Bis­(2-amino-6-methyl­pyridinium) tetra­bromido­cuprate(II)

Rawhi H Al-Far; Basem Fares Ali; Salim F Haddad

doi:10.1107/S1600536808010647

. 2008 Apr 23;64(Pt 5):m689–m690. doi: 10.1107/S1600536808010647

Bis(2-amino-6-methylpyridinium) tetrabromidocuprate(II)

Rawhi H Al-Far ^a,^*, Basem Fares Ali ^b, Salim F Haddad ^c

PMCID: PMC2961314 PMID: 21202225

Abstract

In the crystal structure of the title compound, (C₆H₉N₂)₂[CuBr₄], the geometry around the Cu atom is intermediate between tetrahedral (T_d) and square planar (D_4h). Each [CuBr₄]²⁻ anion is connected non-symmetrically to four surrounding cations through N—H⋯X (pyridine and amine proton) hydrogen bonds, forming chains of the ladder-type running parallel to the crystallographic b axis. These layers are further connected by means of offset face-to-face interactions (parallel to the a axis), giving a three-dimensional network. Cation π–π stacking [centroid separations of 3.69 (9) and 3.71 (1) Å] and Br⋯aryl interactions [3.72 (2) and 4.04 (6) Å] are present in the crystal structure. There are no intermolecular Br⋯Br interactions.

Related literature

For related literature, see: Al-Far & Ali (2007a ▶,b ▶); Ali & Al-Far (2007 ▶, 2008 ▶); Allen et al. (1987 ▶, 1997 ▶); Desiraju & Steiner (1999 ▶); Dolling et al. (2001 ▶); Haddad et al. (2006 ▶); Hunter (1994 ▶); Panunto et al. (1987 ▶); Raithby et al. (2000 ▶); Robinson et al. (2000 ▶); Luque et al. (2001 ▶).

Experimental

Crystal data

(C₆H₉N₂)₂[CuBr₄]
M _r = 601.45
Triclinic,
a = 7.9238 (9) Å
b = 8.2521 (11) Å
c = 15.2916 (18) Å
α = 78.472 (11)°
β = 82.839 (10)°
γ = 89.947 (14)°
V = 971.8 (2) Å³
Z = 2
Mo Kα radiation
μ = 9.35 mm⁻¹
T = 293 (2) K
0.20 × 0.15 × 0.10 mm

Data collection

Bruker P4 diffractometer
Absorption correction: ψ scan (XSCANS; Bruker, 1996 ▶)T _min = 0.199, T _max = 0.392
4381 measured reflections
3567 independent reflections
2018 reflections with I > 2σ(I)
R _int = 0.053

Refinement

R[F ² > 2σ(F ²)] = 0.058
wR(F ²) = 0.153
S = 1.00
3567 reflections
190 parameters
H-atom parameters constrained
Δρ_max = 0.57 e Å⁻³
Δρ_min = −0.65 e Å⁻³

Data collection: XSCANS (Bruker, 1996 ▶); cell refinement: XSCANS; data reduction: SHELXTL (Sheldrick, 2008 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808010647/at2561sup1.cif

e-64-0m689-sup1.cif^{(17.6KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808010647/at2561Isup2.hkl

e-64-0m689-Isup2.hkl^{(174.9KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected geometric parameters (Å, °).

Br1—Cu1	2.3848 (14)
Cu1—Br2	2.3575 (16)
Cu1—Br4	2.3713 (14)
Cu1—Br3	2.3765 (16)

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Br2—Cu1—Br4	101.27 (6)
Br2—Cu1—Br3	132.23 (7)
Br4—Cu1—Br3	100.99 (6)
Br2—Cu1—Br1	98.36 (6)
Br4—Cu1—Br1	129.74 (7)
Br3—Cu1—Br1	98.93 (6)

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Table 2. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1⋯Br3ⁱ	0.86	2.47	3.324 (7)	172
N8—H8⋯Br1	0.86	2.52	3.367 (8)	170
N9—H9B⋯Br4ⁱⁱ	0.86	2.64	3.487 (10)	168
N2—H2B⋯Br2ⁱⁱⁱ	0.86	2.73	3.547 (9)	158

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) .

Acknowledgments

Al al-Bayt University and Al-Balqa’a Applied University are thanked for financial support.

supplementary crystallographic information

Comment

Non-covalent interactions play an important role in organizing structural units in both natural and artificial systems. They exercise important effects on the organization and properties of many materials in areas such as biology (Hunter 1994; Desiraju & Steiner 1999), crystal engineering (see for example: Allen et al.,1997; Dolling et al., 2001) and material science (Panunto et al., 1987; Robinson et al., 2000). The interactions governing the crystal organization are expected to affect the packing and then the specific properties of solids. In connection with ongoing studies (Ali & Al-Far, 2008; Ali & Al-Far, 2007; Al-Far & Ali, 2007a,b) of the structural aspects of halo-metal anion salts, we herein report the crystal structure of title compound (I) along with its crystal supramolecularity.

The asymmetric unit in (I) contains one anion and two cations (Fig. 1). The Cu—Br distances are similar, but Cu—Br2 that is engaged in longest hydrogen bonding is shorter than the others (Table 2). The Cu—Br bond distances fall in the range of bond distances reported previously for compounds containing Cu—Br anions (Luque et al., 2001; Raithby et al., 2000; Haddad et al., 2006). The bond angles are present in two distinguished sets. The first contains four angles in the range 98.36 (6) - 101.27 (6)° which are much lower than the other set which contains two angles 129.74 (7) and 132.23 (7)°. Accordingly the geometry of CuBr₄^2- anion is an intermediate between regular tetrahedral (T_d) and square planar (D_4h) (Table 2).

The cation bond lengths and angles are within expected range (Allen et al. 1987), with the cations (type A contains N1 and type B contains N8) being of course planar.

In the structure (Fig. 2), each anion is connected nonsymmetrically to four cations interacting via N—H···Br and HN—H···Br hydrogen bonding, Table 3, forming chains of the ladder type run approximately parallel to the crystallographic b-axis. The cations type A represnt the rungs while both cations type B and anions represent the rails of a ladder (Fig. 3).

There are no Br···Br interactions were observed (shortest being 4.6651 (17) Å). Cations π···π stacking (in a-ditrection) is observed, with significant ones being X1A···X1A [2 - x, 2 - y, 2 - z] and X1B···X1B [- x, 1 - y, 1 - z] of 3.69 (9) and 3.71 (1), respectively. Also Br···aryl interactions present by the unusually short Br(1) [-x, 2 - y, 1 - z]···X1B contact of 3.72 (2) Å and the longer Br(3)···X1A of 4.04 (6) Å contact.

Experimental

To a warm solution of 2-amino-6-methylpyridine (2 mmol) dissolved in 10 ml absolute ethanol acidified with 3 ml 60% HBr, CuBr₂ (1 mmol) dissolved in 10 ml absolute ethanol was added. The resulting solution was then treated with 2 ml of Br_{2 (}_l₎. The mixture was refluxed for 2 h. The mixture was then allowed to stand and evaporate slowly at room temperature. In two days time, block blue crystals were formed and filtered (yield, 86.5%). A single-crystal suitable for diffraction measurements were chosen and used for data collection.