Isomerism in OBe3F3+ cation: an ab initio study

Ab initio MP2/6-31G*//HF/6-31G*+ZPE(HF/6-31G*) calculations of the potentia l energy surface in the vicinity of stationary points and the pathways of i ntramolecular rearrangements between low-lying structures of the OBe3F3+ ca tion detected in the mass spectra of mu(4)-Be4O(CF3COO)(6) were carried out . Ten stable isomers with di- and tricoordinate oxygen atoms were localized . The relative energies of six structures lie in the range 0-8 kcal mol(-1) and those of the remaining four structures lie in the range 20-40 kcal mol (-1). Two most favorable isomers, a C-2v isomer with a dicoordinate oxygen atom, planar six-membered cycle, and one terminal fluorine atom and a pyram idal C-3v isomer with a tricoordinate oxygen atom and three bridging fluori ne atoms, are almost degenerate in energy. The barriers to rearrangements w ith the breaking of one fluorine bridge am no higher than 4 kcal mol(-1), e xcept for the pyramidal C-3v isomer (similar to 16 kcal mol(-1)). On the co ntrary, rearrangements with the breaking of the O-Be bond occur with overco ming of a high energy barrier (similar to 24 kcal mol(-1)). A planar D-3h i somer with a tricoordinate oxygen atom and linear O-Be-H fragments was foun d to be the most favorable for the OBe3H3+ cation, a hydride analog of the OBe3F3+ ion; the energies of the remaining five isomers are more than 25 kc al mol(-1) higher.