Bis(2,6-di­amino-3,5-di­bromo­pyridinium) tetra­bromo­cuprate(II)

The title compound, (C₅H₆Br₂N₃)₂[CuBr₄], contains isolated substituted pyridinium cations and [CuBr₄]^2- anions. The di­amino­di­bromo­pyridinium ions are planar, while the Cu^II ions have a distorted compressed tetrahedral coordination with C₂ symmetry. The two independent trans-Br-Cu-Br angles are 128.9 (1) and 136.0 (1)°, with Cu-Br distances of 2.3939 (15) and 2.3790 (16) Å.

S1. Comment

The catalytic halogenation of activated pyridine rings by copper(II) halides is a common phenomenon. The bromination step presubably involves reduction of Cu^II to Cu^I, with the subsequent re-oxidation to Cu^II by atmospheric oxygen. In our attempts to prepare various substituted pyridinium salts of copper(II) halides, we have frequently isolated the corresponding halogenated salts (Willett & West, 1987; Willett, 1988, 2000; Place & Willett, 1987; Willett & Halvorson, 1988). With 2,6-diaminopyridine, we have previously reported the formation and isolation of the corresponding 3,5-dichloro derivative (Willett & West, 1987) as the [CuCl₄]²⁻ salt. However, the compound crystallizes in a different space group.

In the title compound, (I), the cation is nearly planar. However, the Br5 atom lies 0.116 Å out of the plane of the pyridine ring. This is probably due to steric repulsion with the adjacent NH₂ group. The [CuBr₄]²⁻ anion has a slightly compressed tetrahedral geometry with a substantial (but not unusual) distortion from idealized D_{2 d} symmetry (Place & Willett, 1988).

S2. Experimental

2,6-Diaminopyridine (0.01 mol, 1.09 g) and CuBr₂ (0.005 mol, 1.12 g) were dissolved in dilute HBr (100 ml, ca 0.1M) and the resultant solution was slowly evaporated at ca 323 K. The compound was obtained as small nearly opaque purple crystals after two days.

S3. Refinement

H atoms were found on difference Fourier syntheses and positional parameters and isotropic displacement parameters refined. The X—H distances were restrained to a distance of 0.96 (5) Å. The largest residual electron-density peaks all lie within 1.06 Å of Br atoms.

Computing details

Data collection: SMART (Bruker, 1997); cell refinement: SMART; data reduction: SAINT (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); software used to prepare material for publication: SHELXL97.

(I)

Crystal data

(C5H6N3Br2)2[CuBr4]	F(000) = 1692
Mr = 919.08	Dx = 2.741 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 20.612 (10) Å	Cell parameters from 5523 reflections
b = 10.053 (5) Å	θ = 2.4–24.7°
c = 13.507 (7) Å	µ = 15.34 mm^−1
β = 127.264 (7)°	T = 293 K
V = 2227.3 (19) Å^3	Plates, purple
Z = 4	0.38 × 0.18 × 0.03 mm

Data collection

Bruker CCD area-detector diffractometer	1849 independent reflections
Radiation source: normal-focus sealed tube	1274 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.056
ϕ and ω scans	θmax = 24.7°, θmin = 2.4°
Absorption correction: empirical (using intensity measurements) (SADABS; Bruker, 1998)	h = −16→24
Tmin = 0.045, Tmax = 0.681	k = −11→11
5523 measured reflections	l = −15→14

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)] = 0.050	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.129	All H-atom parameters refined
S = 1.02	w = 1/[σ^2(Fo^2) + (0.0744P)^2] where P = (Fo^2 + 2Fc^2)/3
1849 reflections	(Δ/σ)max < 0.001
138 parameters	Δρmax = 1.31 e Å^−3
6 restraints	Δρmin = −0.96 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
Cu	0.5000	−0.32918 (15)	0.2500	0.0435 (4)
Br1	0.39440 (7)	−0.43115 (10)	0.24630 (10)	0.0546 (3)
Br2	0.57585 (7)	−0.23991 (9)	0.45615 (9)	0.0523 (3)
N1	0.1810 (5)	0.0220 (8)	0.0548 (7)	0.0433 (19)
H1	0.141 (4)	−0.038 (7)	0.021 (8)	0.04 (3)*
C2	0.2598 (6)	−0.0111 (9)	0.1253 (8)	0.040 (2)
N2	0.2777 (6)	−0.1393 (8)	0.1300 (9)	0.054 (2)
H2A	0.329 (3)	−0.161 (8)	0.165 (7)	0.02 (2)*
H2B	0.232 (6)	−0.191 (13)	0.101 (13)	0.13 (6)*
C3	0.3147 (6)	0.0932 (9)	0.1849 (8)	0.041 (2)
Br3	0.42727 (7)	0.05131 (11)	0.28619 (10)	0.0610 (4)
C4	0.2868 (7)	0.2212 (9)	0.1690 (10)	0.047 (3)
H4	0.318 (6)	0.299 (8)	0.209 (9)	0.09 (4)*
C5	0.2059 (7)	0.2499 (8)	0.0931 (8)	0.040 (2)
Br5	0.16690 (8)	0.42578 (9)	0.06204 (10)	0.0579 (4)
C6	0.1478 (7)	0.1468 (9)	0.0331 (9)	0.044 (2)
N6	0.0681 (6)	0.1620 (9)	−0.0454 (9)	0.061 (3)
H6A	0.044 (7)	0.234 (8)	−0.031 (11)	0.08 (4)*
H6B	0.031 (7)	0.089 (9)	−0.079 (11)	0.10 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu	0.0432 (11)	0.0436 (9)	0.0421 (9)	0.000	0.0250 (9)	0.000
Br1	0.0594 (8)	0.0534 (6)	0.0599 (7)	−0.0096 (5)	0.0407 (6)	−0.0035 (5)
Br2	0.0581 (7)	0.0395 (5)	0.0477 (6)	0.0029 (5)	0.0259 (6)	−0.0071 (4)
N1	0.045 (6)	0.036 (4)	0.043 (5)	0.000 (4)	0.024 (5)	−0.003 (4)
C2	0.052 (7)	0.036 (5)	0.033 (5)	0.004 (5)	0.028 (5)	−0.001 (4)
N2	0.047 (7)	0.045 (5)	0.068 (6)	0.005 (5)	0.034 (6)	−0.005 (4)
C3	0.035 (6)	0.053 (6)	0.033 (5)	0.004 (4)	0.019 (5)	−0.001 (4)
Br3	0.0457 (7)	0.0738 (8)	0.0606 (7)	0.0017 (5)	0.0307 (6)	−0.0097 (5)
C4	0.070 (8)	0.036 (5)	0.048 (6)	−0.006 (5)	0.043 (6)	−0.007 (4)
C5	0.062 (7)	0.029 (5)	0.038 (5)	0.006 (4)	0.034 (5)	0.002 (4)
Br5	0.0830 (9)	0.0376 (5)	0.0605 (7)	0.0093 (5)	0.0473 (7)	0.0014 (4)
C6	0.055 (7)	0.043 (5)	0.035 (5)	0.008 (5)	0.027 (5)	0.007 (4)
N6	0.064 (8)	0.045 (5)	0.061 (6)	0.011 (5)	0.031 (6)	0.001 (4)

Geometric parameters (Å, º)

Cu—Br1	2.3790 (16)	N2—H2B	0.93 (5)
Cu—Br1^i	2.3790 (16)	C3—C4	1.373 (13)
Cu—Br2	2.3939 (15)	C3—Br3	1.894 (9)
Cu—Br2^i	2.3939 (15)	C4—C5	1.358 (15)
N1—C2	1.335 (12)	C4—H4	0.95 (5)
N1—C6	1.374 (12)	C5—C6	1.410 (14)
N1—H1	0.90 (5)	C5—Br5	1.881 (9)
C2—N2	1.331 (12)	C6—N6	1.317 (13)
C2—C3	1.388 (13)	N6—H6A	0.96 (5)
N2—H2A	0.88 (4)	N6—H6B	0.95 (5)
Br1—Cu—Br1^i	128.95 (9)	C4—C3—C2	120.0 (9)
Br1—Cu—Br2	97.52 (5)	C4—C3—Br3	122.4 (8)
Br1^i—Cu—Br2	101.08 (5)	C2—C3—Br3	117.6 (7)
Br1—Cu—Br2^i	101.08 (4)	C5—C4—C3	121.6 (9)
Br1^i—Cu—Br2^i	97.52 (4)	C5—C4—H4	111 (7)
Br2—Cu—Br2^i	135.97 (9)	C3—C4—H4	128 (7)
C2—N1—C6	127.9 (9)	C4—C5—C6	120.3 (8)
C2—N1—H1	123 (6)	C4—C5—Br5	122.1 (7)
C6—N1—H1	108 (6)	C6—C5—Br5	117.6 (8)
N2—C2—N1	117.2 (9)	N6—C6—N1	119.7 (9)
N2—C2—C3	126.7 (10)	N6—C6—C5	126.0 (9)
N1—C2—C3	116.0 (8)	N1—C6—C5	114.1 (9)
C2—N2—H2A	118 (5)	C6—N6—H6A	118 (7)
C2—N2—H2B	110 (10)	C6—N6—H6B	123 (8)
H2A—N2—H2B	131 (10)	H6A—N6—H6B	108 (10)
C6—N1—C2—N2	−178.4 (9)	C3—C4—C5—C6	3.3 (14)
C6—N1—C2—C3	0.7 (14)	C3—C4—C5—Br5	−175.8 (7)
N2—C2—C3—C4	178.7 (9)	C2—N1—C6—N6	176.1 (10)
N1—C2—C3—C4	−0.3 (13)	C2—N1—C6—C5	0.8 (13)
N2—C2—C3—Br3	−1.1 (13)	C4—C5—C6—N6	−177.6 (10)
N1—C2—C3—Br3	180.0 (6)	Br5—C5—C6—N6	1.5 (13)
C2—C3—C4—C5	−1.7 (14)	C4—C5—C6—N1	−2.7 (12)
Br3—C3—C4—C5	178.1 (7)	Br5—C5—C6—N1	176.4 (6)

Symmetry code: (i) −x+1, y, −z+1/2.