The CT and spin density data indicate substantial two-center-three-electron O center dot center dot center dot Cl interaction in CH3OCH3 center dot center dot center dot Cl and CH3OCH2F center dot center dot center dot Cl systems, whereas for highly fluorinated ethers the interaction is predominantly electrostatic in nature. The formation of the complex results in a contraction of the CH bonds, especially in the gauche position. The blue shifts of the C-H stretching vibrations calculated in the partially deuterated isotopomers range between 2 and 54 cm(-1) and are correlated to the variation of the CH distances.