Hydrogen-bonding system in amarillite, NaFe(SO (sub 4) ) (sub 2) (H (sub 2) O) (sub 6) ; the structure refinement

The crystal structure of amarillite, NaFe(SO (sub 4) ) (sub 2) (H (sub 2) O) (sub 6) , was redetermined from a single crystal from Xitieshan, Qinghai Province, China. In complement to previous work, all non-H atoms were refined with anisotropic displacement parameters and H-atoms were located by difference Fourier methods and refined from X-ray diffraction data. The structure can be formally described by octahedral-tetrahedral "sheets" of corner-sharing [NaO (sub 4) (H (sub 2) O) (sub 2) ] octahedra and (SO (sub 4) ) tetrahedra, which constitute a structural sheet with composition [Na(SO (sub 4) ) (sub 2) (H (sub 2) O) (sub 2) ] (super 3-) extending parallel to (001). The resultant sheets are held together by interstitial Fe (super 3+) cations and hydrogen bonds. The [NaO (sub 4) (H (sub 2) O) (sub 2) ] octahedra donate four hydrogen bonds to the oxygen atoms of neighboring (SO (sub 4) ) tetrahedra, thus strengthening connections in three dimensions. The interstitial [FeO (sub 2) (H (sub 2) O) (sub 4) ] octahedra are linked by eight hydrogen bonds to the vertices of the adjacent octahedral-tetrahedral sheets, further stabilizing the crystal structure of amarillite. The FTIR spectrum of amarillite shows a strong absorption between 3000 cm (super -1) and 3500 cm (super -1) with maxima at approximately 3110 cm (super -1) and approximately 3442 cm (super -1) , which is in accordance with the O-H ... O distances derived from structure data.