Structure of selected basic copper(II) sulphate minerals based upon spectroscopy – Implications for hydrogen bonding

Abstract

The application of near-infrared and infrared spectroscopy has been used for identification and distinction of basic Cu-sulphates that include devilline, chalcoalumite and caledonite. Near-infrared spectra of copper sulphate minerals confirm copper in divalent state. Jahn–Teller effect is more significant in chalcoalumite where 2B 1g → 2B 2g transition band shows a larger splitting (490 cm −1) confirming more distorted octahedral coordination of Cu 2+ ion. One symmetrical band at 5145 cm −1 with shoulder band 5715 cm −1 result from the absorbed molecular water in the copper complexes are the combinations of OH vibrations of H 2O. One sharp band at around 3400 cm −1 in IR common to the three complexes is evidenced by Cu OH vibrations. The strong absorptions observed at 1685 and 1620 cm −1 for water bending modes in two species confirm strong hydrogen bonding in devilline and chalcoalumite. The multiple bands in ν 3 and ν 4(SO 4) 2− stretching regions are attributed to the reduction of symmetry to the sulphate ion from T d to C 2V. Chalcoalumite, the excellent IR absorber over the range 3800–500 cm −1 is treated as most efficient heat insulator among the Cu–sulphate complexes.