catena-Poly[[diaquabis(2-chloronicotinato-[kappa]²O,O')cadmium(II)]-[mu]-2-chloronicotinato-[kappa]³O,O':N]

In the title neutral coordination polymer, [Cd(C₆H₃ClNO₂)₂(H₂O)₂]_n, each Cd^II ion is coordinated by one N and four O atoms from three 2-chloro­nicotinate ligands and by two aqua ligands, defining a distorted monocapped octahedral coordination geometry. Adjacent Cd atoms are linked by the pyridyl N atom and the bidentate carboxyl­ate functional group of a 2-­chloro­nicotinate ligand, forming a one-dimensional infinite chain along the b axis. The Cd...Cd distance is 8.112 (3) Å. These chains are linked by O-H...O and O-H...N hydrogen bonds into a three-dimensional network structure.

S1. Comment

Nicotinic acid and its derivatives, which have good biological activities, have been extensively studied over the past decade. Because of their versatile bonding mode with metal ions, the structures of many of the complexes that have been reported (Moore et al., 1972; Lu et al., 2002; Prout et al., 1985; Clegg et al., 1995; Premkumar et al., 2003) show nicotinic acid and its derivatives acting as bridging ligands through the carboxylate groups and pyridyl N atom. In order to investigate the space steric effect of its ortho position, we have synthesized 2-chloronicotinic acid, which is an important pharmaceutical synthesis intermediate and a potential mutilfuctional ligands. However, little is known about the structures of its metal complexes to date (Moncol et al., 2002). In the case of the mononuclear copper complex [Cu(2—Cl-nicotinate)₂(Et₂nia)₂(H₂O)₂] (where Et₂nia is N,N'-diethylnicotinamide), the 2-chloronicotinate group is in a monodentate mode, and the Cu^II atom has an elongated tetragonal bipyramidal geometry. We report here the synthesis and structure of the title coordination polymer, [Cd(2—Cl-niconinate)₂(H₂O)₂]_n, (I).

As illustrated in Fig. 1, the asymmetric unit of (I) is composed of a Cd^II ion, two independent 2-chloronicotinate groups and two coordinated water molecules, in which the carboxylate groups are bonded to the Cd^II ion in a chelating fashion. The Cd^II ion is coordinated by four O atoms from different carboxylate groups, pyridyl atom N2ⁱ [symmetry code: (i) x, 1 + y, z] and two aqua ligands. The coordination geometry can best be described as distorted monocapped octahedral. The equatorial plane of the complex is defined by atoms O3, O4, N2ⁱ and O2W [the r.m.s. deviation for the four ligating atoms is 0.12 (3) Å and the deviation of the Cd atom from the mean plane is 0.14 (3) Å]. Atoms O1 and O1W occupy the apical sites, with a bond angle of 167.71 (8)°. The capping atom, O2, lies 1.768 Å out of the O1/O2W/N2ⁱ plane. The Cd—O2 distance [2.654 (3) Å] lies within the range of the corresponding bond distances [2.639 (2) and 2.879 (2) Å] reported for the related Cd^II nicotinate coordination two-dimensional polymer, [Cd(nicotinate)₂(H₂O)]_n, (II) (Clegg et al., 1995). In (I), the axial Cd—O1W bond length [2.315 (2) Å] is longer than the Cd—O2W distance [2.258 (s.u.?) Å]. The Cd—O(carboxylate) distances range from 2.304 (2) to 2.470 (2) Å, except for Cd—O2, which is considerably longer. The dihedral angle made by the two independent pyridyl ring planes is 75.0 (3)°. The dihedral angles between the carboxyl groups and the attached pyridyl rings of the 2-chloronicotinate ligands are 32.5 (3) and 50.5 (3)° in (I), whereas the corresponding dihedral angles for the nicotinate ligands in (II) are 4.6 and 17.4°.

In (II), each Cd^II ion forms an approximate pentagonal bipyramidal coordination geometry, with the carboxylate O atoms and one N atom in the equatorial plane (the r.m.s. deviation for the five ligating atoms is ca 0.10 Å), and with the second N atom and the aqua ligand in axial positions. The two nicotinate ligands both exhibit tridentate modes, binding to the metal atoms through their N atoms and chelating carboxylate functional groups. In (I), one of 2-chloronicotinate ligands has the same coordination mode as the ligands in (II), while the other 2-chloronicotinate ligand exhibits only the chelating mode through its carboxylate group; pyridine atom N1 is not involved in binding to the metal atom. This difference can be attributed to the steric effect of the ortho position, leading to the formation of the distorted monocapped octahedral geometry in (I), which differs from the approximately pentagonal bipyramidal geometry in (II).

Adjacent Cd atoms are linked by the pyridyl N atom and bidentate carboxylate functional group of one 2-chloronicotinate ligand, forming a one-dimensional infinite chain propagating along the b direction. The Cd···Cd separation in the chain is 8.112 (3) Å. In addition, chains are connected through intermolecular hydrogen bonds (Table 2) involving the 2-chloronicotinate groups and aqua ligands, with O···O/O···N distances of 2.700 (3)–2.867 (3) Å and O—H···O/O—H···N angles of 167 (3)–177 (3)°, thus giving rise to a three-dimensional network structure.

S2. Experimental

2-Chloronicotinic acid was prepared by the reaction of oxidized nicotinic acid and trichlorodeoxyphosphorus (Richter et al., 1982). Cadmium dinitrate tetrahydrate (6.16 g, 20 mmol) and 2-chloronicotinic acid (3.17 g, 20 mmol) were each? dissolved in water (25 ml), and the two solutions? were mixed slowly with stirring at room temperature. The pH was adjusted to 6 with 0.1 M sodium hydroxide. Colorless crystals of (I) separated from the filtered solution after several days (yield ca 49%). Analysis calculated for C₁₂H₁₀CdCl₂N₂O₆: C 31.23, H 2.18, N 6.07%; found: C 31.01, H 2.39, N 5.99%.

S3. Refinement

The final difference Fourier map had a peak of 0.91 e Å⁻³ at 2.5 Å from atom H4. This peak existed in a solvent-accessible void of 31 ų, as suggested by PLATON (Spek, 2003). The magnitude of the peak could be decreased by lowering the σ threshold to 2θ = 50°; refining this peak as a water O atom did not lead to a meaningful outcome. As the spreading of the electron density by the SQUEEZE option (Sluis & Spek, 1990) in PLATON led to a peak of 0.72 e Å⁻³ near the atom Cd1, the peak could not be due to an O atom; the elemental analysis also supported the above results. C-bound H atoms were placed in calculated positions [C—H = 0.93 Å and U_iso(H) = 1.2U_eq(C)] and were refined in the riding-model approximation. H atoms of water molecules were located in difference-density maps and included in the refinement with O—H and H···H distance restraints of 0.85 (1) and 1.39 (1) Å, respectively, and with U_iso(H) values of 1.2U_eq(O).

Computing details

Data collection: RAPID-AUTO (Rigaku, 1998); cell refinement: RAPID-AUTO; data reduction: CrystalStructure (Rigaku/MSC, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. A view of the chain structure of (I), showing 30% probability displacement ellipsoids. [Symmetry code: (i) x, 1 + y, z.]

catena-Poly[diaquabis(2-chloronicotinato)cadmium(II)]

Crystal data

[Cd(C6H3ClNO2)2(H2O)2]	F(000) = 904
Mr = 461.53	Dx = 1.887 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 13628 reflections
a = 10.577 (2) Å	θ = 3.2–27.4°
b = 8.112 (2) Å	µ = 1.70 mm^−1
c = 19.661 (4) Å	T = 293 K
β = 105.60 (3)°	Prism, colorless
V = 1624.8 (6) Å^3	0.42 × 0.23 × 0.18 mm
Z = 4

Data collection

Rigaku R-AXIS RAPID diffractometer	3725 independent reflections
Radiation source: fine-focus sealed tube	3444 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.025
Detector resolution: 10 pixels mm^-1	θmax = 27.5°, θmin = 3.2°
ω scan	h = −13→13
Absorption correction: multi-scan (ABSCOR; Higashi, 1995)	k = −10→9
Tmin = 0.535, Tmax = 0.749	l = −25→25
14573 measured reflections

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)] = 0.030	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.078	H atoms treated by a mixture of independent and constrained refinement
S = 1.06	w = 1/[σ^2(Fo^2) + (0.0367P)^2 + 1.7742P] where P = (Fo^2 + 2Fc^2)/3
3725 reflections	(Δ/σ)max = 0.001
220 parameters	Δρmax = 0.91 e Å^−3
6 restraints	Δρmin = −0.37 e Å^−3

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

	x	y	z	Uiso*/Ueq
Cd1	0.66495 (2)	0.56488 (2)	0.63983 (1)	0.02798 (8)
Cl1	1.08628 (9)	0.6255 (1)	0.57512 (4)	0.0559 (2)
Cl2	0.55744 (8)	−0.05524 (8)	0.64947 (4)	0.0406 (2)
O1	0.8886 (2)	0.5384 (3)	0.6588 (2)	0.0526 (6)
O2	0.8511 (2)	0.7805 (3)	0.6985 (1)	0.0457 (5)
O3	0.6733 (2)	0.2749 (2)	0.64686 (9)	0.0359 (4)
O4	0.6454 (2)	0.3743 (2)	0.5395 (1)	0.0367 (4)
O1W	0.4382 (2)	0.5499 (2)	0.6021 (1)	0.0338 (4)
H1W1	0.409 (3)	0.577 (4)	0.5591 (6)	0.041*
H1W2	0.401 (3)	0.609 (4)	0.627 (1)	0.041*
O2W	0.6377 (2)	0.5898 (3)	0.7494 (1)	0.0372 (4)
H2W1	0.640 (3)	0.491 (2)	0.764 (2)	0.045*
H2W2	0.701 (2)	0.644 (3)	0.776 (1)	0.045*
N1	1.2807 (2)	0.7104 (4)	0.6801 (1)	0.0449 (6)
N2	0.6561 (2)	−0.2104 (3)	0.5614 (1)	0.0318 (5)
C1	1.1523 (3)	0.6872 (4)	0.6624 (2)	0.0358 (6)
C2	1.0720 (3)	0.7093 (3)	0.7069 (2)	0.0335 (6)
C3	1.1323 (3)	0.7639 (4)	0.7744 (2)	0.0415 (6)
C4	1.2672 (3)	0.7871 (4)	0.7949 (2)	0.0465 (7)
C5	1.3379 (3)	0.7585 (4)	0.7468 (2)	0.0493 (8)
C6	0.9267 (3)	0.6742 (4)	0.6861 (2)	0.0343 (6)
C7	0.6357 (3)	−0.0593 (3)	0.5825 (1)	0.0274 (5)
C8	0.6720 (3)	0.0850 (3)	0.5544 (1)	0.0298 (5)
C9	0.7286 (4)	0.0649 (4)	0.4987 (2)	0.0471 (8)
C10	0.7498 (4)	−0.0907 (4)	0.4760 (2)	0.056 (1)
C11	0.7142 (3)	−0.2252 (4)	0.5090 (2)	0.0429 (7)
C12	0.6607 (3)	0.2566 (3)	0.5821 (1)	0.0279 (5)
H3	1.0827	0.7851	0.8059	0.050*
H4	1.3092	0.8214	0.8405	0.056*
H5	1.4284	0.7730	0.7608	0.059*
H9	0.7521	0.1570	0.4767	0.057*
H10	0.7878	−0.1044	0.4388	0.067*
H11	0.7310	−0.3302	0.4944	0.051*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cd1	0.0316 (1)	0.0204 (1)	0.0329 (1)	−0.00152 (6)	0.01030 (8)	−0.00056 (6)
Cl1	0.0513 (5)	0.0805 (6)	0.0379 (4)	−0.0129 (4)	0.0156 (3)	−0.0074 (4)
Cl2	0.0497 (4)	0.0288 (3)	0.0521 (4)	−0.0034 (3)	0.0288 (3)	−0.0005 (3)
O1	0.037 (1)	0.040 (1)	0.083 (2)	−0.0075 (9)	0.020 (1)	−0.010 (1)
O2	0.038 (1)	0.053 (1)	0.047 (1)	0.0110 (9)	0.0127 (9)	−0.007 (1)
O3	0.058 (1)	0.0221 (9)	0.0270 (9)	0.0003 (8)	0.0098 (8)	0.0000 (7)
O4	0.056 (1)	0.0231 (9)	0.0284 (9)	0.0013 (8)	0.0072 (8)	0.0026 (7)
O1W	0.033 (1)	0.039 (1)	0.0291 (9)	−0.0015 (8)	0.0080 (8)	−0.0011 (8)
O2W	0.037 (1)	0.040 (1)	0.032 (1)	−0.0048 (8)	0.0061 (8)	−0.0014 (8)
N1	0.035 (1)	0.055 (2)	0.049 (1)	−0.005 (1)	0.017 (1)	−0.004 (1)
N2	0.040 (1)	0.021 (1)	0.033 (1)	−0.0019 (9)	0.0085 (9)	−0.0027 (8)
C1	0.035 (1)	0.036 (1)	0.039 (1)	−0.003 (1)	0.013 (1)	−0.001 (1)
C2	0.033 (1)	0.028 (1)	0.042 (1)	0.000 (1)	0.014 (1)	0.000 (1)
C3	0.047 (2)	0.040 (2)	0.042 (2)	−0.002 (1)	0.018 (1)	−0.006 (1)
C4	0.047 (2)	0.047 (2)	0.043 (2)	−0.009 (1)	0.009 (1)	−0.006 (1)
C5	0.035 (2)	0.055 (2)	0.057 (2)	−0.008 (1)	0.012 (1)	−0.005 (2)
C6	0.030 (1)	0.039 (2)	0.037 (1)	0.001 (1)	0.014 (1)	0.003 (1)
C8	0.040 (1)	0.023 (1)	0.026 (1)	0.000 (1)	0.008 (1)	−0.0005 (9)
C7	0.031 (1)	0.024 (1)	0.027 (1)	−0.0028 (9)	0.006 (1)	−0.0002 (9)
C9	0.080 (2)	0.030 (2)	0.041 (2)	−0.005 (1)	0.031 (2)	0.002 (1)
C10	0.096 (3)	0.038 (2)	0.047 (2)	0.002 (2)	0.043 (2)	−0.004 (1)
C11	0.066 (2)	0.025 (1)	0.042 (2)	0.0005 (13)	0.022 (1)	−0.007 (1)
C12	0.034 (1)	0.019 (1)	0.029 (1)	−0.0020 (9)	0.007 (1)	−0.0012 (9)

Geometric parameters (Å, º)

Cd1—O1	2.304 (2)	N2—C7	1.330 (3)
Cd1—O2	2.654 (3)	N2—Cd1^ii	2.374 (2)
Cd1—O3	2.356 (2)	N2—C11	1.340 (4)
Cd1—O4	2.470 (2)	C1—C2	1.385 (4)
Cd1—O1W	2.315 (2)	C2—C3	1.381 (4)
Cd1—O2W	2.258 (2)	C2—C6	1.508 (4)
Cd1—N2^i	2.374 (2)	C3—C4	1.388 (5)
Cl1—C1	1.744 (3)	C3—H3	0.9300
Cl2—C7	1.734 (3)	C4—C5	1.374 (5)
O1—C6	1.244 (4)	C4—H4	0.9300
O2—C6	1.244 (3)	C5—H5	0.9300
O3—C12	1.253 (3)	C8—C7	1.392 (3)
O4—C12	1.251 (3)	C8—C9	1.392 (4)
O1W—H1W1	0.85 (2)	C8—C12	1.511 (3)
O1W—H1W2	0.85 (3)	C9—C10	1.378 (4)
O2W—H2W1	0.85 (3)	C9—H9	0.9300
O2W—H2W2	0.85 (3)	C10—C11	1.373 (4)
N1—C1	1.322 (4)	C10—H10	0.9300
N1—C5	1.346 (4)	C11—H11	0.9300
O1—Cd1—O3	82.91 (8)	N2—C7—C8	124.5 (2)
O1—Cd1—O4	86.14 (9)	N2—C7—Cl2	113.9 (2)
O1—Cd1—O1W	167.71 (8)	N2—C11—C10	122.2 (3)
O1—Cd1—N2^i	92.08 (9)	N2—C11—H11	118.9
O3—Cd1—O4	54.26 (6)	C1—N1—C5	117.3 (3)
O3—Cd1—N2^i	143.05 (7)	C1—C2—C6	123.9 (3)
O2—Cd1—O1	51.80 (9)	C2—C1—Cl1	120.5 (2)
O2—Cd1—O3	128.36 (8)	C2—C3—C4	119.7 (3)
O2—Cd1—O4	130.72 (7)	C2—C3—H3	120.1
O2—Cd1—O1W	139.23 (7)	C3—C2—C1	116.4 (3)
O2—Cd1—O2W	78.26 (8)	C3—C2—C6	119.7 (2)
O2—Cd1—N2^i	70.8 (9)	C3—C4—H4	120.5
O1W—Cd1—O3	89.17 (7)	C4—C3—H3	120.1
O1W—Cd1—O4	81.60 (7)	C4—C5—H5	118.8
O1W—Cd1—N2^i	88.60 (8)	C5—C4—C3	119.0 (3)
O2W—Cd1—O1	104.07 (9)	C5—C4—H4	120.5
O2W—Cd1—O3	92.63 (7)	C6—O1—Cd1	100.7 (2)
O2W—Cd1—O4	144.37 (7)	C7—N2—Cd1^ii	119.1 (2)
O2W—Cd1—O1W	85.61 (8)	C7—N2—C11	118.0 (2)
O2W—Cd1—N2^i	123.93 (8)	C7—C8—C9	115.9 (2)
Cd1—O1W—H1W1	112 (2)	C7—C8—C12	125.1 (2)
Cd1—O1W—H1W2	113 (2)	C8—C7—Cl2	121.6 (2)
Cd1—O2W—H2W1	104 (2)	C8—C9—H9	119.9
Cd1—O2W—H2W2	110 (2)	C9—C8—C12	118.9 (2)
O1—C6—O2	123.3 (3)	C9—C10—H10	120.5
O1—C6—C2	118.2 (2)	C10—C9—C8	120.3 (3)
O2—C6—C2	118.5 (3)	C10—C9—H9	119.9
O3—C12—C8	118.6 (2)	C10—C11—H11	118.9
O4—C12—O3	123.3 (2)	C11—N2—Cd1^ii	119.0 (2)
O4—C12—C8	118.1 (2)	C11—C10—C9	119.1 (3)
N1—C1—C2	125.2 (3)	C11—C10—H10	120.5
N1—C1—Cl1	114.2 (2)	C12—O3—Cd1	93.8 (2)
N1—C5—C4	122.3 (3)	C12—O4—Cd1	88.6 (2)
N1—C5—H5	118.8	H1W1—O1W—H1W2	109 (2)
N2^i—Cd1—O4	88.96 (7)	H2W1—O2W—H2W2	109 (2)
Cd1—O1—C6—O2	2.2 (3)	N2^i—Cd1—O1—C6	62.4 (2)
Cd1—O1—C6—C2	−179.7 (2)	N2^i—Cd1—O3—C12	−5.2 (2)
Cd1—O3—C12—O4	−2.2 (3)	N2^i—Cd1—O4—C12	175.0 (2)
Cd1—O3—C12—C8	174.2 (2)	C1—N1—C5—C4	−1.6 (5)
Cd1—O4—C12—O3	2.1 (3)	C1—C2—C3—C4	−2.5 (4)
Cd1—O4—C12—C8	−174.4 (2)	C1—C2—C6—O1	50.2 (4)
Cd1^ii—N2—C7—C8	156.8 (2)	C1—C2—C6—O2	−131.6 (3)
Cd1^ii—N2—C7—Cl2	−23.6 (3)	C2—C3—C4—C5	1.5 (5)
Cd1^ii—N2—C11—C10	−159.1 (3)	C3—C2—C6—O1	−128.5 (3)
C11—N2—C7—Cl2	178.9 (2)	C3—C2—C6—O2	49.8 (4)
C11—N2—C7—C8	−0.7 (4)	C3—C4—C5—N1	0.7 (6)
Cl1—C1—C2—C3	−177.8 (2)	C5—N1—C1—C2	0.4 (5)
Cl1—C1—C2—C6	3.5 (4)	C5—N1—C1—Cl1	179.9 (3)
O1—Cd1—O3—C12	−89.2 (2)	C6—C2—C3—C4	176.3 (3)
O1—Cd1—O4—C12	82.9 (2)	C7—N2—C11—C10	−1.6 (5)
O3—Cd1—O1—C6	−154.4 (2)	C7—C8—C12—O3	31.4 (4)
O3—Cd1—O4—C12	−1.2 (2)	C7—C8—C12—O4	−151.9 (3)
O4—Cd1—O1—C6	151.2 (2)	C7—C8—C9—C10	−2.2 (5)
O4—Cd1—O3—C12	1.2 (2)	C8—C9—C10—C11	0.1 (6)
O1W—Cd1—O1—C6	155.4 (3)	C9—C8—C12—O3	−145.3 (3)
O1W—Cd1—O3—C12	81.4 (2)	C9—C8—C12—O4	31.4 (4)
O1W—Cd1—O4—C12	−96.2 (2)	C9—C8—C7—N2	2.6 (4)
O2W—Cd1—O4—C12	−26.0 (2)	C9—C8—C7—Cl2	−177.1 (2)
O2W—Cd1—O1—C6	−63.4 (2)	C9—C10—C11—N2	1.8 (6)
O2W—Cd1—O3—C12	167.0 (2)	C12—C8—C7—N2	−174.2 (2)
N1—C1—C2—C3	1.6 (5)	C12—C8—C7—Cl2	6.1 (4)
N1—C1—C2—C6	−177.1 (3)	C12—C8—C9—C10	174.8 (3)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1W—H1W1···O4^iii	0.85 (2)	1.91 (2)	2.755 (3)	175 (3)
O1W—H1W2···N1^iv	0.85 (3)	2.03 (3)	2.863 (3)	167 (3)
O2W—H2W1···O2^v	0.85 (3)	1.85 (3)	2.700 (3)	177 (3)
O2W—H2W2···O3^vi	0.85 (3)	2.03 (3)	2.867 (3)	168 (3)

Symmetry codes: (iii) −x+1, −y+1, −z+1; (iv) x−1, y, z; (v) −x+3/2, y−1/2, −z+3/2; (vi) −x+3/2, y+1/2, −z+3/2.