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IR Spectrum of the H 5 O 2 + Cation in the Context of Proton Disolvates L−H + −L

2006; American Chemical Society; Volume: 110; Issue: 48 Linguagem: Inglês

10.1021/jp062879w

1520-5215

Evgenii S. Stoyanov, Christopher A. Reed,

Molecular Spectroscopy and Structure

The H5O2+ ion has been studied in chlorocarbon, benzene, and weakly coordinating anion environments to bridge the gap between the gas-phase and traditional condensed-phase investigations. Symmetrical cations of the type [H5O2+·4Solv] are formed via H-bonding with the terminal O−H groups. In the infrared spectrum, the νsOH and νasOH vibrations behave in a manner similar to those of common water molecules: the stronger is the H-bonding interaction with the surroundings, the lower is the frequency shift. A consistent pattern of IR bands from the central O−H+−O group is identified, regardless of the strength of the interaction of H5O2+ with its environment. Three intense bands develop: a (860−995 cm-1), b (1045−1101 cm-1), and c (1672−1700 cm-1), as well as two weak bands, d (∼1300 cm-1) and e (∼1400−1500 cm-1). These fingerprint bands are highly characteristic for vibrations of O−H−O group irrespective of formal charge. They are seen in symmetrical proton disolvates of the type L−H+−L, where L is an O-atom donor (alcohol, ether, ketone, phosphate, etc.), and in [A−H−A]- acid salts (A- = oxyanion). The commonality is equivalency of the two O-atoms, a short O···O distance (ca. 2.40 Å), and a flat-bottomed potential well for the bridging proton, that is, a short, strong, low-barrier H-bond. Assignments for bands a−e are suggested in an attempt to resolve inconsistencies between experimental and calculated data.