Poly[[aqua­(4,4′-diazenediyldibenzo­ato-κ⁴O,O′:O′′,O′′′)cadmium(II)]: a twofold inter­penetrated three-dimensional coordination polymer of PtS topology

In the title coordination compound, [Cd(C₁₄H₈N₂O₄)(H₂O)]_n, the Cd^II cation and the coordinated water mol­ecule lie on a twofold axis, whereas the ligand lies on an inversion center. The Cd^II center is five-coordinated in a distorted square-pyramidal geometry by four carboxyl­ate O atoms from four different 4,4′-diazenediyldibenzoate (ddb) anions and one water O atom. The three-dimensional frameworks thus formed by the bridging ddb anions interpenetrate to generate a three-dimensional PtS-type network. Additionally, the coordination water mol­ecule and the carboxyl­ate O atom form a hydrogen-bonding inter­action, stabilizing the three-dimensional framework structure.

S1. Comment

The design and synthesis of metal–organic coordination polymers are of great interest, not only because of their tremendous potential applications in nonlinear optics, catalysis, gas absorption, luminescence, magnetism and medicine, but also because of their intriguing variety of architectures and topologies (Batten & Robson, 1998; Eddaoudi et al., 2001; Yang et al., 2008). These coordination polymers can be specially designed by the careful selection of metal cations with preferred coordination geometries, the nature of the anions, the structure of the connecting ligands, and the reaction conditions (Hagrman et al., 1999; Hsu et al., 2008). The selection of the ligand is extremely important because changing its geometry can control the topology of the resulting coordination framework (Hu et al., 2006). In this regard, carboxylate-based ligands have been successfully employed in the generation of many interesting systems. The work of Yaghi and co-workers has succeeded in highlighting the value of carboxylate-based systems in the generation of stable highly porous functionalized open networks (Ockwig et al., 2005). In the last decade, aromatic polycarboxylate ligands, such as 1,4-benzenedicarboxylate, 1,3-benzenedicarboxylate, 1,3,5-benzenecarboxylate and 1,2,4,5-benzenetetracarboxylate, have been employed extensively in the construction of a variety of high-dimensional structures (Ockwig et al., 2005). Azodibenzoate-based systems, as one new type of bridging aromatic carboxylate ligand, have rarely been employed in the generation of coordination networks (Chen et al., 2008). In this work, we chose 4,4'-azodibenzoic acid (H₂adb) as the carboxylate-containing ligand, yielding the title two-fold interpenetrated three-dimensional coordination polymer of PtS topology, [Cd(adb)(H₂O)]_n, (I).

Selected bond distances and angles for (I) are listed in Table 1. As shown in Fig. 1, the asymmetric unit of (I) contains one-half of a Cd^II cation, one-half of an adb anion and one-half of a water molecule. The Cd^II cation and the water molecule lie on a twofold axis, whereas the adb ligand is located around an inversion center. The Cd atom is five-coordinated in a distorted square-pyramidal geometry by four carboxylate O atoms from four different adb anions and one water O atom. Four O atoms from four adb anions (O1, O1ⁱⁱ, O2ⁱⁱⁱ and O2^iv; symmetry codes in Table 1) make up the basal plane, while the apical site is occupied by one water O atom (O1W). The average Cd—O distances in (I) (Table 1) are comparable with those observed for [Cd(1,4-ndc)(L)]_n (1,4-ndc is naphthalene-1,4-dicarboxylate and L is pyrazino[2,3-f][1,10]phenanthroline) (Qiao et al., 2008). In (I), each adb anion coordinates to four Cd^II centers in a tetra-monodentate mode (see scheme), forming a three-dimensional framework structure (Fig. 2). Interestingly, the two equivalent three-dimensional frameworks generate an interpenetrating three-dimensional PtS-type network (Fig. 3). Additionally, the coordinated water molecule and the carboxylate O atom form hydrogen-bonding interactions, stabilizing the three-dimensional framework structure of (I) (Table 2).

The topological structure of (I) can be achieved by reducing the three-dimensional structure to a simple node-and-linker net. As discussed above, each Cd^IIcenter can be defined as a 4-connected node. Each carboxylate O atom of adb connects one Cd^II center, and each adb ligand bridges four adjacent Cd^II atoms through its carboxylate O atoms. Therefore, the adb ligand can also be considered as a 4-connected node. Both the Cd^II and adb nodes are equivalent. Therefore, the framework topology of (I) can be regarded as a three-dimensional 4-connected PtS-type net (4².8⁴) (Carlucci et al., 2003). Furthermore, two such nets interpenetrate (Fig. 4), and there are some earlier examples of interpenetrating PtS nets (Abrahams et al., 1994; Nattinen & Rissanen, 2003; Du et al., 2005; Grosshans et al., 2003; Blatov et al., 2004).

It is noteworthy that the structure of (I) is entirely different from that of the related structure [Cd(adb)(H₂O)₂]_n (Chen et al., 2008). In that reported complex, each carboxylate group of the adb anion chelates one Cd^II atom to form a simple zigzag chain structure. The structure of (I) is also entirely different from that of the related polymer [Cd(adb)(phen)(H₂O)]_n (phen is 1,10-phenanthroline) (Chen et al., 2008). In that structure, each adb anion bridges three Cd^II atoms to yield a two-dimensional sheet structure. The phen molecules are attached on both sides of the sheet.

S2. Experimental

A mixture of CdCl₂.2.5H₂O (0.114 g, 0.5 mmol) and H₂adb (0.135 g, 0.5 mmol) was dissolved in distilled water (12 ml), followed by the addition of triethylamine until the pH of the system was about 5.5. The resulting solution was stirred for about 1 h at room temperature, sealed in a 23 ml Teflon-lined stainless steel autoclave and heated at 423 K for 5 d under autogenous pressure. The reaction system was then slowly cooled to room temperature. Pale-yellow block crystals of (I) suitable for single-crystal X-ray diffraction analysis were collected from the final reaction system by filtration, washed several times with distilled water and dried in air at ambient temperature (yield 45% based on Cd^II).

S3. Refinement

Carbon-bound H atoms were positioned geometrically, with C—H = 0.93 Å, and refined as riding, with U_iso(H) = 1.2U_eq(C). The water H atom was located in a difference Fourier map and was refined with a distance restraint of O—H = 0.82 (3) Å and with U_iso(H) = 1.5U_eq(O). The maximum residual electron-density peak of 1.138 e Å^-3 was located 0.86 Å from atom N1.

Computing details

Data collection: SMART (Bruker, 1997); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT (Bruker, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009); software used to prepare material for publication: publCIF (Westrip, 2009).

Figures

	Fig. 1. A view of the coordination mode of compound (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. H atoms have been omitted for clarity. [Symmetry codes: (i) -x, -y, 1 - z; (ii) 1 - x, y, 1/2 - z; (iii) 1 - x, 1 - y, 1 - z; (iv) x, 1 - y, z - 1/2; (v) x, 1 - y, 1/2 + z.]
	Fig. 2. A view of the three-dimensional framework of (I).
	Fig. 3. A view of the twofold interpenetrated three-dimensional framework of (I).
	Fig. 4. Schematic representation of the twofold interpenetrated PtS nets.

Poly[[aqua(4,4'-diazenediyldibenzoato- κ⁴O,O':O'',O''')cadmium(II)]

Crystal data

[Cd(C14H8N2O4)(H2O)]	F(000) = 392
Mr = 398.64	Dx = 1.983 Mg m^−3
Monoclinic, P2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yc	Cell parameters from 1572 reflections
a = 14.8094 (11) Å	θ = 3.0–29.2°
b = 6.4226 (7) Å	µ = 1.66 mm^−1
c = 7.0194 (8) Å	T = 293 K
β = 90.949 (9)°	Block, pale yellow
V = 667.56 (12) Å^3	0.30 × 0.27 × 0.20 mm
Z = 2

Data collection

Bruker APEX diffractometer	1572 independent reflections
Radiation source: fine-focus sealed tube	1243 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.031
ϕ and ω scans	θmax = 29.2°, θmin = 2.8°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −20→14
Tmin = 0.597, Tmax = 0.715	k = −8→5
3196 measured reflections	l = −9→9

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)] = 0.034	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.072	H atoms treated by a mixture of independent and constrained refinement
S = 0.96	w = 1/[σ^2(Fo^2) + (0.0366P)^2] where P = (Fo^2 + 2Fc^2)/3
1572 reflections	(Δ/σ)max = 0.002
104 parameters	Δρmax = 1.14 e Å^−3
1 restraint	Δρmin = −0.80 e Å^−3

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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
C1	0.3581 (2)	0.4269 (6)	0.4108 (5)	0.0263 (8)
C2	0.2676 (2)	0.3294 (6)	0.4359 (4)	0.0245 (7)
C3	0.2593 (2)	0.1265 (6)	0.5017 (5)	0.0344 (9)
H3	0.3105	0.0486	0.5316	0.041*
C4	0.1733 (3)	0.0405 (7)	0.5227 (5)	0.0422 (10)
H4	0.1670	−0.0950	0.5672	0.051*
C5	0.0973 (2)	0.1576 (8)	0.4771 (5)	0.0418 (10)
C6	0.1065 (2)	0.3577 (8)	0.4139 (5)	0.0416 (11)
H6	0.0552	0.4360	0.3855	0.050*
C7	0.1905 (2)	0.4449 (7)	0.3918 (5)	0.0316 (8)
H7	0.1958	0.5808	0.3476	0.038*
O1	0.36137 (17)	0.6114 (5)	0.3517 (4)	0.0454 (8)
O2	0.42930 (14)	0.3223 (4)	0.4444 (4)	0.0366 (6)
O1W	0.5000	1.0062 (7)	0.2500	0.0628 (13)
H1W	0.517 (4)	1.080 (8)	0.156 (6)	0.094*
Cd1	0.5000	0.66129 (6)	0.2500	0.02656 (13)
N1	0.0020 (3)	0.0925 (6)	0.4916 (6)	0.0533 (10)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0174 (15)	0.038 (2)	0.0234 (17)	−0.0122 (15)	0.0025 (13)	−0.0020 (16)
C2	0.0186 (14)	0.0327 (19)	0.0223 (16)	−0.0081 (16)	0.0017 (12)	−0.0015 (17)
C3	0.0297 (17)	0.039 (3)	0.034 (2)	−0.0098 (17)	0.0003 (15)	0.0019 (18)
C4	0.052 (2)	0.040 (3)	0.035 (2)	−0.024 (2)	0.0080 (18)	0.003 (2)
C5	0.0245 (16)	0.070 (3)	0.0308 (19)	−0.021 (2)	0.0033 (15)	−0.006 (2)
C6	0.0176 (15)	0.070 (3)	0.037 (2)	−0.003 (2)	0.0020 (15)	−0.005 (2)
C7	0.0214 (15)	0.039 (2)	0.0349 (19)	−0.0049 (17)	−0.0001 (14)	0.0007 (19)
O1	0.0273 (13)	0.047 (2)	0.0618 (18)	−0.0135 (13)	−0.0023 (13)	0.0232 (15)
O2	0.0176 (10)	0.0410 (16)	0.0513 (15)	−0.0008 (12)	0.0017 (10)	−0.0153 (14)
O1W	0.094 (3)	0.019 (2)	0.077 (3)	0.000	0.054 (3)	0.000
Cd1	0.01569 (17)	0.0221 (2)	0.0419 (2)	0.000	0.00045 (13)	0.000
N1	0.062 (2)	0.056 (2)	0.0423 (18)	−0.006 (2)	0.0083 (16)	0.003 (2)

Geometric parameters (Å, º)

C1—O1	1.256 (5)	C6—C7	1.377 (5)
C1—O2	1.270 (4)	C6—H6	0.9300
C1—C2	1.492 (4)	C7—H7	0.9300
C2—C3	1.388 (5)	O1W—H1W	0.85 (5)
C2—C7	1.391 (5)	Cd1—O1	2.208 (2)
C3—C4	1.399 (5)	Cd1—O1W	2.215 (5)
C3—H3	0.9300	Cd1—O1^i	2.208 (2)
C4—C5	1.386 (6)	Cd1—O2^ii	2.374 (3)
C4—H4	0.9300	Cd1—O2^iii	2.374 (3)
C5—C6	1.367 (6)	N1—N1^iv	1.196 (7)
C5—N1	1.477 (6)
O1—C1—O2	121.6 (3)	C6—C7—C2	119.8 (4)
O1—C1—C2	118.4 (3)	C6—C7—H7	120.1
O2—C1—C2	120.1 (3)	C2—C7—H7	120.1
C3—C2—C7	119.9 (3)	C1—O1—Cd1	106.6 (2)
C3—C2—C1	121.2 (3)	C1—O2—Cd1^iii	119.8 (2)
C7—C2—C1	119.0 (3)	Cd1—O1W—H1W	124 (4)
C2—C3—C4	119.4 (4)	O1—Cd1—O1^i	163.32 (16)
C2—C3—H3	120.3	O1—Cd1—O1W	98.34 (8)
C4—C3—H3	120.3	O1^i—Cd1—O1W	98.34 (8)
C5—C4—C3	119.9 (4)	O1—Cd1—O2^ii	84.26 (9)
C5—C4—H4	120.0	O1^i—Cd1—O2^ii	96.48 (10)
C3—C4—H4	120.0	O1W—Cd1—O2^ii	87.46 (7)
C6—C5—C4	120.0 (3)	O1—Cd1—O2^iii	96.48 (10)
C6—C5—N1	112.9 (4)	O1^i—Cd1—O2^iii	84.26 (9)
C4—C5—N1	127.1 (4)	O1W—Cd1—O2^iii	87.46 (7)
C5—C6—C7	121.0 (4)	O2^ii—Cd1—O2^iii	174.92 (14)
C5—C6—H6	119.5	N1^iv—N1—C5	109.7 (6)
C7—C6—H6	119.5

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1W—H1W···O2^v	0.85 (5)	1.89 (3)	2.670 (4)	152 (6)

Symmetry code: (v) −x+1, y+1, −z+1/2.