A new polymorph of Ba(AsO3OH): Synthesis, crystal structure and vibrational spectra

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

“…The Raman spectrum shows an additional band at 2324 cm −1 (not observed in literature), which according to the IR results (2332 cm −1 ) is prescribed to the stretching vibrations of the strongly hydrogen‐bonded OH within the AsO 3 OH unit (Table ). The bands at 1603 and 1190 cm −1 are prescribed to the bending vibrations from the H 2 O molecules (the latter with additional contribution from the δ(OH) motion within the hydrogen arsenate anion; Figure a, Table ) whereas the band at 1315 cm −1 could be attributed to the δ(OH) plane vibrations as it appears in some (AsO 3 OH) 2− minerals . The theoretical results support such an assignment (Table ).…”

“…The experimental bands at 1689, 1658, and 1620 cm −1 could be unambiguously assigned as a result of the bending water vibrations of the crystallographically different water molecules (also indicated by both currently implemented theories and previous experience; Figure b, Table ). Similarly, the bands at 1172, 1144, and 1118 cm −1 are attributed to the δ(OH) vibrations from (AsO 3 OH) 2− groups …”

“…The bands at 2339 and 2273 cm −1 appear from hydrogen‐bonded OH vibrations within the AsO 3 OH unit (the A component of the ABC trio), whereas the bands at 1664 and 1578 cm −1 evolve from the bending vibrations of the water molecules (Figure e, Table ), the high‐wavenumber shoulder being attributed to the C component of the ABC trio. The δ(OH) bending vibrations from the AsO 3 OH group, similarly to the bayldonite as well as to Ba(AsO 3 OH) and Sr(AsO 3 OH) spectra, appear at 1425, 1308, and 1100 cm −1 .…”

“…Similarly, the bands at 1172, 1144, and 1118 cm −1 are attributed to the δ(OH) vibrations from (AsO 3 OH) 2− groups. [3,13] The IR spectrum of vladimirite has not been previously presented nor interpreted. However, the band assignment can be inferred from the pharmacolite discussion and following the previously published literature results from structurally similar hydrogen arsenate minerals.…”

“…[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.…”