Theoretical and experimental study of the vibrational spectra of liroconite, Cu2Al(AsO4)(OH)4∙4H2O and bayldonite, Cu3Pb[O(AsO3OH)2(OH)2]

•The first theoretical vibrational spectra predictions for liroconite and bayldonite are presented.•Essentially, all bands in IR and Raman spectra are tentatively assigned.•Theoretical approach correctly reproduce the existence and the order of appearance of essentially all bands.•Thermoanalytical results confirmed vibrational spectroscopy results for the lack of H2O molecules in bayldonite.

Liroconite and bayldonite were studied with vibrational (IR and Raman) spectroscopy, thermal analysis methods and X-ray powder diffraction. In aim to undertake correct spectral interpretation, solid-sample ATR spectra, IR transmission spectra in KBr (at room temperature and liquid nitrogen temperature), and IR spectra in non-volatile inert paraffin oil-Nujol and in fluorinated hydrocarbon oil-Fluorolube, were collected. The lowering of the symmetry of the AsO4 group as a result of the replacement of the O atom by an OH group in bayldonite resulted in band splitting manifested with the enhanced number of the AsO/OH stretching bands compared to the reduced number of AsO stretching bands in liroconite. In addition, conduced thermal analysis determined the mineral thermal stability and depicted the process of solid-state dehydration. Quantum theoretical study based on pseudopotential plane-wave density functional theory provided a support to the empirical band assignments.