Bis(pyrrolidinium) hexa­chlorido­stannate: a redetermination

The crystal structure of the title compound, (C₄H₁₀N)₂[SnCl₆], has been redetermined at 180 K. All atoms were located with higher precision than the previous structure determined at room temperature [Ishida et al. (2000). J Mol. Struct. 524, 95–103]. In the crystal, the Sn^IV atom is located on a special position of site symmetry 2/m and is coordinated by six Cl atoms in a pseudo-octa­hedral geometry. Of the six Cl atoms, two equivalent axial atoms lie on the mirror plane [Sn—Cl = 2.4281 (6) Å] and the other four equivalent equatorial atoms lie on general positions [Sn—Cl = 2.4285 (4) Å]. The N atom of the pyrrolidinium cation lies on a mirror plane and the other atoms of the cation are disordered over two sites with respect to the mirror plane. Each component of the disordered five-membered rings adopts a twist conformation. The cations and anions are connected via N—H⋯Cl hydrogen bonds, forming a tape-like structure propagating along [010].

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Chemical scheme

Structure description

Previously, we have reported structural phase transitions of three bis­(pyrrolidinium) hexa­chloro­metalates, namely, 2C₄H₈NH₂⁺·MCl₆²⁻ (M = Sn, Te, Pt), by using ³⁵Cl nuclear quadrupole resonance (NQR) and differential scanning calorimetry (DSC). The transitions occur at 150, 159 and 134 K for the stannate, tellurate and platinate, respectively, and their crystal structures at room temperature have been determined by single-crystal X-ray diffraction (Ishida et al., 2000). They are isotypic with each other, belonging to the space group C2/m. The pyrrolidinium cation in these crystals are expected to be rather freely packed because of the large free volume created by the bulky MCl₆²⁻ anion. The ring conformation of the pseudo-free cation was, however, not determined precisely at room temperature owing to large thermal motion, including disordering of the cation. In the present study, we have redetermined the crystal structure of the title compound at a low temperature (180 K) in the high-temperature phase, in order to obtain precise information on the conformation of the cation and inter­molecular inter­actions in the crystal.

A search of the Cambridge Structural Database (Version 5.39, last update August 2018; Groom et al., 2016) gave 72 hits for salts of pyrrolidinium ion. The salt of the pyrrolidinium ion with a discrete MX₆ type anion (M = metal X= halogen) other than 2C₄H₁₀N⁺·MCl₆²⁻ (M = Sn, Te, Pt) was reported for C₄H₁₀N⁺·SbCl₆⁻ (Jakubas et al., 2005), in which the cation ring adopts a twist form at 300 K (CSD refcode XAKWEM) but a flat form at 340 K (XAKWEM01) probably due to an averaging of the disordered ring. Although the pyrrolidinium ion is stable in the twist on C2–C3 form in an isolated system (Ishida, 2000), different conformations of the cation are observed in crystals, for example, an N-envelope conformation in C₄H₁₀N⁺·Cl⁻ (EHACUM; Giglmeier et al., 2009) and C-envelope conformations in C₁₈H₁₆OSi·C₄H₁₀N⁺·C₂H₃O₂⁻ (AJIHUY; Bauer & Strohmann, 2015) and C₄H₁₀N⁺·C₆BrF₄O⁻ (BIYFUM; Takemura et al., 2014).

In the title compound, Fig. 1, the Sn^IV atom in the SnCl₆²⁻ anion is located on a special position of site symmetry 2/m and is coordinated by six Cl atoms in a pseudo-octa­hedral geometry. Of the six Cl atoms, two Cl atoms (Cl1 and Cl2) are crystallographically independent; two equivalent axial Cl atoms lie on a mirror plane and four equivalent equatorial Cl atoms lie on general positions. The Sn—Cl bond lengths are experimentally equivalent [Sn1—Cl1 = 2.4281 (6) Å and Sn1—Cl2 = 2.4285 (4) Å]. The N atom of the pyrrolidinium cation lies on a mirror plane and the other atoms of the cation are disordered over two sites about the mirror plane with an occupancy ratio of 0.5:0.5. The puckering parameters [q₂ = 0.424 (11) Å and φ₂ = 89.2 (19)°] and the torsion angles of the five-membered ring show that the cation adopts a conformation close to the twist on C2—C3 form, as expected from the theoretical calculations for an isolated cation (Ishida, 2000).

Figure 1 The mol­ecular structure of the title compound, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. The N—H⋯Cl hydrogen bond is shown as a dashed line (Table 1). Only one component is shown for the disordered cation. [Symmetry codes: (iii) x, −y + 1, z; (iv) −x + 1, −y + 1, −z; (v) −x + 1, y, −z.]

In the crystal, the NH₂ group of the cation is hydrogen-bonded to the equatorial Cl atoms of the neighbouring anions (N1—H1NA⋯Cl2, N1—H1NB⋯Cl2ⁱ and N1—H1NB⋯Cl2ⁱⁱ; symmetry codes as in Table 1), forming a tape-like structure along the b-axis direction (Fig. 2). The anion is surrounded by six cations, four of which are linked to the anions via the N—H⋯Cl hydrogen bonds (Fig. 3).

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1NA⋯Cl2	0.88 (5)	2.54 (5)	3.365 (2)	156 (5)
N1—H1NB⋯Cl2^i	0.89 (4)	2.81 (6)	3.472 (2)	133 (5)
N1—H1NB⋯Cl2^ii	0.89 (4)	2.77 (5)	3.365 (2)	126 (4)
Symmetry codes: (i) -x+1, -y, -z; (ii) x, -y, z.

Figure 2 A partial packing diagram of the title compound, showing the tape-like structure formed by N—H⋯Cl hydrogen bonds (dashed lines; see Table 1). Only one component is shown for the disordered cation. Displacement ellipsoids are drawn at the 50% probability level and H atoms, except those of the NH2 group, have been omitted. [Symmetry codes: (i) −x + 1, −y, −z; (ii) x, −y, z; (v) −x + 1, y, −z.]

Figure 3 A view along the c axis of the crystal packing of the title compound. The N—H⋯Cl hydrogen bonds (Table 1) are shown as dashed lines. Only one component of the disordered cation is shown.

Synthesis and crystallization

The title compound was prepared by adding pyrrolidine to a hydro­chloric acid solution of SnCl₄ according to the method described previously (Ishida et al., 2000). Single crystals suitable for X-ray diffraction were obtained from a concentrated hydro­chloric acid solution.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2.

Table 2
Experimental details

Crystal data
Chemical formula	(C4H10N)2[SnCl6]
Mr	475.67
Crystal system, space group	Monoclinic, C2/m
Temperature (K)	180
a, b, c (Å)	16.3784 (11), 7.3134 (3), 7.1566 (4)
β (°)	91.205 (2)
V (Å^3)	857.04 (8)
Z	2
Radiation type	Mo Kα
μ (mm^−1)	2.41
Crystal size (mm)	0.20 × 0.20 × 0.10
Data collection
Diffractometer	Rigaku R-AXIS RAPIDII
Absorption correction	Multi-scan (ABSCOR; Higashi, 1995)
Tmin, Tmax	0.579, 0.786
No. of measured, independent and observed [I > 2σ(I)] reflections	5281, 1343, 1308
Rint	0.038
(sin θ/λ)max (Å^−1)	0.704
Refinement
R[F^2 > 2σ(F^2)], wR(F^2), S	0.024, 0.057, 1.09
No. of reflections	1343
No. of parameters	68
No. of restraints	2
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å^−3)	0.54, −1.10
Computer programs: RAPID-AUTO (Rigaku, 2006), SHELXT2018/2 (Sheldrick, 2015a), SHELXL2018/3 (Sheldrick, 2015b), ORTEP-3 for Windows (Farrugia, 2012), CrystalStructure (Rigaku, 2018) and PLATON (Spek, 2009).

Structural data

Computing details

Data collection: RAPID-AUTO (Rigaku, 2006); cell refinement: RAPID-AUTO (Rigaku, 2006); data reduction: RAPID-AUTO (Rigaku, 2006); program(s) used to solve structure: SHELXT2018/2 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015b); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: CrystalStructure (Rigaku, 2018) and PLATON (Spek, 2009).

Bis(pyrrolidinium) hexachloridostannate

Crystal data

(C4H10N)2[SnCl6]	F(000) = 468.00
Mr = 475.67	Dx = 1.843 Mg m^−3
Monoclinic, C2/m	Mo Kα radiation, λ = 0.71075 Å
a = 16.3784 (11) Å	Cell parameters from 5181 reflections
b = 7.3134 (3) Å	θ = 3.1–30.0°
c = 7.1566 (4) Å	µ = 2.41 mm^−1
β = 91.205 (2)°	T = 180 K
V = 857.04 (8) Å^3	Platelet, colorless
Z = 2	0.20 × 0.20 × 0.10 mm

Data collection

Rigaku R-AXIS RAPIDII diffractometer	1308 reflections with I > 2σ(I)
Detector resolution: 10.000 pixels mm^-1	Rint = 0.038
ω scans	θmax = 30.0°, θmin = 3.1°
Absorption correction: multi-scan (ABSCOR; Higashi, 1995)	h = −22→22
Tmin = 0.579, Tmax = 0.786	k = −10→9
5281 measured reflections	l = −10→10
1343 independent reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.024	Hydrogen site location: mixed
wR(F^2) = 0.057	H atoms treated by a mixture of independent and constrained refinement
S = 1.09	w = 1/[σ^2(Fo^2) + (0.035P)^2 + 0.3195P] where P = (Fo^2 + 2Fc^2)/3
1343 reflections	(Δ/σ)max = 0.001
68 parameters	Δρmax = 0.54 e Å^−3
2 restraints	Δρmin = −1.10 e Å^−3

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	Occ. (<1)
Sn1	0.500000	0.500000	0.000000	0.02448 (8)
Cl1	0.61941 (4)	0.500000	0.20690 (9)	0.03911 (14)
Cl2	0.56208 (3)	0.26144 (5)	−0.18554 (6)	0.03335 (10)
N1	0.61485 (15)	0.000000	0.1846 (3)	0.0378 (5)
H1NA	0.590 (4)	0.082 (6)	0.113 (7)	0.057*	0.5
H1NB	0.595 (4)	−0.111 (5)	0.163 (7)	0.057*	0.5
C1	0.7040 (2)	−0.015 (5)	0.1454 (6)	0.054 (3)	0.5
H1A	0.718653	−0.141991	0.112102	0.065*	0.5
H1B	0.719081	0.067232	0.041717	0.065*	0.5
C2	0.7455 (2)	0.0412 (6)	0.3229 (7)	0.0512 (12)	0.5
H2A	0.750038	0.175930	0.331790	0.061*	0.5
H2B	0.800714	−0.013262	0.334683	0.061*	0.5
C3	0.6886 (2)	−0.0348 (6)	0.4717 (5)	0.0419 (13)	0.5
H3A	0.694280	−0.169065	0.484205	0.050*	0.5
H3B	0.699197	0.023171	0.594843	0.050*	0.5
C4	0.60557 (18)	0.017 (3)	0.3925 (4)	0.034 (3)	0.5
H4A	0.562866	−0.066758	0.437619	0.041*	0.5
H4B	0.591198	0.143984	0.427417	0.041*	0.5

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sn1	0.02747 (11)	0.01710 (11)	0.02918 (12)	0.000	0.00770 (7)	0.000
Cl1	0.0362 (3)	0.0386 (3)	0.0423 (3)	0.000	−0.0047 (2)	0.000
Cl2	0.0398 (2)	0.02416 (18)	0.0366 (2)	0.00185 (14)	0.01405 (15)	−0.00506 (14)
N1	0.0375 (11)	0.0426 (12)	0.0334 (10)	0.000	0.0050 (8)	0.000
C1	0.0469 (16)	0.059 (10)	0.0573 (18)	0.002 (4)	0.0289 (14)	−0.009 (6)
C2	0.0279 (14)	0.047 (3)	0.079 (3)	−0.0078 (14)	0.0107 (15)	−0.0076 (19)
C3	0.0323 (14)	0.044 (4)	0.0490 (16)	0.0022 (14)	−0.0033 (12)	0.0092 (16)
C4	0.0279 (11)	0.044 (8)	0.0313 (10)	0.006 (3)	0.0072 (8)	0.004 (2)

Geometric parameters (Å, º)

Sn1—Cl1^i	2.4281 (6)	C1—H1A	0.9900
Sn1—Cl1	2.4281 (6)	C1—H1B	0.9900
Sn1—Cl2	2.4285 (4)	C2—C3	1.534 (5)
Sn1—Cl2^i	2.4285 (4)	C2—H2A	0.9900
Sn1—Cl2^ii	2.4285 (4)	C2—H2B	0.9900
Sn1—Cl2^iii	2.4285 (4)	C3—C4	1.512 (8)
N1—C1	1.497 (5)	C3—H3A	0.9900
N1—C4	1.504 (4)	C3—H3B	0.9900
N1—H1NA	0.883 (19)	C4—H4A	0.9900
N1—H1NB	0.89 (2)	C4—H4B	0.9900
C1—C2	1.486 (12)
Cl1^i—Sn1—Cl1	180.0	N1—C1—H1A	110.9
Cl1^i—Sn1—Cl2	90.439 (16)	C2—C1—H1B	110.9
Cl1—Sn1—Cl2	89.560 (16)	N1—C1—H1B	110.9
Cl1^i—Sn1—Cl2^i	89.561 (16)	H1A—C1—H1B	108.9
Cl1—Sn1—Cl2^i	90.440 (16)	C1—C2—C3	102.7 (7)
Cl2—Sn1—Cl2^i	180.000 (18)	C1—C2—H2A	111.2
Cl1^i—Sn1—Cl2^ii	89.561 (16)	C3—C2—H2A	111.2
Cl1—Sn1—Cl2^ii	90.440 (16)	C1—C2—H2B	111.2
Cl2—Sn1—Cl2^ii	88.151 (19)	C3—C2—H2B	111.2
Cl2^i—Sn1—Cl2^ii	91.849 (19)	H2A—C2—H2B	109.1
Cl1^i—Sn1—Cl2^iii	90.439 (16)	C4—C3—C2	101.7 (5)
Cl1—Sn1—Cl2^iii	89.560 (16)	C4—C3—H3A	111.4
Cl2—Sn1—Cl2^iii	91.849 (19)	C2—C3—H3A	111.4
Cl2^i—Sn1—Cl2^iii	88.151 (19)	C4—C3—H3B	111.4
Cl2^ii—Sn1—Cl2^iii	180.000 (13)	C2—C3—H3B	111.4
C1—N1—C4	108.1 (3)	H3A—C3—H3B	109.3
C1—N1—H1NA	112 (5)	N1—C4—C3	104.0 (5)
C4—N1—H1NA	118 (4)	N1—C4—H4A	111.0
C1—N1—H1NB	105 (5)	C3—C4—H4A	111.0
C4—N1—H1NB	102 (4)	N1—C4—H4B	111.0
H1NA—N1—H1NB	110 (4)	C3—C4—H4B	111.0
C2—C1—N1	104.5 (7)	H4A—C4—H4B	109.0
C2—C1—H1A	110.9
C4—N1—C1—C2	−14 (2)	C1—N1—C4—C3	−13 (2)
N1—C1—C2—C3	36 (2)	C2—C3—C4—N1	34.7 (13)
C1—C2—C3—C4	−43.9 (15)

Symmetry codes: (i) −x+1, −y+1, −z; (ii) −x+1, y, −z; (iii) x, −y+1, z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1NA···Cl2	0.88 (5)	2.54 (5)	3.365 (2)	156 (5)
N1—H1NB···Cl2^iv	0.89 (4)	2.81 (6)	3.472 (2)	133 (5)
N1—H1NB···Cl2^v	0.89 (4)	2.77 (5)	3.365 (2)	126 (4)

Symmetry codes: (iv) −x+1, −y, −z; (v) x, −y, z.