A new packing variant of catena-poly[[aquachlorocopper(II)]-μ-pyrazine-2-carboxylato-O,N:N′]

Single crystals of the title coordination polymer, [CuCl(C₅H₃N₂O₂)(H₂O)], have been prepared by hydro­thermal synthesis. The compound is composed of infinite one-dimensional chains of pseudo-square-pyramidal Cu^II ions connected via pyrazine-2-carboxyl­ate ligands. A network of O—H...O hydrogen bonding between adjacent chains is responsible for a bilayer structure different from the previously reported polymorph.

S1. Comment

Pyrazine-2-carboxylato (hereinafter pyzca) complexes of copper(II) (Klein et al., 1982) have recently been used to construct several novel mixed-metal and mixed-valent coordination polymers (Dong et al., 2000; Zheng et al., 2000). The attractiveness of this complex as a `metal-containing building block' for the construction of novel framework materials of varying dimensionality lies in its donor-acceptor versatility. Chelation of the Cu^II center by two pyrazine-2-carboxylato ligands leaves two para N donors and two free carboxylate O atoms available for intermolecular bonding and supramolecular interactions. Since this complex often forms as a bis(aqua) complex, structural diversity through hydrogen-bonding interactions is also possible. Investigation of the hydrothermal reactivity of [Cu(pyzca)₂] with various metal salts has led to the formation of a new polymorph of [CuCl(pyzca)(H₂O)], (I), reported here. \sch

The structure of (I) consists of one-dimensional chains of Cu^II centers connected through pyzca ligands (Fig. 1). The Cu²⁺ ion resides in a pseudo-square-pyramidal coordination environment. An O atom and an N atom from the chelating end of a pyzca ligand, a para N atom from a symmetry-equivalent pyzca ligand [symmetry code: (vi) x, -y, z - 1/2] and a Cl ligand form the base of the pyramid. A water molecule occupies the apical site. The distortion from ideal square-pyramidal geometry is due primarily to the larger size of the Cl ligand (Table I).

Compound (I) is a polymorph of the structure reported by Goher et al. (1998). The central structural unit of both, the one-dimensional chains, is virtually identical. The two structures differ in the pattern of hydrogen bonding linking the chains. In (I), the chains assemble into bilayers parallel to the crystallographic bc plane. The water ligands in (I) point toward the bilayer interior and form a hydrogen-bonding network involving an unchelated carboxylate O atom (O3—H3WA···O2) and a carboxylate O atom bound to Cu (O3—H3WB···O1). Each water molecule is linked to two neighboring chains in this fashion. The Cl ligands protrude outward from the bilayers, which then stack in a centrosymmetric fashion along [001] (Fig. 2).

The structure reported by Goher et al. (1998) was crystallized in low (15%) yield by the ambient temperature evaporation of a 2:1 ethanol-water solution. Due to the noncentrosymmetic stacking of individual chains, each water ligand forms hydrogen bonds to two neighboring chains through a Cl ligand and an unchelated carboxylate O atom of a pyzca ligand, rather than through an exclusively O—H···O network as in (I). Interestingly, although much harsher hydrothermal reaction conditions in pure water produced (I) rather than the previous structure, (I) is in fact isostructural with the azido analog [Cu^II(N₃)(pyrazine-2-carboxylato)(H₂O)], also obtained by Goher et al. by evaporation at room temperature.

Related literature

For related literature, see: Dong et al. (2000); Goher et al. (1998); Klein et al. (1982); Zheng et al. (2000).

S2. Experimental

The title compound was prepared by the hydrothermal reaction of Cu^II(pyrazine-2-carboxylate)₂ (0.0276 g, 0.1 mmol) with CuCl₂·2H₂O (0.0275 g, 0.2 mmol) in water (0.8 ml) in an evacuated sealed Pyrex tube. The reaction was heated to 403 K at 1 K min^-1 and held at 403 K for 24 h before cooling slowly (0.5 K min^-1) to room temperature. The reaction yielded abundant dark blue-green crystals of (I).

S3. Refinement

All H atoms could be located in the Fourier difference maps. Those bound to C atoms were placed in calculated positions (C—H = 0.930 Å) and given U_iso values 1.2 times those of the parent C atom. Water H atoms were refined isotropically, subject to a distance restraint of O—H = 0.8 Å.

Computing details

Data collection: SMART NT (Bruker, 1999); cell refinement: SAINT+ NT (Bruker, 1999); data reduction: SAINT+ NT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1997); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. A view of (I) showing the one-dimensional chains and the atom-numbering scheme in one repeat unit. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. A view of the packing of the double layers in (I) along [010]. Intralayer hydrogen bonds are shown as dotted lines.

catena-Poly[[aquachlorocopper(II)]-µ-pyrazine-2-carboxylato-O,N¹:N⁴]

Crystal data

[CuCl(C5H3N2O2)(H2O)]	F(000) = 952
Mr = 240.10	Dx = 2.111 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 18.8435 (17) Å	Cell parameters from 3228 reflections
b = 6.2038 (6) Å	θ = 3.2–26.3°
c = 13.4129 (12) Å	µ = 3.21 mm^−1
β = 105.534 (2)°	T = 293 K
V = 1510.7 (2) Å^3	Fragment, blue green
Z = 8	0.30 × 0.22 × 0.16 mm

Data collection

Bruker SMART APEX CCD area-detector diffractometer	1547 independent reflections
Radiation source: sealed tube	1323 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.025
ω scans	θmax = 26.4°, θmin = 2.2°
Absorption correction: multi-scan (SADABS; Bruker, 1999)	h = −23→22
Tmin = 0.449, Tmax = 0.599	k = −7→7
4831 measured reflections	l = −16→16

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)] = 0.025	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.063	H atoms treated by a mixture of independent and constrained refinement
S = 1.00	w = 1/[σ^2(Fo^2) + (0.0358P)^2] where P = (Fo^2 + 2Fc^2)/3
1547 reflections	(Δ/σ)max < 0.001
117 parameters	Δρmax = 0.42 e Å^−3
2 restraints	Δρmin = −0.41 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	0.384384 (17)	0.56823 (5)	0.35749 (2)	0.02374 (12)
Cl	0.46448 (4)	0.83711 (12)	0.37073 (5)	0.03774 (19)
C1	0.36240 (13)	0.3766 (4)	0.53576 (18)	0.0221 (5)
C2	0.36048 (14)	0.3388 (4)	0.63671 (18)	0.0256 (5)
H2	0.3427	0.2081	0.6540	0.031*
C3	0.40963 (14)	0.6744 (4)	0.68166 (18)	0.0280 (6)
H3	0.4243	0.7834	0.7305	0.034*
C4	0.41481 (14)	0.7076 (4)	0.58210 (18)	0.0267 (5)
H4	0.4355	0.8344	0.5657	0.032*
C5	0.33198 (14)	0.2205 (4)	0.44837 (18)	0.0244 (5)
N1	0.39020 (11)	0.5583 (3)	0.50923 (14)	0.0225 (4)
N2	0.38405 (11)	0.4895 (4)	0.70953 (14)	0.0244 (4)
O1	0.33849 (10)	0.2827 (3)	0.36047 (12)	0.0293 (4)
O2	0.30234 (10)	0.0545 (3)	0.46599 (13)	0.0313 (4)
O3	0.27682 (13)	0.7284 (4)	0.32162 (17)	0.0456 (5)
H3WA	0.2815 (18)	0.835 (3)	0.355 (2)	0.042 (9)*
H3WB	0.2433 (12)	0.734 (5)	0.2713 (16)	0.045 (10)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu	0.0309 (2)	0.02735 (18)	0.01294 (17)	−0.00202 (13)	0.00588 (12)	−0.00023 (11)
Cl	0.0434 (4)	0.0426 (4)	0.0289 (4)	−0.0150 (3)	0.0126 (3)	−0.0038 (3)
C1	0.0256 (13)	0.0242 (12)	0.0164 (11)	0.0018 (10)	0.0055 (10)	0.0009 (9)
C2	0.0316 (14)	0.0249 (13)	0.0207 (12)	0.0009 (11)	0.0078 (11)	0.0004 (10)
C3	0.0327 (15)	0.0308 (14)	0.0190 (12)	−0.0014 (11)	0.0043 (11)	−0.0047 (10)
C4	0.0325 (15)	0.0259 (13)	0.0202 (13)	−0.0052 (11)	0.0045 (11)	−0.0009 (10)
C5	0.0268 (14)	0.0244 (13)	0.0212 (13)	0.0031 (10)	0.0052 (10)	−0.0022 (10)
N1	0.0252 (11)	0.0262 (11)	0.0154 (10)	0.0012 (9)	0.0043 (8)	0.0004 (8)
N2	0.0288 (12)	0.0300 (11)	0.0144 (10)	0.0012 (9)	0.0058 (9)	0.0005 (8)
O1	0.0460 (12)	0.0270 (9)	0.0142 (8)	−0.0060 (8)	0.0071 (8)	−0.0034 (7)
O2	0.0451 (12)	0.0256 (10)	0.0244 (10)	−0.0066 (8)	0.0114 (9)	−0.0024 (7)
O3	0.0445 (13)	0.0473 (13)	0.0344 (12)	0.0165 (11)	−0.0079 (10)	−0.0171 (11)

Geometric parameters (Å, º)

Cu—O1	1.9762 (17)	C3—N2	1.336 (3)
Cu—N1	2.0095 (19)	C3—C4	1.380 (3)
Cu—N2^i	2.0151 (19)	C3—H3	0.9300
Cu—Cl	2.2245 (7)	C4—N1	1.336 (3)
Cu—O3	2.192 (2)	C4—H4	0.9300
C1—N1	1.331 (3)	C5—O2	1.224 (3)
C1—C2	1.384 (3)	C5—O1	1.277 (3)
C1—C5	1.510 (3)	N2—Cu^ii	2.0151 (19)
C2—N2	1.339 (3)	O3—H3WA	0.788 (10)
C2—H2	0.9300	O3—H3WB	0.792 (10)
O1—Cu—N1	81.81 (7)	C4—C3—H3	119.2
O1—Cu—N2^i	88.54 (8)	N1—C4—C3	120.2 (2)
N1—Cu—N2^i	167.67 (9)	N1—C4—H4	119.9
O1—Cu—O3	91.54 (9)	C3—C4—H4	119.9
N1—Cu—O3	91.87 (8)	O2—C5—O1	126.4 (2)
N2^i—Cu—O3	96.06 (8)	O2—C5—C1	119.2 (2)
O1—Cu—Cl	164.09 (6)	O1—C5—C1	114.3 (2)
N1—Cu—Cl	95.19 (6)	C1—N1—C4	118.4 (2)
N2^i—Cu—Cl	92.00 (6)	C1—N1—Cu	112.23 (15)
O3—Cu—Cl	104.20 (7)	C4—N1—Cu	129.31 (17)
N1—C1—C2	121.4 (2)	C3—N2—C2	118.0 (2)
N1—C1—C5	115.5 (2)	C3—N2—Cu^ii	121.47 (16)
C2—C1—C5	123.1 (2)	C2—N2—Cu^ii	120.48 (17)
N2—C2—C1	120.3 (2)	C5—O1—Cu	116.12 (15)
N2—C2—H2	119.8	Cu—O3—H3WA	107 (2)
C1—C2—H2	119.8	Cu—O3—H3WB	133 (2)
N2—C3—C4	121.5 (2)	H3WA—O3—H3WB	113 (3)
N2—C3—H3	119.2

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3WA···O2^iii	0.79 (2)	1.98 (2)	2.752 (3)	166 (3)
O3—H3WB···O1^iv	0.79 (2)	2.03 (2)	2.821 (3)	174 (3)

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