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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
CCDC reference: 718100
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.
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).
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).
Poly[(µ
4-pyrazine-2,5-dicarboxylato)cadmium(II)]
top
Crystal data top
[Cd(C6H2N2O4)] | F(000) = 528 |
Mr = 278.50 | Dx = 2.741 Mg m−3 Dm = 2.741 Mg m−3 Dm measured by not measured |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ybc | Cell parameters from 3179 reflections |
a = 10.4704 (5) Å | θ = 3.5–26.0° |
b = 5.4606 (3) Å | µ = 3.21 mm−1 |
c = 12.2847 (6) Å | T = 298 K |
β = 106.107 (3)° | Plate, colourless |
V = 674.80 (6) Å3 | 0.20 × 0.15 × 0.05 mm |
Z = 4 | |
Data collection top
Bruke APEXII CCD area-detector diffractometer | 1595 independent reflections |
Radiation source: fine-focus sealed tube | 1369 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.036 |
ϕ and ω scans | θmax = 28.0°, θmin = 2.0° |
Absorption correction: multi-scan (SADABS; Bruker, 2002) | h = −13→11 |
Tmin = 0.566, Tmax = 0.856 | k = −7→7 |
8845 measured reflections | l = −15→16 |
Refinement top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.024 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.054 | H-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 parameters | Δρmax = 0.48 e Å−3 |
0 restraints | Δρmin = −0.54 e Å−3 |
Crystal data top
[Cd(C6H2N2O4)] | V = 674.80 (6) Å3 |
Mr = 278.50 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 10.4704 (5) Å | µ = 3.21 mm−1 |
b = 5.4606 (3) Å | T = 298 K |
c = 12.2847 (6) Å | 0.20 × 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 = 0.856 | Rint = 0.036 |
8845 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.024 | 0 restraints |
wR(F2) = 0.054 | H-atom parameters constrained |
S = 1.08 | Δρmax = 0.48 e Å−3 |
1595 reflections | Δρmin = −0.54 e Å−3 |
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 | x | y | z | Uiso*/Ueq | |
C1 | 0.6226 (3) | 0.7052 (5) | 0.2193 (3) | 0.0207 (7) | |
Cd1 | 0.76861 (2) | 0.21548 (4) | 0.231322 (17) | 0.01999 (9) | |
N1 | 0.6081 (2) | 0.3902 (4) | 0.07534 (19) | 0.0204 (6) | |
O1 | 0.6878 (2) | 0.5609 (4) | 0.29225 (17) | 0.0280 (5) | |
C2 | 0.5553 (3) | 0.5977 (5) | 0.1024 (2) | 0.0187 (6) | |
N2 | 0.9030 (2) | 0.0794 (4) | 0.40569 (19) | 0.0200 (6) | |
O2 | 0.6059 (2) | 0.9299 (4) | 0.23135 (18) | 0.0268 (5) | |
C3 | 0.5523 (3) | 0.2928 (5) | −0.0269 (3) | 0.0225 (7) | |
H3 | 0.5868 | 0.1485 | −0.0474 | 0.027* | |
O3 | 0.9591 (2) | 0.4518 (4) | 0.27813 (17) | 0.0264 (5) | |
C4 | 1.0510 (3) | 0.3850 (5) | 0.3608 (2) | 0.0203 (6) | |
O4 | 1.1675 (2) | 0.4685 (4) | 0.39035 (17) | 0.0322 (6) | |
C5 | 1.0237 (3) | 0.1815 (5) | 0.4355 (2) | 0.0199 (6) | |
C6 | 0.8795 (3) | −0.1032 (5) | 0.4697 (2) | 0.0218 (7) | |
H6 | 0.7967 | −0.1789 | 0.4503 | 0.026* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
C1 | 0.0150 (16) | 0.0219 (15) | 0.0244 (16) | −0.0025 (12) | 0.0041 (13) | −0.0046 (13) |
Cd1 | 0.01936 (15) | 0.01866 (13) | 0.01861 (13) | 0.00255 (9) | −0.00029 (10) | −0.00047 (8) |
N1 | 0.0193 (14) | 0.0199 (13) | 0.0194 (12) | 0.0041 (11) | 0.0009 (11) | 0.0013 (10) |
O1 | 0.0275 (13) | 0.0281 (12) | 0.0227 (11) | 0.0073 (10) | −0.0027 (10) | −0.0029 (9) |
C2 | 0.0186 (16) | 0.0164 (14) | 0.0212 (15) | −0.0010 (12) | 0.0054 (12) | 0.0022 (12) |
N2 | 0.0182 (14) | 0.0226 (14) | 0.0180 (12) | −0.0028 (10) | 0.0028 (10) | 0.0013 (10) |
O2 | 0.0227 (12) | 0.0208 (11) | 0.0357 (12) | −0.0017 (9) | 0.0062 (10) | −0.0060 (10) |
C3 | 0.0238 (18) | 0.0176 (14) | 0.0245 (16) | 0.0029 (12) | 0.0043 (14) | 0.0007 (12) |
O3 | 0.0255 (13) | 0.0234 (12) | 0.0269 (11) | −0.0035 (9) | 0.0019 (10) | 0.0081 (9) |
C4 | 0.0255 (18) | 0.0190 (15) | 0.0170 (14) | −0.0029 (13) | 0.0069 (13) | 0.0011 (12) |
O4 | 0.0254 (14) | 0.0391 (14) | 0.0279 (12) | −0.0135 (11) | 0.0004 (10) | 0.0109 (10) |
C5 | 0.0210 (17) | 0.0213 (15) | 0.0173 (15) | −0.0031 (13) | 0.0052 (13) | −0.0011 (12) |
C6 | 0.0171 (17) | 0.0264 (16) | 0.0206 (15) | −0.0040 (13) | 0.0031 (13) | 0.0009 (13) |
Geometric parameters (Å, º) top
C1—O1 | 1.245 (3) | N1—C2 | 1.342 (4) |
C1—O2 | 1.254 (3) | C2—C3iii | 1.381 (4) |
C1—C2 | 1.530 (4) | N2—C6 | 1.335 (4) |
Cd1—O4i | 2.249 (2) | N2—C5 | 1.335 (4) |
Cd1—O1 | 2.277 (2) | C3—H3 | 0.9300 |
Cd1—O2ii | 2.310 (2) | O3—C4 | 1.244 (3) |
Cd1—O3 | 2.311 (2) | C4—O4 | 1.258 (3) |
Cd1—N2 | 2.334 (2) | C4—C5 | 1.518 (4) |
Cd1—N1 | 2.371 (2) | C5—C6iv | 1.383 (4) |
N1—C3 | 1.340 (4) | C6—H6 | 0.9300 |
| | | |
O1—C1—O2 | 126.9 (3) | N1—C2—C3iii | 120.9 (3) |
O1—C1—C2 | 116.8 (3) | N1—C2—C1 | 116.3 (2) |
O2—C1—C2 | 116.3 (3) | C3iii—C2—C1 | 122.8 (3) |
O4i—Cd1—O1 | 157.16 (8) | C6—N2—C5 | 117.7 (2) |
O4i—Cd1—O2ii | 87.17 (8) | C6—N2—Cd1 | 128.01 (19) |
O1—Cd1—O2ii | 102.59 (8) | C5—N2—Cd1 | 113.72 (19) |
O4i—Cd1—O3 | 96.02 (8) | C1—O2—Cd1v | 122.2 (2) |
O1—Cd1—O3 | 80.17 (8) | N1—C3—C2iii | 121.3 (3) |
O2ii—Cd1—O3 | 164.36 (7) | N1—C3—H3 | 119.3 |
O4i—Cd1—N2 | 101.78 (8) | C2iii—C3—H3 | 119.3 |
O1—Cd1—N2 | 98.42 (8) | C4—O3—Cd1 | 117.25 (19) |
O2ii—Cd1—N2 | 92.41 (8) | O3—C4—O4 | 126.7 (3) |
O3—Cd1—N2 | 71.96 (8) | O3—C4—C5 | 118.4 (3) |
O4i—Cd1—N1 | 88.81 (8) | O4—C4—C5 | 114.9 (2) |
O1—Cd1—N1 | 71.79 (8) | C4—O4—Cd1vi | 117.96 (18) |
O2ii—Cd1—N1 | 85.08 (8) | N2—C5—C6iv | 121.2 (3) |
O3—Cd1—N1 | 110.24 (8) | N2—C5—C4 | 117.5 (3) |
N2—Cd1—N1 | 169.00 (8) | C6iv—C5—C4 | 121.2 (3) |
C3—N1—C2 | 117.8 (2) | N2—C6—C5iv | 121.0 (3) |
C3—N1—Cd1 | 128.65 (19) | N2—C6—H6 | 119.5 |
C2—N1—Cd1 | 112.81 (18) | C5iv—C6—H6 | 119.5 |
C1—O1—Cd1 | 117.86 (19) | | |
| | | |
O4i—Cd1—N1—C3 | 23.5 (3) | N1—Cd1—N2—C6 | 77.4 (5) |
O1—Cd1—N1—C3 | −168.7 (3) | O4i—Cd1—N2—C5 | 84.7 (2) |
O2ii—Cd1—N1—C3 | −63.8 (3) | O1—Cd1—N2—C5 | −84.6 (2) |
O3—Cd1—N1—C3 | 119.5 (3) | O2ii—Cd1—N2—C5 | 172.3 (2) |
N2—Cd1—N1—C3 | −140.9 (4) | O3—Cd1—N2—C5 | −7.9 (2) |
O4i—Cd1—N1—C2 | −167.0 (2) | N1—Cd1—N2—C5 | −111.2 (4) |
O1—Cd1—N1—C2 | 0.7 (2) | O1—C1—O2—Cd1v | 77.1 (4) |
O2ii—Cd1—N1—C2 | 105.7 (2) | C2—C1—O2—Cd1v | −103.0 (3) |
O3—Cd1—N1—C2 | −71.0 (2) | C2—N1—C3—C2iii | 0.4 (5) |
N2—Cd1—N1—C2 | 28.6 (5) | Cd1—N1—C3—C2iii | 169.4 (2) |
O2—C1—O1—Cd1 | −156.0 (3) | O4i—Cd1—O3—C4 | −90.9 (2) |
C2—C1—O1—Cd1 | 24.1 (4) | O1—Cd1—O3—C4 | 111.9 (2) |
O4i—Cd1—O1—C1 | 19.1 (3) | O2ii—Cd1—O3—C4 | 10.3 (4) |
O2ii—Cd1—O1—C1 | −94.5 (2) | N2—Cd1—O3—C4 | 9.6 (2) |
O3—Cd1—O1—C1 | 101.2 (2) | N1—Cd1—O3—C4 | 178.2 (2) |
N2—Cd1—O1—C1 | 171.1 (2) | Cd1—O3—C4—O4 | 169.9 (2) |
N1—Cd1—O1—C1 | −14.1 (2) | Cd1—O3—C4—C5 | −9.8 (4) |
C3—N1—C2—C3iii | −0.4 (5) | O3—C4—O4—Cd1vi | −11.6 (4) |
Cd1—N1—C2—C3iii | −171.1 (2) | C5—C4—O4—Cd1vi | 168.21 (19) |
C3—N1—C2—C1 | −179.3 (3) | C6—N2—C5—C6iv | −0.9 (5) |
Cd1—N1—C2—C1 | 9.9 (3) | Cd1—N2—C5—C6iv | −173.2 (2) |
O1—C1—C2—N1 | −23.1 (4) | C6—N2—C5—C4 | 178.6 (3) |
O2—C1—C2—N1 | 157.0 (3) | Cd1—N2—C5—C4 | 6.2 (3) |
O1—C1—C2—C3iii | 158.0 (3) | O3—C4—C5—N2 | 2.3 (4) |
O2—C1—C2—C3iii | −22.0 (4) | O4—C4—C5—N2 | −177.5 (3) |
O4i—Cd1—N2—C6 | −86.7 (2) | O3—C4—C5—C6iv | −178.3 (3) |
O1—Cd1—N2—C6 | 104.0 (2) | O4—C4—C5—C6iv | 1.9 (4) |
O2ii—Cd1—N2—C6 | 0.9 (2) | C5—N2—C6—C5iv | 0.9 (5) |
O3—Cd1—N2—C6 | −179.3 (3) | Cd1—N2—C6—C5iv | 172.0 (2) |
Symmetry codes: (i) −x+2, y−1/2, −z+1/2; (ii) x, y−1, 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)] |
Mr | 278.50 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 298 |
a, b, c (Å) | 10.4704 (5), 5.4606 (3), 12.2847 (6) |
β (°) | 106.107 (3) |
V (Å3) | 674.80 (6) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 3.21 |
Crystal size (mm) | 0.20 × 0.15 × 0.05 |
|
Data collection |
Diffractometer | Bruke APEXII CCD area-detector diffractometer |
Absorption correction | Multi-scan (SADABS; Bruker, 2002) |
Tmin, Tmax | 0.566, 0.856 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 8845, 1595, 1369 |
Rint | 0.036 |
(sin θ/λ)max (Å−1) | 0.660 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.024, 0.054, 1.08 |
No. of reflections | 1595 |
No. of parameters | 118 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.48, −0.54 |
Selected geometric parameters (Å, º) topCd1—O4i | 2.249 (2) | Cd1—O3 | 2.311 (2) |
Cd1—O1 | 2.277 (2) | Cd1—N2 | 2.334 (2) |
Cd1—O2ii | 2.310 (2) | Cd1—N1 | 2.371 (2) |
| | | |
O4i—Cd1—O1 | 157.16 (8) | O2ii—Cd1—N2 | 92.41 (8) |
O4i—Cd1—O2ii | 87.17 (8) | O3—Cd1—N2 | 71.96 (8) |
O1—Cd1—O2ii | 102.59 (8) | O4i—Cd1—N1 | 88.81 (8) |
O4i—Cd1—O3 | 96.02 (8) | O1—Cd1—N1 | 71.79 (8) |
O1—Cd1—O3 | 80.17 (8) | O2ii—Cd1—N1 | 85.08 (8) |
O2ii—Cd1—O3 | 164.36 (7) | O3—Cd1—N1 | 110.24 (8) |
O4i—Cd1—N2 | 101.78 (8) | N2—Cd1—N1 | 169.00 (8) |
O1—Cd1—N2 | 98.42 (8) | | |
Symmetry codes: (i) −x+2, y−1/2, −z+1/2; (ii) x, y−1, z. |
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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, a–e (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).