IR Spectrum of the H₅O₂⁺ Cation in the Context of Proton Disolvates L−H⁺−L

Abstract

The H 5 O 2 + 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 [H 5 O 2 + ‚4Solv] are formed via H-bonding with the terminal O-H groups. In the infrared spectrum, the ν s OH and ν as OH 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.

Infrared Spectrum of 4-Methoxypicolinic Acid N-Oxide: Computation of Asymmetric O−H Stretching Band

“…[35][36][37] The present contribution is related to the previously published work. 12,14,21,[38][39][40][41] The one-dimensional anharmonic vibrational O-H stretching frequency of MPANO, calculated to 1699 cm -1 , is notably lower than the value of 2129 cm -1 obtained in the same way for an unsubstituted analog (picolinic acid N-oxide, PANO). This indicates that the hydrogen bonding of MPANO is stronger than that of PANO, a fact that is reflected in the infrared and NMR experimental findings.…”

Cooperative interaction of H3O+ with 1,3‐alternate tetrapropoxycalix[4]arene: NMR and theoretical study

“…In analogy with 1 H NMR, carbon 1 has the largest relative shift but the difference to 2 + 6 is much more pronounced and cannot be interpreted as a mere effect of the change of relative directions of the aromatic rings. Bearing in mind the theoretical predictions of relatively strong interactions of the hydroxonium ion or its hydrate with aromatic π systems, [23,24] we propose that the large relative shift of signal 1 both in 1 H and 13 C NMR spectra is partly due to additional hydrogen bonds of the ion to the π electrons at the corresponding carbon atoms. The spectroscopic evidence thus leads to the idea of H 3 O + being bound to the two Ar-O-CH 2 oxygen atoms of one of the opposite moieties of 1 and to the carbons 1 of the opposite moiety.…”

“…The optimal O-O distance in the complexed H 5 O 2 + is predicted to be 2.41´Å, which is the usual distance observed. [24] The structure of the complex has almost C 4h symmetry, which would explain the simplicity of NMR spectra. However, there are several other experimental observations, which do not quite agree with this possibility: (i) our infrared spectra do not indicate that H 5 O 2 + is the main proton hydrate in our systems; (ii) the complex could exchange H 5 O 2 + by an intermolecular mechanism, which would give the corresponding part of the dynamics observed by NMR, but apparently there is no reason for any intramolecular dynamics in this case; (iii) in this optimized arrangement, the outer protons of H 5 O 2 + form strong hydrogen bonds with the phenoxy-oxygen atoms but none with the aromatic systems.…”

“…In the case of proton lower hydrates, such possibility appears to be warranted by the general tendency of cations to bind to suitably oriented π -systems, [22] even more so considering the experimentally proven π -interaction of H 3 O + and H 5 O 2 + with benzene. [23,24] There is another interesting problem connected with a cation binding to a 1,3-alternate calix [4]arene. As binding of two cations to one molecule is highly improbable on grounds of energy, an asymmetric complex with one coordination site occupied and one vacant should be formed if the ion is H 3 O + .…”

Tuning the intermolecular proton bond in the H5O2+ ‘Zundel ion’ scaffold

“…This is easily accomplished by replacing the exterior hydrogen atoms with methyl groups [46,47], since the PA of the isolated molecules incrementally increases from 691 to 754 to 792 kJ/mol in going from water to methanol to dimethyl ether, respectively [48]. Consequently, by studying the various proton-bound, binary complexes of water, methanol, and dimethyl ether, we can systematically follow how the difference in proton affinities between the two molecules affects the value of m sp .…”