catena-Poly[[[diaqua­bis(pyridine-4-carboxamide-[kappa]N)copper(II)]-[mu]₂-squarato-[kappa]O¹:O³] dihydrate]

The asymmetric unit of the title compound, {[Cu(C₄O₄)(C₆H₆N₂O)₂(H₂O)₂]·2H₂O}_n, consists of one pyridine-4-carbox­amide (isonicotinamide or ina) ligand, one-half of a squarate dianion, a coordinated aqua ligand and a solvent water mol­ecule. Both the Cu^II and the squarate ions are located on inversion centers. The Cu^II ions are octa­hedrally surrounded by four O atoms of two water mol­ecules and two squarate anions, and by two N atoms of the isonicotinamide ligands. The crystal structure contains chains of squarate-1,3-bridged Cu^II ions. These chains are held together by N-H...O and O-H...O inter­molecular hydrogen-bond inter­actions, forming an extensive three-dimensional network.

S1. Comment

The coordination chemistry of the squarate anion has attracted increasing attention because it gives rise to a wide variety of complexes and adopts mono- or polydentate coordination modes when acting as a ligand towards first row transition metal ions. The squarate anion does not behave like a chelating ligand but rather like a bridge between two or more metal atoms, ??as a singly or multiply monodentate ligand (Bernardinelli et al., 1989; Castro et al., 1999; Crispini et al., 2000). In all the cases described so far, each coordination site of squaric acid is coordinated to a different metal atom and either a one-dimensional chain or three-dimensional polymers are obtained (Hilberts et al., 1996; Greve & Nather, 2002; Greve et al., 2003). The exchange interactions in such polymer complexes, between transition-metal ions through extended bridging squarate groups, have been studied by both inorganic and bioinorganic chemists in recent years (Van Ooijen et al., 1978; Reinprecht et al., 1980; Yufit et al., 1999; Trombe et al., 2002). We have also used isonicotinamide as a second ligand; this pyridine derivate with an amide group (–CONH₂) in the γ-position possesses strong antitubercular, antipyretic, fibrinolytic and antibacterial properties. Because of their strong pharmacological effects, mixed salts of isonicotinamide find extensive use as drugs in various biological and medicinal processes (Ahuja & Prasad, 1976). Isonicotinamide is also of interest in inorganic chemistry, since the ligand has three donor sites, viz. (i) the pyridine ring N atom, as in the title complex, (ii) the amine N atom and (iii) the carbonyl O atom, acting as a monodentate ligand. To our knowledge, there are only a few reports of the complexes of this ligand with transition metals(II) (Baum et al., 2002). Despite of the structural and magnetic interest, only a few crystal structures containing copper(II) squarate and geometrically demanding N-atom donor ligands have been investigated (Solans et al., 1990; Graf et al., 1997; Bernardinelli et al., 1989). In our ongoing research on squaric acid, we have synthesized some mixed ligand-copper(II) complexes of squaric acid and their structures have been reported. In these compounds, squaric acid behaves as a counter-anion or monodendate ligand (Uçar et al., 2004; Bulut et al., 2004), while in the title compound, (I), it acts as a bridging ligand between the copper(II) ions.

The coordination polyhedron of copper in (I) is best described as a distorted octahedron (Fig. 1). Each Cu atom is trans-connected to two molecules of ina [Cu1—N1 = 2.0029 (14) Å], two aqua ligands [Cu1—O4 = 2.4698 (18) Å] and two squarate O atoms [Cu1—O1 = 1.9921 (11) Å]. In the title complex there are also two solvent water molecules. The metal atoms are connected by the squarate dianions via µ-O,O coordination, forming `zigzag' chains in the direction of the crystallographic b axis (Fig 2). Only one O atom of each squarate dianion is involved in metal coordination, and the mode of? direct coordination in which two neighboring O atoms are involved is not found. The Cu atoms are located nearly in the molecular plane of the squarate dianions and are oriented in the direction of the oxygen lone pair.

In the title complex, the Cu1—O1 bond is considerably shorter than the Cu1—O4 bond because of the electronegative character of the C₄O₄²⁻ ligand. The Cu1—O1 bond distance is nearly identical to that observed in [Cu₂(C₄O₄)(phen)₄](CF₃SO₃)₂·3H₂O (1.995 (7) Å; Castro et al., 1999), whereas this distance is longer that in [Cu(C₄O₄)(phen)(H₂O)₂]·2H₂O [1.967 (2) Å; phen is 1,10-phenanthroline; Solans et al., 1990]. This difference is clearly due to the fact that the squarate ligand is coordinated to the Cu atom in a monodentate fashion (Solans et al., 1990; Bulut et al., 2004) and therefore most of the negative charge is located on the coordinated O atom.

The squarate dianion is planar, with an r.m.s. deviation of 0.0048 Å, and the largest deviation from the mean plane is 0.0079 (14) Å for atom O??. The dihedral angle between the copper equatorial plane and the squarate plane is 36.86 (8)°. The pyridine ring of the isonicotinamide ligand is essentially planar (the r.m.s. deviation is 0.0087 Å) and the largest deviation from the mean plane is −0.0125 Å for atom C1. The dihedral angle between the pyridine ring and the squarate mean plane is 59.45 (5)°, while that between the pyridine and copper equatorial plane is 85.12 (5)°.

In the extended structure, the NH₂ and CO groups of the ina ligand, the aqua ligand and the solvent water molecule, and the uncoordinated squarate O atoms are involved in interchain hydrogen bonding; the polymer chains are connected by interchain N2—H2A···O5(3/2 − x, 1/2 + y, 1/2 − z), N2—H2B···O4(1/2 + x, 3/2 − y, −1/2 + z), O5—H5A···O3(1 − x, 1 − y, −z), and O5—H5B···O2(x, y, z) interactions (Fig. 2). These interactions are also effective in forming a layered structure, and the geometry of the interactions is given in Table 2. The shortest interchain Cu1···Cu1(−x + 1/2,+y − 1/2,-z + 1/2) distance is 7.4251 (6) Å, whereas the the intrachain Cu1···Cu1(x, −1 + y, z) distance is 7.7824 (7) Å.

S2. Experimental

Squaric acid (0.57 g, 5 mmol) dissolved in water (25 ml) was neutralized with NaOH (0.40 g, 10 mmol) and was added to a hot solution of CuCl₂·H₂O (0.77 g, 5 mmol) dissolved in water (50 ml). The mixture was stirred at 333 K for 12 h and then cooled to room temperature. The yellow crystals which formed were filtered and washed with water and alcohol and dried in a vacuum. A solution of isonicotinamide (0.24 g, 2 mmol) in methanol (50 ml) was added dropwise with stirring to a suspension of the CuSq·2H₂O (0.21 g, 1 mmol) in water (50 ml). The green solution was refluxed for about 2 h and then cooled to room temperature. A few days later, well formed dark-green crystals were selected for X-ray studies.

S3. Refinement

H atoms attached to C atoms were placed at calculated positions (C—H = 0.93 Å) and were allowed to ride on the parent atom [U_iso(H) = 1.2U_eq(C)]. The remaining H atoms were located in a difference map and their parameters were refined.

Computing details

Data collection: X-AREA (Stoe & Cie, 2002); cell refinement: X-AREA; data reduction: X-RED32 (Stoe & Cie, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. : The molecular structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii. [Symmetry code: (vi) 1 − x, 1 − y, 1 − z; (vii) 1 − x, −y, 1 − z; (viii) x, −1 + y, z.]
	Fig. 2. : The zigzag chain structure of the copper(II) complex, with intra- and interchain interactions shown as dashed lines.

catena-Poly[[[diaquabis(pyridine-4-carboxamide-κN)copper(II)]-µ₂-squarato- κO¹:O³] dihydrate]

Crystal data

[Cu(C4O4)(C6H6N2O)2(H2O)2]·2H2O	F(000) = 506
Mr = 491.91	Dx = 1.641 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 5487 reflections
a = 11.3221 (9) Å	θ = 1.8–27.9°
b = 7.7824 (4) Å	µ = 1.16 mm^−1
c = 12.6314 (11) Å	T = 297 K
β = 116.535 (6)°	Prism, dark green
V = 995.75 (13) Å^3	0.23 × 0.21 × 0.16 mm
Z = 2

Data collection

Stoe IPDS-II diffractometer	2363 independent reflections
Radiation source: fine-focus sealed tube	1755 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.058
Detector resolution: 6.67 pixels mm^-1	θmax = 27.8°, θmin = 2.0°
ω scans	h = −14→14
Absorption correction: integration (X-RED32; Stoe & Cie, 2002)	k = −10→10
Tmin = 0.768, Tmax = 0.843	l = −16→16
11948 measured reflections

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)] = 0.027	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.061	w = 1/[σ^2(Fo^2) + (0.0355P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.89	(Δ/σ)max < 0.001
2363 reflections	Δρmax = 0.44 e Å^−3
167 parameters	Δρmin = −0.47 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.089 (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	0.4564 (2)	0.5245 (2)	0.25617 (16)	0.0272 (4)
H1	0.3831	0.4579	0.2439	0.033*
C2	0.4706 (2)	0.5804 (2)	0.15966 (17)	0.0309 (4)
H2	0.4067	0.5546	0.0836	0.037*
C3	0.5804 (2)	0.6752 (2)	0.17621 (17)	0.0279 (4)
C4	0.6728 (2)	0.7101 (2)	0.29081 (17)	0.0303 (4)
H4	0.7489	0.7716	0.3051	0.036*
C5	0.6507 (2)	0.6525 (2)	0.38355 (17)	0.0263 (4)
H5	0.7126	0.6777	0.4604	0.032*
C6	0.5888 (2)	0.7436 (3)	0.06805 (19)	0.0360 (5)
C7	0.47616 (18)	0.1230 (2)	0.46798 (14)	0.0192 (4)
C8	0.4363 (2)	−0.0480 (2)	0.41775 (16)	0.0217 (4)
N1	0.54326 (16)	0.56161 (18)	0.36733 (13)	0.0217 (3)
N2	0.7076 (2)	0.7584 (3)	0.0742 (2)	0.0445 (5)
O1	0.44275 (14)	0.27051 (14)	0.42443 (11)	0.0251 (3)
O2	0.35895 (16)	−0.10482 (15)	0.31830 (11)	0.0349 (4)
O3	0.48704 (19)	0.7781 (3)	−0.01906 (14)	0.0564 (5)
O4	0.27134 (16)	0.60109 (19)	0.38144 (13)	0.0313 (3)
O5	0.5605 (2)	0.1112 (3)	0.23878 (18)	0.0593 (6)
Cu1	0.5000	0.5000	0.5000	0.01912 (11)
H2A	0.774 (3)	0.719 (3)	0.131 (3)	0.041 (7)*
H2B	0.720 (3)	0.792 (3)	0.019 (3)	0.053 (8)*
H4A	0.286 (3)	0.691 (4)	0.347 (3)	0.059 (8)*
H4B	0.235 (3)	0.545 (3)	0.332 (2)	0.041 (8)*
H5A	0.540 (4)	0.141 (5)	0.176 (4)	0.094 (14)*
H5B	0.511 (5)	0.046 (6)	0.243 (4)	0.13 (2)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0293 (10)	0.0270 (10)	0.0267 (9)	−0.0071 (7)	0.0138 (8)	−0.0035 (7)
C2	0.0334 (12)	0.0356 (10)	0.0220 (9)	−0.0056 (9)	0.0107 (9)	−0.0035 (8)
C3	0.0319 (12)	0.0308 (9)	0.0239 (9)	−0.0008 (8)	0.0151 (9)	0.0032 (7)
C4	0.0278 (12)	0.0356 (10)	0.0282 (10)	−0.0074 (8)	0.0132 (9)	0.0011 (8)
C5	0.0254 (11)	0.0295 (9)	0.0229 (9)	−0.0031 (7)	0.0098 (9)	0.0000 (7)
C6	0.0452 (14)	0.0392 (10)	0.0269 (10)	−0.0059 (10)	0.0192 (11)	0.0032 (8)
C7	0.0239 (10)	0.0146 (6)	0.0181 (8)	−0.0006 (6)	0.0084 (8)	−0.0004 (6)
C8	0.0278 (11)	0.0134 (7)	0.0225 (8)	0.0011 (6)	0.0099 (8)	0.0009 (6)
N1	0.0257 (9)	0.0192 (6)	0.0217 (7)	−0.0009 (6)	0.0119 (7)	0.0002 (5)
N2	0.0454 (14)	0.0639 (13)	0.0304 (10)	−0.0112 (11)	0.0224 (11)	0.0077 (10)
O1	0.0363 (8)	0.0130 (5)	0.0216 (6)	0.0007 (5)	0.0089 (6)	0.0017 (4)
O2	0.0451 (10)	0.0201 (6)	0.0220 (7)	0.0007 (6)	−0.0007 (7)	−0.0019 (5)
O3	0.0479 (12)	0.0880 (13)	0.0295 (10)	0.0005 (10)	0.0138 (10)	0.0216 (8)
O4	0.0364 (9)	0.0303 (8)	0.0253 (7)	−0.0024 (6)	0.0121 (7)	−0.0047 (6)
O5	0.0511 (13)	0.0868 (15)	0.0392 (11)	−0.0052 (11)	0.0192 (10)	0.0172 (10)
Cu1	0.02873 (19)	0.01169 (13)	0.01919 (15)	−0.00055 (14)	0.01272 (13)	0.00038 (13)

Geometric parameters (Å, º)

C1—N1	1.337 (2)	C7—O1	1.256 (2)
C1—C2	1.370 (2)	C7—C8	1.456 (2)
C1—H1	0.9300	C8—O2	1.248 (2)
C2—C3	1.379 (3)	N1—Cu1	2.0029 (14)
C2—H2	0.9300	N2—H2A	0.83 (3)
C3—C4	1.382 (3)	N2—H2B	0.81 (3)
C3—C6	1.508 (3)	O1—Cu1	1.9921 (11)
C4—C5	1.378 (3)	O4—H4A	0.88 (3)
C4—H4	0.9300	O4—H4B	0.72 (3)
C5—N1	1.341 (2)	O4—Cu1	2.4698 (18)
C5—H5	0.9300	O5—H5A	0.76 (4)
C6—O3	1.216 (3)	O5—H5B	0.78 (5)
C6—N2	1.317 (3)
N1—C1—C2	122.80 (17)	O3—C6—C3	118.7 (2)
N1—C1—H1	118.6	N2—C6—C3	117.0 (2)
C2—C1—H1	118.6	O1—C7—C8	132.07 (17)
C1—C2—C3	119.44 (18)	O2—C8—C7	134.75 (17)
C1—C2—H2	120.3	C1—N1—C5	117.78 (15)
C3—C2—H2	120.3	C1—N1—Cu1	119.11 (13)
C2—C3—C4	118.23 (17)	C5—N1—Cu1	122.85 (12)
C2—C3—C6	117.97 (18)	C6—N2—H2A	121.8 (17)
C4—C3—C6	123.70 (18)	C6—N2—H2B	123 (2)
C5—C4—C3	119.12 (18)	H2A—N2—H2B	115 (3)
C5—C4—H4	120.4	C7—O1—Cu1	129.77 (12)
C3—C4—H4	120.4	H4A—O4—H4B	102 (3)
N1—C5—C4	122.58 (18)	H5A—O5—H5B	113 (5)
N1—C5—H5	118.7	O1—Cu1—N1	87.85 (5)
C4—C5—H5	118.7	O1—Cu1—O4	88.08 (6)
O3—C6—N2	124.4 (2)	O4—Cu1—N1	89.90 (6)
N1—C1—C2—C3	1.8 (3)	O1—C7—C8—O2	0.4 (4)
C1—C2—C3—C4	0.1 (3)	C2—C1—N1—C5	−2.4 (3)
C1—C2—C3—C6	−176.40 (18)	C2—C1—N1—Cu1	171.84 (15)
C2—C3—C4—C5	−1.4 (3)	C4—C5—N1—C1	1.0 (3)
C6—C3—C4—C5	174.92 (19)	C4—C5—N1—Cu1	−172.96 (14)
C3—C4—C5—N1	0.8 (3)	C8—C7—O1—Cu1	178.91 (14)
C2—C3—C6—O3	30.2 (3)	C7—O1—Cu1—N1	127.80 (16)
C4—C3—C6—O3	−146.1 (2)	C1—N1—Cu1—O1	45.88 (14)
C2—C3—C6—N2	−148.5 (2)	C5—N1—Cu1—O1	−140.23 (15)
C4—C3—C6—N2	35.2 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2A···O5^i	0.83 (3)	2.04 (3)	2.871 (3)	176 (2)
N2—H2B···O4^ii	0.81 (3)	2.23 (3)	3.036 (2)	174 (3)
O4—H4A···O2^iii	0.88 (3)	1.90 (3)	2.750 (2)	163 (3)
O4—H4B···O2^iv	0.72 (3)	2.07 (3)	2.790 (2)	175 (3)
O5—H5A···O3^v	0.76 (4)	1.97 (4)	2.720 (3)	172 (4)
O5—H5B···O2	0.78 (5)	2.59 (5)	3.330 (3)	160 (5)

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