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The reaction of cadmium chloride with pyridine-2,6-di­carboxylic acid (PDA) and 98% H2SO4 in ethanol led to the formation of the title compound, bis­[[mu]-6-(ethoxy­carbonyl)­pyridine-2-carboxyl­ato]-1:2[kappa]4O6,N,O2:O2;1:2[kappa]4O2:O2,N,O6-bis­[di­aqua­chloro­cadmium(II)] dihydrate, [Cd2(C9H8NO4)2Cl2(H2O)4]·2H2O. PDA is esterified to monoethyl ­pyridine-2,6-di­carboxyl­ate (MEPD) by the catalysis of H2SO4 during the reaction. The dinuclear CdII complex lies about an inversion centre and the unique Cd atom has a pentagonal-bipyramidal geometry. The two Cd atoms are bridged by two carboxyl­ate O atoms, forming a planar Cd2O2 unit. Stair-like chains are formed via O-H...Cl hydrogen bonds and these are further arranged into two-dimensional layers via hydrogen bonds involving solvate water mol­ecules.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270104017378/ob1187sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270104017378/ob1187Isup2.hkl
Contains datablock I

CCDC reference: 251298

Comment top

Pyridine-2,6-dicarboxylate and diethylpyridine-2,6-dicarboxylate (DEPD) are pentadentate ligands which generally act as tridentate meridional ligands, with their one amino and two carboxyl (or ester) groups acting as the chelating terminals. Many of their metal complexes have been reported (Kapoor et al., 2002; MacDonald et al., 2000; Yang et al., 2002; Odoko et al., 2002). However, a metal complex of monoethylpyridine-2,6-dicarboxylate (MEPD) has not been reported to date. On the other hand, cadmium has increasingly attracted research attention over the years, due to its toxic manifestations in the environment and various animal or human organisms (Hammond & Foulkes, 1986). We report here the synthesis and crystal structure of the title compound, (I), which is the first MEPD complex. \sch

Compound (I) was prepared by reaction of cadmium(II) chloride with pyridine-2,6-dicarboxylic acid and 98% H2SO4 in ethanol. The crystallographic analysis reveals that (I) is a dinuclear complex, [Cd2(MEPD)2(H2O)4Cl2]·2H2O, in which MEPD is derived from the mono-esterification of PDA via the catalysis of sulfuric acid. It is puzzling that we have not obtained PDA or DEPD complexes, but only the mono-esterified MEPD product. At least two kinds of reactions exist in the synthetic system, esterification and self-assembly of the metal complex. MEPD is formed by the mono-esterification of PDA or the mono-hydrolysis of DEPD, or by both reactions.

In the title complex, two Cd atoms are bridged by two carboxylate µ-O atoms from MEPD ligands, forming a centrosymmetric Cd2O2 parallelogram unit. Each CdII atom is coordinated by one N and three O atoms of MEPD ligands, as well as one Cl and two water O atoms, resulting in a distorted pentagonal-bipyramidal coordination with Cl1—Cd1—O2W in the axial direction (Fig. 1 and Table 1). The bond lengths of Cd to the µ-O atoms [Cd1—O4 2.389 (3) and Cd1—O4i 2.370 (3) Å; symmetry code: (i) 1 − x, 1 − y, −z] are apparently shorter than that of the carbonyl O atom on the ester side [Cd1—O1 2.573 (3) Å], and the bond distance to the central pyridine N atom (Cd1—N1) is 2.340 (3) Å, slightly shorter than these Cd1—O bonds.

The investigation of hydrogen bonding is important for many practical applications, such as the design of antibiotics and the development of new materials with programmed properties (Bong et al., 2001). A great variety of supramolecular assemblies owe their well defined structure to the existence of adjacent hydrogen-bond units to complementary constituent parts (MacDonald et al., 2000). In (I), there is an intramolecular O2W—H2WB···Cl1i hydrogen bond, and intermolecular O—H···Cl and O—H···O hydrogen bonds (Table 2). The metal complexes are linked into one-dimensional stairs via an O2W—H2WA···Cl1ii hydrogen bond [Fig. 2; symmetry code: (ii) x − 1, y, z]. In other words, Cd2O2 and Cl2(H2O)2 rings are arranged alternately along the extended direction of the Cd—Cl bond (Fig. 2). The Cd···Cd distance in the Cd2O2 parallelogram unit is 3.849 (5) Å, and the shortest Cd···Cd distance in the stairs is 6.841 (3) Å. The most interesting feature is that the solvate water molecule (O1W) acts as a junction to connect the one-dimensional stairs into a two-dimensional layer via O—H···O and O—H···Cl hydrogen bonds.

Experimental top

A mixture of 8-hydroxyquinoline (0.5 mmol), pyridine-2,6-dicarboxylic acid (0.5 mmol), CdCl2·2H2O (0.5 mmol), dry ethanol (25 ml) and H2SO4 (98%, 1 ml) was stirred at ca 333 K for 2 h and then filtered. The filtrate was kept at room temperature for several days to give pale-red crystals of the title compound (yield 8%).

Refinement top

H atoms bonded to C atoms were located geometrically, with C—H distances of 0.93 Å, and treated as riding atoms, with Uiso(H) = 1.2Ueq(C) or 1.5Ueq(methyl C). H atoms bonded to O atoms were located from difference density maps and refined with O—H bond distances restrained to 0.81–0.84 Å and with Uiso(H) = 1.5Ueq(O). The highest residual peak is 1.02 Å from atom C8, and the deepest hole is 0.99 Å from atom Cd1.

Computing details top

Data collection: SMART (Siemens, 1996); cell refinement: SMART and SAINT (Siemens, 1994); data reduction: XPREP in SHELXTL (Siemens, 1994); program(s) used to solve structure: SHELXTL; program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures top
[Figure 1] Fig. 1. A view of (I) with the atom-labelling scheme, showing some of the intramolecular hydrogen bonds (dashed lines). Displacement ellipsoids are drawn at the 20% probability level. [Symmetry code: (i) 1 − x, 1 − y, −z.] Please check added symmetry code.
[Figure 2] Fig. 2. An illustration of a two-dimensional supramolecular layer (containing one-dimensional stairs) in the crystal of (I). The O—H···O and O—H···Cl interactions are indicated by dashed lines. [Symmetry codes: (i) 1 − x, 1 − y, −z; (ii) x − 1, y, z; (iii) Please provide missing symmetry code.]
bis[µ-6-(ethoxycarbonyl)pyridine-2-carboxylato]- 1:2κ4O6,N,O2:O2;1:2κ4O2:O2,N,O6-bis[diaquachlorocadmium(II)] dihydrate top
Crystal data top
[Cd2(C9H8NO4)2Cl2(H2O)4]·2H2OZ = 1
Mr = 792.12F(000) = 392
Triclinic, P1Dx = 1.948 Mg m3
a = 6.8414 (6) ÅMo Kα radiation, λ = 0.71073 Å
b = 10.7408 (9) ÅCell parameters from 2630 reflections
c = 10.7597 (9) Åθ = 2.1–25.1°
α = 64.042 (2)°µ = 1.84 mm1
β = 77.298 (2)°T = 293 K
γ = 72.810 (2)°Prism, pale red
V = 675.35 (10) Å30.60 × 0.28 × 0.26 mm
Data collection top
Siemens SMART CCD area-detector
diffractometer
2371 independent reflections
Radiation source: fine-focus sealed tube2167 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.021
ϕ and ω scansθmax = 25.1°, θmin = 2.1°
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
h = 68
Tmin = 0.416, Tmax = 0.620k = 1212
3540 measured reflectionsl = 1112
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.033Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.089H atoms treated by a mixture of independent and constrained refinement
S = 1.04 w = 1/[σ2(Fo2) + (0.0526P)2 + 0.9504P]
where P = (Fo2 + 2Fc2)/3
2371 reflections(Δ/σ)max = 0.005
190 parametersΔρmax = 1.04 e Å3
8 restraintsΔρmin = 0.51 e Å3
Crystal data top
[Cd2(C9H8NO4)2Cl2(H2O)4]·2H2Oγ = 72.810 (2)°
Mr = 792.12V = 675.35 (10) Å3
Triclinic, P1Z = 1
a = 6.8414 (6) ÅMo Kα radiation
b = 10.7408 (9) ŵ = 1.84 mm1
c = 10.7597 (9) ÅT = 293 K
α = 64.042 (2)°0.60 × 0.28 × 0.26 mm
β = 77.298 (2)°
Data collection top
Siemens SMART CCD area-detector
diffractometer
2371 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
2167 reflections with I > 2σ(I)
Tmin = 0.416, Tmax = 0.620Rint = 0.021
3540 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0338 restraints
wR(F2) = 0.089H atoms treated by a mixture of independent and constrained refinement
S = 1.04Δρmax = 1.04 e Å3
2371 reflectionsΔρmin = 0.51 e Å3
190 parameters
Special details top

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 (Å2) top
xyzUiso*/Ueq
Cd10.45433 (5)0.43106 (3)0.19947 (3)0.03411 (14)
Cl10.83742 (19)0.31815 (14)0.21558 (14)0.0552 (3)
O10.3240 (6)0.3240 (4)0.4591 (3)0.0499 (8)
O1W0.1843 (8)0.5909 (5)0.5204 (4)0.0740 (12)
H1WA0.163 (14)0.512 (4)0.558 (7)0.111*
H1WB0.194 (13)0.601 (8)0.589 (5)0.111*
O20.1937 (5)0.1439 (4)0.6230 (3)0.0465 (8)
O30.4860 (6)0.2007 (4)0.0596 (3)0.0538 (9)
O40.4818 (5)0.3709 (3)0.0062 (3)0.0366 (7)
O3W0.4605 (7)0.5828 (4)0.2935 (4)0.0607 (10)
H3WB0.346 (6)0.627 (7)0.260 (6)0.091*
H3WA0.405 (9)0.586 (8)0.370 (4)0.091*
O2W0.1129 (5)0.5447 (4)0.1382 (4)0.0493 (8)
H2WB0.108 (10)0.581 (7)0.055 (2)0.074*
H2WA0.030 (8)0.498 (6)0.153 (7)0.074*
N10.3624 (5)0.2148 (4)0.2701 (3)0.0305 (7)
C10.2950 (6)0.1411 (4)0.4018 (4)0.0318 (9)
C20.2521 (7)0.0094 (5)0.4442 (5)0.0381 (10)
H20.20750.04040.53660.046*
C30.2769 (7)0.0462 (5)0.3465 (5)0.0414 (10)
H30.24870.13420.37200.050*
C40.3443 (7)0.0305 (5)0.2099 (5)0.0387 (10)
H40.36220.00550.14270.046*
C50.3848 (6)0.1615 (4)0.1749 (4)0.0320 (9)
C60.2720 (7)0.2138 (5)0.4964 (4)0.0374 (10)
C70.4579 (7)0.2511 (4)0.0274 (4)0.0322 (9)
C80.1609 (10)0.2139 (7)0.7226 (6)0.0605 (14)
H8A0.28950.23000.72980.073*
H8B0.06240.30460.69130.073*
C90.0828 (10)0.1165 (7)0.8565 (6)0.0710 (17)
H9A0.06000.15640.92420.106*
H9B0.18140.02720.88570.106*
H9C0.04450.10190.84770.106*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cd10.0430 (2)0.0331 (2)0.03061 (19)0.01426 (14)0.00153 (13)0.01420 (14)
Cl10.0385 (6)0.0551 (7)0.0615 (8)0.0117 (5)0.0114 (5)0.0106 (6)
O10.071 (2)0.050 (2)0.0363 (18)0.0289 (18)0.0050 (16)0.0198 (16)
O1W0.086 (3)0.075 (3)0.054 (2)0.013 (3)0.000 (2)0.027 (2)
O20.055 (2)0.052 (2)0.0333 (17)0.0209 (16)0.0020 (14)0.0142 (15)
O30.092 (3)0.0413 (18)0.0374 (18)0.0270 (18)0.0042 (17)0.0212 (15)
O40.0541 (19)0.0296 (15)0.0286 (15)0.0151 (13)0.0006 (13)0.0120 (12)
O3W0.100 (3)0.053 (2)0.039 (2)0.032 (2)0.0031 (18)0.0241 (18)
O2W0.0424 (19)0.046 (2)0.056 (2)0.0072 (15)0.0055 (17)0.0190 (18)
N10.0307 (18)0.0324 (18)0.0301 (17)0.0109 (14)0.0031 (14)0.0116 (15)
C10.027 (2)0.035 (2)0.031 (2)0.0098 (16)0.0014 (16)0.0098 (18)
C20.035 (2)0.038 (2)0.036 (2)0.0146 (18)0.0001 (18)0.0068 (19)
C30.046 (3)0.032 (2)0.048 (3)0.018 (2)0.003 (2)0.012 (2)
C40.046 (3)0.035 (2)0.041 (2)0.0118 (19)0.0029 (19)0.019 (2)
C50.032 (2)0.030 (2)0.035 (2)0.0058 (16)0.0055 (17)0.0141 (18)
C60.036 (2)0.044 (3)0.031 (2)0.0125 (19)0.0011 (17)0.0119 (19)
C70.039 (2)0.028 (2)0.033 (2)0.0105 (17)0.0004 (17)0.0148 (17)
C80.068 (4)0.068 (4)0.051 (3)0.025 (3)0.002 (3)0.024 (3)
C90.075 (4)0.087 (5)0.043 (3)0.016 (3)0.006 (3)0.027 (3)
Geometric parameters (Å, º) top
Cd1—O3W2.277 (4)O2W—H2WA0.81 (6)
Cd1—N12.340 (3)N1—C51.339 (5)
Cd1—O4i2.370 (3)N1—C11.340 (5)
Cd1—O2W2.381 (4)C1—C21.384 (6)
Cd1—O42.389 (3)C1—C61.491 (6)
Cd1—Cl12.5508 (13)C2—C31.379 (7)
Cd1—O12.573 (3)C2—H20.9300
O1—C61.208 (6)C3—C41.384 (6)
O1W—H1WA0.81 (6)C3—H30.9300
O1W—H1WB0.81 (7)C4—C51.385 (6)
O2—C61.314 (5)C4—H40.9300
O2—C81.505 (6)C5—C71.515 (6)
O3—C71.228 (5)C8—C91.459 (8)
O4—C71.259 (5)C8—H8A0.9700
O4—Cd1i2.370 (3)C8—H8B0.9700
O3W—H3WB0.85 (6)C9—H9A0.9600
O3W—H3WA0.84 (5)C9—H9B0.9600
O2W—H2WB0.81 (2)C9—H9C0.9600
O3W—Cd1—N1138.56 (13)C1—N1—Cd1122.7 (3)
O3W—Cd1—O4i80.15 (12)N1—C1—C2122.3 (4)
N1—Cd1—O4i140.12 (11)N1—C1—C6113.8 (4)
O3W—Cd1—O2W93.61 (15)C2—C1—C6123.9 (4)
N1—Cd1—O2W87.04 (12)C3—C2—C1118.6 (4)
O4i—Cd1—O2W79.79 (12)C3—C2—H2120.7
O3W—Cd1—O4152.23 (12)C1—C2—H2120.7
N1—Cd1—O468.90 (10)C2—C3—C4119.3 (4)
O4i—Cd1—O472.08 (11)C2—C3—H3120.3
O2W—Cd1—O482.20 (12)C4—C3—H3120.3
O3W—Cd1—Cl192.68 (12)C3—C4—C5119.1 (4)
N1—Cd1—Cl194.23 (9)C3—C4—H4120.5
O4i—Cd1—Cl192.37 (8)C5—C4—H4120.5
O2W—Cd1—Cl1168.95 (10)N1—C5—C4121.6 (4)
O4—Cd1—Cl188.01 (8)N1—C5—C7116.7 (3)
O3W—Cd1—O172.30 (12)C4—C5—C7121.7 (4)
N1—Cd1—O166.27 (11)O1—C6—O2124.5 (4)
O4i—Cd1—O1150.56 (10)O1—C6—C1122.6 (4)
O2W—Cd1—O191.60 (13)O2—C6—C1112.8 (4)
O4—Cd1—O1134.99 (10)O3—C7—O4126.6 (4)
Cl1—Cd1—O198.97 (9)O3—C7—C5117.1 (4)
C6—O1—Cd1114.4 (3)O4—C7—C5116.3 (3)
H1WA—O1W—H1WB99 (7)C9—C8—O2106.2 (5)
C6—O2—C8115.4 (4)C9—C8—H8A110.5
C7—O4—Cd1i132.6 (3)O2—C8—H8A110.5
C7—O4—Cd1119.4 (3)C9—C8—H8B110.5
Cd1i—O4—Cd1107.92 (11)O2—C8—H8B110.5
Cd1—O3W—H3WB83 (5)H8A—C8—H8B108.7
Cd1—O3W—H3WA129 (5)C8—C9—H9A109.5
H3WB—O3W—H3WA89 (3)C8—C9—H9B109.5
Cd1—O2W—H2WB112 (5)H9A—C9—H9B109.5
Cd1—O2W—H2WA121 (5)C8—C9—H9C109.5
H2WB—O2W—H2WA94 (7)H9A—C9—H9C109.5
C5—N1—C1119.2 (4)H9B—C9—H9C109.5
C5—N1—Cd1118.1 (3)
Symmetry code: (i) x+1, y+1, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O2W—H2WB···Cl1i0.81 (2)2.61 (2)3.405 (4)170 (6)
O2W—H2WA···Cl1ii0.81 (6)2.43 (6)3.227 (4)168 (6)
O1W—H1WB···Cl1iii0.81 (6)2.55 (7)3.348 (5)167 (8)
O1W—H1WA···O10.81 (7)2.54 (6)3.054 (6)123 (7)
O3W—H3WA···O1W0.84 (5)1.96 (6)2.757 (6)158 (7)
Symmetry codes: (i) x+1, y+1, z; (ii) x1, y, z; (iii) x+1, y+1, z+1.

Experimental details

Crystal data
Chemical formula[Cd2(C9H8NO4)2Cl2(H2O)4]·2H2O
Mr792.12
Crystal system, space groupTriclinic, P1
Temperature (K)293
a, b, c (Å)6.8414 (6), 10.7408 (9), 10.7597 (9)
α, β, γ (°)64.042 (2), 77.298 (2), 72.810 (2)
V3)675.35 (10)
Z1
Radiation typeMo Kα
µ (mm1)1.84
Crystal size (mm)0.60 × 0.28 × 0.26
Data collection
DiffractometerSiemens SMART CCD area-detector
diffractometer
Absorption correctionMulti-scan
(SADABS; Sheldrick, 1996)
Tmin, Tmax0.416, 0.620
No. of measured, independent and
observed [I > 2σ(I)] reflections
3540, 2371, 2167
Rint0.021
(sin θ/λ)max1)0.596
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.033, 0.089, 1.04
No. of reflections2371
No. of parameters190
No. of restraints8
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)1.04, 0.51

Computer programs: SMART (Siemens, 1996), SMART and SAINT (Siemens, 1994), XPREP in SHELXTL (Siemens, 1994), SHELXTL.

Selected geometric parameters (Å, º) top
Cd1—O3W2.277 (4)O1W—H1WA0.81 (6)
Cd1—N12.340 (3)O1W—H1WB0.81 (7)
Cd1—O4i2.370 (3)O2—C61.314 (5)
Cd1—O2W2.381 (4)O2—C81.505 (6)
Cd1—O42.389 (3)O3—C71.228 (5)
Cd1—Cl12.5508 (13)O4—C71.259 (5)
Cd1—O12.573 (3)O4—Cd1i2.370 (3)
O1—C61.208 (6)
O3W—Cd1—N1138.56 (13)N1—Cd1—Cl194.23 (9)
O3W—Cd1—O4i80.15 (12)O4i—Cd1—Cl192.37 (8)
N1—Cd1—O4i140.12 (11)O2W—Cd1—Cl1168.95 (10)
O3W—Cd1—O2W93.61 (15)O4—Cd1—Cl188.01 (8)
N1—Cd1—O2W87.04 (12)O3W—Cd1—O172.30 (12)
O4i—Cd1—O2W79.79 (12)N1—Cd1—O166.27 (11)
O3W—Cd1—O4152.23 (12)O4i—Cd1—O1150.56 (10)
N1—Cd1—O468.90 (10)O2W—Cd1—O191.60 (13)
O4i—Cd1—O472.08 (11)O4—Cd1—O1134.99 (10)
O2W—Cd1—O482.20 (12)Cl1—Cd1—O198.97 (9)
O3W—Cd1—Cl192.68 (12)Cd1i—O4—Cd1107.92 (11)
Symmetry code: (i) x+1, y+1, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O2W—H2WB···Cl1i0.81 (2)2.61 (2)3.405 (4)170 (6)
O2W—H2WA···Cl1ii0.81 (6)2.43 (6)3.227 (4)168 (6)
O1W—H1WB···Cl1iii0.81 (6)2.55 (7)3.348 (5)167 (8)
O1W—H1WA···O10.81 (7)2.54 (6)3.054 (6)123 (7)
O3W—H3WA···O1W0.84 (5)1.96 (6)2.757 (6)158 (7)
Symmetry codes: (i) x+1, y+1, z; (ii) x1, y, z; (iii) x+1, y+1, z+1.
 

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