Hydrothermal Chemistry, Structures, and Luminescence Studies of Alkali Hafnium Fluorides

Abstract

This paper describes the hydrothermal chemistry of alkali hafnium fluorides, including the synthesis and structural characterization of five new alkali hafnium fluorides. Two ternary alkali hafnium fluorides are described: Li(2)HfF(6) in space group P31m with a = 4.9748(7) Å and c = 4.6449(9) Å and Na(5)Hf(2)F(13) in space group C2/m with a = 11.627(2) Å, b = 5.5159(11) Å, and c = 8.4317(17) Å. Three new alkali hafnium oxyfluorides are also described: two fluoroelpasolites, K(3)HfOF(5) and (NH(4))(3)HfOF(5), in space group Fm3m with a = 8.9766(10) and 9.4144(11) Å, respectively, and K(2)Hf(3)OF(12) in space group R3m with a = 7.6486(11) Å and c = 28.802(6) Å. Infrared (IR) spectra were obtained for the title solids to confirm the structure solutions. Comparison of these materials was made based on their structures and synthesis conditions. The formation of these species in hydrothermal fluids appears to be dependent upon both the concentration of the alkali fluoride mineralizer solution and the reaction temperature. Both X-ray and visible fluorescence studies were conducted on compounds synthesized in this study and showed that fluorescence was affected by a variety of factors, such as alkali metal size, the presence/absence of oxygen in the compound, and the coordination environment of Hf(4+).

Crystallographic features of ammonium fluoroelpasolites: dynamic orientational disorder in crystals of (NH4)3HfF7 and (NH4)3Ti(O2)F5

“…Similarly, the Ti-O bond has a triple character ( + 2) that ensures a rather short Ti-O distance in accordance with our structural determinations, and the Ti-O stretches appear at 870 and 897 cm À1 for (NH 4 ) 3 TiOF 5 and Rb 2 KTiOF 5 , respectively (Udovenko & Laptash, 2011). Thus, the absence of a similar band in the IR spectrum of ammonium hafnium fluoroelpasolite presented by Underwood et al (2013) means that the authors deal with the other compound. According to their elemental analysis (EDX) indicating the presence of oxygen at 6.5À9.1 at.…”

“…Recently the synthesis and crystal structure of ammonium hafnium oxofluoroelpasolite (NH 4 ) 3 HfOF 5 was described (Underwood et al, 2013). The compound was prepared hydrothermally from HfF 4 and an aqueous solution of NH 4 F at 673-848 K over 3-5 d. Interestingly, (NH 4 ) 3 HfOF 5 has been observed regardless of the reaction conditions.…”

Unveiling the Zirconium and Hafnium Speciation in Fluoride‐Nitric Acid Solutions by Paper Spray Ionization Mass Spectrometry Combined with DFT Calculations

“…The crystalline structures of the octahedral anion [HfF 6 ] 2− previously determined have Hf−F bond distances of 1.96 Å, [35] similar to those found by DFT calculations (Table 5). The geometries of the binuclear species of hafnium found in our study, i. e .…”

“…Crystalline structures of zirconium compounds coordinated with fluoride ligands and oxygen donors confirm these results, with 1.99 Å for the ZrÀ F bonds in the monomers and 2.10 Å for the μ 2 -F bridges. [21] The crystalline structures of the octahedral anion [HfF 6 ] 2À previously determined have HfÀ F bond distances of 1.96 Å, [35] similar to those found by DFT calculations ( , which is characterized by the occupation of one H 2 O molecule in the equatorial position in each polyhedron and the presence of the counter-ion (C 4 H 12 N) 2 in the structure. [36] The hydrolyzed species showed an average of bond distances (Zr, Hf)-O from 2.18 to 2.41 Å for coordination with H 2 O and an average shortening of 0.4 Å for bonding to hydroxyl ion.…”

STRUCTURE OF POLYMORPHS OF COMPLEX ZIRCONIUM AND HAFNIUM FLUORIDES WITH THE 4-AMINO-1,2,4-TRIAZOLIUM CATION: (C2H5N4)2MF6 (M = Zr, Hf, ZrxHf1-x)

“…ɂɧɬɟɪɟɫ ɤ ɤɨɦɩɥɟɤɫɧɵɦ ɮɬɨɪɢɞɚɦ ɰɢɪɤɨɧɢɹ ɢ ɝɚɮɧɢɹ ɨɛɭɫɥɨɜɥɟɧ ɨɛɧɚɪɭɠɟɧɢɟɦ ɜɨ ɦɧɨɝɢɯ ɫɨɟɞɢɧɟɧɢɹɯ ɷɬɨɝɨ ɤɥɚɫɫɚ ɰɟɧɧɵɯ ɮɭɧɤɰɢɨɧɚɥɶɧɵɯ ɫɜɨɣɫɬɜ, ɱɬɨ ɩɨɡɜɨɥɢɥɨ ɩɪɟɞɥɨɠɢɬɶ ɢɯ ɩɪɢɦɟɧɟɧɢɟ ɜ ɤɚɱɟɫɬɜɟ ɢɨɧɧɵɯ ɩɪɨɜɨɞɧɢɤɨɜ [1][2][3], ɫɟɝɧɟɬɨɷɥɟɤɬɪɢɤɨɜ [ 4 ], ɥɸɦɢɧɨɮɨɪɨɜ [ 5,6 ]. ɋɨɡɞɚɧɧɵɟ ɧɚ ɨɫɧɨɜɟ ɮɬɨɪɢɞɧɵɯ ɫɨɟɞɢɧɟɧɢɣ ɰɢɪɤɨɧɢɹ ɮɬɨɪɨɰɢɪɤɨɧɚɬɧɵɟ ɫɬɟɤɥɚ ɛɥɚɝɨɞɚɪɹ ɢɯ ɜɵɫɨɤɨɣ ɨɩɬɢɱɟɫɤɨɣ ɩɪɨɡɪɚɱɧɨɫɬɢ ɧɚɲɥɢ ɩɪɢɦɟɧɟɧɢɟ ɞɥɹ ɫɨɡɞɚɧɢɹ ɨɩɬɢɱɟɫɤɢɯ ɬɟɥɟɤɨɦɦɭɧɢɤɚɰɢɨɧɧɵɯ ɭɫɬɪɨɣɫɬɜ, ɨɩɬɢɱɟɫɤɢɯ ɜɨɥɨɤɨɧ, ɨɩɬɢɱɟɫɤɢɯ ɭɫɢɥɢɬɟɥɟɣ ɢ ɞɚɬɱɢɤɨɜ [ 7 ].…”