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

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aInstitute of Chemistry, Far Eastern Branch of RAS, Pr. Stoletiya 159, Vladivostok 690022, Russian Federation, and bFar Eastern Geological Institute, Far Eastern Branch of RAS, Pr. Stoletiya 159, Vladivostok 690022, Russian Federation
*Correspondence e-mail: udovenko@ich.dvo.ru

Edited by N. B. Bolotina, Russian Academy of Sciences, Russia (Received 8 July 2016; accepted 1 November 2016; online 23 January 2017)

A classical elpasolite-type structure is considered with respect to dynamically disordered ammonium fluoro-(oxo­fluoro-)metallates. Single-crystal X-ray diffraction data from high quality (NH4)3HfF7 and (NH4)3Ti(O2)F5 samples enabled the refinement of the ligand and cationic positions in the cubic [Fm \bar 3 m] (Z = 4) structure. Electron-density atomic profiles show that the ligand atoms are distributed in a mixed (split) position instead of 24e. One of the ammonium groups is disordered near 8c so that its central atom (N1) forms a tetrahedron with vertexes in 32f. However, a center of another group (N2) remains in the 4b site, whereas its H atoms (H2) occupy the 96k positions instead of 24e and, together with the H3 atom in the 32f position, they form eight spatial orientations of the ammonium group. It is a common feature of all ammonium fluoroelpasolites with orientational disorder of structural units of a dynamic nature.

1. Introduction

There is a large family of A2BMX6 compounds (A, B = alkali cations or ammonium, RA > RB; M = tri-, tetra-, penta- or hexavalent metal; X = O, F) with an elpasolite structure derived from a perovskite superstructure with doubled cell parameter (Massa & Babel, 1988[Massa, W. & Babel, D. (1988). Chem. Rev. 88, 275-296.]; Flerov et al., 1998[Flerov, I. N., Gorev, M. V., Aleksandrov, K. S., Tressaud, A., Grannec, J. & Couzi, M. (1998). Mater. Sci. Eng. Rep. 24, 81-151.]). Named after the mineral K2NaAlF6, elpasolite-type compounds are cubic face-centered with [Fm \bar 3 m] space group (Z = 4; Morss, 1974[Morss, L. R. J. (1974). Inorg. Nucl. Chem. 36, 3876-3878.]). In this structure of A2BMF6, B ions locate in the octahedral 4b sites surrounded by six F ligands, each of them belonging to a different MF63− anion, and A ions are located in the tetrahedral 8c sites surrounded by 12 F ions, each three of them belonging to one of the four MF63− ions around the A ion. Precision structural determination of the Rb analogue of the mineral elpasolite, synthetic Rb2NaAlF6, was recently performed (Yakubovich et al., 2013[Yakubovich, O. V., Kiryukhina, G. V. & Dimitrova, O. V. (2013). Crystallogr. Rep. 58, 412-415.]) in the classic style with 4a, 4b, 8c and 24e positions of the [Fm \bar 3 m] group for Al, Na, Rb and F atoms, respectively. Most of the structures of cubic elpasolites were solved in a similar way. Nevertheless, the use of a classical 24e ligand position is not able to explain some structural transformations at phase transitions (PTs) inherent to cubic elpasolites. Recently, a synchrotron powder diffraction study of a synthetic cryolite Na3AlF6 revealed that the high-temperature (HT) cubic phase was characterized by static displacive disorder of the F anions from the 24e sites to four nearby 96k sites 25% occupied (Zhou & Kennedy, 2004[Zhou, Q. G. & Kennedy, B. J. (2004). J. Solid State Chem. 177, 654-659.]). However, a simple static displacement of the F atoms is not capable of explaining the structure of the high-temperature β phase (Smrčok et al., 2009[Smrčok, L., Kucharík, M., Tovar, M. & Žižak, I. (2009). Cryst. Res. Technol. 44, 834-840.]). Relatively frequent reorientations of the AlF6 octahedra of the β phase explain the thermal disorder in positions of the F ions observed in X-ray diffraction experiments (Bučko & Šimko, 2016[Bučko, T. & Sˇimko, F. (2016). J. Chem. Phys. 144, 064502.]). The dynamic nature of the β phase was confirmed by the entropy value (close to Rln4) during a first-order phase transition from monoclinic (α phase) symmetry (Yang et al., 1993[Yang, H., Ghose, S. & Hatch, D. M. (1993). Phys. Chem. Miner. 19, 528-544.]). The 96k position was taken into consideration to refine a cubic structure of Rb2KFeF6 (Vasilovsky et al., 2006[Vasilovsky, S. G., Sikolenko, V. V., Beskrovny, A. I., Belushkin, A. V., Flerov, I. N., Tressaud, A. & Balagurov, A. M. (2006). Z. Kristallogr. Suppl. 2006, 467-472.]), while Massa et al. (1986[Massa, W., Babel, D., Epple, M. & Rüdorff, W. (1986). Rev. Chim. Miner. 23, 508-519.]) used the 96j position. The compound undergoes a PT at 170 K with the entropy change ΔS = Rln6. A PT in the related Rb2KTiOF5 at 215 K is accompanied by quite a large change in the entropy, ΔS = Rln8 (Fokina et al., 2008[Fokina, V. D., Flerov, I. N., Molokeev, M. S., Pogorel'tsev, E. I., Bogdanov, E. V., Krylov, A. S., Bovina, A. F., Voronov, V. N. & Laptash, N. M. (2008). Phys. Solid State, 50, 2175-2183.]; Gorev et al., 2010[Gorev, M. V., Flerov, I. N., Bogdanov, E. V., Voronov, V. N. & Laptash, N. M. (2010). Phys. Solid State, 52, 377-383.]), which is characteristic of order–disorder transformations as opposed to displacive ones associated with small octahedral tilts and followed by a rather small entropy change, which is of the order of 0.2R (Flerov et al., 1998[Flerov, I. N., Gorev, M. V., Aleksandrov, K. S., Tressaud, A., Grannec, J. & Couzi, M. (1998). Mater. Sci. Eng. Rep. 24, 81-151.], 2002[Flerov, I. N., Gorev, M. V., Grannec, J. & Tressaud, A. (2002). J. Fluor. Chem. 116, 9-14.], 2004[Flerov, I. N., Gorev, M. V., Aleksandrov, K. S., Tressaud, A. & Fokina, V. D. (2004). Crystallogr. Rep. 49, 100-107.]).

The PT entropy changes should be taken into account to refine the structures of elpasolites. It especially concerns ammonium fluoroelpasolites, which are usually dynamically disordered. Suga and co-authors (Moriya et al., 1977[Moriya, K., Matsuo, T., Suga, H. & Seki, S. (1977). Bull. Chem. Soc. Jpn, 50, 1920-1926.], 1979[Moriya, K., Matsuo, T., Suga, H. & Seki, S. (1979). Bull. Chem. Soc. Jpn, 52, 3152-3162.]; Kobayashi et al., 1985[Kobayashi, K., Matsuo, T., Suga, H., Khairoun, S. & Tressaud, A. (1985). Solid State Commun. 53, 719-722.]; Tressaud et al., 1986[Tressaud, A., Khaïroun, S., Rabardel, L., Kobayashi, T., Matsuo, T. & Suga, H. (1986). Phys. Status Solidi. A, 96, 407-414.]) measured the heat capacity of (NH4)3MF6 (M = Fe, Al, V, Cr, Ga) and interpreted the observed large entropy changes of the phase transition in terms of a model in which the disordered orientations of the tetrahedral NH4 ions at the 4b sites and of the octahedral MF63− ions in the [Fm \bar 3 m] lattice freeze into an ordered state below the transition points. Fluorine octahedra were assumed to be disordered with eight possible orientations in the general 192l position, and one of the ammonium ions at the 4b site was disordered in two distinct orientations. The total entropy change connected with both octahedra and tetrahedra ordering could be given as ΔS = Rln8 + Rln2 = Rln16, which is in good agreement with the experimental values. However, the NH4 group in the 8c position can also take part in the PT. PTs and ionic motions in hexafluoroaluminates (NH4)3 − xKxAlF6 (x = 1, 2) studied by 1H, 19F and 27Al magnetic resonance were interpreted in terms of overall reorientations of NH4+ (8c position) and AlF63− ions. Rapid reorientations of both ions freeze into an ordered state below the PT points (Hirokawa & Furukawa, 1988[Hirokawa, K. & Furukawa, Y. (1988). J. Phys. Chem. Solids, 49, 1047-1056.]). A recent study of the (NH4)3GaF6 structure by 19F and 69,71Ga magic angle spinning NMR in comparison with X-ray Rietveld refinement supported the model of rigid GaF6 octahedra. In spite of the very low deviation of the GaF6 octahedra from exact cubic symmetry, it was concluded that the fluorine 192l position was much subjected to errors. Both NH4+ ions and GaF63− octahedra undergo rapid reorientation rotations (Krahl et al., 2008[Krahl, T., Ahrens, M., Scholz, G., Heidemann, D. & Kemnitz, E. (2008). Inorg. Chem. 47, 663-670.]).

Our structural refinement of a series of ammonium fluoro­elpasolites (NH4)3AlF6, (NH4)3TiOF5, (NH4)3FeF6 and (NH4)3WO3F3 by localizing anions (F, O2−) in four acceptable positions of the [Fm \bar 3 m] system (24e, 96k, 24e + 96j, 192l) revealed that F (O) atoms should be preferably distributed in mixed (split) 24e + 96j positions (Udovenko et al., 2003[Udovenko, A. A., Laptash, N. M. & Maslennikova, I. G. (2003). J. Fluor. Chem. 124, 5-15.]). The same concerns (NH4)3MoO3F3 and seven-coordinated (NH4)3ZrF7 and (NH4)3NbOF6 (Udovenko & Laptash, 2008a[Udovenko, A. A. & Laptash, N. M. (2008a). Acta Cryst. B64, 305-311.], 2008b[Udovenko, A. A. & Laptash, N. M. (2008b). J. Struct. Chem. 49, 482-488.]). Both ammonium groups are disordered: N1H4 is tetrahedrally displaced from the 8c position into the 32f site, and the H atoms of N2H4 are statistically distributed in the 96k and 32f positions, so that it takes eight equivalent spatial orientations instead of two accepted ones (Udovenko & Laptash, 2011[Udovenko, A. A. & Laptash, N. M. (2011). Acta Cryst. B67, 447-454.]). This disorder has a dynamic nature (both ammonium cations and anions are disordered) that was supported by solid-state NMR (Kavun et al., 2010[Kavun, V. Ya., Kozlova, S. G., Laptash, N. M., Tkachenko, I. A. & Gabuda, S. P. (2010). J. Solid State Chem. 183, 2218-2221.]; 2011[Kavun, V. Ya., Gabuda, S. P., Kozlova, S. G., Tkachenko, I. A. & Laptash, N. M. (2011). J. Fluor. Chem. 132, 698-702.]) and calorimetric measurements (Flerov et al., 2011[Flerov, I. N., Gorev, M. V., Tressaud, A. & Laptash, N. M. (2011). Crystallogr. Rep. 56, 9-17.]; Fokina et al., 2007[Fokina, V. D., Flerov, I. N., Gorev, M. V., Bogdanov, E. V., Bovina, A. F. & Laptash, N. M. (2007). Phys. Solid State, 49, 1548-1553.], 2013[Fokina, V. D., Gorev, M. V., Bogdanov, E. V., Pogoreltsev, E. I., Flerov, I. N. & Laptash, N. M. (2013). J. Fluor. Chem. 154, 1-6.]). This concerns equally both six-coordinated and seven-coordinated complexes.

Seven ligand atoms around a central metal atom lead with the need to the splitting of the ligand positions as in the case of ammonium fluoroperoxoelpasolites (NH4)3Ti(O2)F5 and (NH4)3Zr(O2)F5 (Massa & Pausewang, 1978[Massa, W. & Pausewang, G. (1978). Mater. Res. Bull. 13, 361-368.]; Schmidt et al., 1986[Schmidt, R., Pausewang, G. & Massa, W. (1986). Z. Anorg. Allg. Chem. 535, 135-142.]). In this paper, the crystallographic features of ammonium fluoroelpasolite structures are highlighted by examples of the dynamically disordered (NH4)3HfF7 and (NH4)3Ti(O2)F5.

2. Experimental

2.1. Synthesis

All the starting materials were of analytical reagent grade and used without further purification; deionized water was used as a solvent. Either solid NH4HF2 or hydrofluoric acid (40% HF by weight) were used as fluorinating agents. Ammonium hafnium fluoroelpasolite (NH4)3HfF7 (I) was synthesized according to the reactions

[\eqalignno{{\rm HfO}_2 + 3.5{\rm NH}_4{\rm HF}_2 =\, &({\rm NH}_4)_3{\rm HfF}_7 + 0.5{\rm NH}_3 + 2{\rm H}_2{\rm O}\semi\cr {\rm HfF}_4 + 3{\rm NH}_4{\rm HF}_2 =\, &({\rm NH}_4)_3{\rm HfF}_7 + 3{\rm HF} &(1)}]

[{\rm HfO}_2 + 7{\rm HF} + 3{\rm NH}_3 = ({\rm NH}_4)_3{\rm HfF}_7 + 2{\rm H}_2{\rm O}. \eqno(2)]

Excess NH4HF2 or (HF + NH3) is needed to obtain the complex; we used a double excess. In the first case, HfO2 or HfF4 were fluorinated with NH4HF2 at 423–473 K followed by water leaching of the cake with the addition of a small amount of HF to pH = 2–3. The solution was filtered and slowly evaporated in air at ambient conditions with the formation of well faceted colorless octahedral single crystals of (NH4)3HfF7. In the second case, HfO2 was dissolved in the HF solution (40%) followed by the addition of NH3 aq (25%) and slow evaporation of the resulting solution.

An attempt was made to obtain (NH4)3HfOF5 by ammonia hydrolysis of the hot aqueous solution of (NH4)3HfF7 with excess NH4F, similar to (NH4)3TiOF5 (Laptash et al., 1999[Laptash, N. M., Maslennikova, I. G. & Kaidalova, T. A. (1999). J. Fluor. Chem. 99, 133-137.]). At pH = 8 a white precipitate was formed (not identified) but (NH4)3HfF7 crystallized again from the mother liquor. EDX analysis was used to check the composition of the crystal, which corresponded to (NH4)3Hf(OH)xF7 − x (x = 0.2–0.4).

Ammonium titanium peroxofluoroelpasolite (NH4)3Ti(O2)F5 (II) was prepared by synthesis from fluoride solution according to the reaction

[({\rm NH}_4)_2{\rm TiF}_6 + {\rm NH}_4{\rm F} + {\rm H}_2{\rm O}_2 = ({\rm NH}_4)_3{\rm Ti}({\rm O}_2){\rm F}_5 + 2{\rm HF}. \eqno(3)]

An excess (50–100% with respect to the stoichiometric proportion) of NH4F (40% solution) and then a concentrated (30%) solution of H2O2 were added to aqueous (NH4)2TiF6 (the solution pH was adjusted at 7–8 by the addition of ammonia, if necessary). As a result, an abundant yellow–lemon deposition of (NH4)3Ti(O2)F5 formed consisting of fine octahedral single crystals (∼ 10 µm in size). Further slow evaporation of the solution in air resulted in larger bright yellow single crystals suitable for X-ray determination.

2.2. Crystallographic determination

Single-crystal X-ray diffraction data were collected using Bruker KAPPA APEX II and Bruker SMART-1000 CCD diffractometers equipped with a graphite monochromator (Mo Kα radiation, λ = 0.71073 Å). Data collections were carried out at 296 K, 0.3° ω-scans were performed in a hemisphere of reciprocal space with an exposure time of 20 s per frame at a crystal–detector distance of 40 mm. Data collection, reduction and refinement of the lattice parameters were performed using the APEXII software package (Bruker, 1998[Bruker (1998). SMART, Version 5.054. Bruker AXS Inc., Madison, Wisconsin, USA.], 2000[Bruker (2000). SAINT, Version 6.02a. Bruker AXS Inc., Madison, Wisconsin, USA.]). All the calculations were performed using the SHELXL/PC program (Sheldrick, 2015[Sheldrick, G. M. (2015). Acta Cryst. C71, 3-8.]).

The structures were solved by direct methods with an analysis of the electron-density distribution and refined against F2 by the full-matrix least-squares method with anisotropic approximation. At the first stage, the H atoms of ammonium groups were determined from difference electron-density maps. The H1 atoms around N1 form a tetrahedron with the N—H distances of 0.89 and 0.79 Å for (I) and (II), respectively, while the H2 atoms around N2 form an octahedron with the N—H distances of 0.92 and 0.83 Å for (I) and (II), respectively. Next, the coordinates of the H atoms were calculated geometrically in accordance with N1 disordering and the real geometry of N2H4, and they were not refined. Information on the structure determinations is summarized in Table 1[link]. Selected bond distances and angles are listed in Table 2[link]. The hydrogen-bond parameters are presented in Table 3[link].

Table 1
Crystal and experimental data for (NH4)3HfF7 (I) and (NH4)3Ti(O2)F5 (II)

For all structures: Cubic, [Fm\bar 3 m], Z = 4. Experiments were carried out at 296 K with Mo Kα radiation using a Bruker APEXII CCD diffractometer. Absorption was corrected for by multi-scan methods, SADABS (Bruker, 2008[Bruker (2008). SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]). H atom parameters were not refined.

  (I) (II)
Crystal data
Chemical formula (NH4)3HfF7 (NH4)3Ti(O2)F5
Mr 365.62 229.03
a (Å) 9.3964 (1) 9.2327 (1)
V3) 829.63 (3) 787.02 (3)
Dx (Mg m−3) 2.927 1.933
μ (mm−1) 12.645 1.143
Crystal size (mm) 0.25 × 0.23 × 0.22 0.24 × 0.23 × 0.22
     
Data collection
Tmin, Tmax 0.593, 0.750 0.695, 0.749
No. of measured, independent and observed [I > 2σ(I)] reflections 8194, 293, 293 9680, 190, 190
Rint 0.019 0.020
(sin θ/λ)max−1) 1.116 0.961
     
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.009, 0.019, 1.19 0.014, 0.0400, 1.032
No. of reflections 293 190
No. of parameters 22 24
Δρmax, Δρmin (e Å−3) 1.14, −0.66 0.14, −0.33
Computer programs used: SMART (Bruker, 1998[Bruker (1998). SMART, Version 5.054. Bruker AXS Inc., Madison, Wisconsin, USA.]), SAINT (Bruker, 2000[Bruker (2000). SAINT, Version 6.02a. Bruker AXS Inc., Madison, Wisconsin, USA.]), SHELXTL (Sheldrick, 2015[Sheldrick, G. M. (2015). Acta Cryst. C71, 3-8.]).

Table 2
Selected distances (Å) and angles (°) for (I) and (II)

(NH4)3HfF7
Hf—F1 1.963 (2) × 3 F1—F3 2.912 (4) × 4
Hf—F2 2.032 (5) × 2 F1B—F2 2.374 (6) × 2
Hf—F3 2.151 (5) × 2 F2—F3 2.484 (8) × 2
F1—F1B 2.776 (3) × 2 F3—F3A 2.425 (10)
F1—F2 2.826 (4) × 4    
       
F1—Hf—F1A 180 F2—Hf—F3 72.8 (2) × 2
F1—Hf—Feq 90 × 10 F3—Hf—F3A 68.6 (3)
F2—Hf—F1B 72.9 (2) × 2    
       
(NH4)3Ti(O2)F5
Ti—O1 1.974 (3) × 2 O1—O1A 1.491 (4)
Ti—F1 1.895 (1) × 3 O1—F2 2.362 (5) × 2
Ti—F2 1.928 (3) × 2 O1—F1B 2.707 (3) × 2
F1—F1A 2.673 (2) × 2 F1A—F1B 2.483 (3)
F1—F2 2.386 (3) × 2 F1A—F2A 2.816 (2) × 2
    F2—F2A 2.611 (4)
       
F1—Ti—F1A 89.73 (7) × 2 O1—Ti—F1B 88.78 (5) × 2
F1—Ti—F2 77.21 (9) × 2 F1A—Ti—F1B 81.90 (7)
O1—Ti—O1A 44.38 (8) F1A—Ti—F2A 94.89 (5) × 2
O1—Ti—F2 74.5 (1) × 2 F2—Ti—F2A 85.24 (3)

Table 3
Hydrogen-bonding geometry (Å, °) in (I) and (II)

D—H⋯A D—H H⋯A DA D—H⋯A
(NH4)3HfF7
N1—H11⋯F3 0.90 2.04 2.798 (6) 141
N1—H12⋯F2i 0.88 2.25 2.967 (3) 138
N1—H12⋯F2ii 0.88 2.11 2.856 (5) 142
N1—H12⋯F3ii 0.88 1.85 2.584 (4) 140
N1—H12⋯F3i 0.88 1.99 2.695 (3) 136
N1—H12⋯F3iii 0.88 1.89 2.620 (3) 138
N1—H12⋯F2iii 0.88 2.20 2.933 (4) 139
N1—H11⋯F2 0.90 2.32 3.085 (7) 143
         
N2—H2⋯F1iv 0.91 1.88 2.735 (2) 157
N2—H2⋯F2iv 0.91 1.94 2.820 (6) 164
N2—H2⋯F3iv 0.91 2.30 3.163 (5) 158
N2—H2⋯F2v 0.91 2.04 2.820 (6) 143
         
(NH4)3Ti(O2)F5
N1—H13⋯O1vi 0.88 2.00 2.721 (2) 138
N1—H14⋯O1vii 0.88 2.00 2.721 (2) 138
N1—H12⋯F2viii 0.88 2.17 2.908 (2) 140
N1—H11⋯F1 0.87 2.49 3.243 (4) 145
N1—H11⋯O1ix 0.87 2.08 2.838 (4) 145
N1—H12⋯O1x 0.88 1.84 2.613 (3) 145
N1—H12⋯F2xi 0.88 2.06 2.831 (3) 145
N1—H13⋯F1xii 0.88 2.37 3.102 (2) 140
         
N2—H2⋯O1xiii 0.89 2.27 3.130 (4) 161
N2—H2⋯F1xiii 0.89 1.87 2.737 (1) 162
N2—H2⋯F1xiv 0.89 1.90 2.737 (1) 156
N2—H2⋯F2xv 0.89 1.96 2.825 (3) 164
Symmetry codes: (i) [x - {1\over 2}, y - {1\over 2}, z]; (ii) [-x + {1\over 2}, -y, -z + {1\over 2}]; (iii) [-x + {1\over 2}, -y + {1\over 2}, -z]; (iv) [x, -y + {1\over 2}, -z + {1\over 2}]; (v) [x - {1\over 2}, -y, -z +{1\over 2}]; (vi) [-x + {1\over 2}, -z, -y + {1\over 2}]; (vii) [-y + {1\over 2}, -x + {1\over 2}, z]; (viii) [y, -x + {1\over 2}, z + {1\over 2}]; (ix) -z, y, x; (x) [-x + {1\over 2}, -z + {1\over 2}, y]; (xi) [x, -y + {1\over 2}, z + {1\over 2}]; (xii) [-y + {1\over 2}, z, -x +{1\over 2}]; (xiii) [-x + 1, -y + {1\over 2}, -z + {1\over 2}]; (xiv) [-x + 1, -y + {1\over 2}, z + {1\over 2}]; (xv) [-x + 1, y + {1\over 2}, -z + {1\over 2}].

2.3. Spectroscopic measurements and additional characterization

Mid-IR (400–4000 cm−1) spectra were collected in Nujol mull using a Shimadzu FTIR Prestige-21 spectrometer operating at 2 cm−1 resolution. The FT–Raman spectra of the compounds were recorded with an RFS 100/S spectrometer. The 1064 nm line of an Nd:YAG laser (130 mW maximum output) was used for excitation of the samples. The spectra were recorded at room temperature. In addition, the IR spectrum of (NH4)3HfF7 was recorded directly from the pure single crystal using a FT–IR Bruker Vertex 70v spectrometer with the Platinum ATR attachment.

For a description of the vibrational spectra of (NH4)3HfF7, quantum-chemical calculations of the HfF73− anion were performed employing the GAMESS software package (Schmidt et al., 1993[Schmidt, M. W., Baldridge, K. K., Boatz, J. A., Elbert, S. T., Gordon, M. S., Jensen, J. H., Koseki, S., Matsunaga, N., Nguyen, K. A., Su, S., Windus, T. L., Dupuis, M. & Montgomery, J. A. (1993). J. Comput. Chem. 14, 1347-1363.]) within the density functional theory framework (DFT) with exchange–correlation potential B3LYP. The TZVP basis set was used for F atoms and SBKJC basis set for Hf.

The elemental composition of (NH4)3HfF7 was checked using the X-ray microanalyser JXA-8100 Jeol, Japan (the operating voltage is 20 kV, operating current is 1 × 10−8 A) and energy-dispersive spectrometer INCAx–sight, Oxoford (resolution is 137 eV).

3. Results and discussion

3.1. Crystal structures

Both compounds (NH4)3HfF7 (I) and (NH4)3Ti(O2)F5 (II) crystallize in the cubic space group [Fm \bar 3 m]. The crystal structure of (I) consists of isolated statistically disordered polyhedra HfF7 in the form of a pentagonal bipyramid (PB) and two kinds of ammonium groups (Fig. 1[link]). The PB configuration for the related (NH4)3ZrF7 has been reliably established by Hurst & Taylor (1970[Hurst, H. J. & Taylor, J. C. (1970). Acta Cryst. B26, 417-421.]) and confirmed by us (Udovenko & Laptash, 2008b[Udovenko, A. A. & Laptash, N. M. (2008b). J. Struct. Chem. 49, 482-488.]). It is this polyhedron that was realised in most monomeric crystal structures of Zr and Hf fluoride complexes reviewed by Davidovich (1998[Davidovich, R. L. (1998). Russ. J. Coord. Chem. 24, 751-768.]) and Davidovich et al. (2013[Davidovich, R. L., Marinin, D. V., Stavila, V. & Whitmire, K. H. (2013). Coord. Chem. Rev. 257, 3074-3088.]).

[Figure 1]
Figure 1
Disordered structure of (NH4)3HfF7 (a) and the isolated polyhedron HfF73− (b). Green, blue and white balls are the F, N and H atoms, respectively (the central Hf atoms are not seen). Displacement ellipsoid plots are shown at 50% probability.

The crystal structure of (II) is built from disordered polyhedra Ti(O2)F53− in the form of distorted octahedron with the peroxide group at one of the axial corners and two kinds of ammonium groups (Fig. 2[link]). It should be noted that this structure was determined initially by Stomberg et al. (1977[Stomberg, R., Svensson, I.-B., Näsäkkälä, E., Pouchard, M., Hagenmuller, P. & Andresen, A. F. (1977). Acta Chem. Scand. A, 31, 635-637.]) with isolated Ti(O2)F53− in the PB form, and the peroxide group was placed in the equatorial plane of PB. Then Massa & Pausewang (1978[Massa, W. & Pausewang, G. (1978). Mater. Res. Bull. 13, 361-368.]) presented a polyhedron as an octahedron with a peroxide `dumbbell' in the axial position. It can also be represented as a distorted (bevelled) monocapped trigonal prism with an O—O edge.

[Figure 2]
Figure 2
Disordered structure of (NH4)3Ti(O2)F5 (a) and the isolated polyhedron Ti(O2)F53− (b). Red, blue and white balls are the F, N and H atoms, respectively (the central Ti atoms are not seen). Displacement ellipsoid plots are shown at 50% probability.

At the first phase of structural determination it was difficult to isolate the local polyhedral symmetry. Direct methods identified uniquely only the M, N1 and N2 atoms in the 4a, 8c and 4b positions in accordance with the elpasolite structure. Their atomic coordinates were refined by the least-squares method (LS) with anisotropic approximation to R1 = 0.0626 and 0.1445 for (I) and (II), respectively. From electron-density syntheses calculated for these atoms, only the F atoms in the (x,0,0) position are localized, which corresponds to the MF6 octahedron that contradicts the chemical composition of the compound. Therefore, electron-density sections in the range of the F1 atom have been constructed (Figs. 3[link]a and c), which show that two independent additional F (O) atoms surround the Hf and Ti atoms in the 96j position (Figs. 3[link]b and d). The structural refinement with these atoms reduced R1 to 0.0104 and 0.0281 for (I) and (II), respectively. Three independent F atoms (F1, F2 and F3) in (I) form 12 spatial orientations of HfF7 in the PB form (Fig. 1[link]b). Two F atoms (F1 and F2) and one O1 in (II) form 24 orientations of Ti(O2)F5 in the form of a distorted octahedron (Fig. 2[link]b) with the (O2)2− group in the axial vertex.

[Figure 3]
Figure 3
(a) Electron-density distribution of F1 in (NH4)3HfF7 on the (001) plane at z = 0.20. (b) Arrangement of F1, F2 and F3 atoms on the 24e and 96j positions. (c) Electron-density distribution of F2 in (NH4)3Ti(O2)F5 on the (001) plane at z = 0.20. (d) Arrangement of F1, F2 and O atoms on the 24e and 96j positions.

Determined at this stage, our structure of (NH4)3Ti(O2)F5 was similar to those of K3Ti(O2)F5 (Schmidt & Pausewang, 1986[Schmidt, R. & Pausewang, G. (1986). Z. Anorg. Allg. Chem. 537, 175-188.]) and (NH4)3Ti(O2)F5 (Schmidt et al., 1986[Schmidt, R., Pausewang, G. & Massa, W. (1986). Z. Anorg. Allg. Chem. 535, 135-142.]) with a `split-atom' model. Interestingly, K1 and K2 in the K3Ti(O2)F5 structure were located in the 24e and 32f positions, respectively. However, in all cases two significantly short distances O—F2 = 2.17–2.18 Å were present (Fig. 2[link]b). In addition, electron-density synthesis for F1 indicates the 24e position, while Schmidt et al. (1986[Schmidt, R., Pausewang, G. & Massa, W. (1986). Z. Anorg. Allg. Chem. 535, 135-142.]) give the 96k position. The results of structural determination in both cases were very similar, but during several cycles of structural refinement with F1 in the (x,x,z) position the value of x decreased and converged to zero. This is probably owing to the relatively low population of the F1 position and its close surroundings by F2 atoms (F1–F2: 4 × 0.41 Å, Fig. 3[link]d). To find the true F1 position, its difference electron-density profiles were built for (I) and (II) for comparison (Fig. 4[link]; F1 was not specified).

[Figure 4]
Figure 4
(a) Electron-density distribution of the F1 atom in the (001) plane at z = 0.20 of (NH4)3HfF7. (b) Electron-density distribution of the F1 atom in the (001) plane at z = 0.20 of (NH4)3Ti(O2)F5.

The sections show that in the (NH4)3HfF7 structure F1 occupies the 24e position, while in the (NH4)3Ti(O2)F5 structure it is placed in the 96k one, but the problem of short O—F distances was not solved. The next step of the structural revision of (NH4)3Ti(O2)F5 was the change of F1 and F2 populations, wherein two F2 atoms (instead of four) and two F1 atoms were placed in the equatorial octahedral plane. In this case, the structure refinement was successful to R1 = 0.0268 with equalized distances O—F2 = 2.362 and F2—F1 = 2.386 Å instead of 2.183 and 2.623 Å, respectively, and the F1 coordinates remained in the 96k position.

In accordance with our previous work (Udovenko & Laptash, 2011[Udovenko, A. A. & Laptash, N. M. (2011). Acta Cryst. B67, 447-454.]), where the tetrahedral displacement of N1 from the 8c position was found, electron-density sections of N1 for (I) and (II) were constructed. Only the sections for (I) are given (Fig. 5[link]), which are very similar to those for (II). The sections show that N1 is displaced from the 8c position. The structure refinement confirmed the escape of N1 from the initial position on 0.14 and 0.15 Å for (I) and (II), respectively. R1 changed insignificantly (0.0102 and 0.0256, respectively). The coordinates of H atoms in N1H4 were calculated geometrically.

[Figure 5]
Figure 5
Electron-density distribution of N1 in (NH4)3HfF7 on the (001) plane at z = 0.20 (a) and z = 0.30 (b). Disorder of tetrahedrally displaced N1H4 from the 8c position (c).

Next, the real location of N2H4 was found. Two possible models were considered.

Model A: Atom N2 is cubically shifted from the 4b position into the 32f site, and the H2 atoms occupy the 24e position. Taking into account the additional H3 atom in the 32f position, the N2H4 group forms eight spatial orientations in the structure as was described for the case of (NH4)3MoO3F3 (Udovenko & Laptash, 2008a[Udovenko, A. A. & Laptash, N. M. (2008a). Acta Cryst. B64, 305-311.]).

Model B: The N2 atom does not leave the 4b position and the H2 atoms are shifted from the 24e position into the 96k one. Taking into account the additional H3 atom in the 32f position, the N2H4 group also forms eight spatial orientations.

These two models were not previously supported experimentally. The problem has been solved in the present work owing to the good quality of single crystals and a large set of experimental data. Electron-density sections of N2 for (I) and (II) in the (001) plane with z = 0.518 and z = 0.593 were constructed. The z coordinate of N2 and H2 was taken from the (NH4)3MoO3F3 structure (Udovenko & Laptash, 2008a[Udovenko, A. A. & Laptash, N. M. (2008a). Acta Cryst. B64, 305-311.]) and from the (NH4)3AlF6 structure (Udovenko & Laptash, 2011[Udovenko, A. A. & Laptash, N. M. (2011). Acta Cryst. B67, 447-454.]), the H atoms were not specified (Fig. 6[link]). The sections for (I) and (II) are similar.

[Figure 6]
Figure 6
Electron-density distribution of the N2 atom in (NH4)3Ti(O2)F5 on the (001) plane at z = 0.518 (a) and z = 0.593 (b). Statistically disordered arrangement of H2 and H3 atoms in N2H4 (c).

It is seen from Fig. 6[link] that the outer electron cloud of the N2 atom is deformed by the octahedron, while its internal cloud is spherical which is inconsistent with the N2 escape on the cube from the 4b position. The structural refinement with the displaced atom returns it into the initial position and the N2 atom therefore occupies the 4b position.

It follows from Figs. 6[link](a) and (b) that the H2 atoms are statistically distributed in the 96k position, and every vertex of the N2Q6 octahedron is surrounded by four H2 atoms with a side of the square equal to 0.35 Å. A superposition of electron densities from four H2 atoms in squares forms an octahedral surrounding of the N2 atom by the Q electron-density peaks (Fig. 6[link]c). The final refinement of the structure in the space group [Fm \bar 3 m] including H atoms reduced the R1 value to 0.0090 and 0.0140 for (I) and (II), respectively.

Finally, the structural refinements of (I) and (II) were performed in other possible space groups. The results of the refinement of (I) in [Fm \bar 3 m], [F \bar 4 3m] and F432 were identical, while in F23 they became worse [Feq—Feq = 2.58 and 2.27 instead of 2.38 and 2.47 (1) Å; U11 = 0.26 instead of 0.11 (1) Å2]. The refinement of (II) in F432 and F23 resulted in strong distortion of the Ti(O2)F5 polyhedron. The refinement in [F \bar 4 3m] gave the O—F distance 2.20 (1) instead of 2.36 (1) Å for [Fm \bar 3 m] at the same R1 = 0.0140. Thus, the space group for (I) and (II) is [Fm \bar 3 m].

(NH4)3HfF7 is isostructural with (NH4)3ZrF7 and (NH4)3NbOF6, the crystal structures of which were described by us previously in the space group F23 (Udovenko &Laptash, 2008b[Udovenko, A. A. & Laptash, N. M. (2008b). J. Struct. Chem. 49, 482-488.]), which allowed us to eliminate abnormally short F—F distances (2.16 Å) in the equatorial plane of PB determined by Hurst & Taylor (1970[Hurst, H. J. & Taylor, J. C. (1970). Acta Cryst. B26, 417-421.]) for (NH4)3ZrF7 in [Fm \bar 3 m]. Now we repeated the refinement of these structures in both F23 and [Fm \bar 3 m] space groups. The geometrical parameters of the polyhedron NbOF6 in these two groups are the same within experimental error [Feq—Feq 2.36 (1) and 2.37 (1); 2.41 (1) and 2.41 (1); 2.31 (1) and 2.32 (1) Å for F23 and [Fm \bar 3 m], in pairs, respectively], whereas the parameters of ZrF7 are appreciably different [Feq—Feq = 2.47 (1), 2.50 (1) and 2.36 (1) Å in F23 and Feq—Feq = 2.61 (1), 2.67 (1) and 2.26 (1) Å in [Fm \bar 3 m]]. The latter geometry is less preferable than the former one due to the shorter F—F contact (2.26 relative to 2.36 Å). Nevertheless, both cubic space groups ([Fm \bar 3 m] and F23) are characteristic of the crystal structure of (NH4)3ZrF7. The heat capacity (studied by differential scanning microcalorimetry and adiabatic calorimetry), thermal dilation and permittivity investigations revealed the existence of transitions between these two cubic phases (Fokina et al., 2013[Fokina, V. D., Gorev, M. V., Bogdanov, E. V., Pogoreltsev, E. I., Flerov, I. N. & Laptash, N. M. (2013). J. Fluor. Chem. 154, 1-6.]) near room temperature (290 K). Group theory analysis of PTs has shown that both cubic phases can be transformed into an ortho­rhombic one (Immm) found by polarizing optical studies at T1 = 280 K (Misyul et al., 2008[Misyul, S. V., Mel'nikova, S. V., Bovina, A. F. & Laptash, N. M. (2008). Phys. Solid State, 50, 1951-1956.]). The crystal structure determination of the latter was unsuccessful because of its complicated twinning structure. The same concerns (NH4)3HfF7 as our preliminary calorimetric measurements show, different to those for (NH4)3NbOF6 (Fokina et al., 2007[Fokina, V. D., Flerov, I. N., Gorev, M. V., Bogdanov, E. V., Bovina, A. F. & Laptash, N. M. (2007). Phys. Solid State, 49, 1548-1553.]). The refinement of (NH4)3HfF7 in F23 increased the R1 from 0.0090 to 0.0110, and the F—F equatorial distances were less acceptable [F—F 2.274 (8), 2.419 (6), 2.565 (1) Å instead of 2.374 (6), 2.425 (10), 2.484 (8) Å], and the Uii (U11, U22, U33) parameters of F atoms increased significantly (0.20–0.26 instead of 0.06–0.11 Å2). Therefore, the symmetry of (NH4)3HfF7 is really [Fm \bar 3 m], which is the parent phase for both (NH4)3ZrF7 and (NH4)3HfF7 compounds.

We also revised the crystal structures of ammonium fluoro­elpasolites (NH4)3ZrF7, (NH4)3NbOF6, (NH4)3MoO3F3, (NH4)3WO3F3 and (NH4)3AlF6 with respect to the escape of N1 and N2 from the special 8c and 4b positions. It is shown that the N1 atom is displaced from the 8c position into the 32f site and tetrahedrally disordered, while the N2 atom remains in the 4b position. The H atoms of N2H4 statistically occupy the 64k and 32f positions and form eight spatial orientations in the structure.

X-ray crystallographic files in CIF format for the structure determinations of (NH4)3ZrF7, (NH4)3NbOF6, (NH4)3MoO3F3, (NH4)3WO3F3 are in the supporting information and can also be obtained from Fachinformationszentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany [fax: (+49)7247-808-666; e-mail: crystdata@fiz-karlsruhe.de; https://www2.fiz-karlsruhe.de/icsd_home.html] on quoting the deposition numbers: CSD-431917; CSD-431918; CSD-431919 and CSD-431920, respectively.

3.2. On the (NH4)3HfOF5 elpasolite

Recently the synthesis and crystal structure of ammonium hafnium oxofluoroelpasolite (NH4)3HfOF5 was described (Underwood et al., 2013[Underwood, C. C., McMillen, C. D., Chen, H. G., Anker, J. N. & Kolis, J. W. (2013). Inorg. Chem. 52, 237-244.]). The compound was prepared hydrothermally from HfF4 and an aqueous solution of NH4F at 673–848 K over 3–5 d. Interestingly, (NH4)3HfOF5 has been observed regardless of the reaction conditions. The crystal structure of this compound was solved classically with ammonium ions being fully ordered at 4b and 8c sites. The F atom was present at the 24e site. When the substitutional model (5/6 F and 1/6 O at the 24e site) was used, the R1 value was 0.0259. The authors attempted to disorder the F and O atoms between the 24e site and a 96j site in accordance with our mixed ligand position, but their refinements were unsuccessful. The authors also provide the IR spectrum of (NH4)3HfOF5 (Fig. S3 in their paper), which is identical to that of our (NH4)3HfF7 recorded from the sample pressed into pellets with KBr or in the Nujol mull. Fig. 7[link] shows the IR spectrum of a pure single crystal of (NH4)3HfF7 together with its Raman spectrum. It should be noted that the vibrational spectra of (NH4)3HfF7 and (NH4)3ZrF7 (Krylov et al., 2012[Krylov, A. S., Krylova, S. N., Laptash, N. M. & Vtyurin, A. N. (2012). Vibr. Spectrosc. 62, 258-263.]) are very similar. Spectral lines and their positions agree better with D5h symmetry for an isolated Hf(Zr)F73− ion, in spite of this symmetry group not being a subgroup of the Oh factor group of the crystal. The optimization of geometric parameters of ZrF73− (Voit et al., 2015[Voit, E. I., Didenko, N. A. & Galkin, K. N. (2015). Opt. Spectrosc. 118, 114-124.]) resulted in a distorted PB configuration with the C1 (Cs) symmetry, where the F atoms were displaced from the equatorial plane with one of them shifted most strongly. The axial F atoms are also shifted from the axial position that is consistent with a large amplitude vibration of the F1 atoms in our HfF73− (Fig. 1[link]b). This means the non-rigidity of the anion (the F1 atom tends to leave the equatorial plane). Thus, the Raman band at 563 cm−1 (Fig. 7[link]) is assigned to a fully symmetric stretch (νs) of the HfF7 PB (D5h symmetry). Two IR bands at 403 and 466 cm−1 are assigned to the asymmetric stretch of Hf–axial fluorines (νHfF1axνHfF2ax) and to asymmetric doubly degenerate Hf–equatorial fluorines [νas(HfF2eqνHfFeq)], respectively, in accordance with DFT calculations. Minor bands at 730 and 1080 cm−1 are connected with the presence of the hydroxide ion (OH). The first one is a transversal vibration of the proton in the triple system O—H⋯F with a strong hydrogen bond (HB), the second one is the bending vibration of nonbonding OH (δHfO–H). Above 1400 cm−1, bending, combinational and stretching vibrations of NH4 groups lie, typical to ammonium elpasolites (Epple et al., 1982[Epple, M., Rüdorff, W. & Massa, W. (1982). Z. Anorg. Allg. Chem. 495, 200-210.]). Energy-dispersive X-ray (EDX) analysis corroborates the presence of OH at the level of 2–4 at. % (Fig. 8[link]), which corresponds to the composition (NH4)3Hf(OH)xF7 − x (x = 0.3). It is difficult to obtain fluorometallate without the partial substitution of OH for F.

[Figure 7]
Figure 7
Vibrational spectra of (NH4)3HfF7 at room temperature: IR – top image, Raman – lower figure.
[Figure 8]
Figure 8
EDX spectrum of (NH4)3Hf(OH)0.3F6.7.

If the compound composition corresponds to the formula (NH4)3HfOF5, its vibrational spectra should contain the intensive band (both IR and Raman active) in the range 900 cm−1, in accordance with the triple character (one σ + two π) of the Hf—O bond and a short distance of this bond (Gong et al., 2012[Gong, Y., Andrews, L., Bauschlicher, C. W. Jr, Thanthiriwatte, K. S. & Dixon, D. A. (2012). Dalton Trans. 41, 11706-11715.]). Similarly, the Ti—O bond has a triple character (σ + 2π) 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−1 for (NH4)3TiOF5 and Rb2KTiOF5, respectively (Udovenko & Laptash, 2011[Udovenko, A. A. & Laptash, N. M. (2011). Acta Cryst. B67, 447-454.]). Thus, the absence of a similar band in the IR spectrum of ammonium hafnium fluoroelpasolite presented by Underwood et al. (2013[Underwood, C. C., McMillen, C. D., Chen, H. G., Anker, J. N. & Kolis, J. W. (2013). Inorg. Chem. 52, 237-244.]) means that the authors deal with the other compound. According to their elemental analysis (EDX) indicating the presence of oxygen at 6.5−9.1 at. % and fluorine at 51.0−53.6 at %, one can suppose that the real composition of the compound is close to (NH4)3Hf(OH)F6. Our attempts to obtain (NH4)3HfOF5 from solution (by ammonia hydrolysis) were unsuccessful. It seems that is almost impossible. Only zirconium oxofluoroelpasolite with alkali cations A2BZrOF5 are known but they were obtained by solid-state reaction: 2AF + BF + ZrOF2 = A2BZrOF5 (A = Cs, Rb, Tl, K; B = Cs, Rb, Tl, K, Na and Li; Verdine et al., 1972[Verdine, A., Belin, D. & Besse, J.-P. (1972). Bull. Soc. Chim. Fr. 1, 76-78.]). Some of the structures were solved in the classical way.

However, if the compound composition is (NH4)3HfOF5, it would be reasonable to displace a central atom (Hf) from the center of an octahedron towards the O atom to determine the true geometry of the polyhedron. It is possible when the existing disorder has a dynamic nature (Laptash & Udovenko, 2016[Laptash, N. M. & Udovenko, A. A. J. (2016). J. Struct. Chem. 57, 390-398.]).

4. Conclusions

Single crystals of (NH4)3HfF7 and (NH4)3Ti(O2)F5 of high quality were obtained that enabled a large set of experimental data to be collected and the ligand refined with cationic positions in the cubic [Fm \bar 3 m] (Z = 4) structure with respect to the classic version of the elpasolite structure. All our previously investigated crystal structures of ammonium fluoro- or oxofluoroelpasolites characterized by dynamic orientational disorder were revised in accordance with new features of the fluoroelpasolite structure. The electron-density profiles of all the constituent atoms in the compounds investigated show that the ligand atoms are distributed in a mixed (split) position instead of 24e. One of the ammonium groups is disordered near 8c so that its central atom (N1) forms a tetrahedron with vertexes in 32f, but a center of another group (N2) remains in 4b, whereas its H atoms (H2) occupy the 96k position instead of 24e, and together with the H3 atom in the 32f position they form eight spatial orientations of the ammonium group. On cooling these compounds undergo PTs of an order–disorder type with a rather large value of entropy changes. These values are rather different [from Rln3 for (NH4)3Ti(O2)F5 to Rln136 for (NH4)3NbOF6], but they should be taken into account during the structure refinement to clarify the mechanism of PTs. Easy transformation between two cubic phases ([Fm \bar 3 m] and F23) near the room temperature in the case of (NH4)3ZrF7 and (NH4)3HfF7 is very interesting and deserves further special consideration.

Supporting information


Computing details top

For both compounds, data collection: Bruker APEX2; cell refinement: Bruker SAINT; data reduction: Bruker SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014/7 (Sheldrick, 2014); molecular graphics: Bruker SHELXTL; software used to prepare material for publication: Bruker SHELXTL.

(I) ammonium heptafluorohafnate top
Crystal data top
(H12N3HfF7)Mo Kα radiation, λ = 0.71073 Å
Mr = 365.62Cell parameters from 6673 reflections
Cubic, Fm3mθ = 3.8–46.1°
a = 9.3964 (1) ŵ = 12.65 mm1
V = 829.63 (3) Å3T = 296 K
Z = 4Octahedron, colourless
F(000) = 6720.25 × 0.23 × 0.22 mm
Dx = 2.927 Mg m3
Data collection top
Bruker APEX-II CCD
diffractometer
293 reflections with I > 2σ(I)
Detector resolution: 8.33 pixels mm-1Rint = 0.019
ω scansθmax = 52.5°, θmin = 3.8°
Absorption correction: multi-scan
Bruker SADABS
h = 2019
Tmin = 0.593, Tmax = 0.750k = 2019
8194 measured reflectionsl = 2020
293 independent reflections
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.009H-atom parameters not refined
wR(F2) = 0.019 w = 1/[σ2(Fo2) + (0.0032P)2 + 0.6486P]
where P = (Fo2 + 2Fc2)/3
S = 1.19(Δ/σ)max = 0.005
293 reflectionsΔρmax = 1.14 e Å3
22 parametersΔρmin = 0.67 e Å3
0 restraintsExtinction correction: SHELXL-2014/7 (Sheldrick 2014, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.01226 (12)
Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Hf0.00000.00000.00000.02423 (2)
N10.2588 (4)0.2588 (4)0.2588 (4)0.0436 (7)0.25
N20.50000.50000.50000.0558 (9)
F10.00000.00000.2089 (2)0.0765 (9)0.5
F20.00000.0637 (6)0.2067 (6)0.0520 (15)0.0833
F30.00000.1290 (6)0.1891 (6)0.0484 (12)0.0833
H110.20380.20380.20380.086*0.25
H120.20380.31280.31280.086*0.0833
H130.31280.31280.20380.086*0.0833
H140.31280.20380.31280.086*0.0833
H20.59300.48140.48140.065*0.125
H30.44450.44450.44450.065*0.125
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Hf0.02423 (2)0.02423 (2)0.02423 (2)0.0000.0000.000
N10.0436 (7)0.0436 (7)0.0436 (7)0.0005 (12)0.0005 (12)0.0005 (12)
N20.0558 (9)0.0558 (9)0.0558 (9)0.0000.0000.000
F10.1063 (14)0.1063 (14)0.0170 (6)0.0000.0000.000
F20.062 (3)0.065 (3)0.0293 (18)0.0000.0000.0139 (19)
F30.041 (2)0.059 (3)0.044 (2)0.0000.0000.0276 (17)
Geometric parameters (Å, º) top
Hf—F11.963 (2)F1—F2ii2.826 (4)
Hf—F1i1.963 (2)F1—F3xi2.912 (4)
Hf—F1ii1.963 (2)F1—F3ix2.912 (4)
Hf—F22.032 (5)F1—F3x2.912 (4)
Hf—F2iii2.032 (5)F1—F3ii2.912 (4)
Hf—F32.151 (5)N1—N1xii0.234 (10)
Hf—F3iii2.151 (5)N1—F3xiii2.584 (4)
F1—F2iv2.374 (6)N1—F3xiv2.620 (3)
F1—F2v2.374 (6)N1—H110.8952
F2—F3vi2.484 (8)N1—H120.8843
F3—F3vii2.425 (10)N1—H130.8843
F1—F1i2.776 (3)N1—H140.8843
F1—F1viii2.776 (3)N2—F1xv2.735 (2)
F1—F2ix2.826 (4)N2—F2xvi2.820 (6)
F1—F2x2.826 (4)N2—H20.9081
F1—F2xi2.826 (4)N2—H30.9033
F1—Hf—F1i90.0F1ii—Hf—F1v90.0
F1—Hf—F1ii90.0F1i—Hf—F1xvii90.0
F1i—Hf—F1ii180.0F1ii—Hf—F1xvii90.0
F1—Hf—F1viii90.0F1ii—Hf—F272.88 (17)
F1i—Hf—F1viii90.0F1i—Hf—F2iii72.88 (17)
F1ii—Hf—F1viii90.0F2xviii—Hf—F3xix72.8 (2)
F1—Hf—F1v90.0F2vii—Hf—F3iv72.8 (2)
F1i—Hf—F1v90.0F3iv—Hf—F3xx68.6 (3)
Symmetry codes: (i) y, z, x; (ii) y, z, x; (iii) z, y, x; (iv) x, z, y; (v) z, x, y; (vi) x, z, y; (vii) x, y, z; (viii) z, x, y; (ix) z, y, x; (x) z, y, x; (xi) y, z, x; (xii) x, y+1/2, z+1/2; (xiii) z, y+1/2, x+1/2; (xiv) y, x+1/2, z+1/2; (xv) y+1/2, z+1, x+1/2; (xvi) z+1, y+1/2, x+1/2; (xvii) x, y, z; (xviii) x, y, z; (xix) x, z, y; (xx) x, z, y.
(II) pentafluorooxotitanium top
Crystal data top
(H12N3TiO2F5)Mo Kα radiation, λ = 0.71073 Å
Mr = 229.03Cell parameters from 7086 reflections
Cubic, Fm3mθ = 3.8–37.6°
a = 9.2327 (1) ŵ = 1.14 mm1
V = 787.02 (3) Å3T = 296 K
Z = 4Octahedron, colourless
F(000) = 4640.24 × 0.23 × 0.22 mm
Dx = 1.933 Mg m3
Data collection top
Bruker APEX-II CCD
diffractometer
190 reflections with I > 2σ(I)
Detector resolution: 8.33 pixels mm-1Rint = 0.020
w scansθmax = 43.1°, θmin = 3.8°
Absorption correction: multi-scan
Bruker SADABS
h = 1717
Tmin = 0.695, Tmax = 0.749k = 1717
9680 measured reflectionsl = 1517
190 independent reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.014Hydrogen site location: difference Fourier map
wR(F2) = 0.040H-atom parameters not refined
S = 1.03 w = 1/[σ2(Fo2) + (0.0333P)2 + 0.0481P]
where P = (Fo2 + 2Fc2)/3
190 reflections(Δ/σ)max = 0.050
24 parametersΔρmax = 0.14 e Å3
0 restraintsΔρmin = 0.33 e Å3
Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Ti10.00000.00000.00000.02239 (3)
N10.2593 (2)0.2593 (2)0.2593 (2)0.0439 (4)0.25
N20.50000.50000.50000.0592 (6)
O10.1808 (4)0.1142 (3)0.00000.0660 (9)0.0833
F10.20425 (11)0.01404 (17)0.01404 (17)0.0462 (4)0.125
F20.2000 (3)0.0602 (3)0.00000.0498 (8)0.0833
H110.20490.20490.20490.098*0.25
H120.20490.31490.31490.098*0.0833
H130.31490.20490.31490.098*0.0833
H140.31490.31490.20490.098*0.0833
H20.59300.48140.48140.044*0.125
H30.44450.44450.44450.098*0.125
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ti10.02239 (3)0.02239 (3)0.02239 (3)0.0000.0000.000
N10.0439 (4)0.0439 (4)0.0439 (4)0.0058 (6)0.0058 (6)0.0058 (6)
N20.0592 (6)0.0592 (6)0.0592 (6)0.0000.0000.000
O10.0615 (15)0.096 (2)0.0406 (14)0.0518 (12)0.0000.000
F10.0186 (3)0.0600 (5)0.0600 (5)0.0024 (4)0.0024 (4)0.007 (2)
F20.0268 (8)0.0619 (17)0.0608 (17)0.0129 (9)0.0000.000
Geometric parameters (Å, º) top
Ti1—F11.8946 (10)N2—F1xiii2.7367 (10)
Ti1—F1i1.8947 (10)N2—F1xiv2.7367 (10)
N1—N1ii0.243 (6)N2—F1ii2.7367 (10)
N1—N1iii0.243 (6)N2—H20.8923
N1—N1iv0.243 (6)N2—H30.8875
N1—O1v2.613 (3)O1—O1xv1.491 (4)
N1—O1vi2.613 (3)F2—O1xvi2.362 (5)
N1—O1vii2.613 (3)F1—F2xvi2.386 (3)
N1—O1viii2.613 (3)F1—F2xvii2.386 (3)
N1—O1ix2.613 (3)F1—O1xviii2.707 (3)
N1—O1x2.613 (3)F1—O1xix2.707 (3)
N1—O1xi2.6530 (19)F1—F1xx2.6732 (15)
N1—H110.8701F1—F1xxi2.6731 (15)
N1—H120.8828F1—F1xxii2.484 (3)
N1—H130.8827F1—F2xxiii2.816 (2)
N1—H140.8827F1—F2xxiv2.816 (2)
N2—F1xii2.7367 (10)F2—F2xxv2.611 (4)
F1—Ti1—F1xxvi81.90 (10)F1—Ti1—F1xx89.732 (7)
Symmetry codes: (i) y, z, x; (ii) x, y+1/2, z+1/2; (iii) x+1/2, y, z+1/2; (iv) x+1/2, y+1/2, z; (v) z+1/2, y+1/2, x; (vi) x, z+1/2, y+1/2; (vii) y+1/2, z+1/2, x; (viii) z+1/2, x, y+1/2; (ix) x, y+1/2, z+1/2; (x) y+1/2, x, z+1/2; (xi) z+1/2, y, x+1/2; (xii) y+1/2, z+1/2, x+1; (xiii) y+1/2, z+1/2, x; (xiv) x+1, y+1/2, z+1/2; (xv) x, z, y; (xvi) y, x, z; (xvii) y, z, x; (xviii) z, y, x; (xix) z, x, y; (xx) y, z, x; (xxi) z, x, y; (xxii) z, x, y; (xxiii) z, y, x; (xxiv) z, x, y; (xxv) z, y, x; (xxvi) y, z, x.
 

Acknowledgements

We thank T. B. Emelina for DFT calculations of vibrational spectra of (NH4)3HfF7 and Yu. V. Marchenko for recording its IR spectrum.

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