catena-Poly[[triaqua­cadmium(II)]-μ-pyridine-2,3-dicarboxyl­ato-κ³N,O²:O³]

The title polymeric compound, [Cd(C₇H₃NO₄)(H₂O)₃]_n or [Cd(py-2,3-dc)(H₂O)₃]_n, where py-2,3-dcH₂ is pyridine-2,3-dicarboxylic acid, was obtained by the reaction of cadmium(II) nitrate hexa­hydrate with (pipzH₂)(py-2,3-dc) as a proton-transfer compound in aqueous solution (pipz is piperazine). The mol­ecular structure shows that only the anionic fragment of the starting proton-transfer compound is present in the complex, while the (pipzH₂)²⁺ dication has been lost. Each (py-2,3-dc)²⁻ ligand bridges two Cd^II atoms in two different coordination modes, i.e. one end acts as a monodentate and the other end as a bidentate ligand. The three remaining coordination sites on the metal center are occupied by water mol­ecules. The geometric arrangement of the six donor atoms around the Cd^II atom is distorted octa­hedral. In the crystal structure, O—H...O and C—H...O hydrogen bonds play an important role in stabilizing the supra­molecular structure.

Key indicators

• Single-crystal X-ray study
• T = 100 K
• Mean [sigma](C-C) = 0.007 Å
• R factor = 0.029
• wR factor = 0.057
• Data-to-parameter ratio = 14.9

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT731_ALERT_1_C Bond    Calc     0.85(4), Rep   0.850(19) ......       2.11 su-Ra
              O1W  -H1      1.555   1.555
PLAT731_ALERT_1_C Bond    Calc     0.88(4), Rep   0.869(19) ......       2.11 su-Ra
              O1W  -H2      1.555   1.555
PLAT731_ALERT_1_C Bond    Calc     0.86(4), Rep   0.858(19) ......       2.11 su-Ra
              O3W  -H5      1.555   1.555
PLAT764_ALERT_4_C Overcomplete CIF Bond List Detected (Rep/Expd) .       1.11 Ratio

Alert level G
REFLT03_ALERT_4_G Please check that the estimate of the number of Friedel pairs is
            correct. If it is not, please give the correct count in the
            _publ_section_exptl_refinement section of the submitted CIF.
           From the CIF: _diffrn_reflns_theta_max           27.48
           From the CIF: _reflns_number_total               2255
           Count of symmetry unique reflns         1213
           Completeness (_total/calc)            185.90%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured      1042
           Fraction of Friedel pairs measured     0.859
           Are heavy atom types Z>Si present        yes
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......          7

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   4 ALERT level C = Check and explain
   2 ALERT level G = General alerts; check

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

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S1. Comment

Recently, ion pairs or complexes related to the title compound have been reported (Aghabozorg, Daneshvar, Motyeian et al., 2007). Proton transfer from pyridine-2,3-dicarboxylic acid (py-2,3-dcH₂) to amines, such as piperazine (pipz) and propane-1,3-diamine (pn), resulted in the formation of novel systems (Aghabozorg, Manteghi et al., 2007 submitted; Manteghi et al., 2007). The resulting compounds, with some remaining sites as electron donors, can coordinate to metallic ions (Aghabozorg, Sadr-khanlou et al., 2007). The molecular structure of the title compound shows that only the anionic fragment of starting proton transfer compound is incorporated into the complex and that the (pipzH₂)²⁺ dication has been lost. Each cadmium(II) atom is coordinated by five O-atoms and one N-atom. The asymmetric unit consists of one cadmium, one bridging (py-2,3-dc)^2- and three coordinated water molecules (Fig. 1). The (py-2,3-dc)^2- groups bridge two cadmium ions by adopting two different coordination modes, bidentate and monodentate. The existance of both coordination modes is seldom found in pyridine multicarboxylate coordination polymers (Li et al. 2004). The bond lengths and bond angles of the equatorial bonds around the metal center with atoms N1A, O2A, O1W and O2W, and the axial bonds with atoms O4 and O3W, indicate that the geometric arrangement of the six donor atoms around the cadmium(II) atom is distorted octahedral (Table 1). It is noticeable that one of the carboxylate groups is almost coplannar with the pyridine ring and the other is perpendicular to it (Fig. 1). The formation of the polymeric chains along the c axis is illustrated in Fig. 2. There are a number of O—H···O hydrogen bonds (Table 2) involving the coordinated water molecules and other O-atoms, [D···A distances ranging from 2.685 (5) to 2.789 (5) Å], and a C—H···O bond [D···A distance of 3.430 (6) Å], that give rise to the formation of a three-dimensional network (Fig. 3).

Related literature

For related ion pairs or complexes, see: Aghabozorg, Daneshvar, Motyeian et al. (2007); Aghabozorg et al. (2008); Manteghi et al. (2007); Aghabozorg, Sadr-khanlou et al. (2007); Li et al. (2004).

S2. Experimental

The proton transfer ion pair was prepared according to the literature (Aghabozorg et al., 2008, in press). A solution of Cd(NO₃)₂. 6H₂O (158 mg, 0.5 mmol) in water (20 ml) was added to a solution of (pipzH₂)(py- 2,3-dc) (253 mg, 1.0 mmol) in water (20 ml), in a 1:2 molar ratio. Colorless crystals of the title compound suitable for X-ray characterization were obtained after a few days at room temperature.

S3. Refinement

All the hydrogen atoms could be located from the difference Fourier syntheses. The water H-atoms were refined isotropically with U_iso(H) = 0.022. The C-bond H-atoms were included in calculated positions and treated as riding atoms: C—H = 0.95 Å with U_iso(H) = 1.2 U_eq(C).

Computing details

Data collection: APEX2 (Bruker, 2005); cell refinement: APEX2 (Bruker, 2005); data reduction: APEX2 (Bruker, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 1998); program(s) used to refine structure: SHELXTL (Sheldrick, 1998); molecular graphics: SHELXTL (Sheldrick, 1998); software used to prepare material for publication: SHELXTL (Sheldrick, 1998).

Figures

	Fig. 1. Molecular structure of the title compound, showing the atom-numbering scheme and displacement ellipsoids at the 50% probability level. Hydrogen bonds are shown as dashed lines. Atoms marked with suffixes A—E are related by the symmetry codes (A) -x + 3/2, y, z - 1/2; (B) -x + 1, -y + 1, z + 1/2; (C) -x + 1, -y + 1, z - 1/2; (D) -x + 1, -y + 2, z - 1/2; (E) x, y, z - 1).
	Fig. 2. A view of the polymeric chain of the title compound extending along the c axis.
	Fig. 3. A view along the b axis of the crystal packing of the title compound [the hydrogen bonds are shown as dashed lines and the hydrogen atoms of the pyridine-2,3-dicarboxylates ligands are omitted for clarity].

catena-Poly[[triaquacadmium(II)]-µ-pyridine-2,3-dicarboxylato- κ³N,O²:O³]

Crystal data

[Cd(C7H3NO4)(H2O)3]	F(000) = 648
Mr = 331.55	Dx = 2.219 Mg m^−3
Orthorhombic, Pca21	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2c -2ac	Cell parameters from 1136 reflections
a = 16.820 (3) Å	θ = 3.0–24.6°
b = 6.8076 (14) Å	µ = 2.22 mm^−1
c = 8.6658 (17) Å	T = 100 K
V = 992.3 (3) Å^3	Needle, colourless
Z = 4	0.40 × 0.08 × 0.05 mm

Data collection

Bruker APEX 1000 CCD area-detector diffractometer	2255 independent reflections
Radiation source: fine-focus sealed tube	1848 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.060
ω scans	θmax = 27.5°, θmin = 2.4°
Absorption correction: multi-scan (APEX2; Bruker, 2005)	h = −21→21
Tmin = 0.810, Tmax = 0.901	k = −8→8
8990 measured reflections	l = −11→11

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.029	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.056	w = 1/[σ^2(Fo^2) + (0.02P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.01	(Δ/σ)max = 0.001
2255 reflections	Δρmax = 0.61 e Å^−3
151 parameters	Δρmin = −0.84 e Å^−3
7 restraints	Absolute structure: Flack (1983), 1042 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.05 (4)

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
Cd1	0.602315 (16)	0.57263 (4)	1.12348 (5)	0.01148 (8)
O1	0.64375 (15)	0.5438 (4)	1.6269 (10)	0.0146 (4)
O2	0.77114 (19)	0.4893 (5)	1.6812 (4)	0.0146 (4)
O3	0.55536 (18)	0.9159 (5)	1.5507 (4)	0.0139 (7)
O4	0.56140 (18)	0.7169 (5)	1.3472 (4)	0.0131 (8)
C1	0.7384 (3)	0.7512 (7)	1.5083 (6)	0.0114 (10)
C2	0.6813 (3)	0.8656 (7)	1.4333 (6)	0.0120 (11)
C3	0.7065 (3)	1.0220 (8)	1.3431 (7)	0.0110 (11)
H3A	0.6685	1.1023	1.2920	0.013*
C4	0.7868 (3)	1.0616 (8)	1.3272 (7)	0.0149 (11)
H4A	0.8050	1.1660	1.2636	0.018*
C5	0.8403 (3)	0.9424 (8)	1.4080 (6)	0.0168 (11)
H5A	0.8956	0.9694	1.4001	0.020*
C6	0.7166 (2)	0.5813 (6)	1.6146 (9)	0.0146 (4)
C7	0.5934 (3)	0.8271 (7)	1.4475 (5)	0.0113 (10)
N1	0.8168 (2)	0.7919 (6)	1.4961 (5)	0.0125 (9)
O1W	0.5482 (2)	0.2964 (6)	1.2211 (4)	0.0145 (8)
H1	0.526 (3)	0.302 (9)	1.309 (4)	0.022*
H2	0.509 (2)	0.227 (7)	1.183 (5)	0.022*
O2W	0.47743 (19)	0.6981 (5)	1.0383 (4)	0.0134 (7)
H3	0.439 (2)	0.618 (6)	1.065 (6)	0.020*
H4	0.464 (3)	0.818 (4)	1.060 (6)	0.020*
O3W	0.59058 (19)	0.3963 (5)	0.9018 (4)	0.0147 (8)
H5	0.5445 (19)	0.350 (8)	0.879 (7)	0.022*
H6	0.609 (3)	0.420 (8)	0.811 (3)	0.022*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cd1	0.00902 (12)	0.01505 (14)	0.01036 (13)	−0.00047 (13)	0.0004 (3)	0.0018 (3)
O1	0.0109 (8)	0.0186 (11)	0.0144 (10)	0.0005 (8)	0.0029 (11)	0.0048 (12)
O2	0.0109 (8)	0.0186 (11)	0.0144 (10)	0.0005 (8)	0.0029 (11)	0.0048 (12)
O3	0.0112 (16)	0.0158 (18)	0.0146 (16)	−0.0006 (14)	0.0041 (13)	−0.0032 (16)
O4	0.0077 (16)	0.023 (2)	0.0084 (17)	−0.0019 (14)	0.0004 (14)	−0.0031 (16)
C1	0.011 (2)	0.012 (3)	0.011 (2)	−0.0042 (19)	−0.0063 (19)	−0.001 (2)
C2	0.010 (2)	0.014 (3)	0.012 (3)	−0.0018 (19)	0.000 (2)	−0.005 (2)
C3	0.009 (3)	0.013 (3)	0.011 (3)	0.004 (2)	0.000 (2)	−0.002 (2)
C4	0.014 (3)	0.016 (3)	0.014 (3)	−0.002 (2)	−0.001 (2)	0.005 (3)
C5	0.012 (3)	0.020 (3)	0.017 (3)	−0.004 (2)	0.000 (2)	−0.004 (3)
C6	0.0109 (8)	0.0186 (11)	0.0144 (10)	0.0005 (8)	0.0029 (11)	0.0048 (12)
C7	0.013 (2)	0.011 (3)	0.010 (2)	−0.001 (2)	−0.003 (2)	0.0057 (19)
N1	0.011 (2)	0.016 (2)	0.010 (2)	−0.0057 (17)	0.0018 (16)	−0.0007 (18)
O1W	0.0142 (18)	0.022 (2)	0.0070 (17)	−0.0081 (15)	0.0020 (14)	−0.0012 (16)
O2W	0.0127 (17)	0.0119 (19)	0.0156 (19)	0.0014 (14)	−0.0030 (14)	−0.0008 (17)
O3W	0.0113 (18)	0.023 (2)	0.0093 (16)	−0.0033 (15)	0.0003 (14)	−0.0040 (16)

Geometric parameters (Å, º)

Cd1—O1W	2.254 (4)	C2—C7	1.506 (6)
Cd1—O2^i	2.259 (3)	C3—C4	1.385 (6)
Cd1—O3W	2.274 (3)	C3—H3A	0.9500
Cd1—O4	2.279 (3)	C4—C5	1.400 (7)
Cd1—N1^i	2.302 (4)	C4—H4A	0.9500
Cd1—O2W	2.385 (3)	C5—N1	1.338 (7)
O1—C6	1.256 (4)	C5—H5A	0.9500
O2—C6	1.252 (6)	N1—Cd1^ii	2.302 (4)
O2—Cd1^ii	2.259 (3)	O1W—H1	0.850 (19)
O3—C7	1.255 (6)	O1W—H2	0.869 (19)
O4—C7	1.268 (6)	O2W—H3	0.88 (2)
C1—N1	1.351 (6)	O2W—H4	0.866 (19)
C1—C2	1.397 (7)	O3W—H5	0.858 (19)
C1—C6	1.523 (7)	O3W—H6	0.87 (2)
C2—C3	1.387 (7)
O1W—Cd1—O2^i	95.06 (13)	C2—C3—H3A	119.9
O1W—Cd1—O3W	80.89 (13)	C3—C4—C5	117.7 (5)
O2^i—Cd1—O3W	97.84 (12)	C3—C4—H4A	121.1
O1W—Cd1—O4	85.31 (13)	C5—C4—H4A	121.1
O2^i—Cd1—O4	101.79 (12)	N1—C5—C4	122.6 (5)
O3W—Cd1—O4	156.89 (12)	N1—C5—H5A	118.7
O1W—Cd1—N1^i	163.70 (14)	C4—C5—H5A	118.7
O2^i—Cd1—N1^i	73.25 (13)	O2—C6—O1	125.0 (6)
O3W—Cd1—N1^i	89.34 (14)	O2—C6—C1	118.8 (4)
O4—Cd1—N1^i	107.87 (14)	O1—C6—C1	116.2 (5)
O1W—Cd1—O2W	93.38 (13)	O3—C7—O4	123.9 (4)
O2^i—Cd1—O2W	171.30 (12)	O3—C7—C2	118.3 (4)
O3W—Cd1—O2W	81.44 (12)	O4—C7—C2	117.6 (4)
O4—Cd1—O2W	80.96 (12)	C5—N1—C1	119.4 (4)
N1^i—Cd1—O2W	98.06 (13)	C5—N1—Cd1^ii	126.5 (3)
C6—O2—Cd1^ii	117.6 (3)	C1—N1—Cd1^ii	114.0 (3)
C7—O4—Cd1	135.2 (3)	Cd1—O1W—H1	118 (4)
N1—C1—C2	121.3 (5)	Cd1—O1W—H2	128 (3)
N1—C1—C6	116.0 (4)	H1—O1W—H2	92 (5)
C2—C1—C6	122.6 (4)	Cd1—O2W—H3	110 (3)
C3—C2—C1	118.7 (4)	Cd1—O2W—H4	120 (4)
C3—C2—C7	118.6 (4)	H3—O2W—H4	110 (5)
C1—C2—C7	122.7 (4)	Cd1—O3W—H5	118 (4)
C4—C3—C2	120.2 (5)	Cd1—O3W—H6	130 (4)
C4—C3—H3A	119.9	H5—O3W—H6	101 (5)
O1W—Cd1—O4—C7	131.6 (5)	C2—C1—C6—O2	−177.9 (5)
O2^i—Cd1—O4—C7	37.4 (5)	N1—C1—C6—O1	179.6 (6)
O3W—Cd1—O4—C7	−175.1 (4)	C2—C1—C6—O1	2.7 (9)
N1^i—Cd1—O4—C7	−38.6 (5)	Cd1—O4—C7—O3	168.0 (3)
O2W—Cd1—O4—C7	−134.3 (5)	Cd1—O4—C7—C2	−7.0 (7)
N1—C1—C2—C3	0.9 (7)	C3—C2—C7—O3	−87.1 (6)
C6—C1—C2—C3	177.6 (5)	C1—C2—C7—O3	92.4 (6)
N1—C1—C2—C7	−178.5 (4)	C3—C2—C7—O4	88.2 (6)
C6—C1—C2—C7	−1.8 (8)	C1—C2—C7—O4	−92.3 (6)
C1—C2—C3—C4	0.6 (9)	C4—C5—N1—C1	0.2 (8)
C7—C2—C3—C4	−179.9 (5)	C4—C5—N1—Cd1^ii	176.0 (4)
C2—C3—C4—C5	−1.7 (9)	C2—C1—N1—C5	−1.3 (7)
C3—C4—C5—N1	1.3 (9)	C6—C1—N1—C5	−178.3 (5)
Cd1^ii—O2—C6—O1	175.2 (6)	C2—C1—N1—Cd1^ii	−177.7 (4)
Cd1^ii—O2—C6—C1	−4.1 (7)	C6—C1—N1—Cd1^ii	5.4 (6)
N1—C1—C6—O2	−1.0 (8)

Symmetry codes: (i) −x+3/2, y, z−1/2; (ii) −x+3/2, y, z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1W—H1···O2W^iii	0.85 (2)	1.99 (2)	2.782 (5)	156
O1W—H2···O3^iv	0.87 (2)	1.86 (2)	2.702 (5)	164
O2W—H3···O1^iv	0.88 (2)	1.85 (2)	2.731 (5)	178
O2W—H4···O3^v	0.87 (2)	1.84 (2)	2.687 (5)	165
O3W—H5···O4^iv	0.86 (2)	1.86 (2)	2.712 (4)	171
O3W—H6···O1^vi	0.87 (2)	1.89 (2)	2.735 (8)	164
C3—H3A···O1W^vii	0.95 (2)	2.49 (2)	3.420 (6)	165

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