Diaqua­bis­(4-carb­oxy-2-ethyl-1H-imidazole-5-carboxyl­ato-κ² N ³,O ⁴)cadmium dihydrate

Abstract

The asymmetric unit of the title compound, [Cd(C₇H₇N₂O₄)₂(H₂O)₂]·2H₂O, consists of one Cd^II ion, one 4-carb­oxy-2-ethyl-1H-imidazole-5-carboxyl­ate anion, one coordinated water mol­ecule and one lattice water mol­ecule. The Cd^II ion lies on a twofold axis, and is hexa­coordinated by four O atoms from water mol­ecules and carboxyl­ate groups and two N atoms from two imidazole rings, in a distorted octa­hedral arrangement. An extensive framework of N—H⋯O and O—H⋯O hydrogen bonds with the participation of coordinated and free water mol­ecules is found in the crystal structure, which contributes to the formation of a three-dimensional structure.

Related literature

For coordination polymers built up from related imidazole–carboxyl­ate ligands, see: Li et al. (2011 ▶); Wang et al. (2008 ▶); Zhang et al. (2010 ▶); Tian et al. (2010 ▶). For a related Cd^II complex based on the ligand 5-carb­oxy-2-methyl-1H-imidazole-4-carboxyl­ate, see: Nie et al. (2007 ▶).

Experimental

Crystal data

• [Cd(C₇H₇N₂O₄)₂(H₂O)₂]·2H₂O

• M _r = 550.76

• Monoclinic,

• a = 9.844 (2) Å

• b = 17.084 (3) Å

• c = 12.855 (3) Å

• β = 102.21 (3)°

• V = 2113.0 (8) ų

• Z = 4

• Mo Kα radiation

• μ = 1.10 mm⁻¹

• T = 293 K

• 0.30 × 0.25 × 0.18 mm

Data collection

• Bruker SMART 1000 CCD area-detector diffractometer

• Absorption correction: multi-scan (SADABS; Bruker, 2004 ▶) T _min = 0.733, T _max = 0.826

• 8379 measured reflections

• 1898 independent reflections

• 1560 reflections with I > 2σ(I)

• R _int = 0.042

Refinement

• R[F ² > 2σ(F ²)] = 0.028

• wR(F ²) = 0.072

• S = 1.23

• 1898 reflections

• 142 parameters

• 6 restraints

• H-atom parameters constrained

• Δρ_max = 0.77 e Å⁻³

• Δρ_min = −0.78 e Å⁻³

Data collection: SMART (Bruker, 2004 ▶); cell refinement: SAINT (Bruker, 2004 ▶); data reduction: SAINT; 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: SHELXTL.

Supplementary Material

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O3—H3⋯O2	0.81	1.66	2.468 (4)	172
O2W—H4W⋯O4	0.84	2.16	2.904 (4)	147
O2W—H3W⋯O1i	0.84	2.08	2.874 (4)	157
O1W—H1W⋯O2i	0.84	1.97	2.788 (4)	165
O1W—H2W⋯O1ii	0.84	2.01	2.768 (3)	150
N1—H9⋯O2Wiii	0.91	1.86	2.771 (4)	177

Symmetry codes: (i) ; (ii) ; (iii) .

supplementary crystallographic information

Comment

Self-assembly of supramolecular architectures based on imidazole carboxylate ligands has draw much attention during recent decades. To the best of our knowledge, coordination polymers based on 2-ethyl-4,5-imidazolecarboxylate have been rarely reported so far (Wang et al., 2008; Zhang et al., 2010; Li et al., 2011; Tian et al., 2010). Herein we report the synthesis of the title compound by the reaction of cadmium nitrate with 2-ethyl-4,5-imidazoledicarboxylic acid (H₃EIDC) in an aqueous solution under hydrothermal conditions, and its crystal structure.

The title compound, [Cd(C₇H₇N₂O₄)₂(H₂O)₂].2H₂O, differs from the Cd(II) complex based on the similar ligand 5-carboxy-2- methyl-1H-imidazole-4-carboxylate, where the Cd(II) ion is six-coordinated in a centrosymmetric arrangement (Nie et al., 2007). As depicted in Fig. 1, the title complex has two symmetrical coordination water molecules, two interstitial water molecules and two 4-carboxy-2-ethyl-1H-imidazole-5-carboxylate ligands (H₂EIDC). The Cd(II), placed on a 2-fold axis, is surrounded by two terminal water molecules, two N atoms and two O atoms from two different H₂EIDC ligands, forming a distorted octahedral coordination environment.

One solvent water molecule completes the asymmetric unit, and forms hydrogen bonds with the imidazole N atom (N1), the carboxylic O atom (O4) and the O atom from the coordinated water molecule (O1W), whose distances and angles are shown in Table 1. Each H₂EIDC ligand is bonded to Cd(II) ion in a chelating mode. A three-dimensional supramolecular structure is consolidated by intermolecular hydrogen-bonding (N—H···O and O—H···O) and intramolecular hydrogen-bonding O—H···O.

Experimental

A mixture of Cd(NO₃)₂ (0.5 mmol, 0.120 g) and 2-ethyl-1H-imidazole-4,5-dicarboxylic acid (0.5 mmol, 0.95 g) in 15 ml of H₂O solution was placed in a 23 ml Teflon-lined reactor, which was heated to 423 K for 2 days, and then cooled to room temperature at a rate of 10 K h^-1. Crystals of the title compound were obtained by slow evaporation of the solvent at room temperature.

Refinement

The carboxyl H atom H3 was located in a difference map but refined as riding on the parent O atom with O3—H3 = 0.81 Å and U_iso(H3) = 1.5 U_eq(O3). Carbon and nitrogen bound H atoms were placed at calculated positions and were treated as riding on the parent C or N atoms with C—H = 0.96 (methyl), 0.97 (methylene) and N—H = 0.91 Å, U_iso(H) = 1.2 or 1.5 U_eq(C, N). H atoms of the water molecules were located in a difference Fourier map and refined as riding with the O—H bond lengths fixed to their as-found values and U_iso(H) = 1.5 U_eq(carrier O).

Figures

Fig. 1.

The structure of the title compound, showing the atomic numbering scheme with 30% probability displacement ellipsoids [Symmetry codes i: -x, y, 1/2-z].

Crystal data

[Cd(C7H7N2O4)2(H2O)2]·2H2O	F(000) = 1112
Mr = 550.76	Dx = 1.731 Mg m−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 1702 reflections
a = 9.844 (2) Å	θ = 2.5–25.9°
b = 17.084 (3) Å	µ = 1.10 mm−1
c = 12.855 (3) Å	T = 293 K
β = 102.21 (3)°	Block, colourless
V = 2113.0 (8) Å3	0.30 × 0.25 × 0.18 mm
Z = 4

Data collection

Bruker SMART 1000 CCD area-detector diffractometer	1898 independent reflections
Radiation source: fine-focus sealed tube	1560 reflections with I > 2σ(I)
graphite	Rint = 0.042
φ and ω scans	θmax = 25.2°, θmin = 3.2°
Absorption correction: multi-scan (SADABS; Bruker, 2004)	h = −11→10
Tmin = 0.733, Tmax = 0.826	k = −20→20
8379 measured reflections	l = −15→15

Refinement

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)] = 0.028	Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.072	H-atom parameters constrained
S = 1.23	w = 1/[σ2(Fo2) + (0.0164P)2 + 5.0177P] where P = (Fo2 + 2Fc2)/3
1898 reflections	(Δ/σ)max < 0.001
142 parameters	Δρmax = 0.77 e Å−3
6 restraints	Δρmin = −0.78 e Å−3
0 constraints

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

	x	y	z	Uiso*/Ueq
Cd1	0.0000	0.20278 (3)	0.2500	0.03340 (14)
O1	0.5880 (2)	0.14665 (16)	0.0777 (2)	0.0399 (7)
O2	0.5052 (3)	0.26839 (16)	0.0774 (2)	0.0439 (7)
O3	0.3063 (3)	0.33738 (16)	0.1245 (2)	0.0470 (7)
H3	0.3668	0.3140	0.1034	0.071*
O4	0.1229 (2)	0.30656 (16)	0.1896 (2)	0.0414 (6)
N1	0.3597 (3)	0.08847 (17)	0.1520 (2)	0.0288 (7)
H9	0.4044	0.0442	0.1391	0.035*
N2	0.1837 (3)	0.14937 (18)	0.1946 (2)	0.0287 (7)
C1	0.2678 (3)	0.2036 (2)	0.1605 (2)	0.0244 (7)
C2	0.3782 (3)	0.1654 (2)	0.1332 (3)	0.0266 (8)
C3	0.2420 (3)	0.0805 (2)	0.1895 (3)	0.0311 (8)
C4	0.1894 (4)	0.0046 (3)	0.2202 (4)	0.0506 (11)
H4A	0.2676	−0.0260	0.2578	0.061*
H4B	0.1289	0.0145	0.2693	0.061*
C5	0.1137 (8)	−0.0418 (4)	0.1323 (6)	0.127 (3)
H5A	0.0380	−0.0115	0.0927	0.190*
H5B	0.0780	−0.0880	0.1595	0.190*
H5C	0.1750	−0.0565	0.0867	0.190*
C6	0.5001 (3)	0.1949 (2)	0.0929 (3)	0.0316 (8)
C7	0.2289 (3)	0.2871 (2)	0.1586 (3)	0.0320 (8)
O1W	−0.1380 (3)	0.1871 (2)	0.0846 (2)	0.0691 (11)
H2W	−0.2184	0.1706	0.0594	0.104*
H1W	−0.1026	0.2090	0.0386	0.104*
O2W	−0.0139 (3)	0.45120 (19)	0.1075 (3)	0.0695 (10)
H4W	0.0458	0.4235	0.1478	0.104*
H3W	−0.0307	0.4344	0.0448	0.104*

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Cd1	0.02313 (19)	0.0344 (3)	0.0474 (2)	0.000	0.01810 (16)	0.000
O1	0.0283 (13)	0.0410 (18)	0.0557 (16)	−0.0001 (12)	0.0208 (12)	−0.0051 (13)
O2	0.0461 (15)	0.0289 (18)	0.0667 (18)	−0.0072 (12)	0.0345 (14)	0.0007 (13)
O3	0.0492 (16)	0.0276 (16)	0.075 (2)	−0.0021 (13)	0.0379 (15)	0.0003 (14)
O4	0.0338 (13)	0.0300 (16)	0.0671 (17)	0.0057 (12)	0.0261 (13)	0.0010 (14)
N1	0.0266 (14)	0.0189 (17)	0.0439 (17)	0.0022 (12)	0.0143 (13)	−0.0014 (13)
N2	0.0244 (14)	0.0242 (18)	0.0404 (16)	−0.0010 (12)	0.0134 (13)	0.0001 (13)
C1	0.0238 (15)	0.0191 (18)	0.0320 (17)	−0.0039 (15)	0.0098 (14)	−0.0003 (15)
C2	0.0210 (15)	0.030 (2)	0.0307 (18)	−0.0007 (14)	0.0088 (14)	−0.0007 (15)
C3	0.0261 (17)	0.028 (2)	0.041 (2)	0.0000 (15)	0.0115 (16)	0.0016 (16)
C4	0.041 (2)	0.032 (3)	0.084 (3)	0.0013 (18)	0.026 (2)	0.013 (2)
C5	0.173 (7)	0.092 (6)	0.123 (6)	−0.090 (6)	0.049 (5)	−0.033 (5)
C6	0.0250 (17)	0.039 (3)	0.0337 (19)	−0.0047 (17)	0.0123 (15)	−0.0069 (18)
C7	0.0298 (17)	0.030 (2)	0.0383 (19)	−0.0029 (16)	0.0123 (16)	0.0000 (17)
O1W	0.0318 (14)	0.134 (4)	0.0430 (16)	−0.0229 (18)	0.0119 (13)	0.0104 (19)
O2W	0.085 (2)	0.049 (2)	0.068 (2)	0.0309 (18)	0.0014 (18)	−0.0144 (17)

Geometric parameters (Å, °)

Cd1—N2i	2.270 (3)	N2—C1	1.375 (4)
Cd1—N2	2.270 (3)	C1—C2	1.375 (5)
Cd1—O1W	2.284 (3)	C1—C7	1.476 (5)
Cd1—O1Wi	2.284 (3)	C2—C6	1.491 (5)
Cd1—O4	2.368 (3)	C3—C4	1.481 (5)
Cd1—O4i	2.368 (3)	C4—C5	1.450 (7)
O1—C6	1.239 (4)	C4—H4A	0.9700
O2—C6	1.275 (5)	C4—H4B	0.9700
O3—C7	1.284 (4)	C5—H5A	0.9600
O3—H3	0.8096	C5—H5B	0.9600
O4—C7	1.239 (4)	C5—H5C	0.9600
N1—C3	1.353 (4)	O1W—H2W	0.8388
N1—C2	1.356 (5)	O1W—H1W	0.8355
N1—H9	0.9080	O2W—H4W	0.8424
N2—C3	1.317 (5)	O2W—H3W	0.8381
N2i—Cd1—N2	132.60 (15)	N1—C2—C6	122.5 (3)
N2i—Cd1—O1W	83.59 (10)	C1—C2—C6	131.7 (3)
N2—Cd1—O1W	91.00 (11)	N2—C3—N1	110.1 (3)
N2i—Cd1—O1Wi	91.00 (11)	N2—C3—C4	126.1 (3)
N2—Cd1—O1Wi	83.59 (10)	N1—C3—C4	123.9 (3)
O1W—Cd1—O1Wi	166.5 (2)	C5—C4—C3	114.9 (4)
N2i—Cd1—O4	154.13 (10)	C5—C4—H4A	108.5
N2—Cd1—O4	72.67 (10)	C3—C4—H4A	108.5
O1W—Cd1—O4	91.54 (10)	C5—C4—H4B	108.5
O1Wi—Cd1—O4	98.55 (11)	C3—C4—H4B	108.5
N2i—Cd1—O4i	72.67 (10)	H4A—C4—H4B	107.5
N2—Cd1—O4i	154.13 (10)	C4—C5—H5A	109.5
O1W—Cd1—O4i	98.55 (11)	C4—C5—H5B	109.5
O1Wi—Cd1—O4i	91.54 (10)	H5A—C5—H5B	109.5
O4—Cd1—O4i	83.03 (12)	C4—C5—H5C	109.5
C7—O3—H3	108.4	H5A—C5—H5C	109.5
C7—O4—Cd1	115.4 (2)	H5B—C5—H5C	109.5
C3—N1—C2	108.6 (3)	O1—C6—O2	125.3 (3)
C3—N1—H9	117.7	O1—C6—C2	118.1 (4)
C2—N1—H9	133.5	O2—C6—C2	116.6 (3)
C3—N2—C1	106.7 (3)	O4—C7—O3	122.1 (4)
C3—N2—Cd1	139.4 (2)	O4—C7—C1	119.1 (3)
C1—N2—Cd1	113.7 (2)	O3—C7—C1	118.8 (3)
N2—C1—C2	108.9 (3)	Cd1—O1W—H2W	136.5
N2—C1—C7	119.0 (3)	Cd1—O1W—H1W	110.6
C2—C1—C7	132.1 (3)	H2W—O1W—H1W	112.2
N1—C2—C1	105.8 (3)	H4W—O2W—H3W	111.6

Symmetry codes: (i) −x, y, −z+1/2.

Hydrogen-bond geometry (Å, °)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3···O2	0.81	1.66	2.468 (4)	172.
O2W—H4W···O4	0.84	2.16	2.904 (4)	147.
O2W—H3W···O1ii	0.84	2.08	2.874 (4)	157.
O1W—H1W···O2ii	0.84	1.97	2.788 (4)	165.
O1W—H2W···O1iii	0.84	2.01	2.768 (3)	150.
N1—H9···O2Wiv	0.91	1.86	2.771 (4)	177.

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