Syntheses and structures of piperazin-1-ium ABr2 (A = Cs or Rb): hybrid solids containing `curtain wall' layers of face- and edge-sharing ABr6 trigonal prisms

Rickaby, K.A.; Slawin, A.M.Z.; Harrison, W.T.A.

doi:10.1107/S2056989019010375

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Volume 75| Part 8| August 2019| Pages 1249-1252

https://doi.org/10.1107/S2056989019010375

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Syntheses and structures of piperazin-1-ium ABr₂ (A = Cs or Rb): hybrid solids containing `curtain wall' layers of face- and edge-sharing ABr₆ trigonal prisms

Kirstie A. Rickaby,^a Alexandra M. Z. Slawin ^b and William T. A. Harrison ^a ^*

^aDepartment of Chemistry, University of Aberdeen, Meston Walk, Aberdeen AB24 3UE, Scotland, and ^bDepartment of Chemistry, University of St Andrews, St Andrews KY16 9ST, Scotland
^*Correspondence e-mail: w.harrison@abdn.ac.uk

Edited by H. Stoeckli-Evans, University of Neuchâtel, Switzerland (Received 17 July 2019; accepted 20 July 2019; online 26 July 2019)

The isostructural title compounds, poly[piperazin-1-ium [di-μ-bromido-caesium]], {(C₄H₁₁N₂)[CsBr₂]}_n, and poly[piperazin-1-ium [di-μ-bromido-rubidium]], {(C₄H₁₁N₂)[RbBr₂]}_n, contain singly-protonated piperazin-1-ium cations and unusual ABr₆ (A = Cs or Rb) trigonal prisms. The prisms are linked into a distinctive `curtain wall' arrangement propagating in the (010) plane by face and edge sharing. In each case, a network of N—H⋯N, N—H⋯Br and N—H⋯(Br,Br) hydrogen bonds consolidates the structure.

Keywords: crystal structure; hybrid solid; caesium; rubidium; trigonal prism.

CCDC references: 1941895; 1941894

1. Chemical context

Oxide perovskites of generic formula ABO₃, where A and B are metal ions, have been studied for decades because of their physical properties and structural variety (Tilley, 2016 ). The aristotype (highest-possible symmetry) for this familiar structure type is a cubic network (space group Pm $[\overline{3}]$ m) of vertex-sharing, regular, BO₆ octahedra encapsulating the A cations in 12-coordinate cavities bounded by eight octahedra, but lower symmetry structures are very common (Woodward, 1997 ). More recently, `hybrid' RMX₃ perovskites containing organic cations and MX₃ (M = Pb, Sn…; X = halide ion) octahedral networks have attracted intense interest because of their remarkable photophysical properties (Xu et al., 2019 ; Stylianakis et al., 2019 ; Zuo et al., 2019 ). A number of different organic cations occur in these hybrid structures, one of which is the doubly protonated C₄H₁₂N₂²⁺ piperizinium (or piperazin-1,4-diium) ion as found in the C₄H₁₂N₂·ACl₃·H₂O (A = K, Rb, Cs) family (Paton & Harrison, 2010 ) and C₄H₁₂N₂·NaI₃ (Chen et al., 2018 ).

As an extension of these studies, we now describe the title hybrid compounds, containing the singly protonated C₄H₁₁N₂⁺ piperazin-1-ium cation, which have a generic formula of RMX₂ and totally different crystal structures to RMX₃ hybrid perovskites.

2. Structural commentary

Compounds (I) and (II) are isostructural and crystallize in the orthorhombic space group Pbcm. The smaller unit-cell volume (by 5.3%) of (II) presumably reflects the smaller ionic radius (Shannon, 1976 ) of the Rb⁺ cation (r = 1.66 Å) compared to Cs⁺ (r = 1.81 Å). This structure description will focus on (I) and note significant differences for (II) where applicable.

The asymmetric unit of (I) consists of two methylene groups, an NH group and an NH₂⁺ group; both nitrogen atoms and their attached H atoms lie on a (001) crystallographic mirror plan (at z = 1/4 for the asymmetric atoms). The structure is completed by a caesium atom [site symmetry m(001), Wyckoff site 4d] and two bromine atoms: Br1 [m(001); 4d] and Br2 (2[100]; 4c). The structure of (I) is shown in (Fig. 1).

Figure 1
The asymmetric unit of (I)

showing 50% displacement ellipsoids expanded to show the complete organic cation and the caesium coordination polyhedron. The N—H⋯Br hydrogen bond is shown as a double-dashed line. The purple lines linking the bromine atoms emphasize the trigonal–prismatic shape of the CsBr₆ polyhedron. Symmetry codes: (i) x, y, $[{1\over 2}]$ − z; (ii) x − 1, y, $[{1\over 2}]$ − z; (iii) x − 1, y, z.

The complete C₄H₁₁N₂⁺ cation is generated by reflection to result in a typical (Brüning et al., 2009 ) chair conformation for the ring: N1 and N2 deviate from the mean plane of C1/C2/C1ⁱ/C2ⁱ [symmetry code: (i) x, y, $[{1\over 2}]$ − z] by 0.656 (5) and −0.682 (4) Å, respectively. The H atom of the neutral N2—H3N group has an equatorial orientation with respect to the ring.

The caesium coordination polyhedron in (I) is completed by crystal symmetry, resulting in a distinctive CsBr₆ trigonal prism (Fig. 1): the prism has longitudinal (001) mirror symmetry, with the Br1 atoms and the metal atom lying on the mirror. The mean Cs—Br bond length based on four distinct Cs—Br bonds (Table 1) is 3.573 Å [mean Rb—Br bond length for (II) = 3.461 Å; Table 2]. These data may be compared with the shortest Cs—Br separation of 3.716 Å in CsBr (8-coordinate caesium chloride structure) and the shortest Rb—Br separation of 3.427 Å in RbBr (6-coordinate rocksalt structure).

Table 1
Selected bond lengths (Å) for (I)

Cs1—Br2ⁱⁱⁱ	3.5157 (5)	Cs1—Br1	3.6228 (6)
Cs1—Br2	3.5801 (5)	Cs1—Br1ⁱⁱⁱ	3.6392 (7)
Symmetry code: (iii) x-1, y, z.

Table 2
Selected bond lengths (Å) for (II)

Rb1—Br2ⁱⁱⁱ	3.4157 (8)	Rb1—Br1	3.5013 (9)
Rb1—Br2	3.4659 (8)	Rb1—Br1ⁱⁱⁱ	3.5068 (9)
Symmetry code: (iii) x-1, y, z.

In (I), the prism ends (Br1/Br2/Br2ⁱ and Br1ⁱⁱⁱ/Br2ⁱⁱ/Br2ⁱⁱⁱ; see Fig. 1 for symmetry codes) are parallel by symmetry and separated by 4.5787 (8) Å, i.e., the a unit-cell parameter, hence there is no twisting of the end faces and the Br⋯Br⋯Br angles vary from 56.65 (1)–61.68 (1)° [the equivalent prism-end separation for (II) is 4.4675 (13) Å]. The caesium cation in (I) is not quite equidistant from the prism-ends mentioned in the previous sentence, being displaced from them by 2.3177 (6) and 2.2605 (5) Å, respectively. The equivalent data for the Rb atom in (II) are 2.2581 (9) and 2.2091 (9) Å, respectively. The bond-valence sum (BVS) for Cs1 (in valence units) using the formalism of Brese & O'Keeffe (1991 ) in (I) is 1.12 and the equivalent value for Rb1 in (II) is 0.95 (expected value in both cases = 1.00). This indicates that the bond valences of these cations are satisfied without notable underbonding or overbonding in these unusual coordination environments.

It may be finally noted that the bromide ions have very different coordination environments: Br1 bridges to two metal atoms [Cs1—Br1—Cs1^iv = 78.17 (2) in (I); Rb1—Br1—Rb1^iv = 79.21 (3)° in (II); symmetry code: (iv) x + 1, y, z] whereas Br2 has an unusual distorted square planar BrCs₄ arrangement: the cis Cs—Br2—Cs bond angles in (I) vary between 80.367 (13) and 100.865 (16)°; the five atoms are exactly co-planar by symmetry.

3. Supramolecular features

The extended structure of (I) is consolidated by hydrogen bonds (Fig. 2, Table 3. The N1—H1N⋯N2 bond from the protonated NH₂⁺ group to the unprotonated N atom in an adjacent molecule links the organic cations into [100] chains with adjacent cations related by translation symmetry and the N1—H2N⋯Br1 bond connects the organic cation to the inorganic network. The neutral N2—H3N moiety forms a bifurcated N—H⋯(Br2,Br2) hydrogen bond; the H⋯Br contacts are long at 3.07 (3) Å but given their apparent role in bridging the (010) CsBr₂ layers we judge them to be structurally significant. The hydrogen-bonding scheme for (II) (Table 4) is almost identical to that in (I).

Table 3
Hydrogen-bond geometry (Å, °) for (I)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1N⋯N2ⁱⁱ	0.92 (4)	1.95 (4)	2.868 (4)	179 (3)
N1—H2N⋯Br1	0.84 (4)	2.45 (4)	3.284 (3)	174 (4)
N2—H3N⋯Br2ⁱⁱⁱ	0.95 (4)	3.07 (3)	3.756 (2)	130 (1)
N2—H3N⋯Br2^iv	0.95 (4)	3.07 (3)	3.756 (2)	130 (1)
Symmetry codes: (ii) x+1, y, z; (iii) $[-x, -y+1, z+{\script{1\over 2}}]$ ; (iv) -x, -y+1, -z.

Table 4
Hydrogen-bond geometry (Å, °) for (II)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H2N⋯N2ⁱⁱ	0.91	1.92	2.825 (6)	179
N1—H1N⋯Br1	0.91	2.40	3.300 (4)	171
N2—H3N⋯Br2ⁱⁱⁱ	0.94	3.07	3.762 (3)	131
N2—H3N⋯Br2^iv	0.94	3.07	3.762 (3)	131
Symmetry codes: (ii) x+1, y, z; (iii) $[-x, -y+1, z+{\script{1\over 2}}]$ ; (iv) -x, -y+1, -z.

Figure 2
Detail of the structure of (I)

showing the hydrogen-bonding environment of the C₄H₁₁N₂⁺ cation; symmetry codes: (i) x, y, $[{1\over 2}]$ − z; (ii) x + 1, y, z; (iii) $[-x, -y+1, z+{\script{1\over 2}}]$ ; (iv) -x, -y+1, -z.

The CsBr₆ prisms in (I) are linked into a striking (010) `curtain wall' arrangement (Fig. 3) by face sharing in the [100] direction and edge sharing (via a pair of Br2 atoms) in the [001] direction; the Cs⋯Cs separation through the prism-ends is 4.5787 (8) Å (by the symmetry operations x + 1, y, z and x − 1, y, z) and the separation between metal ions in adjacent columns is 5.42014 (12) Å (symmetry operations x, $[{1\over 2}]$ − y, −z and x, $[{1\over 2}]$ − y, $[{1\over 2}]$ + z). The equivalent data for the Rb atoms in (II) are 4.4675 (13) and 5.2338 (14) Å, respectively. When viewed down [100], the prisms adopt a `saw-tooth' arrangement with respect to the [010] direction, with alternating columns of prisms pointing `up' and `down' (Fig. 4).

Figure 3
Polyhedral view of part of an (010) layer of CsBr₆ trigonal prisms in (I)

Figure 4
The unit-cell packing in (I)

viewed down [100]. Note the `saw-tooth' arrangement of stacks of CsBr₆ prisms with respect to the [001] direction.

4. Database survey

So far as we are aware, the RABr₂ topology of the title compounds is a novel one. A search of the Cambridge Structural Database (CSD, version 5.40, last update 19 May 2019; Groom et al., 2016 ) for the mono-protonated C₄H₁₁N₂⁺ cation returned 55 crystal structures but none of them bear a close resemblance to the title compound. As noted in the chemical context section, the doubly protonated C₄H₁₂N₂²⁺ species occurs in several hybrid RMX₃ perovskites including C₄H₁₂N₂·ACl₃·H₂O with A = K (CSD refcode GUYMIX), Rb (GUYMOD) and Cs (GUYMUJ) (Paton & Harrison, 2010) and C₄H₁₂N₂·NaI₃ (MEXMAG; Chen et al., 2018).

5. Synthesis and crystallization

Compound (I) was prepared by adding 0.213 g (1.0 mmol) of CsBr and 0.086 g (1.0 mmol) of piperazine to 11.0 ml (1.1 mmol) of a 0.1 M HBr solution in a Petri dish to result in a clear solution. Colourless rods of (I) formed after a few days as the water evaporated. Colourless rods of (II) were prepared in the same way, with 0.165 g (1.0 mmol) of RbBr replacing the CsBr. The quantity of acid appears to be critical to the syntheses of (I) and (II): smaller amounts lead to recrystallized CsBr and RbBr and larger amounts lead to different structures containing doubly protonated C₄H₁₂N₂²⁺ cations.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 5. The N-bonded H atoms were located in difference-Fourier maps: for (I), their positions were freely refined, for (II) they were refined as riding atoms in their as-found relative positions. The C-bound H atoms were placed geometrically (C—H = 0.99 Å) and refined as riding atoms for both structures. The constraint U_iso(H) = 1.2U_eq(carrier) was applied in all cases. The displacement ellipsoids for the C and N atoms in (II) refined to somewhat elongated shapes suggestive of positional disorder of the C₄H₁₁N₂⁺ cations but attempts to model this did not lead to a significant improvement in fit.

Table 5
Experimental details

	(I)	(II)
Crystal data
Chemical formula	(C₄H₁₁N₂)[CsBr₂]	(C₄H₁₁N₂)[RbBr₂]
M_r	379.88	332.44
Crystal system, space group	Orthorhombic, Pbcm	Orthorhombic, Pbcm
Temperature (K)	93	93
a, b, c (Å)	4.5787 (8), 23.325 (5), 9.1828 (17)	4.4675 (13), 23.036 (7), 9.021 (3)
V (Å³)	980.7 (3)	928.4 (5)
Z	4	4
Radiation type	Mo Kα	Mo Kα
μ (mm⁻¹)	11.86	13.87
Crystal size (mm)	0.20 × 0.05 × 0.05	0.20 × 0.05 × 0.05

Data collection
Diffractometer	Rigaku Pilatus 200K CCD	Rigaku Pilatus 200K CCD
Absorption correction	Multi-scan (CrystalClear; Rigaku, 2013 )	Multi-scan (CrystalClear; Rigaku, 2013)
T_min, T_max	0.639, 1.000	0.597, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	11592, 959, 917	11351, 908, 771
R_int	0.056	0.086
(sin θ/λ)_max (Å⁻¹)	0.603	0.602

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.021, 0.055, 1.10	0.023, 0.057, 0.94
No. of reflections	959	908
No. of parameters	55	48
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	1.34, −0.96	0.74, −0.47
Computer programs: CrystalClear (Rigaku, 2013), SHELXS97 (Sheldrick, 2008 ), SHELXL2018 (Sheldrick, 2015 ), ORTEP-3 for Windows (Farrugia, 2012 ), ATOMS (Shape Software, 2005 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC references: 1941895; 1941894

Crystal structure: contains datablocks I, II, global. DOI: https://doi.org/10.1107/S2056989019010375/su5506sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989019010375/su5506Isup2.hkl

Structure factors: contains datablock II. DOI: https://doi.org/10.1107/S2056989019010375/su5506IIsup3.hkl

checkCIF report

Computing details top

For both structures, data collection: CrystalClear (Rigaku, 2013); cell refinement: CrystalClear (Rigaku, 2013); data reduction: CrystalClear (Rigaku, 2013); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2018 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and ATOMS (Shape Software, 2005); software used to prepare material for publication: publCIF (Westrip, 2010).

Poly[piperazin-1-ium [di-µ-bromido-caesium]] (I) top

Crystal data top

(C₄H₁₁N₂)[CsBr₂]	D_x = 2.573 Mg m⁻³
M_r = 379.88	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbcm	Cell parameters from 3076 reflections
a = 4.5787 (8) Å	θ = 2.8–27.5°
b = 23.325 (5) Å	µ = 11.86 mm⁻¹
c = 9.1828 (17) Å	T = 93 K
V = 980.7 (3) Å³	Rod, colourless
Z = 4	0.20 × 0.05 × 0.05 mm
F(000) = 696

Data collection top

Rigaku Pilatus 200K CCD diffractometer	917 reflections with I > 2σ(I)
Radiation source: rotating anode	R_int = 0.056
ω scans	θ_max = 25.4°, θ_min = 3.5°
Absorption correction: multi-scan (CrystalClear; Rigaku, 2013)	h = −5→5
T_min = 0.639, T_max = 1.000	k = −28→28
11592 measured reflections	l = −11→11
959 independent reflections

Refinement top

Refinement on F²	Hydrogen site location: mixed
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F² > 2σ(F²)] = 0.021	w = 1/[σ²(F_o²) + (0.0387P)²] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.055	(Δ/σ)_max = 0.001
S = 1.10	Δρ_max = 1.34 e Å⁻³
959 reflections	Δρ_min = −0.96 e Å⁻³
55 parameters	Extinction correction: SHELXL2018 (Sheldrick, 2015), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0010 (2)
Primary atom site location: structure-invariant direct methods

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

	x	y	z	U_iso*/U_eq
Cs1	0.02411 (5)	0.31176 (2)	0.250000	0.01125 (13)
Br1	0.52127 (7)	0.43259 (2)	0.250000	0.01635 (15)
Br2	0.53501 (7)	0.250000	0.000000	0.01654 (16)
C1	−0.0049 (5)	0.56445 (11)	0.3834 (4)	0.0205 (7)
H1A	0.120469	0.560779	0.470727	0.025*
H1B	−0.158445	0.534633	0.388670	0.025*
C2	−0.1448 (6)	0.62308 (9)	0.3811 (2)	0.0209 (5)
H2A	−0.267978	0.628079	0.468749	0.025*
H2B	0.008673	0.652975	0.382326	0.025*
N1	0.1740 (7)	0.55578 (12)	0.250000	0.0217 (7)
H1N	0.336 (9)	0.5788 (16)	0.250000	0.026*
H2N	0.251 (8)	0.5231 (17)	0.250000	0.026*
N2	−0.3243 (7)	0.62943 (11)	0.250000	0.0186 (6)
H3N	−0.427 (7)	0.6650 (19)	0.250000	0.022*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cs1	0.01245 (18)	0.00867 (18)	0.01263 (18)	−0.00053 (6)	0.000	0.000
Br1	0.0165 (2)	0.0071 (2)	0.0255 (3)	0.00065 (10)	0.000	0.000
Br2	0.0141 (2)	0.0171 (2)	0.0185 (2)	0.000	0.000	−0.00791 (13)
C1	0.0259 (16)	0.0170 (17)	0.0187 (19)	−0.0048 (8)	−0.0058 (9)	0.0063 (10)
C2	0.0238 (15)	0.0173 (11)	0.0216 (12)	−0.0030 (10)	0.0029 (12)	−0.0062 (9)
N1	0.0218 (19)	0.0067 (14)	0.0367 (16)	0.0036 (12)	0.000	0.000
N2	0.0182 (16)	0.0104 (14)	0.0272 (14)	0.0037 (11)	0.000	0.000

Geometric parameters (Å, º) top

Cs1—Br2ⁱ	3.5157 (5)	C1—H1A	0.9900
Cs1—Br2ⁱⁱ	3.5157 (4)	C1—H1B	0.9900
Cs1—Br2ⁱⁱⁱ	3.5801 (5)	C2—N2	1.465 (3)
Cs1—Br2	3.5801 (5)	C2—H2A	0.9900
Cs1—Br1	3.6228 (6)	C2—H2B	0.9900
Cs1—Br1ⁱ	3.6392 (7)	N1—H1N	0.92 (4)
C1—N1	1.488 (4)	N1—H2N	0.84 (4)
C1—C2	1.510 (3)	N2—H3N	0.95 (4)

Br2ⁱ—Cs1—Br2ⁱⁱ	81.534 (14)	N1—C1—C2	110.2 (2)
Br2ⁱ—Cs1—Br2ⁱⁱⁱ	132.072 (12)	N1—C1—H1A	109.6
Br2ⁱⁱ—Cs1—Br2ⁱⁱⁱ	80.366 (13)	C2—C1—H1A	109.6
Br2ⁱ—Cs1—Br2	80.366 (12)	N1—C1—H1B	109.6
Br2ⁱⁱ—Cs1—Br2	132.072 (12)	C2—C1—H1B	109.6
Br2ⁱⁱⁱ—Cs1—Br2	79.768 (14)	H1A—C1—H1B	108.1
Br2ⁱ—Cs1—Br1	135.970 (7)	N2—C2—C1	110.0 (2)
Br2ⁱⁱ—Cs1—Br1	135.970 (7)	N2—C2—H2A	109.7
Br2ⁱⁱⁱ—Cs1—Br1	84.402 (12)	C1—C2—H2A	109.7
Br2—Cs1—Br1	84.401 (13)	N2—C2—H2B	109.7
Br2ⁱ—Cs1—Br1ⁱ	85.085 (12)	C1—C2—H2B	109.7
Br2ⁱⁱ—Cs1—Br1ⁱ	85.085 (13)	H2A—C2—H2B	108.2
Br2ⁱⁱⁱ—Cs1—Br1ⁱ	136.466 (7)	C1—N1—C1ⁱⁱⁱ	110.9 (3)
Br2—Cs1—Br1ⁱ	136.466 (7)	C1—N1—H1N	111.5 (11)
Br1—Cs1—Br1ⁱ	78.173 (18)	C1ⁱⁱⁱ—N1—H1N	111.5 (11)
Cs1—Br1—Cs1^iv	78.173 (17)	C1—N1—H2N	110.7 (13)
Cs1^iv—Br2—Cs1^v	100.865 (16)	C1ⁱⁱⁱ—N1—H2N	110.7 (13)
Cs1^iv—Br2—Cs1^vi	178.768 (8)	H1N—N1—H2N	101 (3)
Cs1^v—Br2—Cs1^vi	80.367 (13)	C2ⁱⁱⁱ—N2—C2	110.5 (3)
Cs1^iv—Br2—Cs1	80.366 (13)	C2ⁱⁱⁱ—N2—H3N	111.4 (10)
Cs1^v—Br2—Cs1	178.768 (8)	C2—N2—H3N	111.4 (10)
Cs1^vi—Br2—Cs1	98.402 (15)

N1—C1—C2—N2	57.7 (3)	C1—C2—N2—C2ⁱⁱⁱ	−60.2 (3)
C2—C1—N1—C1ⁱⁱⁱ	−55.9 (3)

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

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1N···N2^iv	0.92 (4)	1.95 (4)	2.868 (4)	179 (3)
N1—H2N···Br1	0.84 (4)	2.45 (4)	3.284 (3)	174 (4)
N2—H3N···Br2^vii	0.95 (4)	3.07 (3)	3.756 (2)	130 (1)
N2—H3N···Br2^viii	0.95 (4)	3.07 (3)	3.756 (2)	130 (1)

Symmetry codes: (iv) x+1, y, z; (vii) −x, −y+1, z+1/2; (viii) −x, −y+1, −z.

Poly[piperazin-1-ium [di-µ-bromido-rubidium]] (II) top

Crystal data top

(C₄H₁₁N₂)[RbBr₂]	D_x = 2.378 Mg m⁻³
M_r = 332.44	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbcm	Cell parameters from 1939 reflections
a = 4.4675 (13) Å	θ = 2.9–27.5°
b = 23.036 (7) Å	µ = 13.87 mm⁻¹
c = 9.021 (3) Å	T = 93 K
V = 928.4 (5) Å³	Rod, colourless
Z = 4	0.20 × 0.05 × 0.05 mm
F(000) = 624

Data collection top

Rigaku Pilatus 200K CCD diffractometer	771 reflections with I > 2σ(I)
Radiation source: rotating anode	R_int = 0.086
ω scans	θ_max = 25.3°, θ_min = 2.9°
Absorption correction: multi-scan (CrystalClear; Rigaku, 2013)	h = −5→5
T_min = 0.597, T_max = 1.000	k = −27→25
11351 measured reflections	l = −10→10
908 independent reflections

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Hydrogen site location: mixed
R[F² > 2σ(F²)] = 0.023	H-atom parameters constrained
wR(F²) = 0.057	w = 1/[σ²(F_o²) + (0.036P)²] where P = (F_o² + 2F_c²)/3
S = 0.94	(Δ/σ)_max < 0.001
908 reflections	Δρ_max = 0.74 e Å⁻³
48 parameters	Δρ_min = −0.47 e Å⁻³
0 restraints

Special details top

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Rb1	0.02991 (9)	0.30763 (2)	0.250000	0.01411 (14)
Br1	0.52893 (9)	0.42482 (2)	0.250000	0.01792 (15)
Br2	0.53856 (10)	0.250000	0.000000	0.02184 (16)
C1	0.0103 (9)	0.56211 (19)	0.3859 (5)	0.0433 (13)
H1A	−0.150237	0.532584	0.391919	0.052*
H1B	0.138441	0.558250	0.474894	0.052*
C2	−0.1233 (9)	0.62095 (17)	0.3812 (4)	0.0371 (10)
H2A	−0.247265	0.627233	0.470786	0.045*
H2B	0.037661	0.650481	0.380468	0.045*
N1	0.1926 (10)	0.55235 (19)	0.250000	0.0490 (17)
H1N	0.264148	0.515363	0.250000	0.059*
H2N	0.351831	0.577000	0.250001	0.059*
N2	−0.3067 (9)	0.62729 (18)	0.250000	0.0358 (12)
H3N	−0.409568	0.662828	0.250000	0.043*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Rb1	0.0154 (2)	0.0163 (3)	0.0106 (2)	−0.00032 (16)	0.000	0.000
Br1	0.0178 (3)	0.0145 (3)	0.0215 (3)	0.00069 (17)	0.000	0.000
Br2	0.0161 (3)	0.0330 (3)	0.0165 (3)	0.000	0.000	−0.01151 (19)
C1	0.050 (3)	0.045 (3)	0.035 (2)	−0.027 (2)	−0.031 (2)	0.024 (2)
C2	0.047 (2)	0.038 (2)	0.027 (2)	−0.024 (2)	0.020 (2)	−0.0183 (18)
N1	0.018 (2)	0.010 (2)	0.118 (6)	0.0018 (18)	0.000	0.000
N2	0.020 (2)	0.018 (2)	0.070 (4)	0.0028 (18)	0.000	0.000

Geometric parameters (Å, º) top

Rb1—Br2ⁱ	3.4157 (8)	C1—H1A	0.9900
Rb1—Br2ⁱⁱ	3.4157 (8)	C1—H1B	0.9900
Rb1—Br2	3.4659 (8)	C2—N2	1.447 (5)
Rb1—Br2ⁱⁱⁱ	3.4659 (8)	C2—H2A	0.9900
Rb1—Br1	3.5013 (9)	C2—H2B	0.9900
Rb1—Br1ⁱ	3.5068 (9)	N1—H1N	0.9100
C1—C2	1.482 (6)	N1—H2N	0.9100
C1—N1	1.489 (5)	N2—H3N	0.9389

Br2ⁱ—Rb1—Br2ⁱⁱ	82.64 (3)	C2—C1—N1	109.6 (3)
Br2ⁱ—Rb1—Br2	80.96 (2)	C2—C1—H1A	109.8
Br2ⁱⁱ—Rb1—Br2	134.60 (2)	N1—C1—H1A	109.8
Br2ⁱ—Rb1—Br2ⁱⁱⁱ	134.60 (2)	C2—C1—H1B	109.8
Br2ⁱⁱ—Rb1—Br2ⁱⁱⁱ	80.96 (2)	N1—C1—H1B	109.8
Br2—Rb1—Br2ⁱⁱⁱ	81.19 (3)	H1A—C1—H1B	108.2
Br2ⁱ—Rb1—Br1	135.144 (12)	N2—C2—C1	110.1 (3)
Br2ⁱⁱ—Rb1—Br1	135.143 (12)	N2—C2—H2A	109.6
Br2—Rb1—Br1	82.98 (2)	C1—C2—H2A	109.6
Br2ⁱⁱⁱ—Rb1—Br1	82.984 (19)	N2—C2—H2B	109.6
Br2ⁱ—Rb1—Br1ⁱ	83.63 (2)	C1—C2—H2B	109.6
Br2ⁱⁱ—Rb1—Br1ⁱ	83.63 (2)	H2A—C2—H2B	108.2
Br2—Rb1—Br1ⁱ	135.505 (12)	C1—N1—C1ⁱⁱⁱ	110.8 (4)
Br2ⁱⁱⁱ—Rb1—Br1ⁱ	135.505 (13)	C1—N1—H1N	109.5
Br1—Rb1—Br1ⁱ	79.21 (3)	C1ⁱⁱⁱ—N1—H1N	109.5
Rb1—Br1—Rb1^iv	79.21 (3)	C1—N1—H2N	109.5
Rb1^iv—Br2—Rb1^v	100.02 (3)	C1ⁱⁱⁱ—N1—H2N	109.5
Rb1^iv—Br2—Rb1^vi	179.021 (14)	H1N—N1—H2N	108.1
Rb1^v—Br2—Rb1^vi	80.96 (2)	C2—N2—C2ⁱⁱⁱ	109.8 (4)
Rb1^iv—Br2—Rb1	80.96 (2)	C2—N2—H3N	111.4
Rb1^v—Br2—Rb1	179.021 (14)	C2ⁱⁱⁱ—N2—H3N	111.4
Rb1^vi—Br2—Rb1	98.06 (3)

N1—C1—C2—N2	58.4 (4)	C1—C2—N2—C2ⁱⁱⁱ	−62.1 (5)
C2—C1—N1—C1ⁱⁱⁱ	−55.3 (5)

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

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H2N···N2^iv	0.91	1.92	2.825 (6)	179
N1—H1N···Br1	0.91	2.40	3.300 (4)	171
N2—H3N···Br2^vii	0.94	3.07	3.762 (3)	131
N2—H3N···Br2^viii	0.94	3.07	3.762 (3)	131

Symmetry codes: (iv) x+1, y, z; (vii) −x, −y+1, z+1/2; (viii) −x, −y+1, −z.

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Volume 75| Part 8| August 2019| Pages 1249-1252

https://doi.org/10.1107/S2056989019010375

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