Assembly of ZnII and CdII coordination polymers with different dimensionalities based on the semi-flexible 3-(1H-benzimidazol-2-yl)propanoic acid ligand.

Two new coordination polymers, namely, poly[[μ3-3-(1H-benzimidazol-2-yl)propionato]zinc(II)], [Zn(C10H8N2O2)] n , (1), and poly[bis-[μ2-3-(1H-benzimid-azol-2-yl)propionato]cadmium(II)], [Cd(C10H8N2O2)2] n , (2) have been synthesized from 3-(1H-benzoimidazol-2-yl)propanoic acid ligands through a mixed-ligand synthetic strategy under a solvothermal environment, and studied by single-crystal X-ray diffraction. Complex 1 crystallizes in the ortho-rhom-bic space group Pbca and features a two-dimensional structure formed by a binuclear Zn2O4 core. Complex 2, however, crystallizes in the monoclinic space group P21/c and forms a one-dimensional chain structure. The ZnII and CdII ions have different coordination numbers and the 3-(1H-benzoimidazol-2-yl)propano-ate ligands display different coordination modes. The structures reported here show the importance of the selection of metal ions and suitable ligands.

Chemical context

The structures of coordination polymers are strongly influenced by the organic ligands and metal ions and it is important to choose suitable ligands and metal ions under appropriate synthetic conditions to synthesize coordination complexes with inter­esting structures. The exploration of metal–organic frameworks (MOFs) have received much attention because of their intriguing architectures and wide range of potential applications in different fields (Castellanos et al., 2016 ▸; Zhang et al., 2016 ▸; Kumar et al., 2015 ▸; Liu et al., 2016 ▸; Müller-Buschbaum et al., 2015 ▸; Duerinck & Denayer, 2015 ▸; Mohan et al., 2015 ▸). The assembly of ZnII (Jurcic et al., 2015 ▸; Karmakar et al., 2016a ▸,b ▸; Liang et al., 2016 ▸; Wannapaiboon et al., 2015 ▸; Ying et al., 2015 ▸) and CdII (Xiao et al., 2015 ▸, Wu et al., 2011 ▸, Hu et al., 2015 ▸, Cao et al., 2014 ▸, Zhang et al., 2015 ▸) ions with multidentate nitro­gen-containing ligands has produced various MOFs with fascinating structures and luminescent properties. The selection of chelating or bridging organic linkers often favors a structure-specific assembly and the factors that govern the formation of such complexes are complicated and include not only the nature of the ZnII and CdII ions and ligand structure but also anion-directed inter­actions as well as reaction conditions. In order to explore the coordination chemistry of this type of ligand, 3-(1H-benz­imid­azol-2-yl) propanoic acid (H2BIP) was chosen in the present study to construct new coordination polymers. A two-dimensional ZnII polymer and a one-dimensional CdII coord­ination polymer have been obtained.

Structural commentary

Complex 1 crystallizes in the ortho­rhom­bic crystal system in the centrosymmetric space group Pbca. The 3-(1H-benzoimdazol-2-yl)propano­nic acid ligand deprotonates completely when bonding to ZnII ions. The asymmetric unit of 1 consists of one ZnII ion and one 3-(1λ2-benzoimidazol-2-yl)propano­ate anion. Geometric parameters are given in Table 1 ▸. As shown in Fig. 1 ▸, the ZnII ion has a tetra­hedral ZnO2N2 environment completed by N2 from one 3-(1λ2-benzoimid­azol-2-yl)propano­ate anion, O2(−x + , y + , z) and N1(−x + , y + , z) from the second 3-(1λ2-benzoimidazol-2-yl)propano­ate anion and O1(x − , −y + , −z) from the third 3-(1λ2-benzoimidazol-2-yl)propano­ate anion. All the Zn—N/O bond distances [Zn—O: 1.9563 (16)–2.0208 (17) and Zn—N: 1.9624 (18)–1.9661 (16) Å] and the bond angles around Zn1 [99.22 (6)–120.28 (7)°] fall into the normal range. Each 3-(1λ2-benzoimidazol-2-yl)propano­ate anion shows a tridentate chelating mode bridging three ZnII ions with the Zn⋯Zn distances of 4.066 (1), 5.870 (2) and 6.965 (2) Å. Zn1 and the symmetry-related Zn1 forming the shortest distance are bridged by O1 and O2 to form a binuclear Zn2 cluster. Adjacent clusters are connected by a Zn—N bond of 1.9661 (16) Å to generate 2D square-grid (4,4) layers (Fig. 2 ▸). As there are no classical hydrogen bonds in 1, these layers are packed by normal van der Waals forces into an extended 3D framework (Fig. 3 ▸).

Table 1

Selected geometric parameters (Å, °) for 1

Zn1—O1i	1.9563 (16)	Zn1—N2	1.9661 (16)
Zn1—N1ii	1.9624 (18)	Zn1—O2ii	2.0208 (17)
O1i—Zn1—N1ii	118.50 (7)	O1i—Zn1—O2ii	105.15 (6)
O1i—Zn1—N2	106.84 (7)	N1ii—Zn1—O2ii	99.22 (6)
N1ii—Zn1—N2	120.28 (7)	N2—Zn1—O2ii	104.42 (6)

Symmetry codes: (i) ; (ii) .

Figure 1

The asymmetric unit of 1, with additional symmetry-related atoms. The displacement ellipsoids are drawn at the 30% probability level [symmetry codes: (A) −x + , y + , z; (B) x − , −y + , −z)].

Figure 2

A perspective view of the 4-connected nodes in 1.

Figure 3

View of the three-dimensional framework of 1 formed by two-dimensional undulating sheets and van der Waals forces.

Complex 2 crystallizes in the monoclinic crystal system in the centrosymmetic space group P21/c. The 3-(1H-benzo­imid­azol-2-yl)propano­nic acid ligands do not deprotonate completely when bonding to CdII ions. Geometric parameters are given in Table 2 ▸. As shown in Fig. 4 ▸, the CdII ion is five-coordinated by N3 from one 3-(1H-benzoimidazol-2-yl)propano­ate anion, N1(x, y − 1, z) from the second 3-(1H-benzoimidazol-2-yl)propano­ate anion, O1 from the third and O3(−x, −y, −z + 1) and O4(−x, −y, −z + 1) from the fourth. All the Cd—N/O bond distances [Cd—O: 2.285 (2)–2.362 (2) and Cd—N: 2.262 (3)–2.271 (3) Å] and the bond angles around Cd1 [55.44 (9)–146.52 (9)°] fall into the normal range. A distance of 2.667 (2) Å between Cd1 and O2 indicates the existence of a weak inter­action between them. Two HBIP− anions connects two CdII ions with one bidentate carboxyl­ate and one N atom forming end-to-end binuclear Cd2 cluster with a distance of 7.274 (1) Å. The other two HBIP− anions act as bridges to join two neighboring binuclear Cd2 clusters with one monodentate carboxyl­ate and one N atom to generate 1D ladders along the b-axis direction (Fig. 5 ▸). In the crystal, N—H⋯O hydrogen bonds (Table 3 ▸) and π–π inter­actions involv­ing the imidazole rings and benzimidazole ring systems with centroid–centroid distances of 3.569 (2) and 3.838 (2) Å connect the 1D ladders along a- and c-axis directions into an extended 3D framework (Fig. 6 ▸). Although there are large potential voids within the 1D ladders (7.274 × 8. 025 Å based on the distances of the CdII ions), they are inter­blocked by adjacent ladders.

Table 2

Selected geometric parameters (Å, °) for 2

Cd1—N1i	2.262 (3)	Cd1—O3ii	2.293 (2)
Cd1—N3	2.271 (3)	Cd1—O4ii	2.362 (2)
Cd1—O1	2.285 (2)
N1i—Cd1—N3	103.73 (10)	O1—Cd1—O3ii	144.01 (9)
N1i—Cd1—O1	106.08 (9)	N1i—Cd1—O4ii	146.52 (9)
N3—Cd1—O1	93.38 (9)	N3—Cd1—O4ii	104.51 (10)
N1i—Cd1—O3ii	100.41 (9)	O1—Cd1—O4ii	89.85 (8)
N3—Cd1—O3ii	103.63 (10)	O3ii—Cd1—O4ii	55.44 (9)

Symmetry codes: (i) ; (ii) .

Figure 4

The asymmetric unit of 2, with additional symmetry-related atoms. The displacement ellipsoids are drawn at the 30% probability level [symmetry codes: (A) −x, −y, −z + 1; (B) x, y − 1, z].

Figure 5

A view of the one-dimensional ladders in 2.

Table 3

Hydrogen-bond geometry (Å, °) for 2

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N2—H2A⋯O2iii	0.86	2.10	2.823 (4)	141
N4—H4A⋯O1iv	0.86	2.03	2.862 (4)	161

Symmetry codes: (iii) ; (iv) .

Figure 6

A perspective view of the three-dimensional frameworks in 2 formed by one-dimensional ladders and N—H⋯O hydrogen bonds (Table 3 ▸). The hydrogen bonds are shown as dashed lines.

Supra­molecular features

The structures and the coordination modes of complexes 1 and 2 are quite different, which may be ascribed to a diverse metal coordination habit. The crystal structure of a ZnII complex based on H2BIP is reported for the first time. In a comparison with its counterparts based on similar benzo­imidazole carb­oxy­lic acids ligands, benzimidazole-2-butanoic acid (H2BIB) and 2-(1H-benzimidazol-2-yl­thio)­acetic acid (H2BITA), the same coord­ination modes are found for 1 (μ3-κN,O: κO’: kN′ mode, μ3-BIP2−) and [Zn(BIB)] (μ3-κN,O: κO’: kN′ mode, μ3-BIB2−; Zhang et al., 2015 ▸) and different coordination modes are found for 1 and [Zn2(HBITA)4]·(DMF)2·(H2O)2 (μ2-κN: κO mode, μ2-HBITA− and μ1-κN,O mode, μ1-HBITA−; Yu et al., 2010 ▸), [Zn2(HBITA)4] (μ2-κN: κO mode, μ2-HBITA−; Yu et al., 2010 ▸). Different dimensionalities, like 2D for 1, 3D for [Zn(BIB)], 0D for [Zn2(HBITA)4]·(DMF)2·(H2O)2 and 2D for [Zn2(HBITA)4] are also found. CdII complexes based on H2BIP have already been observed with the appropriate Et3N reagent in a EtOH/H2O mixed solvent. By selection of the EtOH/H2O mixed solvent without any basic reagent, complex 2 was obtained with a relatively simple coordination mode (μ2-κN: κO,O′ mode, μ2-HBIP−) in comparison with diverse modes in {[Cd5Cl2(HBIP)4(BIP)2]·4DMF} (μ2-κN,O: κO,O′ mode, μ2-HBIP−, μ3-κN,O: κO,O′: κN’ mode, μ3-BIP2−, μ3-κN,O: κO,O′: κO’ mode, μ3-HBIP−; Zheng et al., 2012 ▸) and [Cd3(HBIP)2(BIP)2] (μ3-κN,O: κO,O′: κO’ mode, μ3-BIP2−, μ4-κN,O: κO: κO’: κO’ mode, μ4-HBIP−; Zheng et al., 2012 ▸). In comparison with its counterpart based on similar benzo­imidazole carb­oxy­lic acids, H2BIB, the same coordination modes are found for 2 and [Cd(HBIB)2]·(H2O) (μ2-κN: κO,O′ mode, μ2-HBIB−; Zhang et al., 2015 ▸). Different dimensionalities, such as 1D for 2, 2D for {[Cd5Cl2(HBIP)4(BIP)2]·4DMF}, 1D for [Cd3(HBIP)2 (BIP)2] and 2D for [Cd(HBIB)2]·(H2O) were also found. The different coord­ination modes and dimensionalities show the important roles of spacer lengths and flexibilities of ligands. The crystal structures reported here and before show that ligands containing both flexible carb­oxy­lic and benzimidazole groups are suitable for the construction of coordination polymers with inter­esting structures, adopting diverse coordination modes. The significant effect of metal ions, spacer length and flexibility of ligands on the structural assemblies of such crystalline materials is critical to the assemblies of MOFs in some particular systems.

Database Survey

Complexes with benzimidazole-based carb­oxy­lic acid, for example, 1H-benzimidazole-2-carb­oxy­lic acid (Xia et al., 2013 ▸; Qiao et al., 2013 ▸; Małecki & Maroń, 2012 ▸; Machura et al., 2014 ▸; Fernández et al., 2016 ▸) and 3-(1H-benzimidazole-2-yl) propanoic acid (Liu et al., 2015 ▸) have been reported. A limited number of coordination polymers constructed from 3-(1H-benzimidazol-2-yl) propanoic acid (H2BIP) have been reported including [Cd3(HBIP)2(BIP)2] and [Cd5Cl2(BIP)4 (BIP)2] (Zheng et al., 2012 ▸). [Cd3(HBIP)2(BIP)2] presents a fascinating one-dimensional structure with helical character, made of four helical chains weaving together in two reverse orientations. [Cd5Cl2(BIP)4(BIP)2] exhibits a distinct (4,4) network and infinite penta­nuclear secondary building units.

Synthesis and crystallization

3-(1H-Benzimidazol-2-yl)propanoic acid (H2BIP) was prepared by a literature method (Delval et al., 2008 ▸). Other reagents and solvents used in the reactions were purchased from Aladdin-Chemical and used without purification.

Preparation of 1

H2BIP (0.02 mmol, 0.038 g) and Zn(NO3)2·6H2O (0.2 mmol, 0.060 g) were dissolved in EtOH/H2O (1:1 v/v, 8 ml) mixed solvent. The mixture was sealed in a closed vessel and heated at 413 K for 72 h; the mixture was then cooled slowly to room temperature at a rate of 2 K h−1. Many pale-yellow block-shaped crystals were collected.

Preparation of 2

H2BIP (0.02 mmol, 0.038 g), Cd(CH3COO)2·2H2O (0.2mmol, 0.053 g) were dissolved in EtOH/H2O (1:1 v/v, 8 ml) mixed solvent. The mixture was sealed in a closed vessel and heated at 413 K for 72 h; the mixture was then cooled slowly to room temperature at a rate of 2 K h−1. Many brown prismatic crystals were collected.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 4 ▸. H atoms on N atoms were found in the difference-Fourier map and were refined isotrop­ic­ally while restraining the N—H distances to 0.86 Å. Other H atoms were generated geometrically and were allowed to ride on their parent atoms in the riding-model approximation, with C—H = 0.93 Å, U iso(H) = 1.2U eq(C)(aromatic) and C—H = 0.97 Å, U iso(H) = 1.5U eq(C) for methyl hydrogen atoms.

Table 4

Experimental details

	1	2
Crystal data
Chemical formula	[Zn(C10H8N2O2)]	[Cd(C10H8N2O2)2]
M r	253.55	490.79
Crystal system, space group	Orthorhombic, P b c a	Monoclinic, P21/c
Temperature (K)	296	293
a, b, c (Å)	8.956 (4), 10.697 (5), 20.331 (9)	13.6708 (6), 8.0253 (3), 17.3834 (7)
α, β, γ (°)	90, 90, 90	90, 100.972 (4), 90
V (Å3)	1947.8 (15)	1872.31 (13)
Z	8	4
Radiation type	Mo Kα	Mo Kα
μ (mm−1)	2.50	1.20
Crystal size (mm)	0.28 × 0.25 × 0.21	0.28 × 0.25 × 0.19
Data collection
Diffractometer	Bruker SMART CCD area-detector	Bruker SMART CCD area-detector
Absorption correction	Multi-scan (SADABS; Bruker, 2012 ▸)	Multi-scan (SADABS; Bruker, 2012 ▸)
T min, T max	0.541, 0.622	0.923, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	9832, 1725, 1525	6654, 3289, 2685
R int	0.046	0.029
(sin θ/λ)max (Å−1)	0.595	0.595
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.024, 0.063, 1.03	0.031, 0.064, 1.06
No. of reflections	1725	3289
No. of parameters	136	262
H-atom treatment	H-atom parameters constrained	H-atom parameters constrained
Δρmax, Δρmin (e Å−3)	0.29, −0.56	0.33, −0.48

Computer programs: APEX2 and SAINT (Bruker, 2012 ▸), SHELXL2014 (Sheldrick, 2015 ▸), OLEX2 (Dolomanov et al., 2009 ▸), DIAMOND (Brandenburg, 2008 ▸), publCIF (Westrip, 2010 ▸) and PLATON (Spek, 2009 ▸).

Crystal structure: contains datablock(s) 1, 2. DOI: 10.1107/S2056989017017534/lh5857sup1.cif

Structure factors: contains datablock(s) 1. DOI: 10.1107/S2056989017017534/lh58571sup2.hkl

Structure factors: contains datablock(s) 2. DOI: 10.1107/S2056989017017534/lh58572sup3.hkl

CCDC references: 1589668, 1589667

Additional supporting information: crystallographic information; 3D view; checkCIF report

[Zn(C10H8N2O2)]	Dx = 1.729 Mg m−3
Mr = 253.55	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbca	Cell parameters from 5004 reflections
a = 8.956 (4) Å	θ = 3.0–27.6°
b = 10.697 (5) Å	µ = 2.50 mm−1
c = 20.331 (9) Å	T = 296 K
V = 1947.8 (15) Å3	Block, yellow
Z = 8	0.28 × 0.25 × 0.21 mm
F(000) = 1024

Bruker SMART CCD area-detector diffractometer	1525 reflections with I > 2σ(I)
phi and ω scans	Rint = 0.046
Absorption correction: multi-scan (SADABS; Bruker, 2012)	θmax = 25.0°, θmin = 2.0°
Tmin = 0.541, Tmax = 0.622	h = −10→10
9832 measured reflections	k = −12→11
1725 independent reflections	l = −24→24

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) = 0.063	H-atom parameters constrained
S = 1.03	w = 1/[σ2(Fo2) + (0.0338P)2 + 0.8648P] where P = (Fo2 + 2Fc2)/3
1725 reflections	(Δ/σ)max < 0.001
136 parameters	Δρmax = 0.29 e Å−3
0 restraints	Δρmin = −0.56 e Å−3

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.

	x	y	z	Uiso*/Ueq
Zn1	0.61499 (3)	0.44565 (2)	0.08133 (2)	0.02929 (11)
C1	0.8742 (2)	0.31428 (19)	0.14864 (9)	0.0272 (4)
C2	0.9402 (3)	0.4128 (2)	0.18261 (10)	0.0361 (5)
H2	0.8972	0.4919	0.1832	0.043*
C3	1.0712 (3)	0.3886 (2)	0.21531 (12)	0.0487 (6)
H3	1.1175	0.4528	0.2384	0.058*
C4	1.1366 (3)	0.2704 (3)	0.21484 (13)	0.0512 (6)
H4	1.2268	0.2584	0.2366	0.061*
C5	1.0711 (3)	0.1710 (2)	0.18305 (11)	0.0402 (5)
H5	1.1136	0.0917	0.1837	0.048*
C6	0.9381 (2)	0.19494 (18)	0.14985 (9)	0.0278 (4)
C7	0.7378 (2)	0.18898 (16)	0.08956 (9)	0.0273 (4)
C8	0.6243 (2)	0.1407 (2)	0.04189 (11)	0.0326 (5)
H8A	0.5329	0.1886	0.0464	0.039*
H8B	0.6018	0.0542	0.0523	0.039*
C9	0.6791 (2)	0.14918 (19)	−0.02923 (10)	0.0347 (5)
H9A	0.6001	0.1208	−0.0582	0.042*
H9B	0.6992	0.2361	−0.0396	0.042*
C10	0.8184 (2)	0.07312 (18)	−0.04282 (10)	0.0296 (4)
N1	0.84880 (17)	0.11670 (14)	0.11236 (9)	0.0289 (4)
N2	0.74575 (17)	0.30823 (13)	0.10974 (8)	0.0268 (4)
O1	0.91054 (16)	0.11866 (15)	−0.08295 (7)	0.0373 (4)
O2	0.83644 (16)	−0.03094 (12)	−0.01494 (7)	0.0332 (3)

	U11	U22	U33	U12	U13	U23
Zn1	0.03268 (17)	0.01695 (16)	0.03822 (18)	0.00017 (8)	0.00399 (10)	0.00205 (9)
C1	0.0323 (10)	0.0252 (10)	0.0240 (10)	−0.0034 (8)	0.0028 (8)	0.0001 (8)
C2	0.0459 (12)	0.0284 (11)	0.0341 (12)	−0.0065 (9)	0.0030 (10)	−0.0084 (9)
C3	0.0548 (14)	0.0475 (14)	0.0437 (13)	−0.0116 (12)	−0.0098 (12)	−0.0148 (12)
C4	0.0507 (14)	0.0570 (16)	0.0460 (14)	−0.0032 (12)	−0.0209 (11)	−0.0069 (13)
C5	0.0438 (12)	0.0384 (12)	0.0382 (12)	0.0045 (10)	−0.0119 (10)	−0.0008 (10)
C6	0.0329 (10)	0.0256 (10)	0.0250 (9)	−0.0030 (8)	−0.0006 (8)	0.0009 (8)
C7	0.0290 (10)	0.0207 (10)	0.0323 (10)	−0.0013 (8)	−0.0003 (8)	0.0000 (8)
C8	0.0283 (10)	0.0235 (10)	0.0459 (13)	0.0017 (8)	−0.0070 (9)	−0.0045 (9)
C9	0.0337 (11)	0.0287 (11)	0.0416 (12)	0.0044 (8)	−0.0113 (9)	−0.0002 (9)
C10	0.0326 (11)	0.0226 (10)	0.0336 (11)	−0.0011 (8)	−0.0119 (9)	−0.0037 (8)
N1	0.0332 (9)	0.0177 (8)	0.0360 (9)	0.0000 (7)	−0.0054 (7)	−0.0009 (7)
N2	0.0294 (9)	0.0193 (8)	0.0317 (9)	−0.0009 (7)	0.0013 (7)	−0.0006 (7)
O1	0.0330 (8)	0.0327 (9)	0.0461 (9)	0.0019 (6)	−0.0032 (6)	0.0111 (7)
O2	0.0423 (8)	0.0211 (7)	0.0360 (8)	0.0020 (6)	−0.0053 (6)	0.0013 (6)

Zn1—O1i	1.9563 (16)	C6—N1	1.386 (3)
Zn1—N1ii	1.9624 (18)	C7—N2	1.342 (2)
Zn1—N2	1.9661 (16)	C7—N1	1.342 (2)
Zn1—O2ii	2.0208 (17)	C7—C8	1.496 (3)
C1—C2	1.392 (3)	C8—C9	1.530 (3)
C1—N2	1.398 (2)	C8—H8A	0.9700
C1—C6	1.399 (3)	C8—H8B	0.9700
C2—C3	1.374 (3)	C9—C10	1.515 (3)
C2—H2	0.9300	C9—H9A	0.9700
C3—C4	1.393 (4)	C9—H9B	0.9700
C3—H3	0.9300	C10—O1	1.259 (3)
C4—C5	1.375 (3)	C10—O2	1.260 (2)
C4—H4	0.9300	N1—Zn1iii	1.9624 (18)
C5—C6	1.393 (3)	O1—Zn1iv	1.9563 (16)
C5—H5	0.9300	O2—Zn1iii	2.0207 (17)
O1i—Zn1—N1ii	118.50 (7)	N2—C7—C8	124.22 (17)
O1i—Zn1—N2	106.84 (7)	N1—C7—C8	121.86 (16)
N1ii—Zn1—N2	120.28 (7)	C7—C8—C9	111.96 (17)
O1i—Zn1—O2ii	105.15 (6)	C7—C8—H8A	109.2
N1ii—Zn1—O2ii	99.22 (6)	C9—C8—H8A	109.2
N2—Zn1—O2ii	104.42 (6)	C7—C8—H8B	109.2
C2—C1—N2	131.70 (19)	C9—C8—H8B	109.2
C2—C1—C6	120.56 (19)	H8A—C8—H8B	107.9
N2—C1—C6	107.74 (16)	C10—C9—C8	113.88 (16)
C3—C2—C1	117.4 (2)	C10—C9—H9A	108.8
C3—C2—H2	121.3	C8—C9—H9A	108.8
C1—C2—H2	121.3	C10—C9—H9B	108.8
C2—C3—C4	121.8 (2)	C8—C9—H9B	108.8
C2—C3—H3	119.1	H9A—C9—H9B	107.7
C4—C3—H3	119.1	O1—C10—O2	123.33 (19)
C5—C4—C3	121.7 (2)	O1—C10—C9	116.77 (18)
C5—C4—H4	119.1	O2—C10—C9	119.89 (19)
C3—C4—H4	119.1	C7—N1—C6	105.65 (16)
C4—C5—C6	116.7 (2)	C7—N1—Zn1iii	123.27 (13)
C4—C5—H5	121.6	C6—N1—Zn1iii	130.11 (13)
C6—C5—H5	121.6	C7—N2—C1	105.11 (15)
N1—C6—C5	130.48 (19)	C7—N2—Zn1	126.10 (13)
N1—C6—C1	107.75 (17)	C1—N2—Zn1	128.46 (13)
C5—C6—C1	121.75 (18)	C10—O1—Zn1iv	117.83 (13)
N2—C7—N1	113.75 (17)	C10—O2—Zn1iii	124.96 (13)
N2—C1—C2—C3	−178.1 (2)	N2—C7—N1—Zn1iii	−170.56 (13)
C6—C1—C2—C3	1.8 (3)	C8—C7—N1—Zn1iii	4.9 (3)
C1—C2—C3—C4	0.0 (4)	C5—C6—N1—C7	−177.4 (2)
C2—C3—C4—C5	−1.8 (4)	C1—C6—N1—C7	0.7 (2)
C3—C4—C5—C6	1.6 (4)	C5—C6—N1—Zn1iii	−8.6 (3)
C4—C5—C6—N1	178.1 (2)	C1—C6—N1—Zn1iii	169.47 (14)
C4—C5—C6—C1	0.2 (3)	N1—C7—N2—C1	0.6 (2)
C2—C1—C6—N1	179.73 (18)	C8—C7—N2—C1	−174.75 (18)
N2—C1—C6—N1	−0.4 (2)	N1—C7—N2—Zn1	174.49 (13)
C2—C1—C6—C5	−2.0 (3)	C8—C7—N2—Zn1	−0.8 (3)
N2—C1—C6—C5	177.93 (18)	C2—C1—N2—C7	179.8 (2)
N2—C7—C8—C9	90.4 (2)	C6—C1—N2—C7	−0.1 (2)
N1—C7—C8—C9	−84.6 (2)	C2—C1—N2—Zn1	6.1 (3)
C7—C8—C9—C10	61.3 (2)	C6—C1—N2—Zn1	−173.81 (13)
C8—C9—C10—O1	−144.39 (18)	O2—C10—O1—Zn1iv	−19.8 (3)
C8—C9—C10—O2	36.4 (3)	C9—C10—O1—Zn1iv	160.95 (13)
N2—C7—N1—C6	−0.8 (2)	O1—C10—O2—Zn1iii	108.7 (2)
C8—C7—N1—C6	174.63 (18)	C9—C10—O2—Zn1iii	−72.1 (2)

[Cd(C10H8N2O2)2]	F(000) = 984
Mr = 490.79	Dx = 1.741 Mg m−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 13.6708 (6) Å	Cell parameters from 2660 reflections
b = 8.0253 (3) Å	θ = 3.0–27.4°
c = 17.3834 (7) Å	µ = 1.20 mm−1
β = 100.972 (4)°	T = 293 K
V = 1872.31 (13) Å3	Prism, brown
Z = 4	0.28 × 0.25 × 0.19 mm

Bruker SMART CCD area-detector diffractometer	2685 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.029
phi and ω scans	θmax = 25.0°, θmin = 2.4°
Absorption correction: multi-scan (SADABS; Bruker, 2012)	h = −16→15
Tmin = 0.923, Tmax = 1.000	k = −9→6
6654 measured reflections	l = −20→14
3289 independent reflections

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)] = 0.031	Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.064	H-atom parameters constrained
S = 1.06	w = 1/[σ2(Fo2) + (0.0234P)2] where P = (Fo2 + 2Fc2)/3
3289 reflections	(Δ/σ)max < 0.001
262 parameters	Δρmax = 0.33 e Å−3
0 restraints	Δρmin = −0.48 e Å−3

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.

	x	y	z	Uiso*/Ueq
Cd1	0.22103 (2)	0.06562 (3)	0.41588 (2)	0.02433 (9)
C1	0.4463 (3)	1.0429 (4)	0.37316 (19)	0.0254 (8)
C2	0.4459 (3)	1.1926 (4)	0.33279 (19)	0.0343 (9)
H2	0.3890	1.2587	0.3224	0.041*
C3	0.5321 (3)	1.2403 (5)	0.3087 (2)	0.0442 (11)
H3	0.5337	1.3410	0.2825	0.053*
C4	0.6164 (3)	1.1402 (5)	0.3229 (2)	0.0503 (11)
H4	0.6734	1.1750	0.3056	0.060*
C5	0.6179 (3)	0.9902 (5)	0.3622 (2)	0.0444 (10)
H5	0.6740	0.9224	0.3710	0.053*
C6	0.5323 (3)	0.9465 (4)	0.3874 (2)	0.0298 (8)
C7	0.4118 (3)	0.8209 (4)	0.43435 (18)	0.0263 (8)
C8	0.3603 (3)	0.6815 (4)	0.46664 (19)	0.0305 (8)
H8A	0.3197	0.7255	0.5020	0.037*
H8B	0.4094	0.6069	0.4962	0.037*
C9	0.2949 (3)	0.5857 (4)	0.4010 (2)	0.0404 (10)
H9A	0.3250	0.5925	0.3548	0.048*
H9B	0.2308	0.6413	0.3886	0.048*
C10	0.2768 (3)	0.4031 (4)	0.4167 (2)	0.0261 (8)
C11	0.0502 (3)	−0.0701 (4)	0.18100 (19)	0.0274 (8)
C12	0.0484 (3)	−0.0730 (4)	0.1006 (2)	0.0373 (9)
H12	−0.0082	−0.1041	0.0648	0.045*
C13	0.1354 (3)	−0.0273 (4)	0.0773 (2)	0.0390 (10)
H13	0.1371	−0.0271	0.0241	0.047*
C14	0.2200 (3)	0.0185 (5)	0.1299 (2)	0.0397 (10)
H14	0.2769	0.0493	0.1113	0.048*
C15	0.2218 (3)	0.0193 (4)	0.2096 (2)	0.0336 (9)
H15	0.2790	0.0490	0.2452	0.040*
C16	0.1354 (3)	−0.0256 (4)	0.23458 (19)	0.0237 (8)
C17	0.0228 (3)	−0.0925 (4)	0.30217 (19)	0.0272 (8)
C18	−0.0301 (3)	−0.1297 (4)	0.3673 (2)	0.0333 (9)
H18A	0.0190	−0.1575	0.4136	0.040*
H18B	−0.0717	−0.2271	0.3534	0.040*
C19	−0.0936 (3)	0.0092 (5)	0.3873 (2)	0.0433 (10)
H19A	−0.1486	0.0260	0.3436	0.052*
H19B	−0.0544	0.1107	0.3937	0.052*
C20	−0.1353 (3)	−0.0190 (5)	0.4602 (2)	0.0317 (9)
O1	0.21406 (17)	0.3287 (3)	0.36487 (13)	0.0316 (6)
O2	0.32390 (18)	0.3331 (3)	0.47586 (13)	0.0309 (6)
O3	−0.1888 (2)	0.0912 (3)	0.48158 (15)	0.0504 (8)
O4	−0.1163 (2)	−0.1496 (3)	0.49775 (14)	0.0448 (7)
N1	0.3712 (2)	0.9617 (3)	0.40401 (15)	0.0242 (7)
N2	0.5075 (2)	0.8066 (3)	0.42631 (16)	0.0313 (7)
H2A	0.5466	0.7247	0.4426	0.038*
N3	0.1154 (2)	−0.0401 (3)	0.31043 (16)	0.0277 (7)
N4	−0.0197 (2)	−0.1100 (3)	0.22566 (16)	0.0323 (7)
H4A	−0.0800	−0.1408	0.2079	0.039*

	U11	U22	U33	U12	U13	U23
Cd1	0.02465 (15)	0.02141 (14)	0.02708 (15)	0.00049 (12)	0.00527 (10)	0.00198 (12)
C1	0.026 (2)	0.0254 (19)	0.0239 (17)	−0.0039 (16)	0.0022 (15)	−0.0025 (17)
C2	0.037 (2)	0.029 (2)	0.037 (2)	−0.0006 (18)	0.0046 (17)	0.0021 (19)
C3	0.051 (3)	0.040 (2)	0.042 (2)	−0.015 (2)	0.010 (2)	0.009 (2)
C4	0.039 (3)	0.061 (3)	0.054 (3)	−0.016 (2)	0.015 (2)	0.002 (3)
C5	0.026 (2)	0.048 (2)	0.059 (3)	−0.005 (2)	0.005 (2)	−0.005 (2)
C6	0.027 (2)	0.032 (2)	0.0278 (19)	−0.0043 (17)	−0.0002 (16)	−0.0042 (18)
C7	0.029 (2)	0.0229 (18)	0.0250 (18)	0.0007 (16)	0.0010 (15)	−0.0038 (16)
C8	0.035 (2)	0.0219 (18)	0.034 (2)	0.0000 (17)	0.0061 (17)	0.0028 (17)
C9	0.044 (3)	0.0257 (19)	0.045 (2)	−0.0080 (18)	−0.0073 (19)	0.009 (2)
C10	0.022 (2)	0.0234 (18)	0.035 (2)	0.0023 (16)	0.0105 (16)	0.0010 (18)
C11	0.031 (2)	0.0212 (18)	0.0298 (19)	−0.0004 (17)	0.0061 (16)	−0.0025 (17)
C12	0.051 (3)	0.030 (2)	0.027 (2)	0.0007 (19)	−0.0016 (18)	−0.0008 (18)
C13	0.052 (3)	0.040 (2)	0.027 (2)	0.010 (2)	0.0142 (19)	0.0035 (19)
C14	0.037 (2)	0.045 (2)	0.042 (2)	0.005 (2)	0.0196 (19)	0.002 (2)
C15	0.027 (2)	0.040 (2)	0.034 (2)	0.0014 (18)	0.0064 (17)	0.0027 (19)
C16	0.025 (2)	0.0212 (18)	0.0250 (18)	0.0012 (15)	0.0043 (15)	−0.0018 (16)
C17	0.033 (2)	0.0193 (18)	0.0300 (19)	−0.0023 (16)	0.0080 (16)	−0.0010 (16)
C18	0.032 (2)	0.0331 (19)	0.038 (2)	−0.0099 (18)	0.0142 (17)	−0.0029 (19)
C19	0.047 (3)	0.047 (2)	0.039 (2)	0.013 (2)	0.016 (2)	0.015 (2)
C20	0.024 (2)	0.038 (2)	0.033 (2)	−0.0041 (18)	0.0044 (17)	−0.003 (2)
O1	0.0296 (15)	0.0226 (12)	0.0384 (14)	−0.0051 (11)	−0.0042 (11)	0.0023 (12)
O2	0.0314 (15)	0.0244 (13)	0.0347 (13)	0.0038 (11)	0.0008 (11)	0.0087 (12)
O3	0.055 (2)	0.0548 (17)	0.0489 (16)	0.0248 (15)	0.0285 (15)	0.0199 (15)
O4	0.063 (2)	0.0349 (15)	0.0430 (16)	0.0055 (14)	0.0273 (14)	0.0078 (14)
N1	0.0207 (16)	0.0187 (14)	0.0324 (16)	−0.0001 (12)	0.0034 (12)	0.0043 (13)
N2	0.0227 (17)	0.0265 (15)	0.0426 (17)	0.0053 (14)	0.0004 (14)	0.0050 (15)
N3	0.0290 (18)	0.0281 (16)	0.0269 (16)	−0.0065 (14)	0.0073 (13)	−0.0028 (14)
N4	0.0273 (18)	0.0346 (17)	0.0331 (17)	−0.0078 (14)	0.0012 (14)	−0.0014 (16)

Cd1—N1i	2.262 (3)	C10—O1	1.269 (4)
Cd1—N3	2.271 (3)	C11—N4	1.378 (4)
Cd1—O1	2.285 (2)	C11—C12	1.393 (5)
Cd1—O3ii	2.293 (2)	C11—C16	1.393 (4)
Cd1—O4ii	2.362 (2)	C12—C13	1.377 (5)
Cd1—O2	2.667 (2)	C12—H12	0.9300
Cd1—C20ii	2.667 (4)	C13—C14	1.382 (5)
Cd1—C10	2.813 (3)	C13—H13	0.9300
C1—C6	1.389 (5)	C14—C15	1.382 (5)
C1—C2	1.391 (4)	C14—H14	0.9300
C1—N1	1.406 (4)	C15—C16	1.382 (5)
C2—C3	1.377 (5)	C15—H15	0.9300
C2—H2	0.9300	C16—N3	1.401 (4)
C3—C4	1.389 (5)	C17—N3	1.316 (4)
C3—H3	0.9300	C17—N4	1.354 (4)
C4—C5	1.382 (5)	C17—C18	1.485 (4)
C4—H4	0.9300	C18—C19	1.495 (5)
C5—C6	1.371 (5)	C18—H18A	0.9700
C5—H5	0.9300	C18—H18B	0.9700
C6—N2	1.386 (4)	C19—C20	1.503 (5)
C7—N1	1.323 (4)	C19—H19A	0.9700
C7—N2	1.346 (4)	C19—H19B	0.9700
C7—C8	1.487 (4)	C20—O4	1.236 (4)
C8—C9	1.518 (4)	C20—O3	1.249 (4)
C8—H8A	0.9700	C20—Cd1ii	2.667 (4)
C8—H8B	0.9700	O3—Cd1ii	2.293 (2)
C9—C10	1.520 (4)	O4—Cd1ii	2.362 (2)
C9—H9A	0.9700	N1—Cd1iii	2.262 (3)
C9—H9B	0.9700	N2—H2A	0.8600
C10—O2	1.239 (4)	N4—H4A	0.8600
N1i—Cd1—N3	103.73 (10)	O2—C10—O1	123.4 (3)
N1i—Cd1—O1	106.08 (9)	O2—C10—C9	120.6 (3)
N3—Cd1—O1	93.38 (9)	O1—C10—C9	115.9 (3)
N1i—Cd1—O3ii	100.41 (9)	O2—C10—Cd1	70.45 (18)
N3—Cd1—O3ii	103.63 (10)	O1—C10—Cd1	52.94 (15)
O1—Cd1—O3ii	144.01 (9)	C9—C10—Cd1	168.8 (2)
N1i—Cd1—O4ii	146.52 (9)	N4—C11—C12	132.8 (3)
N3—Cd1—O4ii	104.51 (10)	N4—C11—C16	105.3 (3)
O1—Cd1—O4ii	89.85 (8)	C12—C11—C16	121.8 (3)
O3ii—Cd1—O4ii	55.44 (9)	C13—C12—C11	116.2 (4)
N1i—Cd1—O2	84.96 (8)	C13—C12—H12	121.9
N3—Cd1—O2	145.40 (8)	C11—C12—H12	121.9
O1—Cd1—O2	52.26 (7)	C12—C13—C14	122.5 (4)
O3ii—Cd1—O2	107.64 (9)	C12—C13—H13	118.8
O4ii—Cd1—O2	81.96 (8)	C14—C13—H13	118.8
N1i—Cd1—C20ii	124.62 (11)	C15—C14—C13	121.2 (4)
N3—Cd1—C20ii	106.84 (10)	C15—C14—H14	119.4
O1—Cd1—C20ii	116.79 (10)	C13—C14—H14	119.4
O3ii—Cd1—C20ii	27.87 (10)	C16—C15—C14	117.4 (4)
O4ii—Cd1—C20ii	27.60 (9)	C16—C15—H15	121.3
O2—Cd1—C20ii	94.44 (9)	C14—C15—H15	121.3
N1i—Cd1—C10	96.06 (9)	C15—C16—C11	120.9 (3)
N3—Cd1—C10	119.59 (10)	C15—C16—N3	130.4 (3)
O1—Cd1—C10	26.30 (8)	C11—C16—N3	108.6 (3)
O3ii—Cd1—C10	128.08 (10)	N3—C17—N4	111.4 (3)
O4ii—Cd1—C10	85.33 (9)	N3—C17—C18	125.4 (3)
O2—Cd1—C10	25.96 (8)	N4—C17—C18	123.3 (3)
C20ii—Cd1—C10	106.94 (11)	C17—C18—C19	114.6 (3)
C6—C1—C2	119.6 (3)	C17—C18—H18A	108.6
C6—C1—N1	109.1 (3)	C19—C18—H18A	108.6
C2—C1—N1	131.3 (3)	C17—C18—H18B	108.6
C3—C2—C1	118.2 (4)	C19—C18—H18B	108.6
C3—C2—H2	120.9	H18A—C18—H18B	107.6
C1—C2—H2	120.9	C18—C19—C20	114.4 (3)
C2—C3—C4	120.9 (4)	C18—C19—H19A	108.7
C2—C3—H3	119.5	C20—C19—H19A	108.7
C4—C3—H3	119.5	C18—C19—H19B	108.7
C5—C4—C3	121.7 (4)	C20—C19—H19B	108.7
C5—C4—H4	119.2	H19A—C19—H19B	107.6
C3—C4—H4	119.2	O4—C20—O3	121.3 (3)
C6—C5—C4	116.6 (4)	O4—C20—C19	119.9 (3)
C6—C5—H5	121.7	O3—C20—C19	118.8 (3)
C4—C5—H5	121.7	O4—C20—Cd1ii	62.30 (19)
C5—C6—N2	131.8 (4)	O3—C20—Cd1ii	59.13 (18)
C5—C6—C1	123.0 (4)	C19—C20—Cd1ii	176.2 (3)
N2—C6—C1	105.2 (3)	C10—O1—Cd1	100.76 (19)
N1—C7—N2	111.9 (3)	C10—O2—Cd1	83.59 (19)
N1—C7—C8	126.8 (3)	C20—O3—Cd1ii	93.0 (2)
N2—C7—C8	120.9 (3)	C20—O4—Cd1ii	90.1 (2)
C7—C8—C9	110.5 (3)	C7—N1—C1	105.5 (3)
C7—C8—H8A	109.5	C7—N1—Cd1iii	126.7 (2)
C9—C8—H8A	109.5	C1—N1—Cd1iii	127.2 (2)
C7—C8—H8B	109.5	C7—N2—C6	108.3 (3)
C9—C8—H8B	109.5	C7—N2—H2A	125.9
H8A—C8—H8B	108.1	C6—N2—H2A	125.9
C8—C9—C10	116.5 (3)	C17—N3—C16	106.3 (3)
C8—C9—H9A	108.2	C17—N3—Cd1	131.2 (2)
C10—C9—H9A	108.2	C16—N3—Cd1	121.4 (2)
C8—C9—H9B	108.2	C17—N4—C11	108.4 (3)
C10—C9—H9B	108.2	C17—N4—H4A	125.8
H9A—C9—H9B	107.3	C11—N4—H4A	125.8

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2A···O2iv	0.86	2.10	2.823 (4)	141
N4—H4A···O1v	0.86	2.03	2.862 (4)	161