Metal acetates such as manganese (II) acetate are widely characterized using x-ray crystallography and infra-red spectroscopy. Four conformations of metal acetates are known: ionic, unidentate, bidentate and bridging. Correlation between these conformations and difference (delta) in infra-red frequencies of carboxylate stretching in symmetric and anti-symmetric modes in both solid and solution-phase of various types of metal acetates was previously reported. However, it was shown via experiments that this correlation may not be valid under many conditions. In our knowledge, no computional study upon this exists as of yet. This study focuses upon, (a) applying semi-empirical (PM3), ab initio (Hartree-Fock/6-31G* and MP2/6-31G*) density functional methods (B3LYP/6-31G*) to determine the IR frequencies of carboxylate stretching and (b) validating whether the delta-based correlation occurs, in manganese (II) acetate. Calculations of solid and solution-states of manganese (II) acetate have been carried out in gas-phase and with the addition of explicit water molecules respectively. All calculations were conducted using SPARTAN. We found that the symmetric and anti-symmetric carboxylate stretching frequencies to be comparable with that of experiments. It was identified that the delta predicted using ab intio methods agreed more closely to past reports. We determined that the use of explicit water molecules provided better description of bonding modes than gas phase calculations for solution-phase manganese (II) acetate conformations. We confirmed the existence of the correlation between frequencies and bonding modes for manganese (II) acetate in solid and solution states using quantum chemical calculations.

Quantum chemical study to predict carboxylate stretching frequencies of manganese (II) acetate

243rd National Meeting (2012)

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