A novel copper(II) coordination polymer with 2,2'-bipyridyl-3,3'-di­carboxylic acid

A novel copper(II) coordination polymer, poly­[[[aqua­copper(II)]-[mu]₃-2,2'-bipyridyl-3,3'-di­carboxyl­ato-[kappa]⁴N,N':O:O'] dihydrate], {[Cu(C₁₂H₆N₂O₄)(H₂O)]·2H₂O}_n, was obtained by the reaction of CuCl₂·2H₂O and 2,2'-bipyridyl-3,3'-di­carboxylic acid (H₂L) in water. In the mol­ecule, each Cu^II atom is five-coordinated and lies at the centre of a square-pyramidal basal plane, bridged by three L ligands to form a two-dimensional (4,4)-network. Each L moiety acts as a bridging tetradentate ligand, coordinating to three Cu^II atoms through its two aromatic N atoms and two O atoms of the two carboxyl groups. The two-dimensional square-grid sheets superimpose in an off-set fashion through the inorganic water layer.

S1. Comment

In recent years, research on coordination polymers has been rapidly expanding, because of their fascinating structural diversity and potential application as functional materials (Batten & Robson, 1998; Moulton & Zaworotko, 2001). To date, a number of one-, two- and three-dimensional infinite frameworks have been generated with linear N,N'-bidentate spacers (Tong et al., 2002). Much of the work has so far been focused on coordination polymers with rigid ligands, such as 4,4'-bipyridine, and pyrazine and its analogues. However, flexible ligands such as 2,2'-bipyridyl-3,3'-dicarboxylic acid (H₂L) have not been explored as much and only a few examples have been reported to date (Goddard et al., 1990; Kovalev et al., 1989; Memon et al., 1997; Perkovic, 2000; Xie et al., 1999, 2000; Yoo et al., 1997; Zhang et al., 2002, 2003; Zhong et al., 1994). In these known structures based on the 2,2'-bipyridyl-3,3'-dicarboxylate anion, most are one-dimensional polymeric chains, such as [M(C₁₂H₆N₂O₄)(H₂O)₂]_n (M is Co, Cu or Mn) and {[Ni(C₁₂H₆N₂O₄)(H₂O)₃]·H₂O}_n. These one-dimensional chains extend into two-dimensional sheets via O···H—O hydrogen-bonding interactions. Two- or three-dimensional structures of this type based on covalent linkages are rare. In the present work, we report the preparation and crystal structure of the title novel two-dimensional coordination polymer, (I), formulated as {[CuL(H₂O)]·2H₂O}_n. \sch

Single-crystal X-ray diffraction reveals that the molecules of (I) form an extended two-dimensional network involving coordination frameworks of (4,4) topology. In these layers, all metal centres are five-coordinated. As shown in Fig. 1, each Cu^II atom is coordinated by two N atoms of an L ligand, two O atoms of two carboxyl groups from another two L ligands and one O atom of a water molecule, to give a square-pyramidal geometry (Table 1). An additional carboxyl O atom occupies the sixth coordination site at a distance [Cu1···O1 3.060 (1) Å] which is beyond the sum of the van der Waals radii of Cu and O (1.40 Å for Cu and 1.52 Å for O) and which is therefore too long to be considered a significant interaction.

Each L moiety, acting as a tetradentate ligand, coordinates to three Cu^II atoms. As a result, three Cu^II centres are bridged by three L ligands to form a grid (Fig. 2). Within this grid, the Cu···Cu distances are 6.767 (5), 6.908 (5) and 6.967 (1) Å. One Cu atom with one organic ligand constructs a node and these nodes connect to each other to form an extended layer structure with (4,4) topology in the ac plane. As illustrated in Fig. 3, the water molecules occupy channels formed by parallel stacking of two layers.

There are a number of significant contacts between the oxo groups of the two-dimensional layers and the water molecules. These include OW5···O4 2.819 (5), OW6···O1 2.769 (4), OW7···O2 2.915 (5), OW7···O4 2.971 (4) and Ow7···O7 2.800 (6) Å. Therefore, the extended structure of (I) has the metal-organic layers and the inorganic water layers arranged alternately along the b axis.

S2. Experimental

A mixture of CuCl₂·2H₂O (0.168 g, 1 mmol) and H₂L (0.244 g, 1 mmol) in water (30 ml) was refluxed for 20 min then filtered while hot. Dark-green crystals of (I) were obtained by evaporating the filtrate at room temperature for three weeks. The compound is insoluble in common organic solvents, and dissolves in water very slowly. Analysis found: C 40.1, H 3.2, N 8.0%; C₁₂H₁₂N₂O₇Cu requires: C 40.0, H 3.3, N 7.8%.

S3. Refinement

All H atoms on C atoms were generated geometrically and refined as riding atoms, with C—H = 0.93 Å and U_iso(H) = 1.2U_eq(C). The H atoms of the two solvate water molecules and the water ligand could not be located from the electron-density difference map, which may be ascribed to two factors, firstly that there are heavy metallic atoms (Cu) in the crystal structure, and secondly that the H atoms of the two solvate water molecules and the water ligand may be disordered.

Computing details

Data collection: PROCESS-AUTO (Rigaku, 1998); cell refinement: PROCESS-AUTO; data reduction: PROCESS-AUTO; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL-Plus (Sheldrick, 1990).

Figures

	Fig. 1. A view of the local coordination of the Cu^II atom in (I), with the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) x − 1/2, 1/2 − y, 1/2 + z; (ii) 1/2 + x, 1/2 − y, 1/2 + z.]
	Fig. 2. The two-dimensional single-layer (4,4) network in (I). Water molecules have been omitted for clarity.
	Fig. 3. A view perpendicular to the two-dimensional sheets, showing the stacking of these layers in the b direction. Hydrogen-bonding contacts are shown by dashed lines.

poly[[aquacopper(II)]-µ₃-2,2'-bipyridyl-3,3'-dicarboxylato-κ⁴N,N':O:O' dihydrate]

Crystal data

[Cu(C12H6N2O4)(H2O)]·2H2O	F(000) = 732
Mr = 359.78	Dx = 1.861 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 6.7680 (9) Å	Cell parameters from 6856 reflections
b = 19.989 (3) Å	θ = 3.2–25.5°
c = 9.4923 (12) Å	µ = 1.77 mm^−1
β = 90.717 (2)°	T = 293 K
V = 1284.0 (3) Å^3	Prism, dark green
Z = 4	0.24 × 0.23 × 0.11 mm

Data collection

Rigaku R-AXIS RAPID area-detector diffractometer	2498 independent reflections
Radiation source: fine-focus sealed tube	1871 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.045
Detector resolution: 10.0 pixels mm^-1	θmax = 26.0°, θmin = 3.2°
ω scans	h = −8→7
Absorption correction: multi-scan (ABSCOR; Higashi, 1995)	k = −24→20
Tmin = 0.628, Tmax = 0.812	l = −11→11
7065 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)] = 0.039	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.094	H-atom parameters constrained
S = 0.95	w = 1/[σ^2(Fo^2) + (0.048P)^2] where P = (Fo^2 + 2Fc^2)/3
2498 reflections	(Δ/σ)max = 0.001
199 parameters	Δρmax = 0.47 e Å^−3
0 restraints	Δρmin = −0.31 e Å^−3

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
C1	0.4347 (5)	0.37862 (16)	0.3719 (3)	0.0293 (8)
H1	0.4442	0.4227	0.4025	0.035*
C2	0.4380 (5)	0.36570 (17)	0.2292 (4)	0.0304 (8)
H2	0.4600	0.3998	0.1645	0.036*
C3	0.4075 (5)	0.30097 (17)	0.1857 (3)	0.0277 (8)
H3	0.4035	0.2914	0.0898	0.033*
C4	0.3828 (5)	0.25003 (16)	0.2807 (3)	0.0224 (7)
C5	0.4032 (4)	0.26532 (15)	0.4243 (3)	0.0190 (7)
C6	0.4162 (4)	0.21691 (15)	0.5433 (3)	0.0194 (7)
C7	0.4811 (4)	0.15095 (14)	0.5354 (3)	0.0197 (7)
C8	0.4707 (5)	0.11145 (16)	0.6558 (3)	0.0272 (8)
H8	0.4991	0.0660	0.6507	0.033*
C9	0.4184 (5)	0.13941 (16)	0.7821 (3)	0.0281 (8)
H9	0.4119	0.1134	0.8632	0.034*
C10	0.3757 (5)	0.20679 (16)	0.7863 (3)	0.0263 (7)
H10	0.3512	0.2268	0.8728	0.032*
C11	0.3162 (5)	0.18230 (18)	0.2237 (4)	0.0302 (8)
C12	0.5904 (5)	0.12067 (16)	0.4126 (3)	0.0248 (7)
Cu1	0.34847 (6)	0.344115 (19)	0.67357 (4)	0.02614 (15)
O1	0.4024 (5)	0.16084 (13)	0.1177 (3)	0.0509 (7)
N2	0.3685 (4)	0.24435 (12)	0.6690 (3)	0.0204 (6)
O2	0.1714 (4)	0.15582 (12)	0.2837 (3)	0.0393 (6)
O3	0.7141 (3)	0.16050 (10)	0.3558 (2)	0.0249 (5)
N1	0.4184 (4)	0.32980 (12)	0.4680 (3)	0.0227 (6)
O4	0.5636 (4)	0.06164 (12)	0.3844 (3)	0.0453 (7)
O5W	0.3439 (5)	0.44308 (14)	0.6675 (3)	0.0611 (9)
O6W	0.8128 (5)	0.47346 (15)	0.5847 (3)	0.0671 (9)
O7W	0.6416 (5)	0.47782 (19)	0.9044 (5)	0.0927 (13)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.037 (2)	0.0206 (18)	0.0301 (19)	0.0020 (15)	0.0042 (16)	0.0053 (15)
C2	0.038 (2)	0.0268 (19)	0.0267 (18)	0.0036 (15)	0.0037 (16)	0.0106 (15)
C3	0.0268 (19)	0.036 (2)	0.0198 (16)	0.0058 (15)	−0.0026 (14)	0.0030 (14)
C4	0.0193 (17)	0.0262 (17)	0.0216 (16)	0.0035 (13)	−0.0013 (14)	−0.0008 (14)
C5	0.0171 (16)	0.0212 (17)	0.0187 (15)	0.0011 (12)	0.0013 (13)	−0.0013 (13)
C6	0.0165 (16)	0.0209 (17)	0.0208 (16)	−0.0038 (12)	0.0005 (13)	−0.0005 (13)
C7	0.0187 (17)	0.0183 (16)	0.0222 (16)	−0.0033 (12)	0.0019 (13)	0.0006 (13)
C8	0.0272 (19)	0.0222 (18)	0.0323 (19)	0.0026 (14)	0.0020 (15)	0.0029 (14)
C9	0.033 (2)	0.030 (2)	0.0216 (17)	0.0003 (14)	0.0012 (15)	0.0080 (14)
C10	0.0304 (19)	0.0305 (19)	0.0179 (16)	0.0013 (15)	0.0020 (14)	−0.0004 (14)
C11	0.037 (2)	0.0306 (19)	0.0231 (18)	0.0018 (16)	−0.0093 (16)	0.0008 (15)
C12	0.032 (2)	0.0199 (18)	0.0229 (17)	0.0004 (14)	0.0001 (15)	0.0013 (14)
Cu1	0.0377 (3)	0.0196 (2)	0.0213 (2)	−0.00045 (18)	0.00766 (17)	−0.00103 (17)
O1	0.085 (2)	0.0390 (16)	0.0286 (14)	−0.0057 (14)	0.0101 (14)	−0.0126 (12)
N2	0.0241 (15)	0.0200 (14)	0.0170 (13)	−0.0021 (10)	0.0035 (11)	−0.0001 (11)
O2	0.0378 (16)	0.0362 (15)	0.0438 (15)	−0.0078 (12)	−0.0089 (13)	−0.0001 (12)
O3	0.0290 (13)	0.0247 (13)	0.0214 (11)	−0.0011 (10)	0.0077 (10)	0.0008 (9)
N1	0.0256 (15)	0.0199 (15)	0.0227 (14)	0.0008 (11)	0.0015 (12)	0.0009 (11)
O4	0.0642 (19)	0.0232 (14)	0.0492 (16)	−0.0074 (12)	0.0283 (15)	−0.0057 (12)
O5W	0.087 (2)	0.0387 (17)	0.0580 (19)	−0.0001 (15)	0.0238 (17)	−0.0012 (14)
O6W	0.085 (2)	0.052 (2)	0.064 (2)	0.0123 (17)	−0.0070 (18)	0.0086 (16)
O7W	0.067 (3)	0.079 (3)	0.131 (3)	0.0248 (19)	−0.016 (2)	−0.044 (2)

Geometric parameters (Å, º)

C1—N1	1.341 (4)	C8—H8	0.9300
C1—C2	1.379 (5)	C9—C10	1.378 (4)
C1—H1	0.9300	C9—H9	0.9300
C2—C3	1.373 (5)	C10—N2	1.344 (4)
C2—H2	0.9300	C10—H10	0.9300
C3—C4	1.372 (4)	C11—O1	1.246 (4)
C3—H3	0.9300	C11—O2	1.256 (4)
C4—C5	1.402 (4)	C12—O4	1.223 (4)
C4—C11	1.524 (5)	C12—O3	1.280 (4)
C5—N1	1.357 (4)	Cu1—O3^i	1.966 (2)
C5—C6	1.489 (4)	Cu1—O5W	1.979 (3)
C6—N2	1.355 (4)	Cu1—N2	1.999 (3)
C6—C7	1.392 (4)	Cu1—N1	2.034 (3)
C7—C8	1.392 (4)	Cu1—O2^ii	2.411 (2)
C7—C12	1.514 (4)	O2—Cu1^iii	2.411 (2)
C8—C9	1.373 (4)	O3—Cu1^iv	1.966 (2)
N1—C1—C2	122.3 (3)	N2—C10—C9	121.8 (3)
N1—C1—H1	118.9	N2—C10—H10	119.1
C2—C1—H1	118.9	C9—C10—H10	119.1
C3—C2—C1	117.9 (3)	O1—C11—O2	126.6 (3)
C3—C2—H2	121.1	O1—C11—C4	117.0 (3)
C1—C2—H2	121.1	O2—C11—C4	116.3 (3)
C4—C3—C2	121.4 (3)	O4—C12—O3	127.1 (3)
C4—C3—H3	119.3	O4—C12—C7	118.8 (3)
C2—C3—H3	119.3	O3—C12—C7	113.9 (3)
C3—C4—C5	117.8 (3)	O3^i—Cu1—O5W	93.74 (10)
C3—C4—C11	117.6 (3)	O3^i—Cu1—N2	90.27 (9)
C5—C4—C11	124.3 (3)	O5W—Cu1—N2	175.79 (11)
N1—C5—C4	120.7 (3)	O3^i—Cu1—N1	162.38 (10)
N1—C5—C6	112.5 (2)	O5W—Cu1—N1	96.68 (11)
C4—C5—C6	126.9 (3)	N2—Cu1—N1	79.75 (10)
N2—C6—C7	120.6 (3)	O3^i—Cu1—O2^ii	92.60 (9)
N2—C6—C5	113.1 (3)	O5W—Cu1—O2^ii	91.49 (11)
C7—C6—C5	126.2 (3)	N2—Cu1—O2^ii	87.05 (9)
C8—C7—C6	118.3 (3)	N1—Cu1—O2^ii	101.27 (10)
C8—C7—C12	115.8 (3)	C10—N2—C6	119.8 (3)
C6—C7—C12	125.3 (3)	C10—N2—Cu1	122.8 (2)
C9—C8—C7	120.2 (3)	C6—N2—Cu1	116.09 (19)
C9—C8—H8	119.9	C11—O2—Cu1^iii	120.7 (2)
C7—C8—H8	119.9	C12—O3—Cu1^iv	130.8 (2)
C8—C9—C10	118.6 (3)	C1—N1—C5	119.3 (3)
C8—C9—H9	120.7	C1—N1—Cu1	124.9 (2)
C10—C9—H9	120.7	C5—N1—Cu1	114.13 (19)

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