Abstract
In this work, we have used a combination of vibrational spectroscopy (infrared, Raman and inelastic neutron scattering) and periodic density functional theory to investigate six metal methanesulfonate compounds that exhibit four different modes of complexation of the methanesulfonate ion: ionic, monodentate, bidentate and pentadentate. We found that the transition energies of the modes associated with the methyl group (C–H stretches and deformations, methyl rock and torsion) are essentially independent of the mode of coordination. The SO3 modes in the Raman spectra also show little variation. In the infrared spectra, there is a clear distinction between ionic (i.e. not coordinated) and coordinated forms of the methanesulfonate ion. This is manifested as a splitting of the asymmetric S–O stretch modes of the SO3 moiety. Unfortunately, no further differentiation between the various modes of coordination: unidentate, bidentate etc … is possible with the compounds examined. While it is likely that such a distinction could be made, this will require a much larger dataset of compounds for which both structural and spectroscopic data are available than that available here.
Highlights
Metal methanesulfonates (M(CH3SO3)x · nH2O) are compounds of interest because of the role they play as catalysts for numerous reactions in organic synthesis including Mannich, Biginelli reaction, esterification and tetrahydropyranylation of alcohols and phenols [1]
We have used a combination of vibrational spectroscopy and periodic density functional theory to investigate six metal methanesulfonate compounds that exhibit four different modes of complexation of the methanesulfonate ion: ionic, monodentate, bidentate and pentadentate
We found that the transition energies of the modes associated with the methyl group (C–H stretches and deformations, methyl rock and torsion) are essentially independent of the mode of coordination
Summary
Metal methanesulfonates (M(CH3SO3)x · nH2O) are compounds of interest because of the role they play as catalysts for numerous reactions in organic synthesis including (but not limited to) Mannich, Biginelli reaction, esterification and tetrahydropyranylation of alcohols and phenols [1] (figure 1) This is due to their low toxicity, low cost and low reactivity with air and water [2]. Due to nature of their deposition in ice cores, with a particular focus on Mg(CH3SO3)2· nH2O and Na(CH3SO3)2· nH2O—where the sodium salt is the most abundant [5] It is worth noting, though, that the magnesium salt found is restricted to the Last Glacial Maximum ice which forms during the coldest period in the glacial cycle. The assignments are supported by periodic density functional theory (DFT) calculations of the Na, Cs and Cu salts
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