Diaqua­bis­(1H-imidazole-κN³)bis­(4-nitro­benzoato-κO¹)cadmium

In the centrosymmetric title compound, [Cd(C₇H₄NO₄)₂(C₃H₄N₂)₂(H₂O)₂], the Cd^II atom, located on an inversion center, is coordinated by two N atoms and four O atoms in an octa­hedral geometry. The inter­nal cohesion of the mol­ecule is enhanced by an intra­molecular O—H...O hydrogen bond. Inter­molecular O—H...O and C—H...O hydrogen bonds and π–π contacts [centroid–centroid distance = 3.6549 (2) Å] define two-dimensional networks parallel to (001), which are further connected by weaker C—H...O inter­actions into a weakly connected three-dimensional supra­molecular framework.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.005 Å
• R factor = 0.026
• wR factor = 0.076
• Data-to-parameter ratio = 15.0

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT934_ALERT_3_B Number of (Iobs-Icalc)/SigmaW .gt. 10 Outliers .          3

Alert level C
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for         N3
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ....        2.1
PLAT411_ALERT_2_C Short Inter H...H Contact  H10A   ..  H10A    ..       2.06 Ang.
PLAT910_ALERT_3_C Missing # of FCF Reflections Below Th(Min) .....          3
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.600         28
PLAT975_ALERT_2_C Positive Residual Density at 1.10A from N2     .       0.57 eA-3

Alert level G
PLAT002_ALERT_2_G Number of Distance or Angle Restraints on AtSite          3
PLAT005_ALERT_5_G No _iucr_refine_instructions_details in CIF ....          ?
PLAT154_ALERT_1_G The su's on the Cell Angles are Equal ..........    0.03000 Deg.
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported   _diffrn_ambient_temperature        293 K
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......          3
PLAT912_ALERT_4_G Missing # of FCF Reflections Above STh/L=  0.600         33

   0 ALERT level A = Most likely a serious problem - resolve or explain
   1 ALERT level B = A potentially serious problem, consider carefully
   6 ALERT level C = Check. Ensure it is not caused by an omission or oversight
   7 ALERT level G = General information/check it is not something unexpected

   3 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   5 ALERT type 2 Indicator that the structure model may be wrong or deficient
   4 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   1 ALERT type 5 Informative message, check

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S1. Comment

Aromatic carboxyl acid complexes have been paid great attention these years for their potential applications in gas storage, separation, catalysis, magnetism, luminescence, and drug delivery (Kuang et al., 2007). As a N-containing aromatic carboxyl acid, nitrobenzoic acid has been widely used in dye intermediate, organic synthesis, sensitization material, functional pigment (Hsu et al., 2011). So far, to our knowledge, cadmium complexes constructed from 4-nitrobenzoato and imidazole have not been reported. In order to get new Cd^II complexes with novel functions and discover their structure-property relationship, a new complex [Cd(C₇H₄NO₄)(C₃H₄N₂)(H₂O)] was synthesized.

The asymmetric unit of [Cd(C₇H₄NO₄)(C₃H₄N₂)(H₂O)] consists of a Cd²⁺ ion lying on an inversion centre, a 4-NBA^- ion (4-HNBA = 4-nitrobenzoic acid), one imidazole ligand and one lattice water as illustrated in Fig. 1. The Cd²⁺ cation is octahedrally coordinated by two N atoms of imidazole ligands, two O atoms from two 4-NBA^- ions and two O atoms from two lattice water molecules; it takes a (4 + 2) octahedral geometry, with the oxygen atoms located in the equatorial plane (Cd—O1 = 2.364 (2) Å, Cd—O5 = 2.367 (2) Å, and the two nitrogen atoms occupying the axial position (Cd—N1 = 2.255 (2) Å). Table 1 presents the \p···\p contact information involving the C₃N₂ ring (centroid, Cg1) and Table 2, the more meaningful H-bonds in the structure; the most important ones are those involving water H's. The one described in the first entry in Table 2 is intramolecular; the seocnd one, instead defines chains along a (Figure 2, vertical arrays). The weak one involving C2—H2A (Table 2, third entry) and the π–π contact (Table 1) link chains into a two-dimensional supramolecular network parallel to (001) as illustrated in Figure 2. Finaly, the remaining weak H-bonds link these 2D structures into a 3D supramolecular architecture (Figure 3).

Related literature

For general background to aromatic carboxyl acid complexes, see: Kuang et al. (2007); Hsu et al. (2011). For related structures, see: Zheng et al. (2008).

S2. Experimental

Dropwise addition of 1.0 ml (1 M) of K₂CO₃ to a stirred aqueous solution of Cd(CH₃COO)₂.2H₂O (0.266 g, 1.0 mmol) in 10.0 ml of H₂O yielded a fine white precipitate, which was separated by centrifugation and washed with water until no CH₃COO^- anions were detectable in the supernatant. The fresh precipitate was then added to a stirred aqueous solution of 4-nitrobenzoic acid (0.167 g, 1.0 mmol) in C₂H₅OH/H₂O (1:1, 20.0 ml), producing a white suspension, to which imidazole (0.137 g, 2.0 mmol) was added. The mixture was further stirred vigorously for about 0.5 h. After filtration, the white filtrate (pH = 6.59) was maintained at room temperature and colorless crystals were grown.

S3. Refinement

H atoms bonded to C atoms were palced in geometrically calculated positions and were refined using a riding model. H atoms attached to O atoms were found in a difference Fourier synthesis and were refined with restrained O—H = 0.84 (1)Å. In all cases, U_iso(H) values were set at 1.2 Ueq(host).

Computing details

Data collection: RAPID-AUTO (Rigaku, 1998); cell refinement: RAPID-AUTO (Rigaku, 1998); data reduction: CrystalStructure (Rigaku/MSC, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. Figure 1. ORTEP view of the title compound, The dispalcement ellipsoidsare drawn at 45% probability dispalcement ellipsoids. Symmetry code: (v)1-x, 2-y, -z.
	Fig. 2. The two-dimensional supramolecular networks parallel to (001). In order to observe how the complex moleculars form two-dimensional layers clearly, nitrobenzene on 4-nitrobenzoato molecules which are not engaged in link the components into a two-dimensional layers were omitted.
	Fig. 3. The three-dimensional framework of title complex.

Diaquabis(1H-imidazole-κN³)bis(4-nitrobenzoato- κO¹)cadmium

Crystal data

[Cd(C7H4NO4)2(C3H4N2)2(H2O)2]	Z = 1
Mr = 614.80	F(000) = 308
Triclinic, P1	Dx = 1.747 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 5.8017 (12) Å	Cell parameters from 5719 reflections
b = 8.0253 (16) Å	θ = 3.2–27.5°
c = 12.879 (3) Å	µ = 1.00 mm^−1
α = 77.99 (3)°	T = 293 K
β = 88.42 (3)°	Plate, colorless
γ = 85.16 (3)°	0.33 × 0.14 × 0.09 mm
V = 584.4 (2) Å^3

Data collection

Rigaku R-AXIS RAPID diffractometer	2627 independent reflections
Radiation source: fine-focus sealed tube	2511 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.031
ω scans	θmax = 27.5°, θmin = 3.2°
Absorption correction: multi-scan (ABSCOR; Higashi, 1995)	h = −6→7
Tmin = 0.989, Tmax = 0.989	k = −10→10
5719 measured reflections	l = −16→16

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)] = 0.026	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.076	H atoms treated by a mixture of independent and constrained refinement
S = 1.24	w = 1/[σ^2(Fo^2) + (0.0208P)^2 + 0.3927P] where P = (Fo^2 + 2Fc^2)/3
2627 reflections	(Δ/σ)max < 0.001
175 parameters	Δρmax = 0.54 e Å^−3
3 restraints	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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Cd	0.5000	1.0000	0.0000	0.03040 (10)
N1	0.4161 (4)	0.7310 (3)	0.07261 (18)	0.0351 (5)
C1	0.5412 (6)	0.6131 (4)	0.1376 (3)	0.0497 (8)
H1A	0.6844	0.6290	0.1632	0.060*
C2	0.2360 (6)	0.4946 (4)	0.1116 (3)	0.0518 (8)
H2A	0.1261	0.4160	0.1136	0.062*
N2	0.4388 (5)	0.4676 (3)	0.1627 (2)	0.0500 (7)
C3	0.2227 (6)	0.6573 (4)	0.0569 (3)	0.0510 (8)
H3A	0.0992	0.7108	0.0147	0.061*
O1	0.7532 (3)	0.9739 (3)	0.14420 (15)	0.0384 (5)
O2	0.4950 (4)	1.0755 (3)	0.25118 (18)	0.0553 (6)
C4	0.6746 (5)	0.9881 (4)	0.2347 (2)	0.0336 (6)
C5	0.8110 (5)	0.8918 (4)	0.3301 (2)	0.0343 (6)
C6	1.0191 (5)	0.7974 (4)	0.3212 (2)	0.0398 (7)
H6A	1.0781	0.7893	0.2544	0.048*
C7	1.1397 (5)	0.7150 (4)	0.4110 (2)	0.0451 (7)
H7A	1.2798	0.6518	0.4054	0.054*
C8	1.0480 (5)	0.7285 (4)	0.5088 (2)	0.0421 (7)
C9	0.8406 (6)	0.8178 (5)	0.5205 (3)	0.0581 (10)
H9A	0.7807	0.8235	0.5875	0.070*
C10	0.7234 (6)	0.8990 (5)	0.4301 (3)	0.0568 (9)
H10A	0.5821	0.9601	0.4365	0.068*
N3	1.1799 (5)	0.6471 (4)	0.6046 (2)	0.0548 (7)
O3	1.3619 (6)	0.5690 (5)	0.5945 (3)	0.1018 (13)
O4	1.1007 (6)	0.6639 (5)	0.6907 (2)	0.0890 (10)
O5	0.1847 (3)	1.1006 (3)	0.09734 (16)	0.0385 (5)
H5A	0.252 (5)	1.088 (4)	0.1559 (14)	0.046*
H5B	0.069 (4)	1.043 (4)	0.112 (2)	0.046*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cd	0.03111 (16)	0.02902 (15)	0.02818 (15)	−0.00363 (11)	−0.00305 (10)	0.00151 (10)
N1	0.0371 (12)	0.0309 (11)	0.0343 (12)	−0.0032 (10)	−0.0033 (10)	0.0009 (9)
C1	0.0417 (17)	0.0403 (16)	0.060 (2)	−0.0052 (14)	−0.0155 (15)	0.0081 (14)
C2	0.057 (2)	0.0329 (15)	0.063 (2)	−0.0156 (15)	−0.0132 (17)	0.0023 (14)
N2	0.0605 (17)	0.0342 (13)	0.0488 (16)	−0.0008 (13)	−0.0064 (13)	0.0059 (11)
C3	0.0523 (19)	0.0360 (15)	0.061 (2)	−0.0116 (15)	−0.0226 (16)	0.0051 (14)
O1	0.0343 (10)	0.0508 (12)	0.0283 (10)	−0.0078 (9)	−0.0042 (8)	−0.0022 (8)
O2	0.0432 (12)	0.0741 (16)	0.0449 (13)	0.0183 (12)	−0.0127 (10)	−0.0115 (11)
C4	0.0287 (13)	0.0375 (14)	0.0339 (14)	−0.0045 (12)	−0.0064 (11)	−0.0045 (11)
C5	0.0330 (14)	0.0394 (14)	0.0291 (14)	−0.0040 (12)	−0.0038 (11)	−0.0031 (11)
C6	0.0398 (15)	0.0456 (16)	0.0306 (14)	0.0047 (13)	−0.0003 (12)	−0.0034 (12)
C7	0.0398 (16)	0.0488 (17)	0.0413 (17)	0.0117 (14)	−0.0032 (13)	−0.0023 (13)
C8	0.0430 (16)	0.0457 (16)	0.0331 (15)	−0.0038 (14)	−0.0107 (12)	0.0036 (12)
C9	0.052 (2)	0.090 (3)	0.0283 (16)	0.0104 (19)	0.0000 (14)	−0.0078 (16)
C10	0.0446 (18)	0.087 (3)	0.0346 (17)	0.0216 (18)	−0.0033 (14)	−0.0120 (16)
N3	0.0543 (18)	0.0620 (18)	0.0407 (16)	−0.0015 (15)	−0.0138 (13)	0.0067 (13)
O3	0.079 (2)	0.147 (3)	0.0583 (19)	0.052 (2)	−0.0207 (16)	0.0044 (19)
O4	0.090 (2)	0.131 (3)	0.0339 (15)	0.017 (2)	−0.0135 (14)	0.0035 (16)
O5	0.0283 (10)	0.0424 (11)	0.0415 (12)	−0.0039 (9)	−0.0024 (8)	−0.0005 (9)

Geometric parameters (Å, º)

Cd—N1^i	2.254 (2)	C4—C5	1.513 (4)
Cd—N1	2.254 (2)	C5—C10	1.383 (4)
Cd—O1^i	2.364 (2)	C5—C6	1.385 (4)
Cd—O1	2.364 (2)	C6—C7	1.383 (4)
Cd—O5^i	2.370 (2)	C6—H6A	0.9300
Cd—O5	2.370 (2)	C7—C8	1.375 (4)
N1—C1	1.308 (4)	C7—H7A	0.9300
N1—C3	1.351 (4)	C8—C9	1.369 (5)
C1—N2	1.330 (4)	C8—N3	1.471 (4)
C1—H1A	0.9300	C9—C10	1.377 (5)
C2—N2	1.343 (4)	C9—H9A	0.9300
C2—C3	1.345 (4)	C10—H10A	0.9300
C2—H2A	0.9300	N3—O3	1.199 (4)
C3—H3A	0.9300	N3—O4	1.218 (4)
O1—C4	1.263 (3)	O5—H5A	0.842 (10)
O2—C4	1.245 (4)	O5—H5B	0.842 (10)
Cg1···Cg1^ii	3.6549 (2)
N1^i—Cd—N1	180.0	C4—O1—Cd	120.39 (17)
N1^i—Cd—O1^i	86.19 (8)	O2—C4—O1	125.1 (3)
N1—Cd—O1^i	93.81 (8)	O2—C4—C5	117.7 (3)
N1^i—Cd—O1	93.81 (8)	O1—C4—C5	117.2 (2)
N1—Cd—O1	86.19 (8)	C10—C5—C6	118.9 (3)
O1^i—Cd—O1	180.0	C10—C5—C4	118.3 (3)
N1^i—Cd—O5^i	88.39 (8)	C6—C5—C4	122.8 (3)
N1—Cd—O5^i	91.61 (8)	C7—C6—C5	120.5 (3)
O1^i—Cd—O5^i	91.85 (7)	C7—C6—H6A	119.8
O1—Cd—O5^i	88.15 (7)	C5—C6—H6A	119.8
N1^i—Cd—O5	91.61 (8)	C8—C7—C6	118.5 (3)
N1—Cd—O5	88.39 (8)	C8—C7—H7A	120.7
O1^i—Cd—O5	88.15 (7)	C6—C7—H7A	120.7
O1—Cd—O5	91.85 (7)	C9—C8—C7	122.5 (3)
O5^i—Cd—O5	180.0	C9—C8—N3	118.7 (3)
C1—N1—C3	105.2 (2)	C7—C8—N3	118.8 (3)
C1—N1—Cd	128.3 (2)	C8—C9—C10	118.0 (3)
C3—N1—Cd	126.52 (19)	C8—C9—H9A	121.0
N1—C1—N2	111.8 (3)	C10—C9—H9A	121.0
N1—C1—H1A	124.1	C9—C10—C5	121.5 (3)
N2—C1—H1A	124.1	C9—C10—H10A	119.2
N2—C2—C3	106.7 (3)	C5—C10—H10A	119.2
N2—C2—H2A	126.6	O3—N3—O4	122.8 (3)
C3—C2—H2A	126.6	O3—N3—C8	118.8 (3)
C1—N2—C2	106.7 (3)	O4—N3—C8	118.4 (3)
C2—C3—N1	109.6 (3)	Cd—O5—H5A	98 (2)
C2—C3—H3A	125.2	Cd—O5—H5B	120 (2)
N1—C3—H3A	125.2	H5A—O5—H5B	104 (2)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O5—H5A···O2	0.84 (1)	1.88 (1)	2.679 (1)	159
O5—H5B···O1^iii	0.84 (1)	1.97 (1)	2.785 (1)	164
C2—H2A···O5^iv	0.93	2.58	3.244 (1)	129
C3—H3A···O5^v	0.93	2.43	3.344 (1)	169
C10—H10A···O2	0.93	2.42	2.751 (4)	101

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