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The title compound, (C10H11N2)2[CuBr3], contains layers of planar monoprotonated cations. Isolated trigonal-planar [CuBr3]2- anions are hydrogen bonded to cations in adjacent layers, providing three-dimensional stability to the crystal structure.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270101005017/da1178sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270101005017/da1178Isup2.hkl
Contains datablock I

CCDC reference: 166972

Comment top

The triclinic structure of the title compound, (I), contains trigonal planar CuBr3-2 anions and planar monoprotonated 2,3-dimethylquinoxaline cations (henceforth dmqH+). Hydrogen bonding between the two crystallographically independent cations and the CuBr3-2 anions define the basic structural unit in the crystal, as illustrated in Fig. 1. Each protonated nitrogen atom is involved in a short hydrogen bond to one of the bromide ions (Table 1). Interactions between these units build up an interesting layered structure. \sch

The cations aggregrate in sheets that lie approximately normal to the [111] direction with a separation of 3.39 (2) Å between adjacent sheets. As seen in Fig. 2, the dmqH+ cations within each layer are spaced apart by the inorganic cations. The two independent quinoxalinium cations are essentially coplanar, with only 3.5 (1)° between the normals of the two planes, and the two different cations are oriented roughly perpendicular to each other.

As illustrated in Fig. 3, the CuBr3-2 anions span adjacent layers, with the bromine atoms lying in the planes formed by the cations. Each bridging anion is hydrogen bonded by one cation in each of the two layers spanned. These interactions, coupled with π-π interactions between the cations in adjacent layers, provide three dimensional stability to the lattice. The planes of the CuBr32- anions make an angle of approximately 68.69 (4) and 71.90 (4)° to the planes of the two cations.

The steric constraints imposed by the hydrogen-bonding interactions prevent the dmqH+ cations in adjacent layers from maximizing their π-π interactions. Each of the two independent cations is located near a center of inversion in the structure. In this manner, π-π interactions lead to the formation of dimer species. Those are illustrated in Fig. 4a for cation A (containing atoms N1—C3') and in Fig. 4 b for cations B (atoms N3—C13'). Significant interactions are limited to those between crystallographically equivalent pairs. The 90° rotation between the two independent cations and the presence of the CuBr32- anions appear to prevent aggregation of these dimers into more extensive stacks. The π-π interactions appear stronger for the cation A dimers than in the cation B dimers, as indicated by a greater overlap of the conjugated portion of the cations. Not surprisingly, with the cations in the dimers related by inversion symmetry, the distances between positive charges are maximized. Goddard et al. (1995) have discussed the types of π-π interactions observed in planar cojugated polycyclic systems. Two of the motifs are the so-called β and χ types where parallel stacks are formed with short distances between adjacent layers. The prototypical example for the β type is graphite, where the interplanar spacing is 3.35 Å (Wells, 1975). A measure of the strength of the π-π interactions proposed by Goddard was an offset parameter. This was defined as the horizontal displacement of the centroids of the overlapping rings. In graphite, this offset, 1.42 Å, is of the order of the length of the C—C bond length. Short offsets of this nature are characteristic of the β type, while longer offsets are observed for the χ types. In the current study, the offset parameter for cation A is 1.491 (4) Å while it is substantially larger, 2.603 (4) Å, for cation B. This latter type has been labeled a type β* by Kiralj et al. (1999).

This structure contains one of the few reported examples of isolated trigonal planar CuBr3-2 anions. The Cu—Br bond distances range from 2.3349 (6) Å for Br2 to 2.4049 (6) Å for Br3. The Br—Cu—Br angles also show substantial deviation from ideal trigonal values, ranging from 114.93 (2) to 124.52 (2)°.

Previous examples of isolated CuBr3-2 cations have been reported in several different compounds. A CuBr3-2 anion with rigorous threefold symmetry is found in the Me4P+ salt (Andersson & Jagner, 1987). Four other structures containing CuBr3-2 anions have been reported (Bowmaker et al., 1990; Sundberg et al., 1992; Bencini & Mani, 1984; Haddad & Willett, 2001). All of the anions in these compounds show distortions of magnitude similar to those in the structure reported here. Interestingly, the compound reported by Sundberg et al. is a mixed valence system that contains both the CuBr3-2 anion and the CuBr4-2 anion. Two crystalline forms exist of the compound reported by Bowmaker et al. (1990). One form contains the CuBr3-2 anion while the other contains a combination of CuBr2-1 and Br-1 anions. One example of an isolated CuCl3-2 anion has also been reported (Andersson & Jagner, 1988) as well as two CuI3-2 anions (Bhadur et al., 1991; Hartl & Brudgam, 1989).

In addition to its existence as an isolated species, the CuX3-2 (X = Cl, Br) anions act as bridging ligands in several (CuLn)CuX3 linear chain compounds, where the CuLn2+ cations have a square planar coordination (Clegg et al., 1988; Chen et al., 1996; Willett & Vij, 2001). Stacks of CuCl3-2 anions can be found in Cu(N2H5)2(CuCl3)2, with the stacks stabilized by hydrogen bonding from the hydrazinium cations and bridging to the CuII ion (Scott & Willett, 1991). The trigonal planar coordination also occurs in numerous polymeric anionic copper(I) halide salts (Subramanian & Hoffmann, 1992).

Related literature top

For related literature, see: Andersson & Jagner (1987, 1988); Bencini & Mani (1984); Bhadur et al. (1991); Bowmaker et al. (1990); Chen et al. (1996); Clegg et al. (1988); Goddard et al. (1995); Haddad & Willett (2001); Hartl & Brudgam (1989); Kiralj et al. (1999); Scott & Willett (1991); Subramanian & Hoffmann (1992); Sundberg et al. (1992); Willett & Vij (2001).

Experimental top

CuBr (approximately 0.0005 mol, 0.80 g) and 2,3-dimethylquinoxaline (0.0005 mol, 0.72 g) were added to HBr (approximately 50 ml of 0.10 M) in a sealed Erlenmeyer flask. The solution was heated to approximately 323 K and stirred for about 30 min. A portion of the supernatant liquid was placed on a microscope slide. Over a period of about 10 min, yellow crystals formed with maximum dimension of approximately 0.5 mm. One such crystal was selected for X-ray analysis.

Computing details top

Data collection: SMART (Bruker, 1998); cell refinement: SMART; data reduction: SAINTPlus (Bruker, 1998); program(s) used to solve structure: SHELXTL (Bruker, 1998); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures top
[Figure 1] Fig. 1. View of the asymmetric unit. Displacement ellipsoids are drawn at the 50% probability level.
[Figure 2] Fig. 2. Illustration of an individual layer.
[Figure 3] Fig. 3. Side view illustrating the bridging of the CuBr32- anions between layers.
[Figure 4] Fig. 4. Illustration of the π-π interactions between (a) cations 1 and (b) cations 2.
Bis(dimethylquinoxalinium)tribrocuprate(I) top
Crystal data top
(C10H11N2)2(CuBr3)Z = 2
Mr = 621.69F(000) = 608
Triclinic, P1Dx = 1.858 Mg m3
a = 7.2603 (16) ÅMo Kα radiation, λ = 0.71073 Å
b = 10.777 (2) ÅCell parameters from 951 reflections
c = 15.197 (3) Åθ = 3.0–27.8°
α = 73.544 (4)°µ = 6.39 mm1
β = 77.338 (4)°T = 295 K
γ = 83.827 (4)°Needle, yellow
V = 1111.3 (4) Å30.27 × 0.14 × 0.05 mm
Data collection top
Siemens SMART 1000
diffractometer
5273 independent reflections
Radiation source: normal-focus sealed tube3792 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.026
Detector resolution: 8.3 pixels mm-1θmax = 28.3°, θmin = 1.4°
ω scansh = 99
Absorption correction: empirical
(SADABS; Sheldrick, 1999)
k = 1314
Tmin = 0.277, Tmax = 0.741l = 1919
11900 measured reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.031Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.072H atoms treated by a mixture of independent and constrained refinement
S = 0.99 w = 1/[σ2(Fo2) + (0.0362P)2]
where P = (Fo2 + 2Fc2)/3
5273 reflections(Δ/σ)max = 0.001
265 parametersΔρmax = 0.78 e Å3
0 restraintsΔρmin = 0.43 e Å3
Crystal data top
(C10H11N2)2(CuBr3)γ = 83.827 (4)°
Mr = 621.69V = 1111.3 (4) Å3
Triclinic, P1Z = 2
a = 7.2603 (16) ÅMo Kα radiation
b = 10.777 (2) ŵ = 6.39 mm1
c = 15.197 (3) ÅT = 295 K
α = 73.544 (4)°0.27 × 0.14 × 0.05 mm
β = 77.338 (4)°
Data collection top
Siemens SMART 1000
diffractometer
5273 independent reflections
Absorption correction: empirical
(SADABS; Sheldrick, 1999)
3792 reflections with I > 2σ(I)
Tmin = 0.277, Tmax = 0.741Rint = 0.026
11900 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0310 restraints
wR(F2) = 0.072H atoms treated by a mixture of independent and constrained refinement
S = 0.99Δρmax = 0.78 e Å3
5273 reflectionsΔρmin = 0.43 e Å3
265 parameters
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
Cu11.21342 (5)0.98614 (4)0.24862 (3)0.04884 (11)
Br11.25435 (5)0.91464 (3)0.38636 (2)0.05191 (10)
Br21.03969 (5)1.17390 (3)0.22634 (2)0.05123 (10)
Br31.36445 (4)0.84774 (3)0.12768 (2)0.04802 (9)
N110.9821 (3)1.1690 (2)0.45846 (17)0.0421 (6)
H111.063 (5)1.102 (4)0.444 (3)0.077 (12)*
C120.8026 (4)1.1732 (3)0.4172 (2)0.0423 (7)
C130.6945 (4)1.2900 (3)0.4470 (2)0.0494 (8)
N140.7665 (4)1.3878 (3)0.51390 (19)0.0528 (7)
C150.9519 (4)1.3794 (3)0.5559 (2)0.0452 (7)
C161.0317 (6)1.4837 (3)0.6278 (2)0.0622 (9)
H160.95831.55860.64730.075*
C171.2151 (6)1.4752 (4)0.6686 (2)0.0732 (11)
H171.26811.54500.71580.088*
C181.3272 (6)1.3627 (5)0.6410 (3)0.0756 (11)
H181.45321.35900.67080.091*
C191.2560 (5)1.2585 (4)0.5714 (2)0.0594 (9)
H191.33091.18400.55320.071*
C201.0663 (4)1.2683 (3)0.5288 (2)0.0420 (7)
C12'0.7244 (5)1.0575 (3)0.3444 (2)0.0595 (9)
H12A0.82220.99040.33580.089*
H12B0.62401.02730.36370.089*
H12C0.67621.07980.28650.089*
C13'0.4908 (5)1.3015 (4)0.3996 (3)0.0754 (11)
H13A0.42731.37240.43770.113*
H13B0.48431.31680.33970.113*
H13C0.43081.22260.39110.113*
N10.9963 (3)0.7111 (2)0.02534 (17)0.0398 (5)
H11.090 (5)0.749 (3)0.016 (2)0.061 (10)*
C20.8314 (4)0.7743 (3)0.03545 (19)0.0386 (6)
C30.6791 (4)0.7082 (3)0.1035 (2)0.0401 (6)
N40.6991 (3)0.5879 (2)0.15191 (17)0.0432 (6)
C50.8742 (4)0.5252 (3)0.1395 (2)0.0414 (7)
C60.9000 (5)0.3958 (3)0.1911 (2)0.0536 (8)
H60.79850.35180.23230.064*
C71.0745 (5)0.3360 (3)0.1799 (3)0.0599 (9)
H71.09180.25070.21420.072*
C81.2274 (5)0.3994 (3)0.1184 (3)0.0607 (9)
H81.34560.35620.11280.073*
C91.2078 (4)0.5246 (3)0.0657 (2)0.0505 (8)
H91.31040.56650.02390.061*
C101.0286 (4)0.5874 (3)0.0768 (2)0.0405 (6)
C2'0.8116 (4)0.9067 (3)0.0246 (2)0.0517 (8)
H2'A0.93090.93120.06510.078*
H2'B0.77210.96560.01380.078*
H2'C0.71890.90990.06160.078*
C3'0.4936 (4)0.7802 (3)0.1193 (2)0.0536 (8)
H3'A0.40390.72360.16470.080*
H3'B0.44920.81090.06150.080*
H3'C0.50790.85250.14200.080*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cu10.0470 (2)0.0467 (2)0.0496 (2)0.00227 (17)0.00728 (17)0.00962 (18)
Br10.0594 (2)0.05031 (19)0.04677 (19)0.00979 (15)0.01508 (15)0.01526 (14)
Br20.0603 (2)0.04245 (18)0.04978 (19)0.00328 (14)0.01154 (15)0.01220 (14)
Br30.04082 (17)0.05080 (19)0.04626 (18)0.00338 (13)0.00944 (13)0.00461 (14)
N110.0395 (14)0.0422 (14)0.0426 (14)0.0012 (11)0.0119 (11)0.0063 (11)
C120.0401 (16)0.0498 (18)0.0395 (16)0.0057 (13)0.0125 (13)0.0109 (13)
C130.0432 (17)0.057 (2)0.053 (2)0.0063 (14)0.0154 (15)0.0206 (16)
N140.0579 (17)0.0487 (16)0.0504 (16)0.0063 (13)0.0148 (13)0.0111 (13)
C150.0571 (19)0.0404 (17)0.0397 (17)0.0024 (14)0.0120 (14)0.0116 (13)
C160.088 (3)0.047 (2)0.049 (2)0.0084 (18)0.0140 (19)0.0070 (16)
C170.094 (3)0.068 (3)0.050 (2)0.033 (2)0.001 (2)0.0031 (19)
C180.059 (2)0.102 (3)0.064 (2)0.026 (2)0.0118 (19)0.029 (2)
C190.0485 (19)0.067 (2)0.057 (2)0.0053 (16)0.0033 (16)0.0135 (18)
C200.0450 (17)0.0454 (17)0.0367 (16)0.0057 (13)0.0086 (13)0.0110 (13)
C12'0.051 (2)0.063 (2)0.059 (2)0.0133 (16)0.0083 (16)0.0058 (17)
C13'0.046 (2)0.095 (3)0.078 (3)0.009 (2)0.0085 (19)0.019 (2)
N10.0390 (14)0.0383 (14)0.0388 (14)0.0038 (11)0.0005 (11)0.0101 (11)
C20.0398 (15)0.0366 (15)0.0400 (16)0.0006 (12)0.0062 (12)0.0132 (12)
C30.0371 (15)0.0434 (17)0.0405 (16)0.0006 (12)0.0076 (12)0.0134 (13)
N40.0450 (14)0.0405 (14)0.0421 (14)0.0054 (11)0.0053 (11)0.0090 (11)
C50.0448 (16)0.0388 (16)0.0406 (16)0.0021 (12)0.0074 (13)0.0114 (13)
C60.064 (2)0.0405 (18)0.053 (2)0.0058 (15)0.0099 (16)0.0071 (15)
C70.077 (2)0.0402 (18)0.061 (2)0.0072 (17)0.0180 (19)0.0109 (16)
C80.055 (2)0.058 (2)0.071 (2)0.0166 (17)0.0165 (18)0.0234 (19)
C90.0443 (17)0.0494 (19)0.055 (2)0.0043 (14)0.0050 (14)0.0162 (15)
C100.0427 (16)0.0383 (16)0.0404 (16)0.0006 (12)0.0075 (13)0.0123 (13)
C2'0.0500 (18)0.0429 (18)0.055 (2)0.0015 (14)0.0064 (15)0.0040 (15)
C3'0.0437 (17)0.056 (2)0.0513 (19)0.0029 (14)0.0009 (14)0.0073 (16)
Geometric parameters (Å, º) top
Cu1—Br22.3349 (6)C19—C201.394 (4)
Cu1—Br12.3781 (7)N1—C21.313 (3)
Cu1—Br32.4049 (6)N1—C101.366 (4)
N11—C121.319 (4)C2—C31.432 (4)
N11—C201.366 (4)C2—C2'1.472 (4)
C12—C131.424 (4)C3—N41.308 (4)
C12—C12'1.482 (4)C3—C3'1.488 (4)
C13—N141.302 (4)N4—C51.376 (3)
C13—C13'1.506 (4)C5—C101.395 (4)
N14—C151.362 (4)C5—C61.408 (4)
C15—C201.397 (4)C6—C71.357 (4)
C15—C161.400 (4)C7—C81.385 (5)
C16—C171.345 (5)C8—C91.370 (5)
C17—C181.398 (5)C9—C101.400 (4)
C18—C191.363 (5)
Br2—Cu1—Br1124.52 (2)C19—C20—C15121.9 (3)
Br2—Cu1—Br3120.55 (2)C2—N1—C10123.3 (3)
Br1—Cu1—Br3114.93 (2)N1—C2—C3117.5 (3)
C12—N11—C20123.7 (3)N1—C2—C2'118.8 (3)
N11—C12—C13117.1 (3)C3—C2—C2'123.7 (3)
N11—C12—C12'119.0 (3)N4—C3—C2122.1 (2)
C13—C12—C12'123.9 (3)N4—C3—C3'119.6 (3)
N14—C13—C12122.1 (3)C2—C3—C3'118.4 (3)
N14—C13—C13'118.8 (3)C3—N4—C5118.6 (2)
C12—C13—C13'119.1 (3)N4—C5—C10121.3 (3)
C13—N14—C15119.3 (3)N4—C5—C6119.8 (3)
N14—C15—C20121.5 (3)C10—C5—C6118.9 (3)
N14—C15—C16120.0 (3)C7—C6—C5119.2 (3)
C20—C15—C16118.5 (3)C6—C7—C8121.4 (3)
C17—C16—C15119.7 (3)C9—C8—C7121.3 (3)
C16—C17—C18121.0 (3)C8—C9—C10117.9 (3)
C19—C18—C17121.5 (3)N1—C10—C5117.1 (2)
C18—C19—C20117.3 (3)N1—C10—C9121.6 (3)
N11—C20—C19121.7 (3)C5—C10—C9121.3 (3)
N11—C20—C15116.4 (3)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···Br30.86 (3)2.44 (3)3.302 (3)177 (3)
N11—H11···Br10.89 (4)2.39 (4)3.272 (3)173 (3)

Experimental details

Crystal data
Chemical formula(C10H11N2)2(CuBr3)
Mr621.69
Crystal system, space groupTriclinic, P1
Temperature (K)295
a, b, c (Å)7.2603 (16), 10.777 (2), 15.197 (3)
α, β, γ (°)73.544 (4), 77.338 (4), 83.827 (4)
V3)1111.3 (4)
Z2
Radiation typeMo Kα
µ (mm1)6.39
Crystal size (mm)0.27 × 0.14 × 0.05
Data collection
DiffractometerSiemens SMART 1000
diffractometer
Absorption correctionEmpirical
(SADABS; Sheldrick, 1999)
Tmin, Tmax0.277, 0.741
No. of measured, independent and
observed [I > 2σ(I)] reflections
11900, 5273, 3792
Rint0.026
(sin θ/λ)max1)0.668
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.031, 0.072, 0.99
No. of reflections5273
No. of parameters265
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.78, 0.43

Computer programs: SMART (Bruker, 1998), SMART, SAINTPlus (Bruker, 1998), SHELXTL (Bruker, 1998), SHELXTL.

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···Br30.86 (3)2.44 (3)3.302 (3)177 (3)
N11—H11···Br10.89 (4)2.39 (4)3.272 (3)173 (3)
 

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