Dibromidobis(quinoxaline-κN)zinc(II)

In the title complex, [ZnBr₂(C₈H₆N₂)₂], the quinoxaline ligands are monocoordinated to the Zn^II atom and, with the bromide ions, form a distorted tetra­hedral geometry. The combination of π-stacking inter­actions between inversion-related quinoxaline ligands and the bridging Zn creates layers parallel to the bc plane [distances range from 3.250 (1) to 3.51 (1) Å].

Key indicators

• Single-crystal X-ray study
• T = 295 K
• Mean [sigma](C-C) = 0.013 Å
• R factor = 0.055
• wR factor = 0.129
• Data-to-parameter ratio = 13.4

checkCIF/PLATON results

No syntax errors found



Alert level A
PLAT027_ALERT_3_A _diffrn_reflns_theta_full (too) Low ............      24.60 Deg.

Author Response: Data was collected to 25.0 degrees. No data was observed between 24.6 and 25.00 degrees.

Alert level C
THETM01_ALERT_3_C  The value of sine(theta_max)/wavelength is less than 0.590
            Calculated sin(theta_max)/wavelength =    0.5857
PLAT023_ALERT_3_C Resolution (too) Low [sin(th)/Lambda < 0.6].....      24.60 Deg.
PLAT180_ALERT_3_C Check Cell Rounding: # of Values Ending with 0 =          3
PLAT341_ALERT_3_C Low Bond Precision on C-C Bonds (x 1000) Ang ...         13

Alert level G
PLAT794_ALERT_5_G Check Predicted Bond Valency for Zn          (2)       1.89

   1 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   4 ALERT level C = Check and explain
   1 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   5 ALERT type 3 Indicator that the structure quality may be low
   0 ALERT type 4 Improvement, methodology, query or suggestion
   1 ALERT type 5 Informative message, check

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S1. Comment

We are interested in the study of low-dimensional coordination polymers and their magnetic properties. Our previous work on two copper(II) complexes of quinoxaline (quinox) showed that Cu(quinox)X₂ complexes (X = Cl, Br) form structural and magnetic ladders. The rungs of the ladder are formed by bridging halide ions and the rails formed by bridging quinoxaline molecules (Lindroos and Lumme, 1990; Landee et al., 2003). A diamagnetic analogue of these materials would be useful for related experiments and we previously prepared the chloride analogue of (I) (Markowitz et al., 2006). It resulted in a tetrahedral complex which was not a suitable analogue so the bromo complex was prepared and is reported here. Reaction of ZnBr₂ with quinoxaline gave Zn(quinox)Br₂, even in the presence of excess ZnBr₂.

The Zn^II complex (I, Fig. 1) is a distorted tetrahedron with a mean angle at Zn of 120.6 (2)° (Turnbull et al., 2005). The Br1—Zn—Br2 and N1—Zn1—N11 angles are both expanded and correspond with the chloride complex, unlike the pyridine and quinoline analogues (Markowitz et al. 2006 and references therein). The two quinoxaline ligands are nearly planar. The mean deviation from planarity for the N1 containing quinoxaline is 0.013 (12) Å and the angle between the normals to the two component rings is 1.0 (1)°; the comparable values for the N11 ring are 0.019 (17) Å and 1.4 (1)°; both are identical with the chloride complex, within experimental error. The bond lengths and angles within the quinoxaline rings are the same within experimental error and agree with those values seen in chloride analogue and similar mono-coordinated complexes such as [Cu(quinox)₂(H₂O)₃](ClO₄)₂ (Lumme et al., 1988) and [Cu(quinox)₂(C₂N₃)₂] (Luo et al., 2004).

Complex (I) packs in the lattice such that π-stacking is observed between inversion related quinoxaline rings, generating layers parallel to the bc-plane. The ring overlap occurs between both the nitrogen-containing rings and the non-nitrogen containing rings. The interplanar distance between the stacked N1-rings is 3.30 (1)Å and the displacement angle (defined as the angle between the mean plane of the ring and the line connecting the ring centroids) is 19.1 (1)° while the values for the carbocyclic rings containing C6 are 3.41 (1)Å and 13.9 (1)°, respectively. For the stacked N11 rings the distance is 3.25 (2)Å with a displacement angle of 19.3 (1)° while the carbocyclic C16 rings are separated by 3.51 (1) Å and 6.0 (1)°. Both show that the carbocyclic rings are slightly further apart, but show greater overlap compared to the heterocyclic rings.

Related literature

For related literature, see: Landee et al. (2003); Lindroos & Lumme (1990); Lumme et al. (1988); Luo et al. (2004); Markowitz et al. (2006); Turnbull et al. (2005).

S2. Experimental

A solution of quinoxaline (1.4 g, 10 mmol) in absolute ethanol (10 ml) was added to a solution of ZnBr₂ (2.3 g, 10 mmol) in absolute ethanol (10 ml) yielding a pale-orange solution. The flask was wrapped in aluminium foil and allowed to evaporate under a slow flow of argon. After 12 h, light-brown crystals of (I) were collected, washed with cold ethanol and allowed to air dry yielding 1.62 g (67%). IR (KBr, cm^-1): 1504 s, 1466m, 1383w, 1360 s, 1215m, 1147m, 1131m, 1046 s, 965 s,876m, 772 s, 766 s.

Computing details

Data collection: XSCANS (Siemens, 1992); cell refinement: XSCANS; data reduction: SHELXTL (Siemens, 1990); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

Fig. 1. Molecular structure of (I), showing atom labelling scheme and 50% atom displacement ellipsoids.

Dibromidobis(quinoxaline-κN)zinc(II)

Crystal data

[ZnBr2(C8H6N2)2]	Z = 2
Mr = 485.49	F(000) = 472
Triclinic, P1	Dx = 1.911 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 8.2527 (11) Å	Cell parameters from 31 reflections
b = 8.6670 (9) Å	θ = 3.3–15.6°
c = 12.4651 (17) Å	µ = 6.19 mm^−1
α = 80.067 (13)°	T = 295 K
β = 86.260 (12)°	Parallelpiped, colourless
γ = 73.94 (1)°	0.2 × 0.15 × 0.12 mm
V = 843.80 (18) Å^3

Data collection

Bruker P4 diffractometer	1703 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.082
Graphite monochromator	θmax = 24.6°, θmin = 2.5°
ω scans	h = −9→1
Absorption correction: ψ scan (SHELXTL; Siemens, 1990)	k = −10→9
Tmin = 0.363, Tmax = 0.476	l = −14→14
3382 measured reflections	3 standard reflections every 97 reflections
2781 independent reflections	intensity decay: 2.1%

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)] = 0.055	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.129	H-atom parameters constrained
S = 1.01	w = 1/[σ^2(Fo^2) + (0.0507P)^2 + 0.6175P] where P = (Fo^2 + 2Fc^2)/3
2781 reflections	(Δ/σ)max < 0.001
208 parameters	Δρmax = 0.68 e Å^−3
0 restraints	Δρmin = −0.53 e Å^−3

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
Zn	0.34064 (11)	0.66777 (11)	0.75037 (8)	0.0414 (3)
Br1	0.48802 (12)	0.39624 (11)	0.73519 (9)	0.0618 (3)
Br2	0.48360 (11)	0.86374 (11)	0.76689 (8)	0.0560 (3)
N1	0.2157 (8)	0.7537 (7)	0.6045 (5)	0.0396 (16)
C2	0.2853 (11)	0.8412 (10)	0.5272 (7)	0.048 (2)
H2A	0.3835	0.8650	0.5427	0.058*
C3	0.2186 (13)	0.8992 (11)	0.4236 (8)	0.057 (2)
H3A	0.2736	0.9606	0.3733	0.068*
N4	0.0816 (11)	0.8707 (9)	0.3944 (6)	0.058 (2)
C5	0.0051 (11)	0.7813 (10)	0.4701 (8)	0.049 (2)
C6	−0.1435 (11)	0.7466 (12)	0.4439 (8)	0.057 (3)
H6A	−0.1895	0.7856	0.3751	0.069*
C7	−0.2190 (12)	0.6551 (12)	0.5204 (9)	0.060 (3)
H7A	−0.3178	0.6336	0.5035	0.072*
C8	−0.1515 (11)	0.5936 (11)	0.6230 (8)	0.056 (2)
H8A	−0.2055	0.5305	0.6728	0.067*
C9	−0.0086 (10)	0.6229 (10)	0.6527 (7)	0.047 (2)
H9A	0.0359	0.5801	0.7215	0.057*
C10	0.0702 (9)	0.7198 (9)	0.5763 (7)	0.038 (2)
N11	0.2023 (8)	0.6495 (8)	0.8954 (5)	0.0393 (16)
C12	0.2657 (11)	0.5273 (11)	0.9726 (8)	0.051 (2)
H12A	0.3641	0.4501	0.9577	0.061*
C13	0.1906 (13)	0.5087 (12)	1.0769 (8)	0.060 (3)
H13A	0.2438	0.4226	1.1294	0.071*
N14	0.0498 (11)	0.6075 (10)	1.1023 (6)	0.059 (2)
C15	−0.0207 (11)	0.7367 (10)	1.0254 (7)	0.046 (2)
C16	−0.1749 (11)	0.8485 (12)	1.0501 (8)	0.054 (2)
H16A	−0.2280	0.8339	1.1178	0.065*
C17	−0.2415 (12)	0.9746 (12)	0.9740 (8)	0.057 (2)
H17A	−0.3427	1.0474	0.9899	0.068*
C18	−0.1666 (11)	1.0026 (11)	0.8715 (7)	0.051 (2)
H18A	−0.2165	1.0938	0.8216	0.062*
C19	−0.0202 (10)	0.8964 (10)	0.8445 (7)	0.044 (2)
H19A	0.0291	0.9138	0.7759	0.052*
C20	0.0556 (9)	0.7603 (9)	0.9212 (6)	0.0368 (19)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn	0.0367 (6)	0.0398 (6)	0.0459 (7)	−0.0105 (4)	−0.0020 (5)	−0.0017 (5)
Br1	0.0525 (6)	0.0409 (5)	0.0840 (8)	−0.0006 (4)	−0.0017 (5)	−0.0081 (5)
Br2	0.0524 (6)	0.0567 (6)	0.0657 (7)	−0.0249 (5)	0.0031 (5)	−0.0132 (5)
N1	0.031 (4)	0.035 (4)	0.046 (4)	−0.003 (3)	0.003 (3)	0.001 (3)
C2	0.044 (5)	0.045 (5)	0.051 (6)	−0.011 (4)	0.013 (4)	−0.001 (5)
C3	0.072 (7)	0.054 (6)	0.042 (6)	−0.021 (5)	0.014 (5)	0.001 (5)
N4	0.084 (6)	0.043 (4)	0.040 (5)	−0.010 (4)	−0.001 (4)	−0.001 (4)
C5	0.052 (5)	0.040 (5)	0.050 (6)	0.000 (4)	−0.006 (5)	−0.014 (5)
C6	0.047 (6)	0.066 (6)	0.055 (7)	0.000 (5)	−0.013 (5)	−0.020 (5)
C7	0.043 (5)	0.061 (6)	0.080 (8)	−0.008 (5)	−0.010 (5)	−0.030 (6)
C8	0.052 (6)	0.067 (6)	0.053 (7)	−0.021 (5)	0.006 (5)	−0.017 (5)
C9	0.047 (5)	0.051 (5)	0.046 (6)	−0.014 (4)	0.002 (4)	−0.011 (4)
C10	0.032 (5)	0.034 (4)	0.044 (6)	0.000 (4)	0.001 (4)	−0.010 (4)
N11	0.036 (4)	0.041 (4)	0.040 (4)	−0.014 (3)	−0.007 (3)	0.006 (3)
C12	0.044 (5)	0.050 (5)	0.057 (7)	−0.013 (4)	−0.011 (5)	−0.002 (5)
C13	0.068 (7)	0.060 (6)	0.050 (7)	−0.027 (6)	−0.018 (5)	0.017 (5)
N14	0.068 (6)	0.066 (5)	0.047 (5)	−0.031 (5)	−0.004 (4)	0.002 (4)
C15	0.051 (5)	0.051 (5)	0.040 (5)	−0.023 (5)	−0.011 (4)	−0.001 (4)
C16	0.054 (6)	0.069 (6)	0.044 (6)	−0.023 (5)	0.009 (5)	−0.012 (5)
C17	0.049 (5)	0.065 (6)	0.060 (7)	−0.009 (5)	−0.002 (5)	−0.031 (6)
C18	0.054 (6)	0.055 (6)	0.043 (6)	−0.004 (5)	−0.010 (5)	−0.016 (5)
C19	0.041 (5)	0.045 (5)	0.044 (5)	−0.015 (4)	0.001 (4)	0.002 (4)
C20	0.030 (4)	0.046 (5)	0.035 (5)	−0.018 (4)	−0.003 (4)	0.002 (4)

Geometric parameters (Å, º)

Zn—N1	2.068 (7)	C9—C10	1.406 (11)
Zn—N11	2.080 (6)	C9—H9A	0.9300
Zn—Br2	2.3623 (12)	N11—C12	1.315 (10)
Zn—Br1	2.3650 (13)	N11—C20	1.380 (10)
N1—C2	1.323 (10)	C12—C13	1.406 (13)
N1—C10	1.392 (9)	C12—H12A	0.9300
C2—C3	1.391 (13)	C13—N14	1.296 (12)
C2—H2A	0.9300	C13—H13A	0.9300
C3—N4	1.308 (11)	N14—C15	1.361 (11)
C3—H3A	0.9300	C15—C20	1.414 (11)
N4—C5	1.353 (11)	C15—C16	1.422 (12)
C5—C6	1.412 (12)	C16—C17	1.333 (13)
C5—C10	1.421 (12)	C16—H16A	0.9300
C6—C7	1.364 (13)	C17—C18	1.395 (12)
C6—H6A	0.9300	C17—H17A	0.9300
C7—C8	1.386 (13)	C18—C19	1.363 (11)
C7—H7A	0.9300	C18—H18A	0.9300
C8—C9	1.360 (11)	C19—C20	1.406 (11)
C8—H8A	0.9300	C19—H19A	0.9300
N1—Zn—N11	119.5 (2)	N1—C10—C9	119.6 (7)
N1—Zn—Br2	104.56 (18)	N1—C10—C5	119.4 (7)
N11—Zn—Br2	103.95 (18)	C9—C10—C5	121.0 (8)
N1—Zn—Br1	103.70 (18)	C12—N11—C20	116.5 (7)
N11—Zn—Br1	104.58 (18)	C12—N11—Zn	117.3 (6)
Br2—Zn—Br1	121.69 (5)	C20—N11—Zn	125.9 (5)
C2—N1—C10	116.0 (7)	N11—C12—C13	122.7 (9)
C2—N1—Zn	117.5 (6)	N11—C12—H12A	118.7
C10—N1—Zn	126.4 (5)	C13—C12—H12A	118.7
N1—C2—C3	123.2 (9)	N14—C13—C12	122.2 (9)
N1—C2—H2A	118.4	N14—C13—H13A	118.9
C3—C2—H2A	118.4	C12—C13—H13A	118.9
N4—C3—C2	122.6 (8)	C13—N14—C15	117.5 (8)
N4—C3—H3A	118.7	N14—C15—C20	121.1 (8)
C2—C3—H3A	118.7	N14—C15—C16	119.3 (9)
C3—N4—C5	116.9 (8)	C20—C15—C16	119.6 (8)
N4—C5—C6	119.8 (9)	C17—C16—C15	118.4 (8)
N4—C5—C10	122.0 (8)	C17—C16—H16A	120.8
C6—C5—C10	118.3 (8)	C15—C16—H16A	120.8
C7—C6—C5	119.4 (9)	C16—C17—C18	123.1 (9)
C7—C6—H6A	120.3	C16—C17—H17A	118.4
C5—C6—H6A	120.3	C18—C17—H17A	118.4
C6—C7—C8	121.4 (9)	C19—C18—C17	120.0 (9)
C6—C7—H7A	119.3	C19—C18—H18A	120.0
C8—C7—H7A	119.3	C17—C18—H18A	120.0
C9—C8—C7	121.8 (9)	C18—C19—C20	119.6 (8)
C9—C8—H8A	119.1	C18—C19—H19A	120.2
C7—C8—H8A	119.1	C20—C19—H19A	120.2
C8—C9—C10	118.2 (9)	N11—C20—C19	120.7 (7)
C8—C9—H9A	120.9	N11—C20—C15	119.9 (7)
C10—C9—H9A	120.9	C19—C20—C15	119.4 (8)
N11—Zn—N1—C2	145.7 (6)	N1—Zn—N11—C12	145.1 (6)
Br2—Zn—N1—C2	30.0 (6)	Br2—Zn—N11—C12	−98.9 (6)
Br1—Zn—N1—C2	−98.5 (6)	Br1—Zn—N11—C12	29.7 (6)
N11—Zn—N1—C10	−38.9 (7)	N1—Zn—N11—C20	−39.9 (7)
Br2—Zn—N1—C10	−154.6 (5)	Br2—Zn—N11—C20	76.2 (6)
Br1—Zn—N1—C10	76.9 (6)	Br1—Zn—N11—C20	−155.2 (6)
C10—N1—C2—C3	0.8 (11)	C20—N11—C12—C13	−0.4 (11)
Zn—N1—C2—C3	176.7 (7)	Zn—N11—C12—C13	175.1 (6)
N1—C2—C3—N4	−0.4 (14)	N11—C12—C13—N14	2.9 (14)
C2—C3—N4—C5	0.2 (13)	C12—C13—N14—C15	−3.1 (13)
C3—N4—C5—C6	179.8 (8)	C13—N14—C15—C20	1.1 (12)
C3—N4—C5—C10	−0.4 (12)	C13—N14—C15—C16	−179.7 (8)
N4—C5—C6—C7	179.5 (9)	N14—C15—C16—C17	179.7 (8)
C10—C5—C6—C7	−0.3 (12)	C20—C15—C16—C17	−1.1 (13)
C5—C6—C7—C8	−0.9 (14)	C15—C16—C17—C18	−0.4 (14)
C6—C7—C8—C9	0.8 (14)	C16—C17—C18—C19	1.5 (14)
C7—C8—C9—C10	0.6 (13)	C17—C18—C19—C20	−1.0 (12)
C2—N1—C10—C9	177.9 (8)	C12—N11—C20—C19	179.0 (7)
Zn—N1—C10—C9	2.4 (10)	Zn—N11—C20—C19	3.9 (10)
C2—N1—C10—C5	−1.0 (10)	C12—N11—C20—C15	−1.6 (10)
Zn—N1—C10—C5	−176.5 (5)	Zn—N11—C20—C15	−176.7 (5)
C8—C9—C10—N1	179.3 (7)	C18—C19—C20—N11	178.9 (7)
C8—C9—C10—C5	−1.9 (12)	C18—C19—C20—C15	−0.5 (11)
N4—C5—C10—N1	0.8 (12)	N14—C15—C20—N11	1.3 (12)
C6—C5—C10—N1	−179.4 (7)	C16—C15—C20—N11	−177.9 (7)
N4—C5—C10—C9	−178.1 (7)	N14—C15—C20—C19	−179.3 (7)
C6—C5—C10—C9	1.8 (11)	C16—C15—C20—C19	1.5 (12)