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A new polymorph of the title compound, (C8H20N2)[TlBr5], contains cations located about crystallographic centres of inversion and trigonal-bipyramidal anions which have a C2 axis passing through the equatorial plane of the anion. The anion has the least distorted geometry seen so far in any structure possessing this anion and the axial Tl-Br bonds are about 0.13 Å longer than the equatorial Tl-Br bonds, consistent with related structures. The anion in the initially reported polymorph has lower symmetry and a greater distortion of the trigonal-bipyramidal coordination.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270101019746/sk1524sup1.cif
Contains datablocks global, Ib

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270101019746/sk1524Ibsup2.hkl
Contains datablock Ib

CCDC reference: 180145

Comment top

The pentacoordinate [TlBr5]2- anion was characterized only recently as an almost regular trigonal-bipyramidal species in its 1,1,4,4-tetramethylpiperazinium, (I), and N,N'-diethyltriethylenediammonium salts (Linden, Nugent et al., 1999). In both cases, the Brax—Tl—Brax angles (ax is axial) were somewhat distorted from linearity and the Tl—Brax bond distances were quite asymmetric, but significantly longer than the Tl—Breq ones (eq is equatorial). Thus, the anion in these two compounds was shown to have a similar structure to that found for [FeCl5]2-, which also has a quaternized ammonium counter cation (James et al., 1995), but is different from the distorted square pyramidal [InCl5]2- anion found in its tetraethylammonium salt (Joy et al., 1975). During an evaluation of currently available commercial diffractometers having CCD detectors, data sets were collected from a series of crystals with known `difficult' structures (Linden, 1999). One of the compounds chosen was the title compound, (I). A crystal from the original batch was selected and found to exist as a different form, (Ib), to that found in the original structure determination (Ia; Linden, Nugent et al., 1999). It is unknown whether both forms existed simultaneously in the original batch at the time of crystallization, or if this second form evolved from the former structure during the three years that the original crystals were stored.

The original structure determination for the title compound found that the space group was P21/c with two symmetry-independent 1,1,4,4-tetramethylpiperazinium cations sitting across centres of inversion and one unique [TlBr5]2- anion on a general position. In contrast, polymorph (Ib) crystallizes in space group C2/c with one unique cation possessing crystallographic Ci symmetry and one unique anion with crystallographic C2 symmetry (Fig. 1). Although the unit-cell volumes of the two polymorphs are quite similar, as are the lengths of the b axes and the β angles, the lengths of the a and c axes show significant differences and no transformation matrix can be found which would interconvert the two unit cells, thus excluding the possibility that the lower symmetry polymorph was simply defined in the wrong space group.

The twofold axis through the [TlBr5]2- anion of (Ib) passes through the equatorial plane of the anion, one of the equatorial Br atoms and the Tl atom. As a result, both axial Tl—Br bonds are equal in length and the coordination geometry of the anion forms quite a regular trigonal bipyramid, although the symmetry does not constrain it to be a perfect one. Indeed, the axial Tl—Br bonds are slightly distorted from linear geometry by 2.968 (17)° (Table 1) and are also about 0.13 Å longer than the equatorial Tl—Br bonds.

The structures of just four other compounds containing almost regular trigonal-bipyramidal [TlBr5]2- anions are reported in the literature (Linden, Nugent et al., 1999; Linden et al., 2002; Reid et al., 1999), although other much more highly distorted [TlBr5]2- species are known (Linden, James et al., 1999; Linden et al., 2002). Of these four compounds, two possess [TlBr5]2- anions with crystallographic symmetry, namely C2 symmetry in the N,N'-diethyl-N,N,N',N'-tetramethyl-1,2-ethylenediammonium salt (etmeen; Linden et al., 2002) and C2v symmetry in the [Mn(15-crown-5)(H2O)2]2+ salt [Mn(crown); Reid et al., 1999]. The geometric parameters for each of these anions are included in Table 1 and show that the anion in (Ib) has the least distorted trigonal-bipyramidal geometry of the three structures. The Brax—Tl—Brax bonds in the anion of the etmeen salt show the greatest deviation from linearity [7.25 (6)°], although these distortions are still quite small. While the Tl—Br bond lengths in this latter salt are very similar to those of (Ib), the axial Tl—Br bonds in the Mn(crown) salt are significantly longer than in (Ib) and the equatorial bonds are correspondingly shorter, the difference between the axial and equatorial bond lengths now being about 0.34 Å.

The two reported structures in which the [TlBr5]2- anions do not possess any crystallographic symmetry are those of the first polymorph of the title compound, (Ia), and the N,N'-diethyltriethylenediammonium salt (Linden, Nugent et al., 1999). The Brax—Tl—Brax angles are distorted from linearity by 2.67 (4)° in (Ia), and by 10.3 (2) and 6.3 (2)° for the two symmetry-independent anions in the latter structure. Thus, the distortions from linearity are similar to those observed in (Ib) and the other structures in which the anions have crystallographic symmetry. The lengths of the equatorial Tl—Br bonds of these two compounds, being about 2.59 Å, are also similar to those of (Ib) and are shorter than the axial Tl—Br bonds, as expected. However, in contrast to (Ib) and the other symmetrical anions, the lengths of the axial Tl—Br bonds in these two compounds show distinct asymmetry. In (Ia), these distances are 2.840 (1) and 2.737 (1) Å, while for the N,N'-diethyltriethylenediammonium salt, they are 2.914 (4) and 2.706 (4) Å, and 2.915 (5) and 2.725 (5) Å for the two symmetry-independent anions, respectively. This asymmetry leads to a significant distortion of the trigonal bipyramid in that the Tl—Br bonds involving the equatorial Br atoms are bent at the Tl atom away from the closer of the two axial Br atoms towards the more distant one, resulting in a deviation of some Brax—Tl—Breq angles by up to 10° from the ideal value of 90° and a deviation of the Tl atom from the equatorial plane of Br atoms by between 0.10 and 0.18 Å (Linden, Nugent et al., 1999). Such asymmetry and distortions of the trigonal bipyramid are not observed in the structure of (Ib) and the Tl atom lies of necessity on the equatorial plane.

The crystal packing consists of alternating layers of cations and anions stacked parallel to the (100) plane.

Experimental top

The title compound was prepared as described previously (Linden et al., 1999) [Linden, James··· or Linden Nugent··· ?] and crystallized by slow evaporation of its solution in concentrated HBr (m.p. 494–497 K).

Refinement top

The absorption correction was based on a comparison of the intensities of equivalent reflections in the highly redundant data as described by Blessing (1995). Attempts at applying a numerical absorption correction yielded significantly inferior results, presumably because the multi-faceted nature of the crystal inhibited the development of an accurate description of the crystal shape. The largest seven peaks of residual electron density (from 2.22 down to 1.00 e Å-3) were all within 1.2 Å of the Tl or Br atoms. The methyl H atoms were constrained to an ideal geometry with C—H distances of 0.98 Å and Uiso(H) = 1.5Ueq(C), but each group was allowed to rotate freely about its C—N bond. All other H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with C—H distances of 0.99 Å and Uiso(H) = 1.2Ueq(C).

Computing details top

Data collection: KappaCCD Server Software (Nonius, 1999); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. The structure of (Ib) drawn with 50% probability displacement ellipsoids and showing the atom-numbering scheme. H atoms are represented by circles of arbitrary size. [Symmetry codes: (i) 2 - x, y, 3/2 - z; (ii) 1/2 - x, 3/2 - y, 1 - z.]
1,1,4,4-tetramethylpiperazinium pentabromothallate(III) top
Crystal data top
(C8H20N2)[TlBr5]F(000) = 1352
Mr = 748.15Dx = 2.766 Mg m3
Monoclinic, C2/cMelting point: 495 K
Hall symbol: -C 2ycMo Kα radiation, λ = 0.71073 Å
a = 16.0822 (3) ÅCell parameters from 2872 reflections
b = 9.2422 (2) Åθ = 2.9–36.4°
c = 13.2718 (2) ŵ = 20.09 mm1
β = 114.3928 (8)°T = 173 K
V = 1796.56 (6) Å3Prism, yellow
Z = 40.26 × 0.23 × 0.21 mm
Data collection top
Nonius KappaCCD
diffractometer
2740 independent reflections
Radiation source: fine-focus sealed tube2467 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.080
ϕ scans, and ω scans with θ offsets (θ OK? or κ ?)θmax = 30.5°, θmin = 3.4°
Absorption correction: multi-scan
(SORTAV; Blessing, 1995)
h = 022
Tmin = 0.074, Tmax = 0.105k = 013
18998 measured reflectionsl = 1817
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.029H-atom parameters constrained
wR(F2) = 0.068 w = 1/[σ2(Fo2) + (0.0247P)2 + 10.0125P]
where P = (Fo2 + 2Fc2)/3
S = 1.06(Δ/σ)max = 0.001
2740 reflectionsΔρmax = 2.22 e Å3
77 parametersΔρmin = 2.26 e Å3
0 restraintsExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.00183 (8)
Crystal data top
(C8H20N2)[TlBr5]V = 1796.56 (6) Å3
Mr = 748.15Z = 4
Monoclinic, C2/cMo Kα radiation
a = 16.0822 (3) ŵ = 20.09 mm1
b = 9.2422 (2) ÅT = 173 K
c = 13.2718 (2) Å0.26 × 0.23 × 0.21 mm
β = 114.3928 (8)°
Data collection top
Nonius KappaCCD
diffractometer
2740 independent reflections
Absorption correction: multi-scan
(SORTAV; Blessing, 1995)
2467 reflections with I > 2σ(I)
Tmin = 0.074, Tmax = 0.105Rint = 0.080
18998 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0290 restraints
wR(F2) = 0.068H-atom parameters constrained
S = 1.06 w = 1/[σ2(Fo2) + (0.0247P)2 + 10.0125P]
where P = (Fo2 + 2Fc2)/3
2740 reflectionsΔρmax = 2.22 e Å3
77 parametersΔρmin = 2.26 e Å3
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Tl11.00000.80493 (2)0.75000.01561 (8)
Br10.81335 (3)0.81259 (4)0.65966 (3)0.01924 (11)
Br20.99722 (3)0.66359 (6)0.58000 (4)0.03579 (14)
Br31.00001.08881 (7)0.75000.0536 (3)
N10.2298 (2)0.6460 (4)0.4072 (3)0.0154 (6)
C10.1895 (3)0.6316 (4)0.4907 (3)0.0173 (8)
H1A0.12900.67940.46150.021*
H1B0.18000.52770.50100.021*
C20.2515 (3)0.8032 (4)0.3989 (3)0.0165 (8)
H2A0.28310.81210.34910.020*
H2B0.19370.85840.36570.020*
C30.3140 (3)0.5528 (4)0.4365 (4)0.0203 (8)
H3A0.36130.58470.50740.030*
H3B0.33670.56180.37870.030*
H3C0.29840.45160.44230.030*
C40.1603 (3)0.5956 (5)0.2966 (3)0.0216 (8)
H4A0.18550.60530.24110.032*
H4B0.10500.65470.27480.032*
H4C0.14520.49400.30180.032*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Tl10.01864 (12)0.01199 (11)0.01715 (12)0.0000.00833 (9)0.000
Br10.0181 (2)0.0174 (2)0.0214 (2)0.00016 (14)0.00735 (16)0.00235 (14)
Br20.0289 (2)0.0509 (3)0.0340 (3)0.0146 (2)0.0194 (2)0.0256 (2)
Br30.0223 (3)0.0123 (3)0.0876 (6)0.0000.0159 (4)0.000
N10.0148 (15)0.0118 (14)0.0183 (16)0.0009 (12)0.0056 (13)0.0001 (12)
C10.0175 (18)0.0153 (18)0.022 (2)0.0042 (15)0.0105 (16)0.0009 (15)
C20.0187 (19)0.0113 (17)0.0195 (19)0.0019 (14)0.0079 (16)0.0018 (14)
C30.0193 (19)0.0174 (19)0.026 (2)0.0053 (15)0.0109 (16)0.0022 (16)
C40.022 (2)0.0196 (19)0.019 (2)0.0019 (16)0.0046 (16)0.0035 (16)
Geometric parameters (Å, º) top
Tl1—Br12.7350 (4)C1—H1B0.99
Tl1—Br22.5915 (5)C2—H2A0.99
Tl1—Br32.6237 (7)C2—H2B0.99
N1—C11.504 (5)C3—H3A0.98
N1—C41.505 (5)C3—H3B0.98
N1—C21.509 (5)C3—H3C0.98
N1—C31.513 (5)C4—H4A0.98
C1—C2i1.504 (6)C4—H4B0.98
C1—H1A0.99C4—H4C0.98
Br1—Tl1—Br1ii177.032 (17)C1i—C2—N1112.8 (3)
Br1—Tl1—Br290.585 (14)C1i—C2—H2A109.0
Br1—Tl1—Br2ii90.910 (14)N1—C2—H2A109.0
Br1—Tl1—Br388.516 (9)C1i—C2—H2B109.0
Br2—Tl1—Br2ii119.46 (3)N1—C2—H2B109.0
Br2—Tl1—Br3120.270 (14)H2A—C2—H2B107.8
C1—N1—C4108.6 (3)N1—C3—H3A109.5
C1—N1—C2108.8 (3)N1—C3—H3B109.5
C4—N1—C2109.1 (3)H3A—C3—H3B109.5
C1—N1—C3111.9 (3)N1—C3—H3C109.5
C4—N1—C3107.4 (3)H3A—C3—H3C109.5
C2—N1—C3111.0 (3)H3B—C3—H3C109.5
C2i—C1—N1113.1 (3)N1—C4—H4A109.5
C2i—C1—H1A109.0N1—C4—H4B109.5
N1—C1—H1A109.0H4A—C4—H4B109.5
C2i—C1—H1B109.0N1—C4—H4C109.5
N1—C1—H1B109.0H4A—C4—H4C109.5
H1A—C1—H1B107.8H4B—C4—H4C109.5
C4—N1—C1—C2i172.6 (3)C1—N1—C2—C1i53.8 (4)
C2—N1—C1—C2i53.9 (4)C4—N1—C2—C1i172.1 (3)
C3—N1—C1—C2i69.0 (4)C3—N1—C2—C1i69.7 (4)
Symmetry codes: (i) x+1/2, y+3/2, z+1; (ii) x+2, y, z+3/2.

Experimental details

Crystal data
Chemical formula(C8H20N2)[TlBr5]
Mr748.15
Crystal system, space groupMonoclinic, C2/c
Temperature (K)173
a, b, c (Å)16.0822 (3), 9.2422 (2), 13.2718 (2)
β (°) 114.3928 (8)
V3)1796.56 (6)
Z4
Radiation typeMo Kα
µ (mm1)20.09
Crystal size (mm)0.26 × 0.23 × 0.21
Data collection
DiffractometerNonius KappaCCD
diffractometer
Absorption correctionMulti-scan
(SORTAV; Blessing, 1995)
Tmin, Tmax0.074, 0.105
No. of measured, independent and
observed [I > 2σ(I)] reflections
18998, 2740, 2467
Rint0.080
(sin θ/λ)max1)0.714
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.029, 0.068, 1.06
No. of reflections2740
No. of parameters77
H-atom treatmentH-atom parameters constrained
w = 1/[σ2(Fo2) + (0.0247P)2 + 10.0125P]
where P = (Fo2 + 2Fc2)/3
Δρmax, Δρmin (e Å3)2.22, 2.26

Computer programs: KappaCCD Server Software (Nonius, 1999), DENZO-SMN (Otwinowski & Minor, 1997), DENZO-SMN, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEPII (Johnson, 1976), SHELXL97.

Comparison of selected geometric parameters (Å, °) for (Ib) with those of other [TlBr5]2- salts containing symmetrical anions. top
(Ib)Mn(crown) salta,betmeen saltc
Tl1—Br12.7350 (4)2.883 (2)2.762 (2)
Tl1—Br22.5915 (5)2.540 (2)2.596 (2)
Tl1—Br32.6237 (7)2.552 (3)2.619 (2)
Br1—Tl1—Br1i177.032 (17)175.36 (9)172.75 (6)
Br1—Tl1—Br290.585 (14)88.9791.61 (5)
Br1—Tl1—Br2i90.910 (14)88.9792.56 (5)
Br1—Tl1—Br388.516 (9)92.3286.37 (3)
Br2—Tl1—Br2i119.46 (3)127.15 (10)109.89 (8)
Br2—Tl1—Br3120.270 (14)116.43 (5)125.05 (4)
Symmetry code [applies to (Ib) only]: (i) 2-x, y, 3/2-z.

Notes: (a) Reid et al. (1999); (b) original atom numbering altered to match that of (Ib); (c) Linden et al. (2002).
 

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