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.