A Raman spectroscopic study of a hydrated molybdate mineral ferrimolybdite, Fe2(MoO4)3·7–8H2O

• We have studied two well-defined ferrimolybdite samples, Fe23+(Mo6+O4)3·7–8H2O.
• We used Raman spectroscopy to characterise the ferrimolybdate.
• Raman and infrared bands assigned to (MoO4)2− units.
• Approximate O–H⋯O hydrogen bond lengths (2.80–2.73 Å) were inferred.

Raman spectra of two well-defined ferrimolybdite samples, Fe23+(Mo6+O4)3·7–8H2O, from the Krupka deposit (northern Bohemia, Czech Republic) and Hůrky near Rakovník occurrence (central Bohemia, Czech Republic) were studied and tentatively interpreted. Observed bands were assigned to the stretching and bending vibrations of molybdate anions, Fe–O units and water molecules. Number of Raman and infrared bands assigned to (MoO4)2− units and water molecules proved that symmetrically (structurally) nonequivalent (MoO4)2− and H2O are present in the crystal structure of ferrimolybdite. Approximate O–H⋯O hydrogen bond lengths (2.80–2.73 Å) were inferred from the published infrared spectra.

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