Poly­[[aqua­copper(I)-μ-bromo]-μ-(5-methyl­pyrazine-2-carboxyl­ato)-κ³N⁴:O,N¹-[di­aqua­copper(II)]-μ-(5-methyl­pyrazine-2-carboxyl­ato)-κ³O,N¹:N⁴-[aqua­copper(I)-μ-bromo]]

In the structure of the title compound, [Cu₃Br₂(C₆H₅N₂O₂)₂(H₂O)₄], both copper(I) and copper(II) cations are present. The copper(II) cations are located on centres of inversion and are coordinated by two N atoms and two carboxyl­ate O atoms from two symmetry-related 5-methyl­pyrazine-2-carboxyl­ate anions, with two water mol­ecules completing a distorted octahedron. The copper(I) cations are coordinated by the second N atom of the 5-methyl­pyrazine-2-carboxyl­ate anion, one water mol­ecule and two bromide anions within a distorted tetrahedron. Each of the bromide anions connects two symmetry-equivalent copper(I) cations to form zigzag-like CuBr chains. These chains are connected by the [di­aqua­bis(5-methyl­pyrazine-2-carboxyl­ato)]copper(II) complexes, forming corrugated sheets parallel to (100). The CuBr chains and the sheets are connected via O—H...O and O—H...Br hydrogen bonding.

S1. Comment

Recently, we have been interested in the synthesis, structures and properties of new coordination polymers based on copper(I) halides and aromatic amine ligands (Näther et al., 2001; Näther & Greve, 2001; Näther & Je\&s, 2001). Dependent on the copper(I) halide and the nature of the amine ligand, interesting CuX (X = Cl, Br or I) substructures, such as rings, tetramers, and single or double chains, are found (Blake et al., 1999; Graham et al., 2000; Ro\&senbeck & Sheldrick, 2000; Persky et al., 2001). In contrast to the most common octahedral coordination of copper(II) cations, the copper(I) cations in such compounds are four-coordinate within distorted tetrahedra. During our investigations, we isolated red crystals of the title compound, (I), which contain both copper(I) and copper(II) cations in their typical coordination polyhedra.

The copper(II) cations of (I) are coordinated by one N atom and one carboxylate O atom from each of the two symmetry-equivalent 5-methylpyrazine-2-carboxylate anions, which are related by a centre of inversion located at the copper(II) cation. The coordination sphere of the copper(II) cations is completed by two long contacts of 2.552 (3) Å to the O atoms of two symmetry-related water molecules, forming a [diaquabis(5-methylpyrazine-2-carboxylato]copper(II) complex. The copper(II) coordination in this complex shows a typical Jahn–Teller distortion and the coordination polyhedron can be described as a strongly distorted octahedron, with the water molecules in axial positions and the carboxylate O atoms and the N atoms in the basal plane of the octahedron.

The bond lengths and angles about Cu1 of the copper(II) cation are comparable with those in catena-[bis(µ²-2-methylpyrazine-5-carboxylato-N,N',O)diaquacopper(II)- silver(I) tetrafluoroborate] and catena-[bis(µ²-2-methylpyrazine-5-carboxylato-N,N',O)diaquacopper(II)- silver(I) nitrate] (Dong et al., 2000). In the related compound, aquabis(2-methylpyrazine-5-carboxylato-N,O)copper(II) trihydrate (Dong et al., 2000), the copper(II) cation is only five-coordinated by the N atom and the carboxylate O atom of two pyrazine ligands plus just one water molecule. In this structure, the Cu—N and Cu—O bond lengths are comparable to those in the title compound, but the Cu—O distance to the water molecule is shortened by about 0.2 Å.

The copper(II) and copper(I) cations are connected via µ-N:N coordination by the N atoms of the anions. The geometry of this interaction, e.g. the relative orientation of the copper cations and the pyrazine unit, shows that the copper cations are oriented in the direction of the nitrogen lone-pair.

The copper(I) cations are coordinated by the second N atom of the 5-methylpyrazine-2-carboxylate anions involved in copper(II) coordination, one water molecule and two symmetry related bromide anions within a distorted tetrahedron. Each of the bromide anions connect two symmetry equivalent copper(I) cations forming zigzag-like CuBr chains in the direction of the crystallographic c axis. Such zigzag chains are frequently observed in the crystal structures of Cu^IX (X = Cl, Br or I) coordination polymers (Blake et al., 1999). These CuBr chains are connected via the N atoms of the [diaquabis(5-methylpyrazine-2-carboxylato]copper(II) complexes, forming corrugated sheets parallel to (100), which are stacked in the direction of the crystallographically a axis. The water molecules are connected via O—H···O hydrogen bonding to other water molecules and to the carboxylate O atoms which are not involved in copper(II) coordination. There are additional short intermolecular contacts between the water molecules and the bromide anions. The geometry of this interaction indicates O—H···Br hydrogen bonding. The corrugated sheets are further connected by O—H···O hydrogen bonding between the water molecules to form a three-dimensional network.

There are several structures known in which formal copper(I) and copper(II) cations are both present, such as in tetraisothiocyanatocopper(I)- bis(µ²-{2-[(3-aminopropyl)amino]ethanolate}-N,N,µ^O)-dicopper(II) thiocyanato (Nieminen, 1981), but in most of them, the cations are embedded in macrocyclic ligands. To the best of our knowledge, no structure has been reported in which the typical Cu^IX (X = Cl, Br or I) substructures known from Cu^IX coordination polymers are interconnected via typical distorted octahedral copper(II) complexes.

Related literature

For related literature, see: Blake et al. (1999); Dong et al. (2000); Gmelin (1958); Graham et al. (2000); Näther & Greve (2001); Näther & Jeß (2001); Näther, Jeß & Greve (2001); Nieminen (1981); Persky et al. (2001); Roßenbeck & Sheldrick (2000).

S2. Experimental

The title compound was prepared by the reaction of 5-methylpyrazine-2-carboxylic acid (34.6 mg, 0.25 mmol; ACROS) and CuBr [71.7 mg, 0.5 mmol; freshly prepared according to the recipe given in Gmelin (1958)] in (3 ml) at room-temperature in a glass container. After two days, dark-red crystals of the title compound had formed and could be isolated manually. The reaction mixture additionally contained a small amount of a green microcrystalline phase which could not be identified.

S3. Refinement

The positions of all H atoms were initially located from a difference map. The aromatic H atoms were then positioned with idealized geometry and refined using a riding model. The methyl H atoms were disordered and were refined as idealized disordered methyl groups with two positions rotated from each other by 60° and site-occupation factors of 0.69 and 0.31, respectively. The H atoms of the water molecules were identified from difference syntheses but were refined as rigid groups with idealized O—H bond lengths of 0.82 Å. All H atoms were assigned fixed isotropic displacement parameters defined as U_iso(H) = 1.5U_eq[C(methyl)], 1.5U_eqO(OH) or 1.2U_eq[C(aromatic)].

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, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP in SHELXTL (Bruker, 1998); software used to prepare material for publication: CIFTAB in SHELXL97.

Figures

	Fig. 1. The crystal structure of the title compound showing the copper coordination with labelling and displacement ellipsoids drawn at the 50% probability level (the disorder of the methyl H atoms is shown using full and open bonds).
	Fig. 2. View of the structure on (100). The non-water H atoms have been omitted for clarity [symmetry codes: (i) -x + 2, -y + 1, -z + 1; (ii) x, -y + 0.5, z - 0.5; (iii) x, -y + 0.5, z + 0.5].

Poly[[aquacopper(I)-µ-bromo]-µ-(5-methylpyrazine-2-carboxylato)-N⁴:O,N¹– [diaquacopper(II)]-µ-(5-methylpyrazine-2-carboxylato)-O,N¹:N⁴– [aquacopper(I)]-µ-bromo]

Crystal data

[Cu3Br2(C6H5N2O2)2(H2O)4]	F(000) = 678
Mr = 696.74	Dx = 2.307 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 7.1796 (18) Å	Cell parameters from 114 reflections
b = 23.238 (3) Å	θ = 10–19°
c = 6.5358 (16) Å	µ = 7.18 mm^−1
β = 113.069 (18)°	T = 293 K
V = 1003.2 (4) Å^3	Block, red
Z = 2	0.10 × 0.08 × 0.05 mm

Data collection

Philips PW-1100 four-circle diffractometer	1866 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.018
Graphite monochromator	θmax = 28.0°, θmin = 3.1°
ω–θ scans	h = −9→8
Absorption correction: numerical (X-SHAPE; Stoe & Cie, 1998)	k = −1→30
Tmin = 0.341, Tmax = 0.390	l = 0→8
2741 measured reflections	4 standard reflections every 120 min
2420 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)] = 0.026	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.064	H atoms treated by a mixture of independent and constrained refinement
S = 1.02	w = 1/[σ^2(Fo^2) + (0.0279P)^2 + 0.5653P] where P = (Fo^2 + 2Fc^2)/3
2420 reflections	(Δ/σ)max = 0.001
134 parameters	Δρmax = 0.54 e Å^−3
0 restraints	Δρmin = −0.47 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	Occ. (<1)
Cu1	1.0000	0.5000	0.5000	0.02693 (13)
Cu2	0.28020 (6)	0.296630 (18)	0.18925 (7)	0.03403 (11)
Br1	0.16266 (5)	0.293378 (13)	0.50207 (5)	0.02957 (9)
N1	0.8228 (3)	0.43139 (10)	0.4021 (4)	0.0214 (5)
C1	0.6942 (4)	0.42812 (12)	0.5065 (5)	0.0231 (6)
C2	0.5475 (4)	0.38661 (13)	0.4483 (5)	0.0260 (6)
H2	0.4574	0.3858	0.5189	0.031*
N2	0.5295 (3)	0.34678 (10)	0.2917 (4)	0.0252 (5)
C3	0.6626 (4)	0.34869 (12)	0.1928 (5)	0.0240 (6)
C4	0.8096 (4)	0.39216 (12)	0.2504 (5)	0.0228 (6)
H4	0.9001	0.3934	0.1804	0.027*
C5	0.7219 (4)	0.47425 (13)	0.6773 (5)	0.0263 (6)
O1	0.8495 (3)	0.51316 (9)	0.6879 (4)	0.0306 (5)
O2	0.6219 (3)	0.47215 (10)	0.7946 (4)	0.0358 (5)
C6	0.6532 (5)	0.30433 (16)	0.0263 (6)	0.0390 (8)
H6A	0.7800	0.3031	0.0093	0.058*	0.69
H6B	0.5467	0.3137	−0.1138	0.058*	0.69
H6C	0.6269	0.2674	0.0755	0.058*	0.69
H6D	0.5224	0.2864	−0.0286	0.058*	0.31
H6E	0.7557	0.2758	0.0945	0.058*	0.31
H6F	0.6755	0.3221	−0.0949	0.058*	0.31
O3	1.2587 (3)	0.45098 (10)	0.8430 (4)	0.0341 (5)
H1O3	1.2845	0.4731	0.9484	0.051*
H2O3	1.3663	0.4442	0.8316	0.051*
O4	0.0654 (3)	0.35517 (10)	−0.0804 (4)	0.0378 (5)
H1O4	0.1121	0.3844	−0.1126	0.057*
H2O4	0.0507	0.3325	−0.1818	0.057*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.0259 (3)	0.0249 (2)	0.0381 (3)	−0.0093 (2)	0.0213 (2)	−0.0094 (2)
Cu2	0.0313 (2)	0.0337 (2)	0.0364 (2)	−0.01061 (17)	0.01265 (17)	−0.00484 (17)
Br1	0.03620 (17)	0.02869 (16)	0.02826 (15)	0.00700 (13)	0.01742 (13)	0.00549 (12)
N1	0.0191 (11)	0.0227 (12)	0.0245 (12)	−0.0025 (9)	0.0108 (9)	−0.0009 (9)
C1	0.0216 (13)	0.0233 (14)	0.0262 (14)	0.0015 (11)	0.0114 (11)	0.0013 (11)
C2	0.0225 (13)	0.0284 (15)	0.0303 (15)	−0.0049 (12)	0.0140 (12)	−0.0019 (12)
N2	0.0222 (12)	0.0250 (12)	0.0291 (13)	−0.0052 (10)	0.0108 (10)	−0.0008 (10)
C3	0.0198 (13)	0.0238 (14)	0.0262 (14)	−0.0010 (11)	0.0069 (11)	−0.0020 (12)
C4	0.0200 (13)	0.0257 (14)	0.0246 (14)	−0.0003 (11)	0.0106 (11)	−0.0008 (12)
C5	0.0226 (14)	0.0293 (15)	0.0292 (15)	−0.0011 (12)	0.0127 (12)	−0.0021 (12)
O1	0.0287 (10)	0.0312 (12)	0.0398 (13)	−0.0100 (9)	0.0220 (9)	−0.0137 (9)
O2	0.0336 (12)	0.0426 (13)	0.0432 (13)	−0.0111 (10)	0.0279 (10)	−0.0121 (11)
C6	0.0369 (18)	0.045 (2)	0.0389 (18)	−0.0148 (15)	0.0188 (15)	−0.0183 (15)
O3	0.0326 (12)	0.0353 (12)	0.0391 (13)	−0.0052 (10)	0.0189 (10)	−0.0061 (10)
O4	0.0449 (13)	0.0324 (12)	0.0409 (13)	−0.0012 (10)	0.0222 (11)	0.0020 (10)

Geometric parameters (Å, º)

Cu1—O1	1.9517 (19)	C3—C6	1.481 (4)
Cu1—N1	1.983 (2)	C4—H4	0.9300
Cu1—O3	2.552 (3)	C5—O2	1.240 (3)
Cu2—N2	2.018 (2)	C5—O1	1.269 (4)
Cu2—O4	2.281 (2)	C6—H6A	0.9600
Cu2—Br1^i	2.4030 (6)	C6—H6B	0.9600
Cu2—Br1	2.5000 (7)	C6—H6C	0.9600
N1—C4	1.323 (3)	C6—H6D	0.9600
N1—C1	1.348 (3)	C6—H6E	0.9600
C1—C2	1.368 (4)	C6—H6F	0.9600
C1—C5	1.503 (4)	O3—H1O3	0.8200
C2—N2	1.348 (4)	O3—H2O3	0.8199
C2—H2	0.9300	O4—H1O4	0.8201
N2—C3	1.348 (4)	O4—H2O4	0.8199
C3—C4	1.402 (4)
O1—Cu1—O1^ii	180.0	O2—C5—O1	125.0 (3)
O1—Cu1—N1^ii	96.56 (9)	O2—C5—C1	119.4 (3)
O1—Cu1—N1	83.44 (9)	O1—C5—C1	115.6 (2)
O1^ii—Cu1—N1	96.56 (9)	C5—O1—Cu1	114.79 (19)
N1^ii—Cu1—N1	180.0	C3—C6—H6A	109.5
N2—Cu2—O4	98.92 (9)	C3—C6—H6B	109.5
N2—Cu2—Br1^i	139.52 (7)	H6A—C6—H6B	109.5
O4—Cu2—Br1^i	97.44 (6)	C3—C6—H6C	109.5
N2—Cu2—Br1	106.61 (7)	H6A—C6—H6C	109.5
O4—Cu2—Br1	107.89 (6)	H6B—C6—H6C	109.5
Br1^i—Cu2—Br1	103.079 (19)	C3—C6—H6D	109.5
Cu2^iii—Br1—Cu2	106.195 (19)	H6A—C6—H6D	141.1
C4—N1—C1	118.6 (2)	H6B—C6—H6D	56.3
C4—N1—Cu1	130.14 (18)	H6C—C6—H6D	56.3
C1—N1—Cu1	111.23 (18)	C3—C6—H6E	109.5
N1—C1—C2	120.3 (3)	H6A—C6—H6E	56.3
N1—C1—C5	114.7 (2)	H6B—C6—H6E	141.1
C2—C1—C5	124.9 (2)	H6C—C6—H6E	56.3
N2—C2—C1	122.0 (3)	H6D—C6—H6E	109.5
N2—C2—H2	119.0	C3—C6—H6F	109.5
C1—C2—H2	119.0	H6A—C6—H6F	56.3
C3—N2—C2	117.8 (2)	H6B—C6—H6F	56.3
C3—N2—Cu2	124.3 (2)	H6C—C6—H6F	141.1
C2—N2—Cu2	117.20 (18)	H6D—C6—H6F	109.5
N2—C3—C4	119.7 (3)	H6E—C6—H6F	109.5
N2—C3—C6	119.5 (2)	H1O3—O3—H2O3	106.6
C4—C3—C6	120.8 (3)	Cu2—O4—H1O4	118.1
N1—C4—C3	121.6 (2)	Cu2—O4—H2O4	94.3
N1—C4—H4	119.2	H1O4—O4—H2O4	105.0
C3—C4—H4	119.2
N2—Cu2—Br1—Cu2^iii	−100.34 (8)	Br1^i—Cu2—N2—C2	−161.16 (17)
O4—Cu2—Br1—Cu2^iii	154.21 (6)	Br1—Cu2—N2—C2	−25.7 (2)
Br1^i—Cu2—Br1—Cu2^iii	51.81 (3)	C2—N2—C3—C4	−1.6 (4)
O1—Cu1—N1—C4	177.2 (3)	Cu2—N2—C3—C4	168.4 (2)
O1^ii—Cu1—N1—C4	−2.8 (3)	C2—N2—C3—C6	177.6 (3)
O1—Cu1—N1—C1	0.16 (19)	Cu2—N2—C3—C6	−12.4 (4)
O1^ii—Cu1—N1—C1	−179.84 (19)	C1—N1—C4—C3	1.7 (4)
C4—N1—C1—C2	−3.1 (4)	Cu1—N1—C4—C3	−175.1 (2)
Cu1—N1—C1—C2	174.4 (2)	N2—C3—C4—N1	0.7 (4)
C4—N1—C1—C5	179.5 (2)	C6—C3—C4—N1	−178.6 (3)
Cu1—N1—C1—C5	−3.1 (3)	N1—C1—C5—O2	−174.2 (3)
N1—C1—C2—N2	2.1 (4)	C2—C1—C5—O2	8.5 (5)
C5—C1—C2—N2	179.2 (3)	N1—C1—C5—O1	6.0 (4)
C1—C2—N2—C3	0.3 (4)	C2—C1—C5—O1	−171.3 (3)
C1—C2—N2—Cu2	−170.4 (2)	O2—C5—O1—Cu1	174.4 (3)
O4—Cu2—N2—C3	−84.0 (2)	C1—C5—O1—Cu1	−5.8 (3)
Br1^i—Cu2—N2—C3	28.7 (3)	N1^ii—Cu1—O1—C5	−176.7 (2)
Br1—Cu2—N2—C3	164.2 (2)	N1—Cu1—O1—C5	3.3 (2)
O4—Cu2—N2—C2	86.1 (2)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H1O3···O2^iv	0.82	2.00	2.818 (3)	174
O3—H2O3···O2^v	0.82	2.05	2.791 (3)	150
O4—H1O4···O3^vi	0.82	1.96	2.771 (3)	172
O4—H2O4···Br1^vii	0.82	2.65	3.390 (2)	150

Symmetry codes: (iv) −x+2, −y+1, −z+2; (v) x+1, y, z; (vi) x−1, y, z−1; (vii) x, y, z−1.