The fluoroform center dot center dot center dot ethylene oxide complex exhibits a C-H center dot center dot center dot O anti-hydrogen bond

A new, recently discovered type of intermolecular bond, called an anti-hydr ogen bond, is found in the fluoroform ethylene oxide complex. The complex s tructure and properties were predicted on the basis of counterpoise-correct ed gradient optimization performed at a correlated ab initio level. Formati on of the C-H ... O anti-hydrogen bond is manifested by an 0.1 pm contracti on of the C-H bond and a significant (similar to 30 cm(-1)) blue-shift of t he C-H stretching frequency, accompanied by a lowering of intensity of the respective vibration. In contrast to previous cases, the studied C-H ... O anti-hydrogen bond originates from dipole-dipole electrostatic interaction. The fluoroform molecule a has properly oriented dipole moment vector, the size of which is further enhanced by the C-H bond contraction. (C) 1999 Els evier Science B.V. All rights reserved.