Vibrational spectroscopic characterization of the sulphate mineral khademite Al(SO4)F⋅5(H2O)

Abstract

Vibrational spectroscopy has been used to characterize the sulphate mineral khademite Al(SO4)F·5(H2O). Raman band at 991 cm-1 with a shoulder at 975 cm-1 is assigned to the ν1 (SO4)2- symmetric stretching mode. The observation of two symmetric stretching modes suggests that the sulphate units are not equivalent. Two low intensity Raman bands at 1104 and 1132 cm-1 are assigned to the ν3 (SO4)2- antisymmetric stretching mode. The broad Raman band at 618 cm-1 is assigned to the ν4 (SO4)2- bending modes. Raman bands at 455, 505 and 534 cm-1 are attributable to the doubly degenerate ν2 (SO4)2- bending modes. Raman bands at 2991, 3146 and 3380 cm-1 are assigned to the OH stretching bands of water. Five infrared bands are noted at 2458, 2896, 3203, 3348 and 3489 cm-1 are also due to water stretching bands. The observation of multiple water stretching vibrations gives credence to the non-equivalence of water units in the khademite structure. Vibrational spectroscopy enables an assessment of the structure of khademite.

Crystal-chemistry of sulfates from the Apuan Alps, Tuscany, Italy. VIII. New data on khademite, Al(SO4)F(H2O)5

“…(2015) for rostite from Le Cetine di Cotorniano, Italy and Košek et al (2019) for khademite from Libušín, Czech Republic agree, within experimental uncertainties, with those collected on the Monte Arsiccio sample, the Raman spectrum of khademite reported by Frost et al . (2013b) does not fit with previous and current results. These observations have a two-fold implication.…”

“…In addition, the critical examination of available Raman spectroscopic data highlighted some discrepancies in the published spectra. Indeed, whereas the data reported by Frost et al (2015) for rostite from Le Cetine di Cotorniano, Italy and Košek et al (2019) for khademite from Libušín, Czech Republic agree, within experimental uncertainties, with those collected on the Monte Arsiccio sample, the Raman spectrum of khademite reported by Frost et al (2013b) does not fit with previous and current results. These observations have a two-fold implication.…”

“…Data for the Monte Arsiccio sample are in good agreement, within experimental uncertainties, with those given by Frost et al (2015) and Košek et al (2019). On the contrary, the sample of khademite studied by Frost et al (2013b) shows a completely different Raman spectrum; this disagreement is probably due to the fact that these authors studied a specimen that had not been fullycharacterised. It is very likely that their spectrum does not belong to khademite.…”

“…On the contrary, the sample of khademite studied by Frost et al . (2013b) shows a completely different Raman spectrum; this disagreement is probably due to the fact that these authors studied a specimen that had not been fully-characterised. It is very likely that their spectrum does not belong to khademite.…”

Vibrational Spectroscopic Properties of a [C(NH2)3]4Cl2SO4Ferroelectric Crystal - An Experimental and Theoretical Study

“…500 cm −1 can be distinguished, some of them of the weak intensity. The bands at 979, 621, and 454 cm −1 are assigned to ν(SO 2− 4 ) vibrations and are named as ν 1 , ν 4 , and ν 2 modes, respectively [17,18]. According to [19] the existence of all the ν 1 , ν 2 , ν 3 , and ν 4 bands of SO 2− 4 ion at IR spectrum and ν 1 , ν 2 , and ν 4 bands in Raman spectrum indicates a lowering of symmetry from T d to C s , which is consistent with the crystallographical data [6].…”