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The title complex, trans-{μ-2,2′-[(1,2-dioxoethane-1,2-diyl)­diimino]­diethano­ato(4−)}bis­[di­aqua­copper(II)] dihydrate, [Cu2(C6H4N2O6)(H2O)4]·2H2O, with a three-dimensional framework, displays a square-pyramidal coordination geometry. The structure consists of a neutral centrosymmetric binuclear unit in which the ox­amide ligand has a trans geometry, is fully deprotonated and acts in a bis-tridentate fashion.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270105019529/av1246sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270105019529/av1246Isup2.hkl
Contains datablock I

CCDC reference: 269995

Comment top

Many research efforts have been dedicated to studying oxamide-bridged transition metal complexes because of their expected magnetic properties and biological relevance (Santana et al., 2004; Messori et al., 2003; Kou et al., 2003). One of the most outstanding characteristics of oxamide ligands is their versatile bonding mode with metal ions, which makes it practical to design tunable molecular materials with extended structures (Li et al., 1998; Lloret, Julve et al., 1992 or Lloret, Sletten et al., 1992?). Taking into account the above facts and in continuation of our work on polynuclear complexes with bridging oxamide groups (Li et al., 2003), in this paper, we describe the synthesis of a new binuclear copper(II) complex, [Cu2(obe)(H2O)4]·2H2O, (I), using oxamidobis(ethanoate) {obe; 2,2'-[(1,2-dioxoethane-1,2-diyl)diimino]diethanoate} as bridging ligand. The crystal structure of (I) was determined in order to examine the effect of pH upon the bonding mode of the obe ligand with copper(II).

The molecular structure of (I) is illustrated in Fig. 1. Single-crystal X-ray analysis reveals that the complex contains a neutral centrosymmetric binuclear molecule in which the oxamide ligand has a trans geometry, is fully deprotonated and acts in a bis-tridentate fashion. The Cu atom has a square-pyramidal coordination geometry, with three atoms (N1, O2 and O3) from the oxamide ligand and one water molecule (O5) in the basal plane, and with one water molecule (O4) in the apical position. The deviations of atoms N1, O2, O3 and O5 from the least-squares plane through these atoms are 0.0408 (10), 0.0365 (9), 0.0358 (8) and 0.0315 (7))Å, respectively, while the Cu atom is displaced 0.1322 (9) Å from this plane. The Cu—O distance of 2.314 (2) Å in the axial direction is longer than those in the basal plane by 0.315, 0.299, and 0.392 Å (Table 1). The Cu···Cu separation within each binuclear unit is 5.228 (4) Å.

As shown in Fig. 2, a two-dimensional network paralleling the crystal plane (1, 0, 1) is formed via hydrogen bonding between the coordinated water molecule (O5) in the basal plane and atoms O1 and O2 from the carboxylate group (the hydrogen bonding geometries are listed in Table 2). Moreover, through hydrogen bonds between the other coordinated water molecule (O4), in the apical position, and atom O3 of the oxamide group, the two-dimensional hydrogen-bonding network is assembled into a three-dimensional supramolecular structure (Fig. 3), in which the uncoordinated water molecules participate by hydrogen bonding to atom O1(x, y, z + 1).

Compared with the previously reported complex {[Cu(H2obe)(H2O)3].4H2O}n (Lloret, Julve et al., 1992 or Lloret, Sletten et al., 1992?), which was obtained from aqueous solutions of copper(II) nitrate trihydrate and H4(obe) in a 1:1 molar ratio at a pH of ~3 by slow evaporation, the present complex has two important differences in the obe ligand. The previously reported complex consists of one-dimensional [Cu(H2obe)]n chains in which the ligand is deprotonated only at the terminal carboxylate groups and is bis-monodentate, and the N1—C3 and O3—C3 bond distances in the oxamide group are 1.326 (1) and 1.228 (1) Å. In the present complex, the ligand is fully deprotonated, not only at the carboxylate groups but also at the oxamide group. The deprotonation at atom N1 and copper coordination at atoms N1 and O3 lead to highly significant changes in the N1—C3 [1.289 (3) Å] and O3—C3 [1.277 (3) Å] bond distances, which indicate a more effective π delocalization in the NCO fragment.

Experimental top

All chemicals were of reagent grade and were used without further purification. The ligand oxamidobis(ethanoic acid), H4(obe), was synthesized by the reported method (Yu et al., 1991). The complex was prepared by the following procedure. A solution of copper(II) chloride dihydrate (68.2 mg, 0.4 mmol) dissolved in methanol (5 ml) was added dropwise to a water/methanol (20 ml, 1:5, v/v) mixture containing the ligand (0.2 mmol). An appropriate amount of piperidine was then added to adjust the pH to 7. The mixture was heated at reflux with stirring for 12 h. The precipitate was filtered off, washed with cold water, methanol and diethyl ether in turn, and then redissolved in water. Green crystals (yield 49.6 mg, 57%) were obtained from the solution after 5 d by slow evaporation at room temperature. Analysis calculated: C 16.55, H 3.70, N 6.44%; found: C 16.48, H 3.62, N 6.37%. IR (KBr pellet, cm−1): ν(O—H) 3157 (s, br), νa(COO) 1661 (vs), ν(N—CO) 1585 (vs), νas(COO) 1384 (s).

Refinement top

H atoms attached to C atoms were positioned geometrically and were treated as riding on their parent C atoms, with C—H distances of 0.97 Å and Uiso(H) = 1.2Ueq(C). Water H atoms were located in a difference Fouier map and were included in the structure-factor calculation with fixed positional and isotropic displacement parameters [O—H = 0.83–0.90 Å; Uiso(H) = 0.08 Å2].

Computing details top

Data collection: SMART (Bruker, 2000); cell refinement: SMART [or SAINT?] (Bruker, 2000); data reduction: SAINT; 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, 1999).

Figures top
[Figure 1] Fig. 1. The molecular structure of (I), with 30% probability displacement ellipsoids. [Symmetry code: (i) 1 − x, 1 − y, 1 − z.]
[Figure 2] Fig. 2. A two-dimensional hydrogen-bonding network paralleling the crystal plane (101). Dashed lines indicate hydrogen bonds. [Symmetry codes: (ii) x, y + 1, z; (iii) x, y − 1, z; (iv) 2 − x, 1 − y, −z.]
[Figure 3] Fig. 3. A view of the three-dimensional supramolecular structure. Dashed lines indicate hydrogen bonds. [Symmetry codes: (v) 2 − x, 1 − y, 1 − z; (vi) x, y, z + 1.]
trans-{µ-2,2'-[(1,2-dioxoethane-1,2- diyl)diimino]diethanoato}bis[diaquacopper(II)] dihydrate top
Crystal data top
[Cu2(C6H4N2O6)(H2O)4]·2H2OZ = 1
Mr = 435.31F(000) = 220
Triclinic, P1Dx = 2.064 Mg m3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 6.870 (6) ÅCell parameters from 1696 reflections
b = 7.283 (7) Åθ = 2.7–27.6°
c = 7.929 (7) ŵ = 3.10 mm1
α = 73.693 (14)°T = 293 K
β = 87.795 (14)°Block, green
γ = 67.342 (14)°0.19 × 0.15 × 0.12 mm
V = 350.3 (6) Å3
Data collection top
Bruker APEX area-detector
diffractometer
1541 independent reflections
Radiation source: fine-focus sealed tube1431 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.021
ϕ and ω scansθmax = 27.0°, θmin = 2.7°
Absorption correction: multi-scan
(SADABS; Bruker, 2000)
h = 58
Tmin = 0.578, Tmax = 0.689k = 79
2108 measured reflectionsl = 910
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)] = 0.026Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.071H-atom parameters constrained
S = 1.06 w = 1/[σ2(Fo2) + (0.0378P)2 + 0.2235P]
where P = (Fo2 + 2Fc2)/3
1541 reflections(Δ/σ)max = 0.001
100 parametersΔρmax = 0.37 e Å3
0 restraintsΔρmin = 0.67 e Å3
Crystal data top
[Cu2(C6H4N2O6)(H2O)4]·2H2Oγ = 67.342 (14)°
Mr = 435.31V = 350.3 (6) Å3
Triclinic, P1Z = 1
a = 6.870 (6) ÅMo Kα radiation
b = 7.283 (7) ŵ = 3.10 mm1
c = 7.929 (7) ÅT = 293 K
α = 73.693 (14)°0.19 × 0.15 × 0.12 mm
β = 87.795 (14)°
Data collection top
Bruker APEX area-detector
diffractometer
1541 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2000)
1431 reflections with I > 2σ(I)
Tmin = 0.578, Tmax = 0.689Rint = 0.021
2108 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0260 restraints
wR(F2) = 0.071H-atom parameters constrained
S = 1.06Δρmax = 0.37 e Å3
1541 reflectionsΔρmin = 0.67 e Å3
100 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
Cu0.73780 (4)0.53068 (4)0.23673 (3)0.02237 (12)
N10.5643 (3)0.3828 (3)0.3331 (2)0.0211 (3)
O10.6915 (3)0.1363 (3)0.0072 (2)0.0354 (4)
O20.7700 (2)0.3790 (2)0.05608 (19)0.0245 (3)
O30.3581 (2)0.3369 (2)0.5671 (2)0.0249 (3)
O41.0407 (3)0.2828 (3)0.4064 (2)0.0341 (4)
H4A1.13130.31940.44300.080*
H4B1.10980.17240.37690.080*
O50.8686 (3)0.7155 (3)0.1139 (3)0.0448 (5)
H5A0.79870.85380.07470.080*
H5B0.98620.69550.06610.080*
O60.8870 (4)0.0693 (3)0.6909 (3)0.0485 (5)
H6A0.87210.17670.61010.080*
H6B0.82890.10200.78120.080*
C10.6828 (3)0.2479 (3)0.0875 (3)0.0220 (4)
C20.5565 (3)0.2321 (3)0.2499 (3)0.0229 (4)
H2A0.41110.26150.21570.027*
H2B0.61750.09320.33080.027*
C30.4756 (3)0.4182 (3)0.4734 (2)0.0196 (4)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cu0.02759 (17)0.02631 (18)0.02251 (16)0.01714 (12)0.01307 (10)0.01307 (11)
N10.0244 (8)0.0259 (9)0.0209 (8)0.0150 (7)0.0091 (6)0.0121 (7)
O10.0557 (11)0.0344 (9)0.0301 (8)0.0253 (8)0.0195 (8)0.0216 (7)
O20.0296 (8)0.0260 (7)0.0235 (7)0.0142 (6)0.0123 (6)0.0122 (6)
O30.0290 (8)0.0325 (8)0.0265 (7)0.0211 (6)0.0145 (6)0.0168 (6)
O40.0290 (8)0.0378 (9)0.0419 (9)0.0150 (7)0.0017 (7)0.0183 (8)
O50.0502 (11)0.0271 (9)0.0649 (13)0.0236 (8)0.0396 (10)0.0177 (8)
O60.0663 (13)0.0440 (11)0.0344 (9)0.0193 (10)0.0200 (9)0.0156 (8)
C10.0255 (9)0.0224 (9)0.0190 (9)0.0086 (8)0.0058 (7)0.0087 (7)
C20.0285 (10)0.0261 (10)0.0219 (9)0.0157 (8)0.0093 (8)0.0127 (8)
C30.0202 (9)0.0223 (9)0.0203 (9)0.0105 (7)0.0043 (7)0.0094 (7)
Geometric parameters (Å, º) top
Cu—N11.903 (2)O4—H4A0.8531
Cu—O21.999 (2)O4—H4B0.8539
Cu—O3i2.015 (2)O5—H5A0.897
Cu—O42.314 (2)O5—H5B0.8568
Cu—O51.922 (2)O6—H6A0.833
N1—C21.448 (3)O6—H6B0.8541
N1—C31.289 (3)C1—C21.527 (3)
O1—C11.237 (3)C2—H2A0.9700
O2—C11.276 (3)C2—H2B0.9700
O3—C31.277 (3)C3—C3i1.521 (4)
O3—Cui2.015 (2)
N1—Cu—O282.22 (8)H4A—O4—H4B107.08
N1—Cu—O3i83.85 (8)Cu—O5—H5A123.07
N1—Cu—O494.39 (10)Cu—O5—H5B132.88
N1—Cu—O5169.86 (9)H5A—O5—H5B103.02
O2—Cu—O3i165.42 (7)H6A—O6—H6B109.7
O2—Cu—O493.80 (8)O1—C1—O2123.9 (2)
O3i—Cu—O491.50 (9)O1—C1—C2118.4 (2)
O5—Cu—O296.84 (10)O2—C1—C2117.69 (17)
O5—Cu—O3i96.13 (9)N1—C2—C1107.46 (17)
O5—Cu—O495.75 (11)N1—C2—H2A110.2
C2—N1—Cu117.22 (14)C1—C2—H2A110.2
C3—N1—Cu116.19 (14)N1—C2—H2B110.2
C3—N1—C2126.44 (18)C1—C2—H2B110.2
C1—O2—Cu115.06 (13)H2A—C2—H2B108.5
C3—O3—Cui109.13 (13)O3—C3—N1129.27 (18)
Cu—O4—H4A120.22O3—C3—C3i118.8 (2)
Cu—O4—H4B119.42N1—C3—C3i112.0 (2)
O5—Cu—N1—C393.3 (4)Cu—O2—C1—O1177.96 (18)
O2—Cu—N1—C3178.61 (17)Cu—O2—C1—C23.4 (2)
O3i—Cu—N1—C32.89 (16)C3—N1—C2—C1179.6 (2)
O4—Cu—N1—C388.15 (17)Cu—N1—C2—C15.1 (2)
O5—Cu—N1—C290.9 (4)O1—C1—C2—N1177.80 (19)
O2—Cu—N1—C25.58 (15)O2—C1—C2—N10.9 (3)
O3i—Cu—N1—C2178.70 (16)Cui—O3—C3—N1177.80 (19)
O4—Cu—N1—C287.66 (16)Cui—O3—C3—C3i2.0 (3)
N1—Cu—O2—C14.95 (15)C2—N1—C3—O32.3 (4)
O5—Cu—O2—C1174.78 (15)Cu—N1—C3—O3177.68 (18)
O3i—Cu—O2—C122.1 (3)C2—N1—C3—C3i177.8 (2)
O4—Cu—O2—C188.97 (16)Cu—N1—C3—C3i2.5 (3)
Symmetry code: (i) x+1, y+1, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O4—H4A···O3ii0.85311.9382.773 (3)166.13
O5—H5A···O1iii0.8971.8212.713 (4)172.33
O5—H5B···O2iv0.85681.8732.721 (3)169.73
O6—H6B···O1v0.85411.9232.770 (3)171.16
Symmetry codes: (ii) x+1, y, z; (iii) x, y+1, z; (iv) x+2, y+1, z; (v) x, y, z+1.

Experimental details

Crystal data
Chemical formula[Cu2(C6H4N2O6)(H2O)4]·2H2O
Mr435.31
Crystal system, space groupTriclinic, P1
Temperature (K)293
a, b, c (Å)6.870 (6), 7.283 (7), 7.929 (7)
α, β, γ (°)73.693 (14), 87.795 (14), 67.342 (14)
V3)350.3 (6)
Z1
Radiation typeMo Kα
µ (mm1)3.10
Crystal size (mm)0.19 × 0.15 × 0.12
Data collection
DiffractometerBruker APEX area-detector
diffractometer
Absorption correctionMulti-scan
(SADABS; Bruker, 2000)
Tmin, Tmax0.578, 0.689
No. of measured, independent and
observed [I > 2σ(I)] reflections
2108, 1541, 1431
Rint0.021
(sin θ/λ)max1)0.640
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.026, 0.071, 1.06
No. of reflections1541
No. of parameters100
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.37, 0.67

Computer programs: SMART (Bruker, 2000), SMART [or SAINT?] (Bruker, 2000), SAINT, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEP-3 for Windows (Farrugia, 1997), WinGX (Farrugia, 1999).

Selected geometric parameters (Å, º) top
Cu—N11.903 (2)Cu—O51.922 (2)
Cu—O21.999 (2)N1—C31.289 (3)
Cu—O3i2.015 (2)O3—C31.277 (3)
Cu—O42.314 (2)
N1—Cu—O282.22 (8)O2—Cu—O493.80 (8)
N1—Cu—O3i83.85 (8)O3i—Cu—O491.50 (9)
N1—Cu—O494.39 (10)O5—Cu—O296.84 (10)
N1—Cu—O5169.86 (9)O5—Cu—O3i96.13 (9)
O2—Cu—O3i165.42 (7)O5—Cu—O495.75 (11)
Symmetry code: (i) x+1, y+1, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O4—H4A···O3ii0.85311.9382.773 (3)166.13
O5—H5A···O1iii0.8971.8212.713 (4)172.33
O5—H5B···O2iv0.85681.8732.721 (3)169.73
O6—H6B···O1v0.85411.9232.770 (3)171.16
Symmetry codes: (ii) x+1, y, z; (iii) x, y+1, z; (iv) x+2, y+1, z; (v) x, y, z+1.
 

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