Oxygen-bound fluorine (O-F): Ab initio investigations of the hypofluorous acid dimer

Ab initio calculations have been carried out on dimers of hypofluorous acid -(HOF)(2). Two stable structures were found, the first one with an almost l inear O ... H-O hydrogen bridge and F ... H-O hydrogen bond and the second one being a cyclic dimer with two F ... H-O bonds. The most stable complex determined at the CCSD(T)/6-311++G(2d,2p)//MP2/6-311++G(2d,2p) level is the linear structure, having a stabilization energy of 2.50 kcal/mol. The cycl ic structure is only 0.35 kcal/mol higher in energy than the linear one. Th e organization of the attractors achieved by the topological analysis of th e electron localization function (ELF) classifies the interaction in both d imer structures as the unshared-electron type. A transfer of 0.03e between the HOF monomers in the Linear structure is deduced from the comparison of the basin populations. The integral density over the F-O attractor basins y ields 0.32e for the cyclic structure and 0.27 and 0.37 e for the linear one . The large amount of electron density is concentrated in the regions of th e nonbonding valence pairs. The influence, which a dielectric surrounding h as on the HOF dimers, has been investigated with the SCRF method, with diel ectric constants ranging from 2 to 10 at the B3LYP/6-31G(d,p) level. The cy clic structure which assumed planar (C-2h) geometry was found to be unstabl e (transition state) within a dielectric medium. The calculated frequencies for the linear complex (C-1) agree reasonably well with those observed in a matrix, particularly in the H-O-F deformation region between 1365-1396 cm (-1).