Raman spectroscopy of hydrogen‐arsenate group (AsO₃OH) in solid‐state compounds: cobalt mineral phase burgessite Co₂(H₂O)₄[AsO₃OH]₂·H₂O

Abstract

Raman spectrum of burgessite, Co 2 (H 2 O) 4 [AsO 3 OH] 2 · H 2 O, was studied, interpreted and compared with its infrared spectrum.The stretching and bending vibrations of (AsO 3 ) and As-OH units, as well as the stretching, bending and libration modes of water molecules and hydroxyl ions were assigned. The range of O-H· · ·O hydrogen bond lengths was inferred from the Raman and infrared spectra of burgessite. The presence of (AsO 3 OH) 2− units in the crystal structure of burgessite was proved, which is in agreement with its recently solved crystal structure. Raman and infrared spectra of erythrite inferred from the RRUFF database are used for comparison.

Vibrational spectra of the rare‐occurring complex hydrogen arsenate minerals pharmacolite, picropharmacolite, and vladimirite: Dominance of Raman over IR spectroscopy to discriminate arsenate and hydrogen arsenate units

“…Here, we found that the Raman spectra of the studied minerals below 1000 cm −1 perfectly illustrate the number of the present crystallographically different AsO 4 and AsO 3 OH units in their structures and it might serve as an indicator to deduce the number of these units for each mineral ( Figure 5). In accordance with the tentative assignments found in great number of published articles for Raman spectral behavior of hydrogen arsenate minerals, [3,[10][11][12][13][14][15][16][17]25] the highest wavenumber bands are attributed to antisymmetric ν 3 (AsO 3 OH) modes followed by one or two stronger bands from symmetric ν 1 (AsO 3 OH) modes at somewhat lower wavenumbers. These bands in the pharmacolite mineral, which consist of structurally equivalent (AsO 3 OH) 2− units, [6] were registered at 891, 862, and 841 cm −1 (Figure 5a) bearing close resemblance with their position in literature data (Table 3).…”

“…However, the band assignment can be inferred from the pharmacolite discussion and following the previously published literature results from structurally similar hydrogen arsenate minerals. [10][11][12][13][14][15][16][17] The strongest maximum at 3542 cm −1 originates from OH stretchings of the non-hydrogen-bonded (or only weakly hydrogen bonded) OH oscillators of the water molecule. The shoulder appearing at about 3500 as well as the band at 3216 cm −1 may be attributed to the same mode, whereas the bands at 3055 and 2954 cm −1 (Figure 1d) are primarily attributed to the OH stretchings of the OH oscillator within the hydrogen arsenate molecular anion as well as from the OH stretchings from the hydrogen-bonded water molecules (Table 2).…”

“…[9] The structure consists of layers joined by hydrogen bonds formed by both water molecules and OH groups within the layers. The reported vibrational spectra of pharmacolite [10] and some arsenate minerals and compounds containing the AsO 3 OH groups [11][12][13][14][15][16][17] will facilitate the interpretation of the spectra of the studied picropharmacolite and vladimirite. However, neither infrared (IR) liquid nitrogen temperature (LNT) spectra of the minerals have been reported (providing important information for hydrogen bonding) nor theoretically simulated spectra have been derived.…”

THE CRYSTAL STRUCTURE OF VLADIMIRITE, WITH A REVISED CHEMICAL FORMULA, Ca4(AsO4)2(AsO3OH){middle dot}4H2O

“…There have been numerous studies on a variety of arsenate minerals and compounds, especially those containing the AsO 3 OH groups, by means of infrared and Raman spectroscopic techniques (e.g., Mihajlović et al 2004, Đorđević & Karanović 2008, 2011a, 2011b, Čejka et al 2011. We present our Raman spectroscopic measurements of vladimirite in Figure 3.…”

A vibrational spectroscopic study of the phosphate mineral vantasselite Al4(PO4)3(OH)3·9H2O

“…Raman spectroscopy has proven most useful for the study of mineral structures [14][15][16][17][18][19]. The objective of this research is to report the Raman and infrared spectra of vantasselite and to relate the spectra to the molecular structure of the minerals.…”