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In the title compound, [Cu(C6H4NO3)2(H2O)2], the CuII ion lies on an inversion centre and has an elongated octahedral environment, equatorially trans-coordinated by two N,O-bidentate picolinate ligands and axially coordinated by two water O atoms. The complex mol­ecules form layers, which are linked by O—H...O hydrogen bonds between the aqua ligands and neighbouring carboxyl­ate groups. An intramolecular hydrogen bond between the coordinated carboxyl­ate O atom and the hydroxy H atom is also observed.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270104031178/jz1676sup1.cif
Contains datablocks global, (I)

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270104031178/jz1676Isup2.hkl
Contains datablock I

CCDC reference: 268077

Comment top

Copper complexes play an important role in catalyzing enzymatic activity, and much attention has been paid to copper complexes of organic acids because of their special biocatalytic functions (Hong et al., 2002). Recently, considerable attention has been paid to the complexes of hydroxypicolinates, which pose structural ambiguities since they display a number of possible bonding modes (Constantino et al., 1994; Gatto et al., 1998). It is well known that the incorporation of carboxylic acid groups into coordination compounds gives interesting supramolecular architectures (Puddephatt et al., 2002). The 6-hydroxypicolinate ligand (HP) is a potential chelate with interesting possibilities, exhibiting either N,O-chelation (through the pyridine N atom and the carboxylate group, forming a five-membered chelate ring) (Nogueira et al., 2000) or N,O,O-chelation (through the pyridine N atom and the carboxylate group, and further through the deprotonated hydroxy group as a bridging ligand). The latter coordination mode was reported for [Mn2(µ-O)(C6H3NO3)2(py)4]·H2O by Takayoshi et al. (2004). Owing to the inherent coordination and hydrogen-bonding donor/acceptor functionalities, this dimanganese complex formed a three-dimensional structure. To the best of our knowledge, the crystal structures of no metal complexes with the HP ligand, other than those with dimanganese (see above), have been reported to date, although there are several crystal structures of complexes with analogous ligands, the 2-, 3- and 4-hydroxy derivatives (Nogueira et al., 2000). We report here our efforts to establish the preferred coordination mode of HP to copper(II) in the structure of the title compound, (I).

An ORTEP-3 (Farrugia, 1997) view of (I) and a packing diagram are shown in Figs. 1 and 2, respectively and selected bond lengths and angles are shown in Table 1. Compound (I) displays a distorted octahedral coordination geometry, with the metal ion at a centre of inversion. The two bidentate ligands are necessarily trans to one another, and coordinate to the central metal ion through the pyridine N atoms and the carboxylate O atoms, to form a five-membered ring in the equatorial plane. Two O atoms of the aqua ligands complete the octahedron at the axial positions.

The coordination bond length in the axial direction [Cu1—O4 = 2.491 (2) Å] is longer than those in the equatorial plane [Cu1—O1 1.9364 (16) Å and Cu1—N1 1.9931 (18) Å]. Similar behavior is found for the complex trans-bis(5-n-butylpyridine-2-carboxylato-κ2N,O)-bis(methanol-KO)copper(II), in which the bond lengths in the equatorial plane are 2.596 (3) and 1.952 (2) Å, respectively (Okabe et al., 2002), and for hydrated bis(pyridine-2-carboxylato)copper(II) [2.752 (2) and 1.940 (2) Å, respectively; Faure et al., 1973]. These long bonds in the axial direction, compared with those in the equatorial plane, are usually observed in copper complexes of octahedral coordination geometry and are usually explained by a Jahn–Teller effect. This agrees with the EPR spectrum of the title compound, which resembles those of the analogously distorted octhahedral CuII complexes (Hathaway et al., 1970).

As shown in Table 1, the Cu1—O1 distance is slightly shorter than the Cu1—N1 distance. This effect is usually observed for the metal complexes of analogous compounds, such as bis(µ-6-hydroxypicolinato)-µ-oxo-bis[dipyridinemanganese(III)] monohydrate [Mn1—O2eq = 1.939 (2) Å and Mn1—N1 = 2.094 (2) Å; Takayoshi et al., 2004], 5-n-butylpyridine-2-carboxylate-copper(II) [Cu—Oeq = 1.952 (2) Å and Cu—N = 1.977 (2) Å; Okabe et al., 2002] and trans-bis(isoquinoline-3-carboxylato-κ2N,O)bis(methanol-κO) copper(II) [Cu—Oeq = 1.963 (2) Å and Cu—N 1.979 (2) Å; Okabe et al., 2004]. In the title compound, the angles around the Cu atom are slightly distorted from ideal octahedral [O1—Cu1—N1 = 83.07 (7)°]. Similar bond angles are observed in some related metal complexes, such as trans-bis(isoquinoline-3-carboxylato-κ2N,O)bis(methanol-κO)copper(II) [O—Cu—N = 83.77 (7)°; Okabe et al., 2004] and trans-diaqua-bis-(3-hydroxypicolinato)zinc(II) [O—Zn—N = 79.3 (1)°; Bombi et al., 2004].

The molecular packing of (I) is shown in Fig. 2. The intramolecular hydrogen bonds, O3—H3A···O1i (Table 2) between carbonyl and the hydroxy groups of the bidenate ligands reinforce the planarity of the equatorial groupings. The water molecules coordinated to the Cu atom in the apical position participate in two hydrogen bonds, O4—H1A···O2ii and O4—H1B···O2iii, which link the layers to form a three-dimensional structure (Fig. 2).

Experimental top

HP was dissolved in aqueous ammonia and refluxed for 2 h. Upon complete dissolution of the solid, the solvent was evaporated under vacuum to dryness. The residue was redissolved in methanol, and copper(II) acetate in methanol at a 2:1 molar ratio was added with vigorous stirring at 333 K. After stirring at this temperature for 2 h, the mixture was filtered and the deep-blue filtrate was left to stand, allowing slow evaporation of the solvent at room temperature. Finally, blue crystals of (I) were obtained by repeated recrystallization from acetonitrile at room temperature. Analysis calculated for C12H12CuN2O8: C 38.36, H 3.22, N 7.46%; found: C 38.40, H 3.32, N 7.47%. IR (KBr pellet, cm−1): 3420 (b), 3093 (m), 2792 (sh), 2597 (sh), 1666 (s), 1617.(versus), 1575 (s), 1394 (s), 1319 (versus), 1253 (s), 1149 (m), 1070 (w), 1018 (m), 827 (s), 746 (s), 554 (m), 431 (m). EPR (77.0 K): g1 = 2.26, g2 = 2.07 and g3 = 2.01.

Refinement top

The three aromatic H atoms were refined using a riding model [with C—H = 0.93 Å and Uiso(H) = 1.2Ueq(C)]. The O-bound H atoms were refined freely.

Computing details top

Data collection: X-AREA (Stoe & Cie, 2002); cell refinement: X-AREA; data reduction: X-RED (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 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1998).

Figures top
[Figure 1] Fig. 1. The title compound (I), with displacement ellipsoids shown at the 40% probability level.
[Figure 2] Fig. 2. A packing diagram for (I). Hydrogen bonds are indicated by dashed lines.
trans-Diaquabis(6-hydroxypicolinato-κ2N,O2)copper(II) top
Crystal data top
[Cu(C6H4NO3)2(H2O)2]Z = 1
Mr = 375.78F(000) = 191
Triclinic, P1Dx = 1.830 Mg m3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 6.1036 (8) ÅCell parameters from 7424 reflections
b = 7.2946 (11) Åθ = 2.4–27.2°
c = 8.5571 (13) ŵ = 1.65 mm1
α = 99.605 (12)°T = 296 K
β = 92.776 (12)°Prism, blue
γ = 113.758 (11)°0.24 × 0.18 × 0.14 mm
V = 340.98 (9) Å3
Data collection top
Stoe IPDS-II
diffractometer
1341 independent reflections
Radiation source: fine-focus sealed tube1190 reflections with I > 2σ(I)
Plane graphite monochromatorRint = 0.057
Detector resolution: 6.67 pixels mm-1θmax = 26.0°, θmin = 2.4°
rotation method scansh = 77
Absorption correction: integration
(X-RED; Stoe & Cie, 2002)
k = 88
Tmin = 0.726, Tmax = 0.826l = 1010
5001 measured reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.029Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.071H atoms treated by a mixture of independent and constrained refinement
S = 0.99 w = 1/[σ2(Fo2) + (0.0439P)2]
where P = (Fo2 + 2Fc2)/3
1341 reflections(Δ/σ)max < 0.001
118 parametersΔρmax = 0.38 e Å3
0 restraintsΔρmin = 0.35 e Å3
Crystal data top
[Cu(C6H4NO3)2(H2O)2]γ = 113.758 (11)°
Mr = 375.78V = 340.98 (9) Å3
Triclinic, P1Z = 1
a = 6.1036 (8) ÅMo Kα radiation
b = 7.2946 (11) ŵ = 1.65 mm1
c = 8.5571 (13) ÅT = 296 K
α = 99.605 (12)°0.24 × 0.18 × 0.14 mm
β = 92.776 (12)°
Data collection top
Stoe IPDS-II
diffractometer
1341 independent reflections
Absorption correction: integration
(X-RED; Stoe & Cie, 2002)
1190 reflections with I > 2σ(I)
Tmin = 0.726, Tmax = 0.826Rint = 0.057
5001 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0290 restraints
wR(F2) = 0.071H atoms treated by a mixture of independent and constrained refinement
S = 0.99Δρmax = 0.38 e Å3
1341 reflectionsΔρmin = 0.35 e Å3
118 parameters
Special details top

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 (Å2) top
xyzUiso*/Ueq
C10.7474 (4)0.7411 (3)0.2894 (3)0.0343 (5)
C20.8042 (5)0.8426 (4)0.1671 (3)0.0444 (6)
H20.96310.92880.16070.053*
C30.6181 (5)0.8143 (4)0.0516 (3)0.0485 (6)
H30.65180.88280.03270.058*
C40.3873 (5)0.6863 (4)0.0628 (3)0.0450 (6)
H40.26200.66560.01390.054*
C50.3411 (4)0.5863 (4)0.1911 (3)0.0366 (5)
C70.9332 (4)0.7592 (3)0.4209 (3)0.0360 (5)
N10.5188 (3)0.6149 (3)0.3029 (2)0.0332 (4)
O10.8470 (3)0.6545 (3)0.5285 (2)0.0425 (4)
O21.1468 (3)0.8652 (3)0.4215 (2)0.0470 (4)
O30.1154 (3)0.4588 (3)0.1990 (2)0.0488 (4)
O40.4596 (4)0.8038 (3)0.6540 (2)0.0494 (5)
Cu10.50000.50000.50000.03532 (16)
H1A0.361 (7)0.810 (6)0.598 (5)0.089 (15)*
H1B0.572 (6)0.893 (5)0.645 (4)0.058 (10)*
H3A0.112 (5)0.418 (4)0.277 (3)0.035 (7)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0315 (11)0.0350 (12)0.0364 (11)0.0144 (10)0.0047 (9)0.0061 (9)
C20.0403 (13)0.0443 (13)0.0478 (14)0.0130 (11)0.0113 (11)0.0177 (11)
C30.0562 (16)0.0535 (15)0.0413 (13)0.0230 (13)0.0123 (12)0.0221 (11)
C40.0484 (14)0.0532 (14)0.0361 (12)0.0240 (12)0.0020 (10)0.0112 (10)
C50.0349 (12)0.0387 (12)0.0350 (11)0.0156 (10)0.0004 (9)0.0051 (9)
C70.0293 (11)0.0343 (11)0.0431 (12)0.0129 (10)0.0042 (9)0.0053 (9)
N10.0294 (9)0.0345 (9)0.0337 (9)0.0120 (8)0.0017 (7)0.0061 (7)
O10.0291 (8)0.0486 (9)0.0453 (9)0.0095 (7)0.0007 (7)0.0165 (7)
O20.0295 (9)0.0473 (10)0.0598 (11)0.0098 (8)0.0060 (8)0.0156 (8)
O30.0335 (9)0.0597 (11)0.0448 (10)0.0098 (8)0.0061 (7)0.0173 (9)
O40.0474 (11)0.0452 (11)0.0539 (11)0.0157 (10)0.0072 (10)0.0149 (9)
Cu10.0246 (2)0.0405 (3)0.0360 (2)0.00662 (17)0.00005 (15)0.01435 (16)
Geometric parameters (Å, º) top
C1—N11.351 (3)C7—O21.218 (3)
C1—C21.360 (3)C7—O11.290 (3)
C1—C71.509 (3)N1—Cu11.9931 (18)
C2—C31.393 (4)O1—Cu11.9364 (16)
C2—H20.9300O3—H3A0.78 (3)
C3—C41.360 (4)O4—Cu12.491 (2)
C3—H30.9300O4—H1A0.77 (4)
C4—C51.396 (3)O4—H1B0.75 (4)
C4—H40.9300Cu1—O1i1.9364 (16)
C5—O31.328 (3)Cu1—N1i1.9931 (18)
C5—N11.336 (3)
N1—C1—C2122.6 (2)C5—N1—C1118.94 (19)
N1—C1—C7114.29 (19)C5—N1—Cu1129.17 (15)
C2—C1—C7123.1 (2)C1—N1—Cu1111.88 (14)
C1—C2—C3118.4 (2)C7—O1—Cu1115.89 (14)
C1—C2—H2120.8C5—O3—H3A108.5 (19)
C3—C2—H2120.8Cu1—O4—H1A101 (3)
C4—C3—C2119.8 (2)Cu1—O4—H1B105 (2)
C4—C3—H3120.1H1A—O4—H1B104 (4)
C2—C3—H3120.1O1i—Cu1—O1180.0
C3—C4—C5119.1 (2)O1i—Cu1—N196.91 (7)
C3—C4—H4120.5O1—Cu1—N183.09 (7)
C5—C4—H4120.5O1i—Cu1—N1i83.09 (7)
O3—C5—N1120.3 (2)O1—Cu1—N1i96.91 (7)
O3—C5—C4118.4 (2)N1—Cu1—N1i180.000 (1)
N1—C5—C4121.3 (2)O1i—Cu1—O490.57 (8)
O2—C7—O1124.2 (2)O1—Cu1—O489.43 (8)
O2—C7—C1121.0 (2)N1—Cu1—O489.99 (7)
O1—C7—C1114.81 (19)N1i—Cu1—O490.01 (7)
N1—C1—C2—C30.1 (4)C7—C1—N1—C5179.13 (18)
C7—C1—C2—C3179.9 (2)C2—C1—N1—Cu1177.92 (18)
C1—C2—C3—C40.5 (4)C7—C1—N1—Cu12.1 (2)
C2—C3—C4—C50.4 (4)O2—C7—O1—Cu1179.65 (18)
C3—C4—C5—O3178.8 (2)C1—C7—O1—Cu10.7 (2)
C3—C4—C5—N10.3 (4)C7—O1—Cu1—N11.47 (16)
N1—C1—C7—O2178.7 (2)C7—O1—Cu1—N1i178.53 (16)
C2—C1—C7—O21.3 (3)C7—O1—Cu1—O488.59 (16)
N1—C1—C7—O11.0 (3)C5—N1—Cu1—O1i0.6 (2)
C2—C1—C7—O1179.0 (2)C1—N1—Cu1—O1i178.04 (14)
O3—C5—N1—C1178.17 (19)C5—N1—Cu1—O1179.4 (2)
C4—C5—N1—C11.0 (3)C1—N1—Cu1—O11.96 (14)
O3—C5—N1—Cu13.3 (3)C5—N1—Cu1—O491.1 (2)
C4—C5—N1—Cu1177.56 (16)C1—N1—Cu1—O487.47 (15)
C2—C1—N1—C50.9 (3)
Symmetry code: (i) x+1, y+1, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O3—H3A···O1i0.78 (3)1.86 (3)2.631 (2)172 (3)
O4—H1A···O2ii0.77 (4)2.14 (4)2.902 (3)168 (4)
O4—H1B···O2iii0.75 (4)2.09 (4)2.831 (3)169 (4)
Symmetry codes: (i) x+1, y+1, z+1; (ii) x1, y, z; (iii) x+2, y+2, z+1.

Experimental details

Crystal data
Chemical formula[Cu(C6H4NO3)2(H2O)2]
Mr375.78
Crystal system, space groupTriclinic, P1
Temperature (K)296
a, b, c (Å)6.1036 (8), 7.2946 (11), 8.5571 (13)
α, β, γ (°)99.605 (12), 92.776 (12), 113.758 (11)
V3)340.98 (9)
Z1
Radiation typeMo Kα
µ (mm1)1.65
Crystal size (mm)0.24 × 0.18 × 0.14
Data collection
DiffractometerStoe IPDS-II
diffractometer
Absorption correctionIntegration
(X-RED; Stoe & Cie, 2002)
Tmin, Tmax0.726, 0.826
No. of measured, independent and
observed [I > 2σ(I)] reflections
5001, 1341, 1190
Rint0.057
(sin θ/λ)max1)0.617
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.029, 0.071, 0.99
No. of reflections1341
No. of parameters118
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.38, 0.35

Computer programs: X-AREA (Stoe & Cie, 2002), X-AREA, X-RED (Stoe & Cie, 2002), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEP-3 for Windows (Farrugia, 1997), WinGX (Farrugia, 1998).

Selected geometric parameters (Å, º) top
C5—O31.328 (3)N1—Cu11.9931 (18)
C7—O21.218 (3)O1—Cu11.9364 (16)
C7—O11.290 (3)O4—Cu12.491 (2)
O3—C5—N1120.3 (2)O1—Cu1—N183.09 (7)
O2—C7—O1124.2 (2)O1i—Cu1—O490.57 (8)
O2—C7—C1121.0 (2)O1—Cu1—O489.43 (8)
O1—C7—C1114.81 (19)N1—Cu1—O489.99 (7)
N1—C1—C7—O2178.7 (2)N1—C1—C7—O11.0 (3)
Symmetry code: (i) x+1, y+1, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O3—H3A···O1i0.78 (3)1.86 (3)2.631 (2)172 (3)
O4—H1A···O2ii0.77 (4)2.14 (4)2.902 (3)168 (4)
O4—H1B···O2iii0.75 (4)2.09 (4)2.831 (3)169 (4)
Symmetry codes: (i) x+1, y+1, z+1; (ii) x1, y, z; (iii) x+2, y+2, z+1.
 

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