catena-Poly[[aqua­(2,2'-bipyridine-[kappa]²N,N')cadmium(II)]-[mu]-4-carboxyl­atophenoxy­acetato-[kappa]³O:O⁴,O^4']

In the title compound, [Cd(C₉H₆O₅)(C₁₀H₈N₂)(H₂O)]_n, the Cd^II atom is coordinated in a distorted octa­hedral fashion by two carboxyl­ate groups (one in a monodentate and one in a bidentate fashion) from two 4-carboxyl­ato­phenoxy­acetate anions, two N atoms from a 2,2'-bipyridine ligand and one aqua ligand. The structure is a helix with a long pitch of 16.441 (5) Å. A three-dimensional supra­molecular network is further constructed through [pi]-[pi] stacking and hydrogen-bonding inter­actions between the helices.

S1. Comment

It has been noted that employment of flexible or V-shaped exo-bidentate organic bridges can improve the helicity of polymeric chains (Ye et al., 2005). Therefore, we assumed that the 4-carboxylatophenoxyacetate (cpoa^2-) anion, as a multidentate ligand with two different carboxylate groups, one at a flexible site, may be useful in the formation of single-stranded helical chains in the presence of aromatic chelate ligands, such as 2,2'-bipyridine (2,2'-bipy) and 1,10-phenanthroline (phen). These aromatic chelate ligands are important in maintaining the one-dimensionality and may provide potential supramolecular recognition sites for π–π stacking interaction (Chen et al., 2002; Zhang et al., 2004) to form multi-stranded helices. Using 4-carboxyphenoxyacetic acid (H₂cpoa) and 2,2'-bipy, we have hydrothermally prepared the title compound, (I), namely [Cd(cpoa)(2,2'-bipy)(H₂O)]_n, which is a new neutral infinite Cd^II dicarboxylate helical coordination polymer. The structure is reported in this paper.

The asymmetric unit of (I) contains one Cd^II atom, one cpoa^2- ligand, one 2,2'-bipy ligand and one water molecule (Fig. 1). The Cd atom is coordinated by three O atoms from one monodentate and one 1,3-bidentate cpoa ligands, the aqua ligand and two N atoms from the 2,2'-bipy ligand to furnish a distorted octahedral geometry. The Cd1—O3ⁱ and Cd1—O4ⁱ bond distances are longer than the Cd1—O1 bond (see Table 1 for distances and symmetry codes). Each pair of adjacent Cd^II atoms are bridged by cpoa^2- ligands to form a chiral helical chain running along the 2₁ axis in the c direction with a pitch of 16.441 (5) Å; this is longer than the pitch of 11.25 (1) Å in [Cu(ipa)(2,2'-bipy)]_n.2nH₂O (H₂ipa is isophthalic acid; Chen et al., 2002) because the cpoa^2- dianion is larger than the ipa^2- dianion. These chains are decorated with 2,2'-bipy ligands, positioned alternately on two sides and pointing in outwards, as depicted in Fig. 2. The benzene rings of the cpoa^2- ions at each side of the helix are arranged in a parallel fashion, with a vertical inter-ring distance of 5.04 (1) Å; adjacent chiral helices are connected into a two-dimensional network through hydrogen bonds involving aqua ligands (Table 2 and Fig. 3). The two-dimensional network is extended into a three-dimensional supramolecular network by π–π stacking through intercalation of the 2,2'-bipy rings (the face-to-face distance is 3.42 (1) Å; Fig. 4)

S2. Experimental

2,2'-Bipyridine (0.157 g, 1 mmol) and cadmium nitrate (0.308 g, 1 mmol) were dissolved in a hot aqueous solution of 4-carboxyphenoxyacetic acid (0.196 g, 1 mmol) and the pH of the solution was adjusted to 6 with triethylamine. The solution was sealed in a 15 ml Teflon-lined stainless steel bomb and held at 413 K for 96 h. The bomb was then cooled naturally to room temperature. Colorless prismatic crystals were filtered off, washed with water and dried at room temperature (yield 58%).

S3. Refinement

The water H atoms were located from difference Fourier maps and refined freely. All other H atoms were positioned geometrically and refined with a riding model, with distances 0.97 (CH₂) or 0.93 (aromatic) Å, and with U_iso(H) = 1.2 U_eq(C).

Computing details

Data collection: SMART (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT; 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 (I), showing 30% probability displacement ellipsoids. [Symmetry code: (i) -x + 1/2, -y + 1, z - 1/2.]
	Fig. 2. A chiral helical chain of (I).
	Fig. 3. The two-dimensional layer of (I), formed through hydrogen bonds (dashed lines). H atoms have been omitted.
	Fig. 4. The three-dimensional network of (I), formed through hydrogen bonds and π–π stacking. H atoms have been omitted.

catena-Poly[[aqua(2,2'-bipyridine-κ²N,N')cadmium(II)]-µ-4- carboxylatophenoxyacetato-κ³O,O':O'']

Crystal data

[Cd(C9H6O5)(C10H8N2)(H2O)]	F(000) = 960
Mr = 480.74	Dx = 1.804 Mg m^−3
OrthorhombicP212121	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 947 reflections
a = 6.799 (2) Å	θ = 2.5–26.8°
b = 15.834 (5) Å	µ = 1.28 mm^−1
c = 16.441 (5) Å	T = 293 K
V = 1769.9 (9) Å^3	Prism, colorless
Z = 4	0.37 × 0.21 × 0.17 mm

Data collection

Bruker APEX area-detector diffractometer	3866 independent reflections
Radiation source: fine-focus sealed tube	3417 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.028
φ and ω scans	θmax = 27.1°, θmin = 2.5°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −8→8
Tmin = 0.650, Tmax = 0.812	k = −20→12
10675 measured reflections	l = −19→21

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.026	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.050	w = 1/[σ^2(Fo^2) + (0.0231P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.06	(Δ/σ)max = 0.001
3866 reflections	Δρmax = 0.56 e Å^−3
262 parameters	Δρmin = −0.27 e Å^−3
0 restraints	Absolute structure: Flack (1983), 1617 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.36 (2)

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	0.79697 (3)	0.597549 (13)	0.340650 (12)	0.03146 (6)
O1	0.7358 (3)	0.46184 (13)	0.35751 (14)	0.0454 (6)
O2	0.4563 (4)	0.50229 (15)	0.41487 (13)	0.0492 (6)
O3	0.0214 (3)	0.36815 (15)	0.77036 (12)	0.0426 (6)
O4	−0.2507 (3)	0.39258 (15)	0.70274 (12)	0.0424 (6)
O1W	1.1313 (4)	0.56505 (18)	0.33104 (18)	0.0469 (6)
H1A	1.226 (6)	0.597 (2)	0.310 (2)	0.064 (13)*
H1B	1.194 (6)	0.537 (2)	0.358 (2)	0.054 (13)*
N1	0.8241 (4)	0.63920 (15)	0.47599 (14)	0.0360 (6)
N2	0.8478 (3)	0.74367 (14)	0.34756 (15)	0.0330 (6)
C1	0.8248 (6)	0.5843 (2)	0.53766 (19)	0.0506 (9)
H1	0.8146	0.5271	0.5258	0.061*
C2	0.8401 (5)	0.6083 (3)	0.61783 (19)	0.0541 (10)
H2	0.8398	0.5685	0.6594	0.065*
C3	0.8556 (5)	0.6928 (2)	0.63458 (19)	0.0530 (10)
H3	0.8648	0.7111	0.6882	0.064*
C4	0.8576 (5)	0.7501 (2)	0.57218 (18)	0.0408 (8)
H4	0.8685	0.8076	0.5830	0.049*
C5	0.8433 (4)	0.7215 (2)	0.49240 (17)	0.0327 (7)
C6	0.8474 (4)	0.7801 (2)	0.42158 (17)	0.0321 (7)
C7	0.8513 (5)	0.8670 (2)	0.4300 (2)	0.0485 (10)
H7	0.8475	0.8916	0.4813	0.058*
C8	0.8611 (6)	0.9168 (2)	0.3606 (2)	0.0644 (12)
H8	0.8651	0.9753	0.3652	0.077*
C9	0.8647 (6)	0.8797 (2)	0.2862 (2)	0.0601 (12)
H9	0.8728	0.9122	0.2392	0.072*
C10	0.8561 (5)	0.7933 (2)	0.2819 (2)	0.0456 (9)
H10	0.8561	0.7680	0.2308	0.055*
C11	0.5668 (5)	0.4486 (2)	0.38684 (18)	0.0322 (7)
C12	0.5068 (5)	0.3567 (2)	0.38631 (19)	0.0359 (8)
H12A	0.5417	0.3324	0.3341	0.043*
H12B	0.5812	0.3270	0.4278	0.043*
O5	0.3036 (4)	0.34298 (14)	0.40022 (11)	0.0410 (5)
C14	0.2279 (5)	0.35086 (17)	0.47679 (16)	0.0297 (7)
C15	0.3360 (5)	0.3502 (2)	0.54816 (18)	0.0397 (8)
H15	0.4722	0.3450	0.5467	0.048*
C16	0.2384 (4)	0.35730 (19)	0.62191 (17)	0.0363 (8)
H16	0.3108	0.3564	0.6699	0.044*
C17	0.0369 (5)	0.36572 (18)	0.62600 (16)	0.0289 (6)
C18	−0.0660 (5)	0.3652 (2)	0.55345 (18)	0.0383 (8)
H18	−0.2022	0.3705	0.5545	0.046*
C19	0.0275 (5)	0.3573 (2)	0.48011 (19)	0.0403 (8)
H19	−0.0456	0.3562	0.4323	0.048*
C20	−0.0700 (5)	0.37613 (18)	0.70540 (18)	0.0316 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cd1	0.03449 (11)	0.03069 (10)	0.02921 (9)	0.00025 (10)	−0.00330 (10)	−0.00314 (10)
O1	0.0328 (15)	0.0373 (12)	0.0662 (15)	−0.0056 (9)	0.0021 (10)	0.0105 (11)
O2	0.0561 (17)	0.0392 (15)	0.0524 (15)	0.0083 (12)	0.0002 (12)	−0.0029 (12)
O3	0.0401 (14)	0.0576 (16)	0.0300 (12)	−0.0067 (11)	0.0015 (10)	0.0014 (10)
O4	0.0367 (16)	0.0557 (14)	0.0347 (10)	0.0067 (11)	0.0093 (8)	0.0055 (11)
O1W	0.0284 (13)	0.0531 (15)	0.0593 (16)	0.0020 (12)	−0.0008 (13)	0.0071 (13)
N1	0.0435 (18)	0.0360 (14)	0.0285 (12)	−0.0020 (13)	−0.0005 (13)	−0.0011 (11)
N2	0.0352 (16)	0.0325 (12)	0.0313 (12)	−0.0019 (10)	−0.0072 (12)	0.0006 (11)
C1	0.065 (3)	0.046 (2)	0.0416 (18)	−0.001 (2)	−0.0017 (17)	0.0054 (15)
C2	0.060 (3)	0.067 (3)	0.0351 (17)	−0.007 (2)	−0.0047 (15)	0.0104 (18)
C3	0.044 (2)	0.084 (3)	0.0317 (17)	−0.0041 (19)	−0.0006 (13)	−0.0084 (17)
C4	0.036 (2)	0.051 (2)	0.0362 (17)	0.0013 (15)	−0.0021 (13)	−0.0090 (15)
C5	0.0239 (18)	0.0404 (18)	0.0337 (15)	−0.0011 (13)	−0.0018 (11)	−0.0076 (13)
C6	0.0275 (19)	0.0307 (16)	0.0380 (16)	−0.0006 (12)	−0.0053 (12)	−0.0049 (13)
C7	0.057 (3)	0.0357 (19)	0.053 (2)	0.0014 (17)	−0.0136 (18)	−0.0110 (17)
C8	0.084 (3)	0.026 (2)	0.083 (3)	−0.0039 (17)	−0.020 (2)	0.0024 (18)
C9	0.082 (3)	0.038 (2)	0.061 (2)	−0.0103 (18)	−0.024 (2)	0.0173 (18)
C10	0.053 (2)	0.042 (2)	0.0414 (18)	−0.0047 (17)	−0.0123 (15)	0.0041 (16)
C11	0.0327 (19)	0.0320 (18)	0.0318 (16)	0.0018 (14)	−0.0082 (14)	0.0029 (14)
C12	0.0333 (19)	0.040 (2)	0.0342 (16)	−0.0025 (15)	0.0083 (14)	−0.0041 (15)
O5	0.0350 (12)	0.0559 (14)	0.0320 (10)	−0.0122 (13)	0.0067 (11)	−0.0093 (9)
C14	0.0296 (19)	0.0304 (15)	0.0292 (13)	−0.0069 (13)	0.0050 (13)	−0.0029 (12)
C15	0.026 (2)	0.054 (2)	0.0391 (17)	−0.0037 (15)	0.0003 (13)	−0.0074 (15)
C16	0.034 (2)	0.0460 (19)	0.0289 (14)	−0.0039 (14)	−0.0034 (13)	−0.0014 (13)
C17	0.0333 (18)	0.0228 (15)	0.0307 (14)	−0.0023 (13)	0.0018 (13)	0.0022 (12)
C18	0.0229 (18)	0.053 (2)	0.0394 (17)	0.0033 (15)	−0.0004 (14)	0.0041 (15)
C19	0.038 (2)	0.052 (2)	0.0309 (15)	−0.0028 (16)	−0.0042 (14)	0.0028 (16)
C20	0.036 (2)	0.0254 (16)	0.0335 (16)	−0.0055 (13)	0.0067 (14)	0.0003 (12)

Geometric parameters (Å, º)

Cd1—O1	2.206 (2)	C5—C6	1.490 (4)
Cd1—O4^i	2.295 (2)	C6—C7	1.383 (4)
Cd1—N1	2.328 (2)	C7—C8	1.388 (5)
Cd1—O1W	2.336 (3)	C7—H7	0.9300
Cd1—N2	2.342 (2)	C8—C9	1.357 (6)
Cd1—O3^i	2.513 (2)	C8—H8	0.9300
O1—C11	1.264 (4)	C9—C10	1.372 (5)
O2—C11	1.225 (4)	C9—H9	0.9300
O3—C20	1.242 (4)	C10—H10	0.9300
O3—Cd1^ii	2.513 (2)	C11—C12	1.512 (4)
O4—C20	1.256 (4)	C12—O5	1.417 (4)
O4—Cd1^ii	2.295 (2)	C12—H12A	0.9700
O1W—H1A	0.89 (4)	C12—H12B	0.9700
O1W—H1B	0.76 (4)	O5—C14	1.366 (3)
N1—C1	1.335 (4)	C14—C19	1.367 (4)
N1—C5	1.336 (4)	C14—C15	1.384 (4)
N2—C10	1.337 (4)	C15—C16	1.387 (4)
N2—C6	1.347 (4)	C15—H15	0.9300
C1—C2	1.376 (5)	C16—C17	1.378 (5)
C1—H1	0.9300	C16—H16	0.9300
C2—C3	1.369 (5)	C17—C18	1.383 (4)
C2—H2	0.9300	C17—C20	1.503 (4)
C3—C4	1.370 (5)	C18—C19	1.369 (4)
C3—H3	0.9300	C18—H18	0.9300
C4—C5	1.392 (4)	C19—H19	0.9300
C4—H4	0.9300	C20—Cd1^ii	2.739 (3)
O1—Cd1—O4^i	99.5 (1)	C6—C7—H7	120.5
O1—Cd1—N1	99.8 (1)	C8—C7—H7	120.5
O4^i—Cd1—N1	159.4 (1)	C9—C8—C7	119.7 (3)
O1—Cd1—O1W	88.7 (1)	C9—C8—H8	120.1
O4^i—Cd1—O1W	94.7 (1)	C7—C8—H8	120.1
N1—Cd1—O1W	92.86 (10)	C8—C9—C10	118.5 (3)
O1—Cd1—N2	169.70 (9)	C8—C9—H9	120.7
O4^i—Cd1—N2	90.05 (8)	C10—C9—H9	120.7
N1—Cd1—N2	70.25 (9)	N2—C10—C9	123.1 (3)
O1W—Cd1—N2	94.43 (9)	N2—C10—H10	118.5
O1—Cd1—O3^i	96.09 (8)	C9—C10—H10	118.5
O4^i—Cd1—O3^i	54.03 (7)	O2—C11—O1	125.9 (3)
N1—Cd1—O3^i	116.52 (9)	O2—C11—C12	120.4 (3)
O1W—Cd1—O3^i	148.72 (9)	O1—C11—C12	113.8 (3)
N2—Cd1—O3^i	86.33 (8)	O5—C12—C11	114.2 (3)
C11—O1—Cd1	112.4 (2)	O5—C12—H12A	108.7
C20—O3—Cd1^ii	86.72 (19)	C11—C12—H12A	108.7
C20—O4—Cd1^ii	96.54 (18)	O5—C12—H12B	108.7
Cd1—O1W—H1A	127 (2)	C11—C12—H12B	108.7
Cd1—O1W—H1B	130 (3)	H12A—C12—H12B	107.6
H1A—O1W—H1B	99 (4)	C14—O5—C12	120.1 (2)
C1—N1—C5	118.7 (3)	O5—C14—C19	114.8 (3)
C1—N1—Cd1	122.8 (2)	O5—C14—C15	125.5 (3)
C5—N1—Cd1	118.47 (19)	C19—C14—C15	119.7 (3)
C10—N2—C6	118.6 (3)	C14—C15—C16	119.1 (3)
C10—N2—Cd1	123.2 (2)	C14—C15—H15	120.4
C6—N2—Cd1	117.82 (19)	C16—C15—H15	120.4
N1—C1—C2	123.2 (3)	C17—C16—C15	121.7 (3)
N1—C1—H1	118.4	C17—C16—H16	119.1
C2—C1—H1	118.4	C15—C16—H16	119.1
C3—C2—C1	117.9 (3)	C16—C17—C18	117.4 (3)
C3—C2—H2	121.0	C16—C17—C20	122.3 (3)
C1—C2—H2	121.0	C18—C17—C20	120.3 (3)
C2—C3—C4	119.8 (3)	C19—C18—C17	121.7 (3)
C2—C3—H3	120.1	C19—C18—H18	119.1
C4—C3—H3	120.1	C17—C18—H18	119.1
C3—C4—C5	119.3 (3)	C14—C19—C18	120.3 (3)
C3—C4—H4	120.4	C14—C19—H19	119.8
C5—C4—H4	120.4	C18—C19—H19	119.8
N1—C5—C4	121.0 (3)	O3—C20—O4	122.7 (3)
N1—C5—C6	116.8 (2)	O3—C20—C17	119.6 (3)
C4—C5—C6	122.2 (3)	O4—C20—C17	117.7 (3)
N2—C6—C7	121.1 (3)	O3—C20—Cd1^ii	66.36 (16)
N2—C6—C5	116.1 (3)	O4—C20—Cd1^ii	56.35 (15)
C7—C6—C5	122.8 (3)	C17—C20—Cd1^ii	173.9 (2)
C6—C7—C8	119.0 (3)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1W—H1A···O3^iii	0.89 (4)	1.92 (4)	2.773 (3)	161 (3)
O1W—H1B···O2^iv	0.76 (4)	2.09 (4)	2.787 (4)	154 (4)

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