The structural characterization of whiteite-(CaFeMg), a natural orthophosphate from Crosscut Creek, Yukon, Canada, with chemical composition (Ca0.86Na0.05)?=0.91(Fe0.88Mn0.02)?=0.90Mg2.17Al1.93(PO4)4(OH)2?8H2O obtained by WDS-EMPA, was carried out by means of single crystal X-ray diffraction. The structure was solved in the P2/a monoclinic space group, with the following unit cell constants: a = 14.8700(15), b = 6.9785(5), c = 9.9268(10) Å, ? = 110.110(1)°, V = 967.31(15) Å3. Structure refinement lead to the crystal chemical formula (Ca0.95Na0.11)?=1.06Fe0.90Mg2.01Al2.05(PO4)4(OH)1.99?8.17H2O. Phosphorus atoms display tetrahedral (PO4) coordination, while magnesium, iron(II) and aluminum display regular octahedral coordination; calcium displays a complex CaO8 coordination. MgO2(H2O)4, FeO6, AlO4(OH)2, CaO8 polyhedra and PO4 groups are arranged such as to form a three-dimensional framework via edge- and vertex-sharing arrangements. Strong O-H...O hydrogen bonds contribute to stabilize the array: such interactions were also investigated by means of Libowitzky formula (Libowitzky, 1999) application, owing to the results of IR spectroscopy.
Crystal structure of whiteite-(CaFeMg) from Crosscut Creek, Canada.
Capitelli F;Chita G;
2011
Abstract
The structural characterization of whiteite-(CaFeMg), a natural orthophosphate from Crosscut Creek, Yukon, Canada, with chemical composition (Ca0.86Na0.05)?=0.91(Fe0.88Mn0.02)?=0.90Mg2.17Al1.93(PO4)4(OH)2?8H2O obtained by WDS-EMPA, was carried out by means of single crystal X-ray diffraction. The structure was solved in the P2/a monoclinic space group, with the following unit cell constants: a = 14.8700(15), b = 6.9785(5), c = 9.9268(10) Å, ? = 110.110(1)°, V = 967.31(15) Å3. Structure refinement lead to the crystal chemical formula (Ca0.95Na0.11)?=1.06Fe0.90Mg2.01Al2.05(PO4)4(OH)1.99?8.17H2O. Phosphorus atoms display tetrahedral (PO4) coordination, while magnesium, iron(II) and aluminum display regular octahedral coordination; calcium displays a complex CaO8 coordination. MgO2(H2O)4, FeO6, AlO4(OH)2, CaO8 polyhedra and PO4 groups are arranged such as to form a three-dimensional framework via edge- and vertex-sharing arrangements. Strong O-H...O hydrogen bonds contribute to stabilize the array: such interactions were also investigated by means of Libowitzky formula (Libowitzky, 1999) application, owing to the results of IR spectroscopy.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
