The crystal structure and the chemical composition of a paravauxite from the Siglo Veinte Mine, Llallagua, Bustillo Province, Potosi Department, Bolivia [(Fe)(Fe 2+0.916Mn0.0162+Mg0.064Ca0.002)(Sigma 0.998)Al-Al(1) Al(2)(2.005)P(P1.998Si0.002) O-Sigma 2(8)(OH) (2)center dot 8H(2)O, a = 5.242(1) angstrom, b = 10.569(2) angstrom, c = 6.970(2) angstrom, alpha = 106.78(3)(o), beta = 110.81(2)(o) and gamma = 72.29(2)(o), space group P (1) over bar], was investigated by single-crystal neutron diffraction and electron microprobe analysis in wavelength-dispersive mode. Neutron-intensity data were collected at 293 K and anisotropic structure refinement was performed. At the end of the refinement no peak larger than +/- 1.3 fm/angstrom(3) was present in the final difference-Fourier map of the nuclear density. The final statistical index was R-1 = 0.0495 for 194 refined parameters and 1678 unique reflections with F-o > 4 sigma(F-o). Eleven independent H sites (i.e. H(1), H(2), H(3), H(4A), H(4B), H(5), H(6), H(7), H(8), H(9A) and H(9B)), all at similar to 1 angstrom from the respective O sites, were located successfully. H(4A) and H(4B) and H(9A) and H(9B) are two mutually exclusive subsite couples only 0.4 0.6 angstrom apart. The complex H-bonding scheme in the paravauxite structure is now well defined and 12 independent H bonds, with an energetically favourable bonding configuration, are described. A comparison between the previous experimental findings based on Raman and infrared spectroscopy and those obtained in this present study is carried out. Paravauxite provides the rare opportunity to investigate the H-bond configuration of coexisting hydroxyl groups and H2O molecules in minerals by single-crystal neutron diffraction. H2O is present as zeolitic (i.e. lying in the cavities) and non-zeolitic H2O (i.e. bonded to Al or Fe to form Al or Fe octahedra).
On the complex H-bonding network in paravauxite, Fe2+Al2(PO4)(2)(OH)(2)center dot 8H(2)O: A single-crystal neutron diffraction study
Gatta G D;Vignola P;
2014
Abstract
The crystal structure and the chemical composition of a paravauxite from the Siglo Veinte Mine, Llallagua, Bustillo Province, Potosi Department, Bolivia [(Fe)(Fe 2+0.916Mn0.0162+Mg0.064Ca0.002)(Sigma 0.998)Al-Al(1) Al(2)(2.005)P(P1.998Si0.002) O-Sigma 2(8)(OH) (2)center dot 8H(2)O, a = 5.242(1) angstrom, b = 10.569(2) angstrom, c = 6.970(2) angstrom, alpha = 106.78(3)(o), beta = 110.81(2)(o) and gamma = 72.29(2)(o), space group P (1) over bar], was investigated by single-crystal neutron diffraction and electron microprobe analysis in wavelength-dispersive mode. Neutron-intensity data were collected at 293 K and anisotropic structure refinement was performed. At the end of the refinement no peak larger than +/- 1.3 fm/angstrom(3) was present in the final difference-Fourier map of the nuclear density. The final statistical index was R-1 = 0.0495 for 194 refined parameters and 1678 unique reflections with F-o > 4 sigma(F-o). Eleven independent H sites (i.e. H(1), H(2), H(3), H(4A), H(4B), H(5), H(6), H(7), H(8), H(9A) and H(9B)), all at similar to 1 angstrom from the respective O sites, were located successfully. H(4A) and H(4B) and H(9A) and H(9B) are two mutually exclusive subsite couples only 0.4 0.6 angstrom apart. The complex H-bonding scheme in the paravauxite structure is now well defined and 12 independent H bonds, with an energetically favourable bonding configuration, are described. A comparison between the previous experimental findings based on Raman and infrared spectroscopy and those obtained in this present study is carried out. Paravauxite provides the rare opportunity to investigate the H-bond configuration of coexisting hydroxyl groups and H2O molecules in minerals by single-crystal neutron diffraction. H2O is present as zeolitic (i.e. lying in the cavities) and non-zeolitic H2O (i.e. bonded to Al or Fe to form Al or Fe octahedra).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
