Crystal structure and Hirshfeld surface analysis of bis­­[hydrazinium(1+)] hexa­fluorido­silicate: (N₂H₅)₂SiF₆

In the title inorganic mol­ecular salt, (N₂H₅)₂SiF₆, the silicon atom at the centre of the slightly distorted SiF₆ octa­hedron [range of Si—F distances = 1.6777 (4)–1.7101 (4) Å] lies on a crystallographic inversion centre. In the crystal, the ions are connected by N—H⋯N and N—H⋯F hydrogen bonds; the former link the cations into [010] chains and the latter (some of which are bifurcated or trifurcated) link the ions into a three-dimensional network. The two-dimensional fingerprint plots show that F⋯H/H⋯F inter­actions dominate the Hirshfeld surface (75.5%) followed by H⋯H (13.6%) and N⋯H/H⋯N (8.4%) whereas F⋯F (1.9%) and F⋯N/N⋯F (0.6%) have negligible percentages. The title compound is isostructural with its germanium-containing analogue.

1. Chemical context

Hydrazinium hexa­fluorido­metalate compounds have been studied by X-ray diffraction, vibrational spectroscopy and thermal analyses: they have been found to exist with two different formulae: N₂H₆MF₆ (Kojić-Prodić et al., 1971a,b; Frlec et al., 1980; Golič et al., 1980; Cameron et al., 1983; Knop et al., 1983; Ouasri et al., 2002) and (N₂H₅)₂MF₆ (Gantar & Rahten, 1988; Leban et al., 1994) where M = Ga, Si, Ti, Zr and Hf. The name `hydrazinium hexa­fluorido­silicate' has been applied to both compounds: N₂H₆SiF₆ and (N₂H₅)₂SiF₆.

The crystal structure of N₂H₆SiF₆ is well described by Frlec et al. (1980) and by Cameron et al. (1983), whereas that of (N₂H₅)₂SiF₆ has not previously been reported to our best knowledge. However, this compound was characterized by chemical analysis, vibrational spectroscopy and X-ray powder photography by Gantar & Rahten (1986), who determined the unit-cell parameters and the space group. We now describe the synthesis, single crystal structure and Hirshfeld surface analysis of the title compound, (I), at room temperature.

2. Structural commentary

Compound (I) is an inorganic mol­ecular salt built up from N₂H₅⁺ cations and SiF₆²⁻ anions, as shown in Fig. 1. In this structure, all atoms are in general positions except for the silicon atom, which is located at the Wyckoff position 2d on the inversion centre of the space group P2₁/n. Thus, the silicon atom is connected to three unique fluorine atoms and their symmetry equivalents, forming a slightly elongated octa­hedron with Si—F distances in the range of 1.6777 (4) to 1.7101 (4) Å. The minimum and maximum cis F—S—F angles are 89.26 (2) and 90.74 (2)°, respectively. The N—N separation in the cation is 1.4416 (8) Å.

Figure 1 Mol­ecular structure of (I) with displacement ellipsoids drawn at the 50% probability level.

3. Supra­molecular features and Hirshfeld surface analysis

In the extended structure of (I), the hydrazinium cations are linked by strong N—H⋯N hydrogen bonds (Table 1), building an infinite zigzag chain propagating along the [010] direction as shown in Fig. 2. The [SiF₆]²⁻ anion inter­acts with the (N₂H₅)⁺ cations through electrostatic attraction and accepts no fewer than ten simple, bifurcated or trifurcated N—H⋯F hydrogen bonds (Fig. 3, Table 1). This results in a three-dimensional network in which the hydrazinium cations build zigzag chains parallel to the b-axis direction and the [SiF₆]²⁻ anions are stacked along the [100] direction (Fig. 4).

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1A⋯F1^i	0.89	2.36	2.8436 (7)	114
N1—H1A⋯F3^ii	0.89	2.04	2.9174 (7)	170
N1—H1B⋯N2^iii	0.89	2.03	2.8963 (8)	165
N1—H1C⋯F3^iv	0.89	2.02	2.9025 (7)	170
N1—H1C⋯F2^v	0.89	2.49	2.9078 (7)	109
N2—H2A⋯F1^vi	0.83	2.52	3.0952 (7)	127
N2—H2A⋯F2^vi	0.83	2.64	3.0725 (7)	114
N2—H2A⋯F3^vi	0.83	2.43	3.2373 (7)	167
N2—H2B⋯F3^vii	0.86	2.49	3.2683 (7)	150
N2—H2B⋯F2^v	0.86	2.51	3.1036 (7)	127
N2—H2B⋯F1^iv	0.86	2.60	3.0124 (7)	110
Symmetry codes: (i) x, y+1, z; (ii) -x+1, -y+1, -z+1; (iii) ; (iv) ; (v) ; (vi) ; (vii) .

Figure 2 A view of the hydrazinium (1+) cations building an [010] chain through N—H⋯F hydrogen bonds (dashed blue lines).

Figure 3 Details of the hydrogen bonds between the hydrazinium (1+) cations and (SiF6)^2− anions in (I).

Figure 4 The crystal structure of (I) with the anions shown as polyhedra.

The packing of (I) was further investigated and qu­anti­fied with a Hirshfeld surface analysis (McKinnon et al., 2004; Spackman & Jayatilaka, 2009) and two-dimensional fingerprint plots generated using the CrystalExplorer package (Turner et al., 2017).

The acceptor atoms in the inter­actions are shown with negative electrostatic potentials (red regions), and donor atoms are shown with positive electrostatic potentials (blue regions). The N—H⋯F inter­actions in the structure are apparent from the relatively bright red-spots on the Hirshfeld surface of (I) mapped over d_norm (Fig. S1 in the supporting information). In order to provide qu­anti­tative information on the contribution of the inter­molecular inter­actions to the crystal packing, the three-dimensional d_norm surface is resolved into two-dimensional fingerprint plots, generated based on d_e and d_i distance scales and illustrated in Fig. 5(a)–(f) The F⋯H/H⋯F inter­actions appear as distinct spikes in the fingerprint plot, and occupy the majority of the total Hirshfeld surface (75.5%) as illustrated in Fig. 5(a); the characteristic `wingtip' features indicate the N—H⋯F hydrogen bonds. The H⋯F inter­action are represented by a spike (d_i = 0.8, d_e = 1.1 Å) at the bottom left (donor), whereas the F⋯H inter­actions are represented by a spike (d_i = 1.1, d_e = 0.8 Å) at the bottom right (acceptor) of the fingerprint plot. The H⋯H contacts appear in the middle of the scattered points; these contacts comprise 13.6% of the total Hirshfeld surface [Fig. 5(c)]. The N⋯H contacts cover 8.4% of the total surface, as the third important contributor in the crystal packing, Fig. 5(d) while the F⋯F and F⋯N/N⋯F contacts make negligible contributions of 1.9% [Fig. 5(e)] and 0.6% [Fig. 5(f)], respectively.

Figure 5 Fingerprint plots for the inter­actions present in the crystal packing of (I) showing (a) all contacts and those delineated into (b) F⋯H, (c) H⋯H, (d) N⋯H, (e) F⋯F and (f) F⋯N. The outline of the full fingerprint is shown in grey.

4. Database survey

Hydrazinium (2+) hexa­fluorido­silicate, N₂H₆SiF₆, at room temperature, crystallizes in a pseudo-tetra­gonal ortho­rhom­bic space group (Pbca, Z = 4), with a = 7.605 (1) Å, b = 7.586 (2) Å and c = 8.543 (1) Å (Frlec et al., 1980; Cameron et al., 1983). Its structure consists of centrosymmetric N₂H₆²⁺ and SiF₆²⁻ ions arranged in a NaC1-type packing and connected by N—H⋯F hydrogen bonds, forming layers of cations and anions lying parallel to (001) plane.

Hydrazinium (1+) hexa­halogenometallates were studied by Gantar and co-workers (Gantar et al., 1985; Gantar & Rahten, 1986) who showed that (N₂H₅)₂GeF₆ crystallizes in the monoclinic system, space group P2₁/n (Z = 2), with cell parameters a = 6.015 (2) Å, b = 5.249 (1) Å, c = 11.181 (2)Å and β = 100.15 (2)° and is clearly isostructural with (I).

Fluoride complexes of titanium (IV) with ammonium cation derivatives include two hydrazinium hexa­fluorido­titanates (IV), (N₂H₅)₂TiF₆ (Leban et al., 1994) and N₂H₆TiF₆ (Kojić-Prodić et al.,1971a,b). The monoclinic crystals of (N₂H₅)₂TiF₆ [P2₁; Z = 4; a = 7.815 (1) Å, b = 10.019 (1) Å, c = 9.338 (1) Å; β = 93.58 (1)°] exhibit racemic twinning but are not isostructural with (I). The crystal structure of (N₂H₅)₂TiF₆ consists of N₂H₅⁺ cations and two types of slightly distorted octa­hedral (TiF₆)²⁻ anions. The N₂H₅⁺ cations and (TiF₆)²⁻ anions are linked via N—H⋯F and N—H⋯N hydrogen bonds, building a three-dimensional network. Two other isostructural hydrazinium (l+) hexa­fluorido complexes, (N₂H₅)₂ZrF₆ and (N₂H₅)₂HfF₆, were prepared and characterized by chemical analysis, vibrational spectroscopy and X-ray powder diffraction (Gantar & Rahten, 1988). The infrared spectrum analysis of the title compound at room temperature confirms the obtained results by Gantar & Rahten with the exception of the assignments of two infrared bands (see supporting information).

5. Synthesis and Infrared measurement technique.

Hydrazinium (1+) hexa­fluorido­silicate (N₂H₅)₂SiF₆ crystals in the form of colourless blocks were obtained by slow evaporation, at room temperature, of an aqueous solution containing stoichiometric amounts of hydrazine NH₂NH₂ and H₂SiF₆. The infrared spectrum was recorded in the range 450–4000 cm⁻¹ with a Vertex 70 FTIR spectrometer.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms were located in a difference-Fourier map and refined using a riding model with N—H = 0.86 Å and U_iso(H) = 1.2U_eq(N). The highest peak and the deepest hole in the final Fourier map are at 0.67 Å from F3 and 0.0 Å from Si1.

Table 2
Experimental details

Crystal data
Chemical formula	F6H10N4Si
Mr	208.21
Crystal system, space group	Monoclinic, P21/n
Temperature (K)	296
a, b, c (Å)	5.9496 (3), 5.2484 (2), 11.0029 (5)
β (°)	100.245 (1)
V (Å^3)	338.10 (3)
Z	2
Radiation type	Mo Kα
μ (mm^−1)	0.42
Crystal size (mm)	0.31 × 0.24 × 0.16
Data collection
Diffractometer	Bruker D8 VENTURE Super DUO
Absorption correction	Multi-scan (SADABS; Krause et al., 2015)
Tmin, Tmax	0.638, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	19683, 1488, 1379
Rint	0.027
(sin θ/λ)max (Å^−1)	0.806
Refinement
R[F^2 > 2σ(F^2)], wR(F^2), S	0.021, 0.059, 1.06
No. of reflections	1488
No. of parameters	54
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å^−3)	0.27, −0.22
Computer programs: APEX3 and SAINT-Plus (Bruker, 2016), SHELXT2014/7 (Sheldrick, 2015a), SHELXL2014/7 (Sheldrick, 2015b), ORTEP-3 for Windows (Farrugia, 2012), Mercury (Macrae et al., 2008)and publCIF (Westrip, 2010).

Supporting information

Computing details

Data collection: APEX3 (Bruker, 2016); cell refinement: SAINT-Plus (Bruker, 2016); data reduction: SAINT-Plus (Bruker, 2016); program(s) used to solve structure: SHELXT2014/7 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014/7 (Sheldrick, 2015b); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: Mercury (Macrae et al., 2008)and publCIF (Westrip, 2010).

Bis[hydrazinium(1+)] hexafluoridosilicate

Crystal data

F6H10N4Si	F(000) = 212
Mr = 208.21	Dx = 2.045 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 5.9496 (3) Å	Cell parameters from 1488 reflections
b = 5.2484 (2) Å	θ = 3.7–35.0°
c = 11.0029 (5) Å	µ = 0.42 mm^−1
β = 100.245 (1)°	T = 296 K
V = 338.10 (3) Å^3	Block, colourless
Z = 2	0.31 × 0.24 × 0.16 mm

Data collection

Bruker D8 VENTURE Super DUO diffractometer	1488 independent reflections
Radiation source: INCOATEC IµS micro-focus source	1379 reflections with I > 2σ(I)
HELIOS mirror optics monochromator	Rint = 0.027
Detector resolution: 10.4167 pixels mm^-1	θmax = 35.0°, θmin = 3.7°
φ and ω scans	h = −9→9
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	k = −8→8
Tmin = 0.638, Tmax = 0.746	l = −17→17
19683 measured reflections

Refinement

Refinement on F^2	Hydrogen site location: mixed
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.021	w = 1/[σ^2(Fo^2) + (0.0348P)^2 + 0.036P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.059	(Δ/σ)max = 0.001
S = 1.06	Δρmax = 0.27 e Å^−3
1488 reflections	Δρmin = −0.22 e Å^−3
54 parameters	Extinction correction: SHELXL-2018/3 (Sheldrick 2015b), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.093 (10)

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
Si1	0.500000	0.000000	0.500000	0.01562 (7)
F1	0.28419 (6)	−0.13785 (8)	0.55514 (4)	0.02516 (10)
F3	0.31234 (7)	0.21784 (8)	0.42375 (4)	0.02473 (10)
F2	0.55101 (7)	0.18926 (8)	0.62475 (4)	0.02576 (10)
N1	0.46840 (9)	0.60149 (11)	0.77712 (5)	0.02307 (11)
H1A	0.530893	0.639080	0.711612	0.035*
H1B	0.334122	0.525916	0.752445	0.035*
H1C	0.560407	0.497003	0.826736	0.035*
N2	0.43562 (9)	0.83227 (11)	0.84285 (5)	0.02447 (11)
H2A	0.390725	0.785787	0.906243	0.037*
H2B	0.567906	0.898565	0.869296	0.037*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Si1	0.01429 (10)	0.01983 (11)	0.01242 (10)	0.00065 (6)	0.00149 (6)	−0.00092 (6)
F1	0.02032 (17)	0.0332 (2)	0.02288 (17)	−0.00450 (14)	0.00636 (13)	0.00188 (14)
F3	0.02217 (17)	0.02512 (18)	0.02510 (18)	0.00506 (13)	−0.00071 (13)	0.00348 (13)
F2	0.02585 (18)	0.0309 (2)	0.01981 (17)	0.00025 (14)	0.00210 (13)	−0.01005 (14)
N1	0.0199 (2)	0.0245 (2)	0.0237 (2)	−0.00006 (16)	0.00101 (16)	0.00587 (18)
N2	0.0222 (2)	0.0289 (2)	0.0220 (2)	−0.00171 (18)	0.00320 (17)	0.00167 (18)

Geometric parameters (Å, º)

Si1—F2^i	1.6777 (4)	N1—N2	1.4416 (8)
Si1—F2	1.6777 (4)	N1—H1A	0.8900
Si1—F1^i	1.6785 (4)	N1—H1B	0.8900
Si1—F1	1.6785 (4)	N1—H1C	0.8900
Si1—F3^i	1.7101 (4)	N2—H2A	0.8268
Si1—F3	1.7101 (4)	N2—H2B	0.8624
F2^i—Si1—F2	180.0	F1^i—Si1—F3	90.52 (2)
F2^i—Si1—F1^i	89.90 (2)	F1—Si1—F3	89.48 (2)
F2—Si1—F1^i	90.10 (2)	F3^i—Si1—F3	180.0
F2^i—Si1—F1	90.10 (2)	N2—N1—H1A	109.5
F2—Si1—F1	89.90 (2)	N2—N1—H1B	109.5
F1^i—Si1—F1	180.0	H1A—N1—H1B	109.5
F2^i—Si1—F3^i	90.74 (2)	N2—N1—H1C	109.5
F2—Si1—F3^i	89.26 (2)	H1A—N1—H1C	109.5
F1^i—Si1—F3^i	89.48 (2)	H1B—N1—H1C	109.5
F1—Si1—F3^i	90.52 (2)	N1—N2—H2A	105.6
F2^i—Si1—F3	89.26 (2)	N1—N2—H2B	108.1
F2—Si1—F3	90.74 (2)	H2A—N2—H2B	104.3

Symmetry code: (i) −x+1, −y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···F1^ii	0.89	2.36	2.8436 (7)	114
N1—H1A···F3^iii	0.89	2.04	2.9174 (7)	170
N1—H1B···N2^iv	0.89	2.03	2.8963 (8)	165
N1—H1C···F3^v	0.89	2.02	2.9025 (7)	170
N1—H1C···F2^vi	0.89	2.49	2.9078 (7)	109
N2—H2A···F1^vii	0.83	2.52	3.0952 (7)	127
N2—H2A···F2^vii	0.83	2.64	3.0725 (7)	114
N2—H2A···F3^vii	0.83	2.43	3.2373 (7)	167
N2—H2B···F3^viii	0.86	2.49	3.2683 (7)	150
N2—H2B···F2^vi	0.86	2.51	3.1036 (7)	127
N2—H2B···F1^v	0.86	2.60	3.0124 (7)	110

Symmetry codes: (ii) x, y+1, z; (iii) −x+1, −y+1, −z+1; (iv) −x+1/2, y−1/2, −z+3/2; (v) x+1/2, −y+1/2, z+1/2; (vi) −x+3/2, y+1/2, −z+3/2; (vii) −x+1/2, y+1/2, −z+3/2; (viii) x+1/2, −y+3/2, z+1/2.