Microhydration of selenate, chromate and sulphate dianions: observation of indistinguishable IR spectra

Abstract

ABSTRACTStructures, energetics and infrared (IR) spectra of the SeO42−.nH2O, CrO42−.nH2O and SO42−.nH2O clusters at ωB97X-D/aug-cc-pvtz level of theory are studied. It is observed that both the microhydrated SeO42− and CrO42− clusters are stabilised by double-hydrogen bonding (DHB), single-hydrogen bonding (SHB) and H-bonded cyclic water ring arrangements like the microhydrated SO42− cluster. It is also observed that the conformations having cyclic water network are found to be more stable in contrast to the other conformers having SHB or DHB arrangements. The calculated solute–solvent interaction energy for a particular structure is found to be nearly same (within 2%–6%) for all the hydrated clusters. The structure having at least one cyclic water ring is characterised by a peak in the range of 3450–3480 cm−1 in the IR spectra for all the systems. A single sharp peak at ∼3520 cm−1 is observed for the structure with six double-hydrogen arrangements. We do observe a near indistinguishable IR spectral pattern (within 1%) in the O–H stretching region for a particular structure in all the systems. It may be attributed to the same oxidation state of the central atom, identical geometry of the hydrated cluster and nearly same solute–solvent interaction energy.