catena-Poly[[(acetonitrile-N)dichlorocopper(II)]-μ-2,5-dimethylpyrazine-κ²N:N′]

In the structure of the title compound, [CuCl₂­(C₂H₃N)(C₆H₈N₂)], each Cu²⁺ cation is surrounded by two 2,5-di­methyl­pyrazine ligands, one aceto­nitrile ligand and two Cl⁻ anions within a distorted tetragonal pyramid. The aceto­nitrile ligand, which forms the apex of the pyramid, the Cu²⁺ cation and the Cl⁻ anions are all located in general positions, whereas each of the 2,5-di­methyl­pyrazine ligands is located about a centre of inversion. The 2,5-di­methyl­pyrazine ligands connect the Cu²⁺ cations via μ-N:N′ coordination to form chains.

S1. Comment

This study of the title compound, (I), is part of a project dealing with the synthesis and structural characterization of coordination polymers based on copper halides and multidentate amino ligands (Näther et al., 2001; Näther & Greve, 2001; Näther & Jess, 2001). 2,5-Dimethylpyrazine was selected because it is a suitable compound for the formation of coordination polymers via µ-N:N' coordination of two different metal cations. There are only a few compounds described in the literature which are based on this ligand, such as catena[(trifluoromethanesulfonato-O-)(µ₂-2,5-dimethylpyrazine-N,N')- (2,5-dimethylpyrazine-N)copper(I)] (Otieno et al., 1990), and catena[tris(µ₂-2,5-dimethylpyrazine)dicopper(I) bis(hexafluorophosphate)] and catena[bis(µ₂-2,5-dimethylpyrazine)copper(I) hexafluorophosphate] (Otieno et al., 1993). In all of these compounds, one- or two-dimensional coordination polymers are formed in which the 2,5-dimethylpyrazine acts as a bridging ligand. \sch

In the crystal structure of (I), the Cu²⁺ cations are fivefold coordinated by two N atoms of two crystallographically independent 2,5-dimethylpyrazine ligands, one N atom of an acetonitrile ligand and two crystallographically independent Cl^- anions (Fig. 1). The 2,5-dimethylpyrazine ligands are located around centres of inversion, whereas the Cu²⁺ cation, the Cl^- anion and the acetonitrile molecule are located in general positions.

The coordination polyhedron around the Cu²⁺ cation can be described as a distorted tetragonal pyramid, with the Cl^- anions and the N atoms of the 2,5-dimethylpyrazine ligands in the basal plane and the N atom of the acetonitrile ligand at the apex of the pyramid. The deviation of the Cu²⁺ cation from the plane formed by Cu1, Cl1, Cl2, N1 and N2 amounts to 0.1764 (7) Å. The Cu—Cl bond lengths are 2.2577 (9) and 2.2608 (8) Å, and the Cu—N distances to the 2,5-dimethylpyrazine ligand are 2.067 (2) and 2.071 (2) Å. The Cu—N distance of 2.349 (3) Å to the apical N atom is elongated compared with the other Cu—N distances, showing that this is a much weaker interaction. The N—Cu—N, Cl—Cu—Cl and N—Cu—Cl angles are in the ranges 168.36 (9)–168.22 (3)° or 88.32 (6)–90.78 (6)° (Table 1).

There are several structures known in the literature in which Cu²⁺ cations are five-coordinated by two Cl^- ligands and three N atoms of organic ligands. A detailed analysis of their coordination polyhedra shows that most of them have a distorted tetragonal pyramidal coordination. In these cases, either the Cl^- or the N ligand can occupy the apical position. However, the Cu—X distance to the apical ligand (X is Cl or N) is always much longer than those within the basal plane. The geometrical parameters in (I) are comparable with those found in some of the structures mentioned above if they contain one N atom in the apical position, e.g. dichloro-[6-ethoxy-6-hydroxy- 1,3,5-tri(2,6)pyridacyclohexaphane-2,4-dione]copper(II) ethanol solvate (Newkome et al., 1990) or dichloro-[1-(pent-3-ynyl)-1,4,7-triazacyclononane]copper(II) (Ellis et al., 1999). However, the exact geometry depends strongly on the nature of the organic ligands, e.g. whether mono- or multidentate ligands are present.

The 2,5-dimethylpyrazine ligands in (I) connect the Cu²⁺ cations into chains via µ-N:N' coordination (Fig. 2). The C—N—Cu angles deviate only slightly from 120° and the Cu²⁺ cation is located in the plane of the six-membered ring, which shows that the cation is oriented in the direction of the lone-pair on the N atom. For the longer Cu—N distance to the apical N atom, the lone-pair directionality is much less distinctive. The methyl groups of the 2,5-dimethylpyrazine ligands are located below the basal plane of the pyramid. Therefore, a possible coordination of the cations with the formation of an octahedral geometry, which is frequently observed for Cu²⁺ cations, is prevented.

There are some short intermolecular Cl···H distances between the Cl^- anions and the methyl H atoms of neighbouring parallel chains, which may be interpreted as hydrogen bonds (Table 2).

Related literature

For related literature, see: Ellis et al. (1999); Gmelin (1958); Näther & Greve (2001); Näther & Jess (2001); Näther, Jess & Greve (2001); Newkome et al. (1990); Otieno et al. (1990, 1993).

S2. Experimental

Compound (I) was prepared by the reaction of CuCl (155.25 mg, 1.60 mmol), freshly prepared using the method given in Gmelin (1958), and 2,5-dimethylpyrazine (81 mg, 0.75 mmol) in acetonitrile (6 ml) at room temperature in a glass container. After stirring for 2 d, the mixture was allowed to stand at room temperature until most of the solvent had evaporated. The resulting precipitate was filtered off. The product consisted of a phase mixture of equivalent amounts of blue crystals of (I) and red crystals of a new compound, CuCl-2,5-dimethylpyrazine, which could be separated by hand.

S3. Refinement

Aromatic H atoms were positioned with idealized geometry and refined isotropically using a riding model, with C—H = 0.96 Å and U_iso(H) = 1.2U_eq(C). Methyl H atoms were identified from difference syntheses and their positions idealized, and then refined as rigid groups allowed to rotate but not tip, with C—H = 0.93 Å and U_iso(H) = 1.5U_eq(C). Query constraints.

Computing details

Data collection: DIF4 (Stoe & Cie, 1992); cell refinement: DIF4; data reduction: REDU4 (Stoe & Cie, 1992); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP in SHELXTL (Bruker, 1998); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The molecular structure of (I), showing the copper coordination and the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii [symmetry codes: (i) 1 - x, 2 - y, 1 - z; (ii) 2 - x, 1 - y, 1 - z].
	Fig. 2. A view of the crystal structure of (I) along (010) showing the infinite chains.

Catena-poly[[(acetonitrile-N)dichlorocopper(II)]-µ-2,5-dimethylpyrazine-N:N']

Crystal data

[CuCl2(C6H8N2)(C2H3N)]	F(000) = 572
Mr = 283.64	Dx = 1.703 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 11.653 (2) Å	Cell parameters from 46 reflections
b = 7.3533 (12) Å	θ = 12.5–17.5°
c = 13.443 (2) Å	µ = 2.42 mm^−1
β = 106.190 (12)°	T = 293 K
V = 1106.2 (3) Å^3	Block, blue
Z = 4	0.11 × 0.09 × 0.08 mm

Data collection

Stoe AED-II diffractometer	1678 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.027
Graphite monochromator	θmax = 27.0°, θmin = 2.7°
ω/θ scans	h = 0→14
Absorption correction: numerical (X-SHAPE; Stoe & Cie, 1998)	k = −9→1
Tmin = 0.770, Tmax = 0.824	l = −17→16
3045 measured reflections	4 standard reflections every 120 min
2415 independent reflections	intensity decay: none

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)] = 0.029	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.073	H-atom parameters constrained
S = 1.00	w = 1/[σ^2(Fo^2) + (0.0369P)^2] where P = (Fo^2 + 2Fc^2)/3
2415 reflections	(Δ/σ)max = 0.001
130 parameters	Δρmax = 0.34 e Å^−3
0 restraints	Δρmin = −0.28 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
Cu1	0.73261 (3)	0.71726 (5)	0.48792 (2)	0.02628 (11)
Cl1	0.72904 (7)	0.59965 (11)	0.64217 (6)	0.0410 (2)
Cl2	0.75918 (7)	0.88033 (11)	0.35349 (6)	0.0423 (2)
N1	0.59361 (19)	0.8873 (3)	0.49430 (16)	0.0260 (5)
C1	0.6161 (2)	1.0527 (4)	0.5397 (2)	0.0264 (6)
C2	0.4796 (2)	0.8372 (4)	0.4560 (2)	0.0279 (6)
H2	0.4633	0.7235	0.4250	0.033*
N2	0.89359 (19)	0.5888 (3)	0.49796 (17)	0.0265 (5)
C3	0.7414 (2)	1.1131 (4)	0.5843 (2)	0.0368 (7)
H3A	0.7799	1.0357	0.6413	0.055*
H3B	0.7421	1.2363	0.6082	0.055*
H3C	0.7832	1.1065	0.5321	0.055*
C4	0.8976 (2)	0.4497 (4)	0.4342 (2)	0.0300 (6)
H4	0.8267	0.4120	0.3873	0.036*
C5	0.9972 (2)	0.6406 (4)	0.5650 (2)	0.0278 (6)
C6	0.9991 (3)	0.7970 (5)	0.6356 (3)	0.0478 (8)
H6A	0.9851	0.9077	0.5962	0.072*
H6B	1.0756	0.8031	0.6862	0.072*
H6C	0.9377	0.7813	0.6699	0.072*
N3	0.6138 (2)	0.4894 (4)	0.38692 (19)	0.0400 (6)
C7	0.5697 (3)	0.3725 (4)	0.3344 (2)	0.0336 (7)
C8	0.5158 (3)	0.2221 (4)	0.2678 (2)	0.0425 (7)
H8A	0.5638	0.1150	0.2880	0.064*
H8B	0.5110	0.2517	0.1972	0.064*
H8C	0.4370	0.2002	0.2743	0.064*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.02129 (17)	0.02640 (17)	0.03379 (18)	0.00768 (16)	0.01206 (12)	0.00112 (16)
Cl1	0.0475 (5)	0.0413 (4)	0.0403 (4)	0.0119 (4)	0.0220 (4)	0.0075 (3)
Cl2	0.0407 (4)	0.0456 (5)	0.0471 (4)	0.0092 (4)	0.0228 (4)	0.0135 (4)
N1	0.0235 (12)	0.0248 (12)	0.0319 (12)	0.0064 (10)	0.0116 (10)	0.0026 (10)
C1	0.0262 (14)	0.0234 (14)	0.0323 (14)	0.0049 (12)	0.0125 (12)	0.0012 (11)
C2	0.0258 (14)	0.0226 (13)	0.0371 (15)	0.0043 (11)	0.0120 (12)	−0.0016 (11)
N2	0.0221 (12)	0.0277 (12)	0.0316 (11)	0.0064 (10)	0.0105 (10)	0.0016 (10)
C3	0.0277 (15)	0.0314 (16)	0.0515 (18)	0.0042 (13)	0.0113 (14)	−0.0062 (14)
C4	0.0221 (14)	0.0344 (16)	0.0336 (14)	0.0024 (12)	0.0081 (12)	−0.0058 (13)
C5	0.0217 (14)	0.0281 (14)	0.0341 (15)	0.0010 (12)	0.0085 (12)	−0.0021 (12)
C6	0.0276 (16)	0.050 (2)	0.063 (2)	0.0022 (16)	0.0074 (15)	−0.0252 (18)
N3	0.0321 (14)	0.0418 (16)	0.0468 (16)	−0.0017 (12)	0.0124 (13)	−0.0026 (13)
C7	0.0252 (15)	0.0374 (17)	0.0404 (16)	0.0062 (14)	0.0128 (13)	0.0050 (15)
C8	0.0381 (16)	0.0420 (18)	0.0475 (16)	0.0002 (15)	0.0117 (14)	−0.0037 (16)

Geometric parameters (Å, º)

Cu1—N1	2.067 (2)	C3—H3B	0.9600
Cu1—N2	2.071 (2)	C3—H3C	0.9600
Cu1—Cl1	2.2577 (9)	C4—C5^ii	1.392 (4)
Cu1—Cl2	2.2608 (8)	C4—H4	0.9300
Cu1—N3	2.349 (3)	C5—C4^ii	1.392 (4)
N1—C2	1.336 (3)	C5—C6	1.487 (4)
N1—C1	1.354 (3)	C6—H6A	0.9600
C1—C2^i	1.392 (4)	C6—H6B	0.9600
C1—C3	1.483 (4)	C6—H6C	0.9600
C2—C1^i	1.392 (4)	N3—C7	1.140 (4)
C2—H2	0.9300	C7—C8	1.451 (4)
N2—C4	1.343 (3)	C8—H8A	0.9600
N2—C5	1.345 (3)	C8—H8B	0.9600
C3—H3A	0.9600	C8—H8C	0.9600
N1—Cu1—N2	168.36 (9)	H3A—C3—H3B	109.5
N1—Cu1—Cl1	88.75 (6)	C1—C3—H3C	109.5
N2—Cu1—Cl1	90.78 (6)	H3A—C3—H3C	109.5
N1—Cu1—Cl2	89.77 (6)	H3B—C3—H3C	109.5
N2—Cu1—Cl2	88.32 (6)	N2—C4—C5^ii	123.1 (3)
Cl1—Cu1—Cl2	168.22 (3)	N2—C4—H4	118.5
N1—Cu1—N3	96.50 (9)	C5^ii—C4—H4	118.5
N2—Cu1—N3	95.12 (9)	N2—C5—C4^ii	119.6 (2)
Cl1—Cu1—N3	95.67 (7)	N2—C5—C6	119.8 (2)
Cl2—Cu1—N3	96.11 (7)	C4^ii—C5—C6	120.6 (2)
C2—N1—C1	117.9 (2)	C5—C6—H6A	109.5
C2—N1—Cu1	121.62 (18)	C5—C6—H6B	109.5
C1—N1—Cu1	120.46 (18)	H6A—C6—H6B	109.5
N1—C1—C2^i	119.0 (2)	C5—C6—H6C	109.5
N1—C1—C3	119.8 (2)	H6A—C6—H6C	109.5
C2^i—C1—C3	121.3 (2)	H6B—C6—H6C	109.5
N1—C2—C1^i	123.1 (3)	C7—N3—Cu1	170.8 (2)
N1—C2—H2	118.5	N3—C7—C8	178.9 (3)
C1^i—C2—H2	118.5	C7—C8—H8A	109.5
C4—N2—C5	117.3 (2)	C7—C8—H8B	109.5
C4—N2—Cu1	119.84 (18)	H8A—C8—H8B	109.5
C5—N2—Cu1	122.82 (18)	C7—C8—H8C	109.5
C1—C3—H3A	109.5	H8A—C8—H8C	109.5
C1—C3—H3B	109.5	H8B—C8—H8C	109.5

Symmetry codes: (i) −x+1, −y+2, −z+1; (ii) −x+2, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C3—H3B···Cl1^iii	0.96	2.72	3.673 (3)	171
C8—H8A···Cl2^iv	0.96	2.80	3.724 (3)	163

Symmetry codes: (iii) x, y+1, z; (iv) x, y−1, z.