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.

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.

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 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’ RMX 3 perovskites containing organic cations and MX 3 (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 C4H12N2 2+ 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 RMX 2 and totally different crystal structures to RMX 3 hybrid perovskites.

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,  − z; (ii) x − 1, y,  − 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,  − 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) .

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) .

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—Cs1iv = 78.17 (2) in (I); Rb1—Br1—Rb1iv = 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.

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).

Figure 2

Detail of the structure of (I) showing the hydrogen-bonding environment of the C4H11N2 + cation; symmetry codes: (i) x, y,  − z; (ii) x + 1, y, z; (iii) ; (iv) .

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⋯Br2iv	0.95 (4)	3.07 (3)	3.756 (2)	130 (1)

Symmetry codes: (ii) ; (iii) ; (iv) .

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⋯Br2iv	0.94	3.07	3.762 (3)	131

Symmetry codes: (ii) ; (iii) ; (iv) .

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,  − y, −z and x,  − y,  + 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.

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 C4H12N2 2+ species occurs in several hybrid RMX 3 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 ▸).

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 C4H12N2 2+ cations.

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, P b c m	Orthorhombic, P b c m
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[F 2 > 2σ(F 2)], wR(F 2), 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
Δρmax, Δρmin (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 ▸).

Crystal structure: contains datablock(s) I, II, global. DOI: 10.1107/S2056989019010375/su5506sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989019010375/su5506Isup2.hkl

Structure factors: contains datablock(s) II. DOI: 10.1107/S2056989019010375/su5506IIsup3.hkl

CCDC references: 1941895, 1941894

Additional supporting information: crystallographic information; 3D view; checkCIF report

(C4H11N2)[CsBr2]	Dx = 2.573 Mg m−3
Mr = 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

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

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(Fo2) + (0.0387P)2] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.055	(Δ/σ)max = 0.001
S = 1.10	Δρmax = 1.34 e Å−3
959 reflections	Δρmin = −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

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.

	x	y	z	Uiso*/Ueq
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*

	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

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—Cs1iv	78.173 (17)	C1—N1—H2N	110.7 (13)
Cs1iv—Br2—Cs1v	100.865 (16)	C1iii—N1—H2N	110.7 (13)
Cs1iv—Br2—Cs1vi	178.768 (8)	H1N—N1—H2N	101 (3)
Cs1v—Br2—Cs1vi	80.367 (13)	C2iii—N2—C2	110.5 (3)
Cs1iv—Br2—Cs1	80.366 (13)	C2iii—N2—H3N	111.4 (10)
Cs1v—Br2—Cs1	178.768 (8)	C2—N2—H3N	111.4 (10)
Cs1vi—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)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1N···N2iv	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···Br2vii	0.95 (4)	3.07 (3)	3.756 (2)	130 (1)
N2—H3N···Br2viii	0.95 (4)	3.07 (3)	3.756 (2)	130 (1)

(C4H11N2)[RbBr2]	Dx = 2.378 Mg m−3
Mr = 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

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

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(Fo2) + (0.036P)2] where P = (Fo2 + 2Fc2)/3
S = 0.94	(Δ/σ)max < 0.001
908 reflections	Δρmax = 0.74 e Å−3
48 parameters	Δρmin = −0.47 e Å−3
0 restraints

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.

	x	y	z	Uiso*/Ueq
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*

	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

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—Rb1iv	79.21 (3)	C1—N1—H2N	109.5
Rb1iv—Br2—Rb1v	100.02 (3)	C1iii—N1—H2N	109.5
Rb1iv—Br2—Rb1vi	179.021 (14)	H1N—N1—H2N	108.1
Rb1v—Br2—Rb1vi	80.96 (2)	C2—N2—C2iii	109.8 (4)
Rb1iv—Br2—Rb1	80.96 (2)	C2—N2—H3N	111.4
Rb1v—Br2—Rb1	179.021 (14)	C2iii—N2—H3N	111.4
Rb1vi—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)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H2N···N2iv	0.91	1.92	2.825 (6)	179
N1—H1N···Br1	0.91	2.40	3.300 (4)	171
N2—H3N···Br2vii	0.94	3.07	3.762 (3)	131
N2—H3N···Br2viii	0.94	3.07	3.762 (3)	131