Buy article online - an online subscription or single-article purchase is required to access this article.
Download citation
Download citation
link to html
A hexagonal modification (P63mc) of (NH4)2SiF6 was grown accidentally. This new modification has the unit-cell c parameter doubled with respect to a previously reported trigonal form (P\overline 3m1) of the title compound. The H atoms in the present structure are ordered. Three or even four F atoms are hydrogen-bond acceptors for each H atom. The structure is isostructural with modifications of (NH4)2MnF6, K2GeF6 and Rb2GeF6.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S160053680101501X/wn6052sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S160053680101501X/wn6052Isup2.hkl
Contains datablock I

Key indicators

  • Single-crystal X-ray study
  • T = 290 K
  • Mean [sigma](Si-F) = 0.001 Å
  • R factor = 0.018
  • wR factor = 0.022
  • Data-to-parameter ratio = 11.6

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


Yellow Alert Alert Level C:
PLAT_420 Alert C D-H Without Acceptor N(2) - H(22N) ? General Notes
REFLT_03 From the CIF: _diffrn_reflns_theta_max 29.98 From the CIF: _reflns_number_total 361 Count of symmetry unique reflns 191 Completeness (_total/calc) 189.01% TEST3: Check Friedels for noncentro structure Estimate of Friedel pairs measured 170 Fraction of Friedel pairs measured 0.890 Are heavy atom types Z>Si present yes Please check that the estimate of the number of Friedel pairs is correct. If it is not, please give the correct count in the _publ_section_exptl_refinement section of the submitted CIF.
0 Alert Level A = Potentially serious problem
0 Alert Level B = Potential problem
1 Alert Level C = Please check

Comment top

Until now, two modifications of (NH4)2SiF6 have been known (ICSD; Bergerhoff et al., 1983; PDF-2, 2001): trigonal P3m1 (Schlemper & Hamilton, 1966; PDF-2 44–1424 and 72–1548) and cubic Fm3 m (Hanic, 1966; PDF-2 07–0013, 72–1552 and 72–1759). The trigonal and cubic modifications are also known by their respective mineralogical names bararite and cryptohalite. The cubic modification is stable at room temperature (Schlemper & Hamilton, 1966). In the cubic modification, the positions of the H atoms were determined; they were not determined in the trigonal modification. According to both, the neutron-diffraction study (Schlemper & Hamilton, 1966) and the electron-diffraction study (Vainshtein & Stasova, 1956) the H atoms in the cubic modification are disordered.

In this study, two modifications were grown in the same beaker, viz. hexagonal and cubic. The crystals of each modification were quite easily distinguishable in cross-polarized light as well as by their habit. While the habit of the cubic modification was cubic, the hexagonal modification grew as trigonal or hexagonal pyramids. The typical size of both crystal modifications was several tenths of a millimetre.

Attempts at chemical analysis were hindered by the small amount of available crystals. An electron microprobe analysis [Jeol JXA733 (Jeol Ltd., Tokyo, Japan) with X-ray analyzer KEVEX (Delta Class Analyzer; Kevex Instruments, San Carlos, California, USA)] was not successful in the determination of the proportion of constituent elements P, Si, O and F because of the fluffy grains on the surface of the sample. These fluffy grains contained predominantly Si, F and K. It should be noted that the microprobe analysis was not performed on the sample that was used for the structure determination. Nevertheless, the satisfactory result of the structure analysis shows that (NH4)2SiF6 can also form a superstructure, either as a transitory state or stabilized by traces of K.

The previously determined trigonal modification shows similarities with the present structure in the orientation of the Si—F bonds with regard to the unit-cell axes. It should be noted that the structure determined in this study is isostructural with one of the known modifications of K2GeF6 (Bode & Brockmann, 1952) and Rb2GeF6 (ibid.). The structure is also isostructural with (NH4)2MnF6 (Kaskel & Straehle, 1997) where the positions of the H atoms were determined.

The H atoms were readily seen in the difference Fourier maps and could be easily refined with no applied constraints or restraints. All the H atoms are ordered. Each N atom in the structure is surrounded by six F atoms with fairly similar N···F distances. The distribution of four H atoms among six surrounding F atoms results in the distances between the H and F atoms being unequal despite the regularity of the N···F distances. Table 2 lists the closest N···F distances and angles.

Experimental top

The present compound grew from a solution which was prepared by neutralization of stoichiometric amounts of (NH4)2CO3 and H2PO3F in the molar proportion 1:1. Most probably some of the fluorophosphate anions have decomposed with production of HF which reacted with the glass of the beaker. In addition to the structure which is reported here, the cubic modification was also grown, in fact, in larger amount. Its lattice parameters corresponded to those determined by e.g. Hanic (1966).

Refinement top

No restraints or constraints were applied. The inversion-twinning proportion determined by refinement turned out to be insignificant.

Computing details top

Cell refinement: KM4B8; data reduction: JANA2000 (Petříček & Dušek, 2000); program(s) used to solve structure: JANA2000; program(s) used to refine structure: JANA2000; molecular graphics: ORTEPIII (Burnett & Johnson, 1996).

Figures top
[Figure 1] Fig. 1. The unit-cell contents of (NH4)2SiF6 viewed along the c axis.
(I) top
Crystal data top
2(NH4)·(SiF6)Dx = 2.047 Mg m3
Mr = 178.15Mo Kα radiation, λ = 0.71069 Å
Hexagonal, P63mcCell parameters from 68 reflections
a = 5.8955 (10) Åθ = 8.5–19.1°
c = 9.599 (1) ŵ = 0.46 mm1
V = 288.93 (8) Å3T = 290 K
Z = 2Pyramid, colourless
F(000) = 1800.40 × 0.35 × 0.30 mm
Data collection top
Kuma-4
diffractometer
θmax = 30.0°, θmin = 4.0°
w/2θ scansh = 77
1682 measured reflectionsk = 07
361 independent reflectionsl = 1313
348 reflections with I > 3σ(I)3 standard reflections every 200 reflections
Rint = 0.020 intensity decay: 1.5%
Refinement top
Refinement on FAll H-atom parameters refined
R[F2 > 2σ(F2)] = 0.018Weighting scheme based on measured s.u.'s w = 1/(σ2(F) + 0.0001F2)
wR(F2) = 0.022(Δ/σ)max = 0.0001
S = 1.70Δρmax = 0.39 e Å3
361 reflectionsΔρmin = 0.39 e Å3
31 parameters
Crystal data top
2(NH4)·(SiF6)Z = 2
Mr = 178.15Mo Kα radiation
Hexagonal, P63mcµ = 0.46 mm1
a = 5.8955 (10) ÅT = 290 K
c = 9.599 (1) Å0.40 × 0.35 × 0.30 mm
V = 288.93 (8) Å3
Data collection top
Kuma-4
diffractometer
Rint = 0.020
1682 measured reflections3 standard reflections every 200 reflections
361 independent reflections intensity decay: 1.5%
348 reflections with I > 3σ(I)
Refinement top
R[F2 > 2σ(F2)] = 0.01831 parameters
wR(F2) = 0.022All H-atom parameters refined
S = 1.70Δρmax = 0.39 e Å3
361 reflectionsΔρmin = 0.39 e Å3
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Si0.3333330.6666670.250.01751 (12)
F10.06201 (16)0.53101 (8)0.14734 (10)0.0276 (2)
F20.19679 (9)0.39358 (19)0.35039 (10)0.0289 (3)
N10.6666670.3333330.3731 (2)0.0235 (4)
N2000.5855 (2)0.0269 (5)
H1n10.586 (3)0.172 (6)0.394 (4)0.089 (10)*
H1n20.146 (4)0.073 (2)0.549 (3)0.071 (8)*
H2n10.6666670.3333330.291 (13)0.19 (5)*
H2n2000.675 (8)0.10 (2)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
N10.0239 (5)0.0239 (5)0.0227 (7)0.0119 (2)00
N20.0247 (5)0.0247 (5)0.0315 (12)0.0123 (2)00
Si0.01716 (15)0.01716 (15)0.0182 (2)0.00858 (7)00
F10.0221 (4)0.0301 (3)0.0279 (4)0.0110 (2)0.0072 (2)0.00360 (14)
F20.0297 (3)0.0244 (4)0.0308 (4)0.0122 (2)0.00440 (15)0.0088 (3)
Geometric parameters (Å, º) top
Si—F11.700 (1)Si—F21.695 (1)
Si—F1i1.700 (1)Si—F2i1.695 (1)
Si—F1ii1.700 (1)Si—F2ii1.695 (1)
H1n1—N1—H1n1iii115 (3)F1—Si—F289.68 (5)
H1n1—N1—H1n1iv115 (3)F1—Si—F2i179.22 (5)
H1n1—N1—H2n1104 (2)F1—Si—F2ii89.68 (5)
H1n1iii—N1—H1n1iv115 (3)F1i—Si—F1ii89.77 (5)
H1n1iii—N1—H2n1104 (2)F1i—Si—F289.68 (5)
H1n1iv—N1—H2n1104 (2)F1i—Si—F2i89.68 (5)
H1n2—N2—H1n2v103 (3)F1i—Si—F2ii179.22 (5)
H1n2—N2—H1n2vi103 (3)F1ii—Si—F2179.22 (5)
H1n2—N2—H2n2115 (2)F1ii—Si—F2i89.68 (5)
H1n2v—N2—H1n2vi103 (3)F1ii—Si—F2ii89.68 (5)
H1n2v—N2—H2n2115 (2)F2—Si—F2i90.87 (6)
H1n2vi—N2—H2n2115 (2)F2—Si—F2ii90.87 (6)
F1—Si—F1i89.77 (5)F2ii—Si—F2i90.87 (6)
F1—Si—F1ii89.77 (5)
Symmetry codes: (i) y+1, xy+1, z; (ii) x+y, x+1, z; (iii) y+1, xy, z; (iv) x+y+1, x+1, z; (v) y, xy, z; (vi) x+y, x, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1n1···F1vii0.85 (3)2.49 (4)2.975 (2)117 (3)
N1—H1n1···F1vi0.85 (3)2.65 (4)2.962 (2)103 (3)
N1—H1n1···F2iii0.85 (3)2.28 (2)2.972 (1)139 (3)
N1—H1n1···F2vi0.85 (3)2.28 (2)2.972 (1)139 (3)
N2—H1n2···F1viii0.82 (3)2.58 (3)3.023 (1)115 (2)
N2—H1n2···F1ix0.82 (3)2.58 (3)3.023 (1)115 (2)
N2—H1n2···F2v0.82 (3)2.29 (3)3.022 (2)149 (3)
N1—H2n1···F1x0.8 (1)2.45 (7)2.962 (2)124 (3)
N1—H2n1···F1i0.8 (1)2.45 (7)2.962 (2)124 (3)
N1—H2n1···F1vi0.8 (1)2.45 (7)2.962 (2)124 (3)
N2—H2n2···F2viii0.86 (8)2.62 (5)3.241 (2)130 (1)
N2—H2n2···F2xi0.86 (8)2.62 (5)3.241 (2)130 (1)
N2—H2n2···F2xii0.86 (8)2.62 (5)3.241 (2)130 (1)
Symmetry codes: (i) y+1, xy+1, z; (iii) y+1, xy, z; (v) y, xy, z; (vi) x+y, x, z; (vii) xy+1, x, z+1/2; (viii) xy, x, z+1/2; (ix) y1, x+y1, z+1/2; (x) x+1, y, z; (xi) y, x, z+1/2; (xii) x, y, z+1/2.

Experimental details

Crystal data
Chemical formula2(NH4)·(SiF6)
Mr178.15
Crystal system, space groupHexagonal, P63mc
Temperature (K)290
a, c (Å)5.8955 (10), 9.599 (1)
V3)288.93 (8)
Z2
Radiation typeMo Kα
µ (mm1)0.46
Crystal size (mm)0.40 × 0.35 × 0.30
Data collection
DiffractometerKuma-4
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 3σ(I)] reflections
1682, 361, 348
Rint0.020
(sin θ/λ)max1)0.703
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.018, 0.022, 1.70
No. of reflections361
No. of parameters31
No. of restraints?
H-atom treatmentAll H-atom parameters refined
Δρmax, Δρmin (e Å3)0.39, 0.39

Computer programs: KM4B8, JANA2000 (Petříček & Dušek, 2000), JANA2000, ORTEPIII (Burnett & Johnson, 1996).

Selected bond lengths (Å) top
Si—F11.700 (1)Si—F21.695 (1)
Si—F1i1.700 (1)Si—F2i1.695 (1)
Si—F1ii1.700 (1)Si—F2ii1.695 (1)
Symmetry codes: (i) y+1, xy+1, z; (ii) x+y, x+1, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1n1···F1iii0.85 (3)2.49 (4)2.975 (2)117 (3)
N1—H1n1···F1iv0.85 (3)2.65 (4)2.962 (2)103 (3)
N1—H1n1···F2v0.85 (3)2.28 (2)2.972 (1)139 (3)
N1—H1n1···F2iv0.85 (3)2.28 (2)2.972 (1)139 (3)
N2—H1n2···F1vi0.82 (3)2.58 (3)3.023 (1)115 (2)
N2—H1n2···F1vii0.82 (3)2.58 (3)3.023 (1)115 (2)
N2—H1n2···F2viii0.82 (3)2.29 (3)3.022 (2)149 (3)
N1—H2n1···F1ix0.8 (1)2.45 (7)2.962 (2)124 (3)
N1—H2n1···F1i0.8 (1)2.45 (7)2.962 (2)124 (3)
N1—H2n1···F1iv0.8 (1)2.45 (7)2.962 (2)124 (3)
N2—H2n2···F2vi0.86 (8)2.62 (5)3.241 (2)130 (1)
N2—H2n2···F2x0.86 (8)2.62 (5)3.241 (2)130 (1)
N2—H2n2···F2xi0.86 (8)2.62 (5)3.241 (2)130 (1)
Symmetry codes: (i) y+1, xy+1, z; (iii) xy+1, x, z+1/2; (iv) x+y, x, z; (v) y+1, xy, z; (vi) xy, x, z+1/2; (vii) y1, x+y1, z+1/2; (viii) y, xy, z; (ix) x+1, y, z; (x) y, x, z+1/2; (xi) x, y, z+1/2.
 

Subscribe to Acta Crystallographica Section E: Crystallographic Communications

The full text of this article is available to subscribers to the journal.

If you have already registered and are using a computer listed in your registration details, please email support@iucr.org for assistance.

Buy online

You may purchase this article in PDF and/or HTML formats. For purchasers in the European Community who do not have a VAT number, VAT will be added at the local rate. Payments to the IUCr are handled by WorldPay, who will accept payment by credit card in several currencies. To purchase the article, please complete the form below (fields marked * are required), and then click on `Continue'.
E-mail address* 
Repeat e-mail address* 
(for error checking) 

Format*   PDF (US $40)
   HTML (US $40)
   PDF+HTML (US $50)
In order for VAT to be shown for your country javascript needs to be enabled.

VAT number 
(non-UK EC countries only) 
Country* 
 

Terms and conditions of use
Contact us

Follow Acta Cryst. E
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds