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Poly[(μ4-pyrazine-2,5-dicarboxyl­ato)cadmium(II)], [Cd(C6H2N2O4)]n or [Cd(pzdc)]n (pzdc is the pyrazine-2,5-dicarboxyl­ate dianion), has been synthesized hydro­thermally. The asymmetric unit consists of a CdII atom and two independent halves of pzdc ligands that can be expanded via inversion through the centres of the ligands so that each ligand binds to four CdII atoms with the same binding mode using six donor atoms. The CdII centre is in a distorted octa­hedral coordination geometry with four O- and two N-atom donors from four pzdc ligands. The infinite linkage of the metal atoms and ligands forms a three-dimensional framework with a recta­ngular channel which is so narrow that there is no measurable void space in the overall structure. This coordination polymer represents the first example of (4,4,4)-connected three-nodal framework.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270108040080/ln3119sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270108040080/ln3119Isup2.hkl
Contains datablock I

CCDC reference: 718100

Comment top

There has been significant growth in recent years in the field of metal–organic frameworks (MOFs), because of their intriguing structural diversity and wide range of potential applications as functional materials (Tranchemontagne et al., 2008; Banerjee et al., 2008; Zhang & Kitagawa, 2008; Zheng et al., 2008). Bridging ligands are essential in constructing MOFs. Among the many kinds of bridging ligands, N-heterocyclic multicarboxylic acids have been used frequently (Evans & Lin, 2002; Blake et al., 1999; Moulton & Zaworotko, 2001). These ligands combine the advantages of both carboxyl and aromatic N-heterocyclic components and are able to connect various metal ions via a variety of coordination modes. The dianionic ligand pyrazine-2,5-dicarboxylate (pzdc), derived from deprotonation of pyrazine-2,5-dicarboxylic acid, displays five bridging modes, ae (see scheme), in its coordination polymers with some metal ions, including the alkaline earth metal SrII (Ptasiewicz-Bak & Leciejewicz, 1998), the transition metals MnII (Xu et al.; Beobide et al., 2003; Beobide et al., 2006), FeII, ZnII and CuII (Beobide et al., 2006), and the rare earth metals LaIII (Zheng & Jin, 2005), PrIII, NdIII, SmIII, EuIII and GdIII (Yang et al., 2008). The metal centres have a large impact on the crystal structure, including the binding modes of the ligand and the molecular packing. For example, in {[Ln(pzdc)1.5(H2O)3].0.5H2O}n (Ln = Pr, Nd, Sm, Eu, Gd), we found that the pzdc binding modes b, c and d exist simultaneously and there is an ultramicroporous channel (Yang et al., 2008), while in [La(pzdc)1.5(H2O)]n, binding modes c and e were observed and there was no channel inside (Zheng & Jin, 2005). The second-row transition metal CdII has been used to construct coordination polymers with some other pyrazinecarboxylates, such as 2-pyrazinecarboxylate (Ciurtin et al., 2002, 2003a,b), 2,3-pyrazinedicarboxylate (Yin & Liu, 2007; Mao et al., 1996; Maji et al., 2004, 2005; Ma et al., 2006; Liu et al., 2007) and 2,3,5,6-pyrazinetetracarboxylate (Wang et al., 2007; Ghosh & Bharadwaj, 2006), and exhibits ligand-dependent coordination numbers 6, 7 and 8 (Wang et al., 2007). However, there has been no report to date on the binding between CdII and pyrazine-2,5-dicarboxylate. Here, we report the preparation of the title compound, [Cd(pzdc)]n, (I), and its crystal structure.

Complex (I) was obtained by the hydrothermal method. In a hydrothermal reaction, water molecules are easily introduced into the crystal structure as a binding ligand or lattice component. However, (I) has no water in the crystal structure. Double deprotonation of pyrazine-2,5-dicarboxylic acid was accomplished without adding bases such as sodium hydroxide, as occasionally applied (Xu et al., 2003, Zheng & Jin, 2005).

Selected bond lengths and angles for (I) are given in Table 1. The Cd—O and Cd—N distances fall into the common range. The asymmetric unit of (I) consists of one CdII atom and two independent halves of pzdc ligands. Each pzdc ligand sits about an inversion centre. Expansion of the structure through the symmetry elements of the space group P21/c generates four pzdc ligands bound to each CdII centre. The coordination environment around the CdII centre is shown in Fig. 1. The CdII atom resides in a distorted octahedral environment surrounded by four carboxylate O atoms and two pyrazine N atoms from four different pzdc ligands. Two cis-related ligands coordinate to the CdII atom through a single carboxylate O atom, while the other two ligands have bidentate coordination to the CdII atom through adjacent (N, O) sites. It is noteworthy that atom O3 is 3.225 (2) Å from the same Cd atom that atom O4 is bonded to. This is only slightly longer than the sum of the van der Waals radii (3.10 Å; Reference?), so atom O3 has some bridging function between two CdII atoms.

The angle between the least-squares planes through atoms N2, C4, C5 and C6, and atoms C4, C5, O3 and O4, is 2.2 (3)°, implying that the N2-containing ligand is almost planar, as would be expected. In contrast, the corresponding dihedral angle for the N1-containing ligand (between the planes through atoms N1, C1, C2 and C3, and through atoms C1, C2, O1 and O2) is 23.0 (3)°, almost an order of magnitude larger. This large angle leads to the somewhat long C1—C2 distance [1.530 (4) Å] and puckered five-membered chelate ring (atoms N1, C2, C1, O1 and Cd1). The dihedral angle between the two least-squares planes through the N1- and N2-containing ligands is 68.92 (13)°.

The pzdc ligands in (I) display only one type of hexadentate binding mode (mode c as defined in the first scheme) and bind four symmetry-related CdII atoms. This binding mode makes each pzdc a four-connected linker. Along the [111] direction the Cd atoms are connected by N atoms via the pyrazine rings. The other two directions, [010] and [110], are dominated by CdOCOCd··· chains bridged via a single carboxylate group, O1/C1/O2 or O3/C4/O4, respectively, from different pzdc ligands. This expansion of the coordination environment leads to a three-dimensional network. In the [010] direction, a rectangular channel seems to exist, as illustrated in Fig. 2. However, the width of the `channel' is so narrow (around 2.2 Å) that the space-filling model of the crystal structure implies that the atoms around it compact quite closely and there are no significant voids, as confirmed by PLATON (Spek, 2003). This could be the reason that there are no solvent molecules inside the framework.

Topological analysis of the coordination net reveals that (I) is a three-nodal net with one four-connected Cd node and two distinct four-connected ligand nodes, as shown in Fig. 3. The Schläfli symbol is {416382}2{426282}{6284}, which has not been reported previously and which therefore represents a new topological type (Blatov, 2006).

Experimental top

Colourless plate crystals of (I) were synthesized hydrothermally in a 23 ml Teflon-lined autoclave by heating a mixture of pzdcH2 (0.5 mmol) and CdCl2 (0.5 mmol) in water (10 ml) at 413 K for 3 d.

Refinement top

All H atoms were located in a difference map and then treated as riding in geometrically idealized positions, with C—H = 0.93 Å and Uiso(H) = 1.2Ueq(C).

Computing details top

Data collection: APEX2 (Bruker, 2004); cell refinement: APEX2 (Bruker, 2004); data reduction: APEX2 (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1999); software used to prepare material for publication: PLATON (Spek, 2003).

Figures top
[Figure 1] Fig. 1. The coordination environment of (I), showing the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability and H atoms are shown as small spheres of arbitrary radii. [Symmetry codes: (i) x, -1/2 - y, -1/2 + z; (ii) 2 - x, -1/2 + y, 1/2 - z; (iii) 1 - x, 1 - y, -z; (iv) 1 - x, -y, -z; (v) x, -1 + y, z; (vi) 2 - x, -y, 1 - z.]
[Figure 2] Fig. 2. A perspective view of the packing of (I), down the b axis, showing the narrow rectangular channel.
[Figure 3] Fig. 3. A topological representation of the coordination framework of (I).
Poly[(µ4-pyrazine-2,5-dicarboxylato)cadmium(II)] top
Crystal data top
[Cd(C6H2N2O4)]F(000) = 528
Mr = 278.50Dx = 2.741 Mg m3
Dm = 2.741 Mg m3
Dm measured by not measured
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 3179 reflections
a = 10.4704 (5) Åθ = 3.5–26.0°
b = 5.4606 (3) ŵ = 3.21 mm1
c = 12.2847 (6) ÅT = 298 K
β = 106.107 (3)°Plate, colourless
V = 674.80 (6) Å30.20 × 0.15 × 0.05 mm
Z = 4
Data collection top
Bruke APEXII CCD area-detector
diffractometer
1595 independent reflections
Radiation source: fine-focus sealed tube1369 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.036
ϕ and ω scansθmax = 28.0°, θmin = 2.0°
Absorption correction: multi-scan
(SADABS; Bruker, 2002)
h = 1311
Tmin = 0.566, Tmax = 0.856k = 77
8845 measured reflectionsl = 1516
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.024Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.054H-atom parameters constrained
S = 1.08 w = 1/[σ2(Fo2) + (0.0269P)2]
where P = (Fo2 + 2Fc2)/3
1595 reflections(Δ/σ)max < 0.001
118 parametersΔρmax = 0.48 e Å3
0 restraintsΔρmin = 0.54 e Å3
Crystal data top
[Cd(C6H2N2O4)]V = 674.80 (6) Å3
Mr = 278.50Z = 4
Monoclinic, P21/cMo Kα radiation
a = 10.4704 (5) ŵ = 3.21 mm1
b = 5.4606 (3) ÅT = 298 K
c = 12.2847 (6) Å0.20 × 0.15 × 0.05 mm
β = 106.107 (3)°
Data collection top
Bruke APEXII CCD area-detector
diffractometer
1595 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2002)
1369 reflections with I > 2σ(I)
Tmin = 0.566, Tmax = 0.856Rint = 0.036
8845 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0240 restraints
wR(F2) = 0.054H-atom parameters constrained
S = 1.08Δρmax = 0.48 e Å3
1595 reflectionsΔρmin = 0.54 e Å3
118 parameters
Special details top

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 (Å2) top
xyzUiso*/Ueq
C10.6226 (3)0.7052 (5)0.2193 (3)0.0207 (7)
Cd10.76861 (2)0.21548 (4)0.231322 (17)0.01999 (9)
N10.6081 (2)0.3902 (4)0.07534 (19)0.0204 (6)
O10.6878 (2)0.5609 (4)0.29225 (17)0.0280 (5)
C20.5553 (3)0.5977 (5)0.1024 (2)0.0187 (6)
N20.9030 (2)0.0794 (4)0.40569 (19)0.0200 (6)
O20.6059 (2)0.9299 (4)0.23135 (18)0.0268 (5)
C30.5523 (3)0.2928 (5)0.0269 (3)0.0225 (7)
H30.58680.14850.04740.027*
O30.9591 (2)0.4518 (4)0.27813 (17)0.0264 (5)
C41.0510 (3)0.3850 (5)0.3608 (2)0.0203 (6)
O41.1675 (2)0.4685 (4)0.39035 (17)0.0322 (6)
C51.0237 (3)0.1815 (5)0.4355 (2)0.0199 (6)
C60.8795 (3)0.1032 (5)0.4697 (2)0.0218 (7)
H60.79670.17890.45030.026*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0150 (16)0.0219 (15)0.0244 (16)0.0025 (12)0.0041 (13)0.0046 (13)
Cd10.01936 (15)0.01866 (13)0.01861 (13)0.00255 (9)0.00029 (10)0.00047 (8)
N10.0193 (14)0.0199 (13)0.0194 (12)0.0041 (11)0.0009 (11)0.0013 (10)
O10.0275 (13)0.0281 (12)0.0227 (11)0.0073 (10)0.0027 (10)0.0029 (9)
C20.0186 (16)0.0164 (14)0.0212 (15)0.0010 (12)0.0054 (12)0.0022 (12)
N20.0182 (14)0.0226 (14)0.0180 (12)0.0028 (10)0.0028 (10)0.0013 (10)
O20.0227 (12)0.0208 (11)0.0357 (12)0.0017 (9)0.0062 (10)0.0060 (10)
C30.0238 (18)0.0176 (14)0.0245 (16)0.0029 (12)0.0043 (14)0.0007 (12)
O30.0255 (13)0.0234 (12)0.0269 (11)0.0035 (9)0.0019 (10)0.0081 (9)
C40.0255 (18)0.0190 (15)0.0170 (14)0.0029 (13)0.0069 (13)0.0011 (12)
O40.0254 (14)0.0391 (14)0.0279 (12)0.0135 (11)0.0004 (10)0.0109 (10)
C50.0210 (17)0.0213 (15)0.0173 (15)0.0031 (13)0.0052 (13)0.0011 (12)
C60.0171 (17)0.0264 (16)0.0206 (15)0.0040 (13)0.0031 (13)0.0009 (13)
Geometric parameters (Å, º) top
C1—O11.245 (3)N1—C21.342 (4)
C1—O21.254 (3)C2—C3iii1.381 (4)
C1—C21.530 (4)N2—C61.335 (4)
Cd1—O4i2.249 (2)N2—C51.335 (4)
Cd1—O12.277 (2)C3—H30.9300
Cd1—O2ii2.310 (2)O3—C41.244 (3)
Cd1—O32.311 (2)C4—O41.258 (3)
Cd1—N22.334 (2)C4—C51.518 (4)
Cd1—N12.371 (2)C5—C6iv1.383 (4)
N1—C31.340 (4)C6—H60.9300
O1—C1—O2126.9 (3)N1—C2—C3iii120.9 (3)
O1—C1—C2116.8 (3)N1—C2—C1116.3 (2)
O2—C1—C2116.3 (3)C3iii—C2—C1122.8 (3)
O4i—Cd1—O1157.16 (8)C6—N2—C5117.7 (2)
O4i—Cd1—O2ii87.17 (8)C6—N2—Cd1128.01 (19)
O1—Cd1—O2ii102.59 (8)C5—N2—Cd1113.72 (19)
O4i—Cd1—O396.02 (8)C1—O2—Cd1v122.2 (2)
O1—Cd1—O380.17 (8)N1—C3—C2iii121.3 (3)
O2ii—Cd1—O3164.36 (7)N1—C3—H3119.3
O4i—Cd1—N2101.78 (8)C2iii—C3—H3119.3
O1—Cd1—N298.42 (8)C4—O3—Cd1117.25 (19)
O2ii—Cd1—N292.41 (8)O3—C4—O4126.7 (3)
O3—Cd1—N271.96 (8)O3—C4—C5118.4 (3)
O4i—Cd1—N188.81 (8)O4—C4—C5114.9 (2)
O1—Cd1—N171.79 (8)C4—O4—Cd1vi117.96 (18)
O2ii—Cd1—N185.08 (8)N2—C5—C6iv121.2 (3)
O3—Cd1—N1110.24 (8)N2—C5—C4117.5 (3)
N2—Cd1—N1169.00 (8)C6iv—C5—C4121.2 (3)
C3—N1—C2117.8 (2)N2—C6—C5iv121.0 (3)
C3—N1—Cd1128.65 (19)N2—C6—H6119.5
C2—N1—Cd1112.81 (18)C5iv—C6—H6119.5
C1—O1—Cd1117.86 (19)
O4i—Cd1—N1—C323.5 (3)N1—Cd1—N2—C677.4 (5)
O1—Cd1—N1—C3168.7 (3)O4i—Cd1—N2—C584.7 (2)
O2ii—Cd1—N1—C363.8 (3)O1—Cd1—N2—C584.6 (2)
O3—Cd1—N1—C3119.5 (3)O2ii—Cd1—N2—C5172.3 (2)
N2—Cd1—N1—C3140.9 (4)O3—Cd1—N2—C57.9 (2)
O4i—Cd1—N1—C2167.0 (2)N1—Cd1—N2—C5111.2 (4)
O1—Cd1—N1—C20.7 (2)O1—C1—O2—Cd1v77.1 (4)
O2ii—Cd1—N1—C2105.7 (2)C2—C1—O2—Cd1v103.0 (3)
O3—Cd1—N1—C271.0 (2)C2—N1—C3—C2iii0.4 (5)
N2—Cd1—N1—C228.6 (5)Cd1—N1—C3—C2iii169.4 (2)
O2—C1—O1—Cd1156.0 (3)O4i—Cd1—O3—C490.9 (2)
C2—C1—O1—Cd124.1 (4)O1—Cd1—O3—C4111.9 (2)
O4i—Cd1—O1—C119.1 (3)O2ii—Cd1—O3—C410.3 (4)
O2ii—Cd1—O1—C194.5 (2)N2—Cd1—O3—C49.6 (2)
O3—Cd1—O1—C1101.2 (2)N1—Cd1—O3—C4178.2 (2)
N2—Cd1—O1—C1171.1 (2)Cd1—O3—C4—O4169.9 (2)
N1—Cd1—O1—C114.1 (2)Cd1—O3—C4—C59.8 (4)
C3—N1—C2—C3iii0.4 (5)O3—C4—O4—Cd1vi11.6 (4)
Cd1—N1—C2—C3iii171.1 (2)C5—C4—O4—Cd1vi168.21 (19)
C3—N1—C2—C1179.3 (3)C6—N2—C5—C6iv0.9 (5)
Cd1—N1—C2—C19.9 (3)Cd1—N2—C5—C6iv173.2 (2)
O1—C1—C2—N123.1 (4)C6—N2—C5—C4178.6 (3)
O2—C1—C2—N1157.0 (3)Cd1—N2—C5—C46.2 (3)
O1—C1—C2—C3iii158.0 (3)O3—C4—C5—N22.3 (4)
O2—C1—C2—C3iii22.0 (4)O4—C4—C5—N2177.5 (3)
O4i—Cd1—N2—C686.7 (2)O3—C4—C5—C6iv178.3 (3)
O1—Cd1—N2—C6104.0 (2)O4—C4—C5—C6iv1.9 (4)
O2ii—Cd1—N2—C60.9 (2)C5—N2—C6—C5iv0.9 (5)
O3—Cd1—N2—C6179.3 (3)Cd1—N2—C6—C5iv172.0 (2)
Symmetry codes: (i) x+2, y1/2, z+1/2; (ii) x, y1, z; (iii) x+1, y+1, z; (iv) x+2, y, z+1; (v) x, y+1, z; (vi) x+2, y+1/2, z+1/2.

Experimental details

Crystal data
Chemical formula[Cd(C6H2N2O4)]
Mr278.50
Crystal system, space groupMonoclinic, P21/c
Temperature (K)298
a, b, c (Å)10.4704 (5), 5.4606 (3), 12.2847 (6)
β (°) 106.107 (3)
V3)674.80 (6)
Z4
Radiation typeMo Kα
µ (mm1)3.21
Crystal size (mm)0.20 × 0.15 × 0.05
Data collection
DiffractometerBruke APEXII CCD area-detector
diffractometer
Absorption correctionMulti-scan
(SADABS; Bruker, 2002)
Tmin, Tmax0.566, 0.856
No. of measured, independent and
observed [I > 2σ(I)] reflections
8845, 1595, 1369
Rint0.036
(sin θ/λ)max1)0.660
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.024, 0.054, 1.08
No. of reflections1595
No. of parameters118
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.48, 0.54

Computer programs: APEX2 (Bruker, 2004), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 (Farrugia, 1999), PLATON (Spek, 2003).

Selected geometric parameters (Å, º) top
Cd1—O4i2.249 (2)Cd1—O32.311 (2)
Cd1—O12.277 (2)Cd1—N22.334 (2)
Cd1—O2ii2.310 (2)Cd1—N12.371 (2)
O4i—Cd1—O1157.16 (8)O2ii—Cd1—N292.41 (8)
O4i—Cd1—O2ii87.17 (8)O3—Cd1—N271.96 (8)
O1—Cd1—O2ii102.59 (8)O4i—Cd1—N188.81 (8)
O4i—Cd1—O396.02 (8)O1—Cd1—N171.79 (8)
O1—Cd1—O380.17 (8)O2ii—Cd1—N185.08 (8)
O2ii—Cd1—O3164.36 (7)O3—Cd1—N1110.24 (8)
O4i—Cd1—N2101.78 (8)N2—Cd1—N1169.00 (8)
O1—Cd1—N298.42 (8)
Symmetry codes: (i) x+2, y1/2, z+1/2; (ii) x, y1, z.
 

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