Poly[aqua­[μ₄-3,3′-(diazenediyl)dibenzo­ato]zinc]

The solvothermal reaction of Zn(OAc)₂·2H₂O with 3,3′-(di­az­enediyl)dibenzoic acid (H₂ADB) in H₂O at 393 K afforded the title complex, [Zn(C₁₄H₈N₂O₄)(H₂O)]_n. The asymmetric unit contains half a Zn^II cation, half an ADB ligand and half a water mol­ecule. Each Zn^II centre lies on a crystallographic twofold rotation axis and is five-coordinated by four O atoms of bridging carboxyl­ate groups from four ADB ligands and one O atom from a water mol­ecule, forming a distorted trigonal–bipyramidal coordination geometry. The [Zn(H₂O)] subunits are bridged by carboxyl­ate groups to give one-dimensional [Zn(μ-COO)₄(H₂O)]_n chains. The chains are linked by ADB ligands into two-dimensional sheets, and these sheets are further connected to neighbouring sheets via hydrogen bonds (OW—HW...O), forming a three-dimensional hydrogen-bond-stabilized structure with an unprecedented 3⁷4¹⁷5²6² topology.

S1. Comment

In recent years, azobenzoic acid derivatives such as azobenzenedicarboxylic, azobenzenetricarboxylic and azobenzenetetracarboxylic acids have been employed as good bridging ligands for constructing various types of functional metal–organic frameworks (MOFs) (Cairns et al., 2008; Lee et al., 2008; Bhattacharya et al., 2011; Yang et al., 2011; Liu, Ren et al., 2011; Liu, Wan et al., 2011; Liu & Xu, 2009). For example, Yaghi and co-workers used 4,4'-azodibenzoic acid (4,4'-H₂ADB) reacted with Tb(NO₃)₃.5H₂O to form an interpenetrating network of {Tb₂(ADB)₃[(CH₃)₂SO]₄.16[(CH₃)₂SO]}_n with a large free volume (Reineke et al., 2000). Recently, Lu and co-workers reported three porous MOFs constructed from azobenzene-3,5,4'-tricarboxylic acid (H₃ABTC) and Cd(NO₃)₂.4H₂O or MnCl₂.4H₂O (Meng et al., 2011). Qiu and co-workers used 3,3',5,5'-azobenzenetetracarboxylic acid (H₄ABTC) to construct three three-dimensional microporous MOFs with NbO and PtS topologies, which show hydrogen storage and luminescent properties (Xue et al., 2008). As for 3,3'-(diazenediyl)dibenzoic acid (H₂ADB), Cudic et al. (1999) studied the host–guest chemistry between cyclo-bis-intercaland and ADB, and recently Chen et al. (2008) reported seven coordination polymers based on the assembly of H₂ADB with Zn(OAc)₂, PbI₂, Co(OAc)₂, Y(OAc)₃, Sm(OAc)₃ or Er(OAc)₃, and/or 1,10-phenanthroline, which displayed considerable structural variety. Chen's Zn^II ADB coordination polymer, [Zn(ADB)(EtOH)]_n, was synthesized from Zn(OAc)₂, pyridine and H₂ADB in a mixture of solvents (DMF/H₂O/EtOH) and shows a two-dimensional (4,4) network with Zn₂ units serving as four-connecting square nodes (Chen et al., 2008). To better understand the coordination chemistry of 3,3'-(diazenediyl)dibenzoic acid, we have employed it in a reaction with Zn(OAc)₂.2H₂O in H₂O and obtained the title three-dimensional coordination polymer [Zn(ADB)(H₂O)]_n, (I).

Polymer (I) crystallizes in the monoclinic space group P2/c and its asymmetric unit contains half a [Zn(ADB)(H₂O)] unit. As shown in Fig. 1, each Zn^II cation adopts a tetragonal–pyramidal coordination geometry, coordinated by four O atoms of bridging carboxylate groups from four ADB ligands (O1, O1ⁱⁱ, O1ⁱⁱⁱ and O1^iv; see Fig. 1 for symmetry codes) and one O atom from a water molecule (O1W). The Zn—O bond lengths range from 1.950 (3) to 2.184 (2) Å. The mean Zn—O bond length [2.047 (2) Å] in (I) is longer than the corresponding bond length in [Zn₄(mip)₄(dabco)(H₂O)₂] [2.038 (2) Å; mip is 5-methylisophthalate and dabco is diazabicyclo[2.2.2]octane; Chun et al., 2009], and the N═N bond length [1.245 (5) Å] is slightly longer than that observed in [Zn(ADB)(EtOH)]_n [1.209 (4) Å; Chen et al., 2008]. The O1—Zn1—O1ⁱⁱ and O2ⁱⁱⁱ—Zn1—O2^iv angles (see Fig. 1 for symmetry codes) are 139.82 (13) and 174.46 (11)°, respectively, and the other O—Zn—O angles are in the range 87.23 (5)–110.09 (7)°, consistent with the tetragonal–pyramidal configuration. The carboxylate groups of the ADB ligand in (I) only display a bridging coordination mode.

In (I), each [Zn(H₂O)] subunit is interlinked by four bridging carboxylate groups to form a one-dimensional [Zn(µ-COO)₄(H₂O)]_n chain extending along the c axis (Fig. 2), in which the [Zn(µ-COO)₄(H₂O)] units are arranged in an up–down fashion. These [Zn(µ-COO)₄(H₂O)]_n chains are bridged by ADB ligands to form two-dimensional six-connected sheets extending along the ac plane (Fig. 3). Atom O2 of the carboxylate group acts as an acceptor to interact with a coordinated water molecule of an adjacent sheet, forming an intermolecular hydrogen bond (O1W—H1W···O2^v; see Table 1 for symmetry code). These hydrogen bonds connect the two-dimensional sheets, giving rise to a three-dimensional hydrogen-bonded structure extending parallel to the bc plane (Fig. 4). Topologically (Wells, 1997), if the Zn^II centres are considered as nodes and the ADB ligands and hydrogen bonds are considered as linkers, the structure of (I) can be specified by a new Schläfli symbol of 3⁷4¹⁷5²6² (Fig. 5).

An interesting related structure was reported by Fu et al. (2009), based on 4,4'-(diazenediyl)dibenzoic acid instead of the 3,3'-(diazenediyl)dibenzoic acid used in this study. Fu's compound has the same formula as (I) and crystallizes in the same space group with approximately the same unit-cell parameters, and the frameworks of the two structures are extremely similar. The Zn^II cations in both structures adopt a tetragonal–pyramidal coordination geometry and both structures possess two-dimensional sixfold-connected sheets in which the one-dimensional [Zn(µ-COO)₄(H₂O)]_n chains are bridged by ADB ligands. However, it is interesting to note that, while the two-dimensional sheets of (I) are linked by hydrogen bonds giving rise to a three-dimensional network with a 3⁷4¹⁷5²6² topology, in the structure reported by Fu et al. the sheets are bridged by another ligand arm in the [010] direction to form the three-dimensional network. This may be possible due to the longer arms of the linear 4,4'-(diazenediyl)dibenzoic acid ligands. It should also be noted that the network of Fu's 4,4'-ADB structure is large enough to allow another equivalent network generated by the ADB arms in the [010] direction to interpenetrate with that formed by the Zn^II cations, giving rise to a twofold-interpenetrated three-dimensional PtS framework. This suggests that ligand geometry plays an important role in the construction of coordination polymers with different topological structuresm, and it is expected that such ligand-dependent synthetic strategies may be applicable to other systems to produce other multidimensional coordination polymers with new topological structures.

Related literature

For related literature, see: Bhattacharya et al. (2011); Cairns et al. (2008); Chen et al. (2008); Chun et al. (2009); Cudic et al. (1999); Fu et al. (2009); Lee et al. (2008); Liu & Xu (2009); Liu, Ren, Zhu, Wang, Yan & Lang (2011); Liu, Wan, Ren & Lang (2011); Meng et al. (2011); Reineke et al. (2000); Wells (1997); Xue et al. (2008); Yang et al. (2011).

S2. Experimental

A mixture of Zn(OAc)₂.2H₂O (11 mg, 0.05 mmol), H₂ADB ligand (7 mg, 0.025 mmol) and H₂O (4 ml) was sealed in a 10 ml Pyrex glass tube and heated at 393 K for 4 d, then cooled to room temperature at a rate of 5 K h^-1. Orange blocks of (I) were collected, washed thoroughly with H₂O and dried in air (yield 12 mg, 68% based on Zn). Spectroscopic analysis: IR (KBr disc, ν, cm^-1): 3350 (m), 3272 (m), 3070 (w), 2930 (w), 1651 (s), 1590 (s), 1552 (s), 1475 (m), 1430 (m), 1390 (s), 1315 (w), 1255 (w), 1222 (w), 1159 (m), 1110 (m), 1077 (m), 936 (w), 819 (m), 780 (m), 686 (m), 538 (w), 401 (w).

S3. Refinement

The H atom (H1W) of the coordinated water molecule (O1W) was located from a difference Fourier map and refined with the help of a distance restraint [O—H = 0.83 (2) Å]. The second water H atom is generated by the crystallographic twofold axis. All other H atoms were placed in geometrically idealized positions, with C—H = 0.93 Å, and constrained to ride on their parent atoms, with U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2003); data reduction: SAINT (Bruker, 2003); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP (Sheldrick, 2008) and DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures

Fig. 1. The coordination environment of the Zn^II atom in (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) -x + 2, -y, -z + 1; (ii) -x + 1, y, -z + 1/2; (iii) -x + 1, -y, -z + 1; (iv) x, -y, z + 1/2.]

Fig. 2. A projection of the structure of (I) along the a axis, showing a section of the one-dimensional [Zn(µ-COO)₄(H₂O)]_n chain extending along the c-axis direction. All H atoms and ADB ligands (except for the bridging carboxylate groups) have been omitted for clarity.

Fig. 3. A projection of the structure of (I) along the b axis, showing the two-dimensional sheets extending parellel to the ac plane. All H atoms have been omitted for clarity.

Fig. 4. A projection of the structure of (I) along the a axis, showing the three-dimensional hydrogen-bonded structure. All C-bound H atoms have been omitted for clarity. Dashed lines indicate hydrogen bonds.

Fig. 5. An illustration of the topological structure of (I). Spheres represent eight-connected nodes and lines represent ADB ligands and hydrogen-bond linkers (pink and blue lines, respectively, in the electronic version of the paper).

Poly[aqua[µ₄-3,3'-(diazenediyl)dibenzoato]zinc]

Crystal data

[Zn(C14H8N2O4)(H2O)]	F(000) = 356
Mr = 351.61	Dx = 1.767 Mg m^−3
Monoclinic, P2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yc	Cell parameters from 3032 reflections
a = 14.424 (4) Å	θ = 3.2–26.4°
b = 6.3401 (16) Å	µ = 1.89 mm^−1
c = 7.234 (2) Å	T = 296 K
β = 92.51 (3)°	Block, orange
V = 660.9 (3) Å^3	0.17 × 0.12 × 0.10 mm
Z = 2

Data collection

Bruker APEXII CCD area-detector diffractometer	1172 independent reflections
Radiation source: fine-focus sealed tube	1085 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.038
ϕ and ω scans	θmax = 25.0°, θmin = 2.8°
Absorption correction: multi-scan (SADABS; Bruker, 2003)	h = −13→17
Tmin = 0.740, Tmax = 0.834	k = −7→6
8726 measured reflections	l = −8→8

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)] = 0.030	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.072	H atoms treated by a mixture of independent and constrained refinement
S = 1.10	w = 1/[σ^2(Fo^2) + (0.0261P)^2 + 1.0926P] where P = (Fo^2 + 2Fc^2)/3
1172 reflections	(Δ/σ)max < 0.001
105 parameters	Δρmax = 0.53 e Å^−3
1 restraint	Δρmin = −0.33 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
Zn1	0.5000	−0.18449 (7)	0.2500	0.02324 (16)
C1	0.62679 (17)	0.0934 (5)	0.4312 (4)	0.0249 (6)
C2	0.72252 (18)	0.1732 (5)	0.4768 (4)	0.0270 (6)
C3	0.7360 (2)	0.3753 (5)	0.5473 (4)	0.0318 (7)
H3	0.6852	0.4621	0.5653	0.038*
C4	0.8251 (2)	0.4480 (5)	0.5908 (4)	0.0360 (7)
H4	0.8338	0.5844	0.6357	0.043*
C5	0.9005 (2)	0.3197 (5)	0.5680 (4)	0.0356 (7)
H5	0.9600	0.3690	0.5979	0.043*
C6	0.88782 (19)	0.1155 (5)	0.4999 (4)	0.0306 (7)
C7	0.79900 (18)	0.0438 (5)	0.4523 (4)	0.0284 (6)
H7	0.7906	−0.0911	0.4038	0.034*
N1	0.96059 (16)	−0.0347 (4)	0.4789 (4)	0.0371 (6)
O1	0.61964 (12)	−0.0788 (3)	0.3460 (3)	0.0335 (5)
O2	0.55768 (12)	0.2011 (3)	0.4762 (3)	0.0288 (5)
O1W	0.5000	−0.4950 (5)	0.2500	0.0466 (9)
H1W	0.521 (3)	−0.565 (5)	0.338 (4)	0.050 (11)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.0140 (2)	0.0218 (2)	0.0337 (3)	0.000	−0.00125 (17)	0.000
C1	0.0173 (13)	0.0326 (15)	0.0247 (14)	−0.0006 (11)	0.0005 (10)	0.0031 (12)
C2	0.0189 (13)	0.0355 (16)	0.0266 (14)	−0.0032 (12)	0.0011 (11)	0.0003 (12)
C3	0.0229 (14)	0.0321 (16)	0.0403 (17)	−0.0015 (12)	0.0006 (12)	−0.0018 (13)
C4	0.0305 (15)	0.0324 (16)	0.0446 (19)	−0.0064 (13)	−0.0038 (13)	−0.0048 (14)
C5	0.0210 (14)	0.0447 (18)	0.0406 (17)	−0.0108 (13)	−0.0046 (12)	0.0010 (15)
C6	0.0191 (14)	0.0425 (17)	0.0299 (15)	−0.0018 (12)	−0.0018 (11)	0.0003 (13)
C7	0.0185 (13)	0.0362 (16)	0.0305 (15)	−0.0050 (12)	0.0010 (11)	−0.0049 (13)
N1	0.0162 (10)	0.0496 (17)	0.0451 (16)	−0.0040 (11)	−0.0020 (10)	−0.0042 (13)
O1	0.0156 (9)	0.0421 (12)	0.0429 (12)	−0.0034 (9)	0.0013 (8)	−0.0163 (10)
O2	0.0188 (9)	0.0324 (11)	0.0354 (11)	0.0041 (8)	0.0024 (8)	0.0056 (9)
O1W	0.077 (3)	0.0219 (16)	0.039 (2)	0.000	−0.0193 (18)	0.000

Geometric parameters (Å, º)

Zn1—O1	1.9503 (19)	C3—H3	0.9300
Zn1—O1^i	1.9503 (19)	C4—C5	1.374 (4)
Zn1—O1W	1.969 (3)	C4—H4	0.9300
Zn1—O2^ii	2.184 (2)	C5—C6	1.394 (4)
Zn1—O2^iii	2.184 (2)	C5—H5	0.9300
C1—O1	1.256 (3)	C6—C7	1.389 (4)
C1—O2	1.263 (3)	C6—N1	1.430 (4)
C1—C2	1.494 (4)	C7—H7	0.9300
C2—C3	1.389 (4)	N1—N1^iv	1.245 (5)
C2—C7	1.393 (4)	O2—Zn1^ii	2.184 (2)
C3—C4	1.389 (4)	O1W—H1W	0.822 (18)
O1—Zn1—O1^i	139.82 (13)	C4—C3—H3	119.9
O1—Zn1—O1W	110.09 (7)	C5—C4—C3	120.4 (3)
O1^i—Zn1—O1W	110.09 (7)	C5—C4—H4	119.8
O1—Zn1—O2^ii	93.45 (8)	C3—C4—H4	119.8
O1^i—Zn1—O2^ii	88.46 (8)	C4—C5—C6	120.0 (3)
O1W—Zn1—O2^ii	87.23 (5)	C4—C5—H5	120.0
O1—Zn1—O2^iii	88.46 (8)	C6—C5—H5	120.0
O1^i—Zn1—O2^iii	93.45 (8)	C7—C6—C5	119.8 (3)
O1W—Zn1—O2^iii	87.23 (5)	C7—C6—N1	115.4 (3)
O2^ii—Zn1—O2^iii	174.46 (11)	C5—C6—N1	124.8 (3)
O1—C1—O2	123.2 (2)	C6—C7—C2	120.2 (3)
O1—C1—C2	117.3 (2)	C6—C7—H7	119.9
O2—C1—C2	119.5 (3)	C2—C7—H7	119.9
C3—C2—C7	119.4 (3)	N1^iv—N1—C6	113.9 (3)
C3—C2—C1	120.5 (2)	C1—O1—Zn1	121.72 (17)
C7—C2—C1	120.1 (3)	C1—O2—Zn1^ii	122.96 (17)
C2—C3—C4	120.2 (3)	Zn1—O1W—H1W	123 (3)
C2—C3—H3	119.9
O1—C1—C2—C3	170.9 (3)	C3—C2—C7—C6	0.8 (4)
O2—C1—C2—C3	−7.9 (4)	C1—C2—C7—C6	−178.0 (3)
O1—C1—C2—C7	−10.3 (4)	C7—C6—N1—N1^iv	179.4 (3)
O2—C1—C2—C7	170.9 (3)	C5—C6—N1—N1^iv	−2.5 (5)
C7—C2—C3—C4	0.7 (4)	O2—C1—O1—Zn1	6.7 (4)
C1—C2—C3—C4	179.5 (3)	C2—C1—O1—Zn1	−172.13 (18)
C2—C3—C4—C5	−1.2 (5)	O1^i—Zn1—O1—C1	30.4 (2)
C3—C4—C5—C6	0.3 (5)	O1W—Zn1—O1—C1	−149.6 (2)
C4—C5—C6—C7	1.2 (5)	O2^ii—Zn1—O1—C1	−61.3 (2)
C4—C5—C6—N1	−176.9 (3)	O2^iii—Zn1—O1—C1	124.0 (2)
C5—C6—C7—C2	−1.7 (4)	O1—C1—O2—Zn1^ii	96.4 (3)
N1—C6—C7—C2	176.5 (3)	C2—C1—O2—Zn1^ii	−84.8 (3)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1W—H1W···O2^v	0.82 (2)	1.85 (2)	2.639 (3)	160 (4)

Symmetry code: (v) x, y−1, z.