Poly­[(2,2′-bi­pyridine)copper(II)-μ₄-oxalato]

The crystal structure of the title compound, [Cu(C₂O₄)(C₁₀H₈N₂)]_n, is reported. The Cu^II atom is six-coordinated with distorted octahedral geometry and the bi­pyridine ligand acts as a chelating ligand. The oxalate anion bridges the metal ions forming infinite chains.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.015 Å
• R factor = 0.051
• wR factor = 0.108
• Data-to-parameter ratio = 9.0

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



ABSTM_02  Alert C The ratio of expected to reported Tmax/Tmin(RR) is > 1.10
          Tmin and Tmax reported:      0.408     0.458
          Tmin and Tmax expected:      0.531     0.666
          RR =      1.117
          Please check that your absorption correction is appropriate.

STRVAL_01
         From the CIF: _refine_ls_abs_structure_Flack    0.350
         From the CIF: _refine_ls_abs_structure_Flack_su    0.040
           Alert C Flack test results are ambiguous.

PLAT_369  Alert C Long   C(sp2)-C(sp2) Bond  C(1)   -   C(2)   =       1.55 Ang.

General Notes



ABSTM_02  When printed, the submitted absorption T values will be replaced
          by the scaled T values. Since the ratio of scaled T's is
          identical to the ratio of reported T values, the scaling does
          not imply a change to the absorption corrections used in the
          study.
          Ratio of Tmax expected/reported      1.455
          Tmax scaled      0.666 Tmin scaled      0.593

REFLT_03
         From the CIF: _diffrn_reflns_theta_max           25.05
         From the CIF: _reflns_number_total               1545
         Count of symmetry unique reflns         1053
         Completeness (_total/calc)            146.72%
         TEST3: Check Friedels for noncentro structure
         Estimate of Friedel pairs measured       492
         Fraction of Friedel pairs measured     0.467
         Are heavy atom types Z>Si present          yes
          WARNING: Large fraction of Friedel related reflns may
                   be needed to determine absolute structure


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 3 Alert Level C = Please check

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S1. Comment

Oxalate-bridged polymeric compounds have attracted much attention due to their interesting magnetic properties (Decurtins et al., 1994, and references therein). By reacting CuCl₂, 2,2'-bipyridine (2,2'-bipy) and tetrahydroxy-1,4-benzoquinone, the title complex, [Cu(C₂O₄)(2,2'-bipy)]_n, was obtained, with oxalate anions as bridging ligands. So far, there have been only a few such compounds reported, viz. [Cu(C₂O₄)(2,2'-bipy)].2H₂O (Fitzgerald et al., 1982), [Mn(C₂O₄)(2,2'-bipy)]_n (Deguenon et al., 1990) and [Fe(C₂O₄)(2,2'-bipy)]_n (Fun et al., 1999).

The crystal structure of the title compound, which is isostructural with the Fe^II compound, consists of neutral [Cu(C₂O₄)(2,2'-bipy)] units, with the Cu atoms linked by C₂O₄ ligands to form infinite zigzag chains along the a axis. The Cu atom has a distorted octahedral coordination consisting of two N atoms from the chelating 2,2'-bipy ligand, two O atoms of the oxalate ligands in equatorial positions, and two O atoms of the oxalate ligands in axial positions. The largest deviation from the plane defined by Cu, N1, N2, O2 and O3ⁱ is -0.089Å at atom N1 [symmetry code: (i) x-1/2, -y+1/2, z]. The Cu—N bond lengths [1.991 (7) and 2.018 (7)Å] and the Cu—N—Cu bite angle [80.4 (3)°] are comparable to the corresponding values in [Cu₂(bipy)₂(H₂0)₂(C₂O₄)]X₂.[Cu(bipy)(C₂O₄)] (X = NO₃^{-_{, BF}4 _{or ClO}4_{), [1.992 (2), 1.987 (2)Å and 82.92°; Gleizes et al., 1992]. The Cu—O distances [1.972 (6)–2.369 (7) Å] and the O—Cu—O bite angles [90.6 (2) and 85.3 (3)°] are in agreement with those in [Cu}2_(bipy)2_(C2_O4_)(H2₀₎2_][Cu(bipy)(C2_O4_)](NO3₎2 _{[1.971 (1)–2.247 (1)Å and 84.64 (3)°; Shi et al., 1997]; the bite angles are also close to those in [Mn(C}2_O4_{)(2,2'-bipy)]}n _{(Deguenon et al., 1990) and [Fe(C}2_O4_{)(2,2'-bipy)]}n _{(Fun et al., 1999). The dihedral angle between the planar pyridyl rings is 2.01°. The shortest Cu···Cu distances within the chain is 5.507Å. Neighbouring chains are connected to each other by van der Waals interactions, with the bipyridyl ligands stacked between the chains. The shortest Cu···Cu distance between adjacent chains is 7.793Å.}}

S2. Experimental

A solution of CuCl₂·6H₂O (0.085 g, 0.5 mmol) and tetrahydroxy-1,4-benzoquinone (0.10 g, 0.5 mmol) in methanol solution (20 ml) was stirred for 30 min at room temperature, then 2,2'-bipyridine (0.5 mmol) was added and the mixture was stirred for 1 h to give a green solution; this was filtered. Deep-green crystals were obtained by keeping the solution exposed to air for about a week. A green single-crystal was selected for X-ray diffraction.

S3. Refinement

H-atom positions were generated geometrically and the H atoms were allowed to ride on their respective parent C atoms.

Computing details

Data collection: SMART (Siemens, 1994); cell refinement: SMART; data reduction: SMART; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXL97; software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. Part of the polymer chain of (I), showing 50% probability displacement ellipsoids and the labelling of the asymmetric unit.

Poly[(2,2'-bipyridine)copper(II)-µ₄-oxalato]

Crystal data

[Cu(C2O4)(C10H8N2)]	Dx = 1.799 Mg m^−3
Mr = 307.74	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pna21	Cell parameters from 172 reflections
a = 8.0762 (11) Å	θ = 2.5–25.1°
b = 9.9366 (13) Å	µ = 1.93 mm^−1
c = 14.1558 (19) Å	T = 293 K
V = 1136.0 (3) Å^3	Plate, green
Z = 4	0.35 × 0.28 × 0.21 mm
F(000) = 620

Data collection

Siemens SMART CCD diffractometer	1545 independent reflections
Radiation source: fine-focus sealed tube	1084 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.060
ω scans	θmax = 25.1°, θmin = 2.5°
Absorption correction: empirical (using intensity measurements) (SADABS; Sheldrick, 1996)	h = −9→9
Tmin = 0.408, Tmax = 0.458	k = −11→6
3348 measured reflections	l = −16→9

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)] = 0.051	H-atom parameters constrained
wR(F^2) = 0.109	w = 1/[σ^2(Fo^2) + (0.0407P)^2 + 0.3497P] where P = (Fo^2 + 2Fc^2)/3
S = 1.05	(Δ/σ)max < 0.001
1545 reflections	Δρmax = 0.41 e Å^−3
172 parameters	Δρmin = −0.46 e Å^−3
1 restraint	Absolute structure: Flack (1983), 100 Friedel pairs treated independently
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.35 (4)

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
Cu1	0.12533 (13)	0.43841 (8)	0.13972 (12)	0.0312 (3)
N1	0.2076 (10)	0.5805 (6)	0.2270 (5)	0.0292 (18)
N2	0.0617 (10)	0.6035 (6)	0.0650 (5)	0.0295 (17)
C1	0.3229 (14)	0.2147 (10)	0.1817 (6)	0.027 (2)
C2	0.4065 (15)	0.2653 (9)	0.0896 (8)	0.037 (3)
C3	0.2798 (14)	0.5587 (9)	0.3112 (6)	0.041 (2)
H1	0.2996	0.4706	0.3301	0.049*
H2	0.3792	0.6410	0.4255	0.049*
H3	0.3125	0.8607	0.3876	0.049*
H4	0.1987	0.9018	0.2380	0.049*
H5	0.0677	0.9232	0.0968	0.049*
H6	−0.0537	0.9206	−0.0497	0.049*
H7	−0.1046	0.7167	−0.1245	0.049*
H8	−0.0245	0.5232	−0.0497	0.049*
C4	0.3246 (14)	0.6604 (12)	0.3692 (8)	0.058 (3)
C5	0.2896 (18)	0.7907 (12)	0.3463 (9)	0.055 (3)
C6	0.2177 (13)	0.8146 (8)	0.2582 (8)	0.045 (3)
C7	0.1746 (13)	0.7099 (10)	0.2020 (7)	0.031 (2)
C8	0.0942 (13)	0.7189 (9)	0.1094 (6)	0.030 (3)
C9	0.0485 (13)	0.8425 (8)	0.0659 (7)	0.038 (2)
C10	−0.0240 (14)	0.8408 (9)	−0.0207 (8)	0.048 (3)
C11	−0.0542 (18)	0.7206 (11)	−0.0654 (8)	0.046 (3)
C12	−0.0070 (13)	0.6056 (9)	−0.0195 (7)	0.043 (3)
O1	0.3684 (9)	0.1046 (5)	0.2147 (5)	0.0405 (16)
O2	0.2098 (9)	0.2882 (6)	0.2169 (4)	0.0379 (16)
O3	0.5154 (8)	0.1896 (5)	0.0536 (4)	0.0361 (16)
O4	0.3647 (8)	0.3769 (5)	0.0591 (4)	0.0355 (15)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.0360 (5)	0.0233 (4)	0.0343 (5)	−0.0008 (5)	−0.0004 (7)	−0.0027 (7)
N1	0.041 (5)	0.025 (4)	0.021 (4)	−0.003 (4)	0.000 (4)	−0.002 (3)
N2	0.032 (4)	0.025 (4)	0.031 (4)	−0.001 (3)	0.000 (4)	−0.004 (3)
C1	0.030 (6)	0.027 (5)	0.026 (5)	0.001 (5)	−0.004 (4)	0.006 (4)
C2	0.040 (8)	0.028 (6)	0.043 (6)	−0.003 (5)	−0.004 (5)	0.001 (5)
C3	0.055 (7)	0.042 (5)	0.025 (5)	−0.005 (6)	−0.005 (5)	0.002 (5)
C4	0.063 (9)	0.073 (8)	0.038 (6)	−0.006 (6)	−0.008 (6)	−0.006 (6)
C5	0.056 (10)	0.061 (8)	0.049 (8)	−0.009 (7)	−0.001 (7)	−0.027 (7)
C6	0.046 (7)	0.030 (5)	0.058 (7)	−0.006 (5)	0.015 (6)	−0.016 (5)
C7	0.031 (6)	0.035 (5)	0.027 (6)	−0.013 (5)	0.005 (5)	−0.015 (5)
C8	0.037 (7)	0.019 (4)	0.033 (7)	−0.005 (4)	0.008 (5)	−0.003 (4)
C9	0.047 (6)	0.020 (4)	0.046 (6)	0.009 (5)	0.010 (6)	0.004 (5)
C10	0.051 (7)	0.042 (6)	0.050 (6)	0.009 (5)	0.009 (6)	0.016 (6)
C11	0.058 (9)	0.047 (6)	0.032 (6)	0.006 (6)	0.000 (6)	0.010 (5)
C12	0.053 (7)	0.032 (5)	0.043 (6)	0.006 (5)	−0.003 (6)	−0.006 (5)
O1	0.038 (4)	0.035 (3)	0.049 (4)	0.002 (3)	0.006 (4)	0.017 (3)
O2	0.047 (5)	0.033 (3)	0.033 (4)	0.008 (3)	0.007 (3)	0.005 (3)
O3	0.046 (4)	0.031 (3)	0.031 (4)	0.014 (3)	0.007 (3)	0.008 (3)
O4	0.047 (4)	0.024 (3)	0.035 (3)	0.001 (3)	0.003 (4)	0.013 (3)

Geometric parameters (Å, º)

Cu1—O2	1.972 (6)	C2—O4	1.237 (10)
Cu1—O3^i	1.973 (6)	C2—O3	1.265 (11)
Cu1—N1	1.991 (7)	C3—C4	1.352 (13)
Cu1—N2	2.018 (7)	C4—C5	1.365 (15)
Cu1—O4	2.327 (6)	C5—C6	1.395 (16)
Cu1—O1^i	2.369 (7)	C6—C7	1.355 (13)
N1—C3	1.343 (11)	C7—C8	1.466 (12)
N1—C7	1.360 (11)	C8—C9	1.423 (12)
N2—C12	1.319 (12)	C9—C10	1.359 (14)
N2—C8	1.334 (11)	C10—C11	1.373 (14)
C1—O1	1.245 (10)	C11—C12	1.369 (14)
C1—O2	1.271 (11)	O1—Cu1^ii	2.369 (7)
C1—C2	1.552 (10)	O3—Cu1^ii	1.973 (6)
O2—Cu1—O3^i	90.6 (2)	O2—C1—C2	117.1 (8)
O2—Cu1—N1	94.5 (3)	O4—C2—O3	125.6 (11)
O3^i—Cu1—N1	172.4 (3)	O4—C2—C1	117.8 (9)
O2—Cu1—N2	173.6 (3)	O3—C2—C1	116.6 (8)
O3^i—Cu1—N2	94.9 (3)	N1—C3—C4	122.3 (9)
N1—Cu1—N2	80.4 (3)	C3—C4—C5	120.6 (10)
O2—Cu1—O4	77.6 (2)	C4—C5—C6	117.4 (10)
O3^i—Cu1—O4	84.3 (2)	C7—C6—C5	120.0 (9)
N1—Cu1—O4	102.3 (3)	C6—C7—N1	121.5 (10)
N2—Cu1—O4	99.7 (2)	C6—C7—C8	126.3 (10)
O2—Cu1—O1^i	85.3 (3)	N1—C7—C8	112.2 (9)
O3^i—Cu1—O1^i	76.5 (2)	N2—C8—C9	119.2 (9)
N1—Cu1—O1^i	98.2 (3)	N2—C8—C7	117.1 (9)
N2—Cu1—O1^i	99.1 (3)	C9—C8—C7	123.7 (9)
O4—Cu1—O1^i	154.15 (17)	C10—C9—C8	119.4 (8)
C3—N1—C7	117.9 (8)	C9—C10—C11	120.2 (9)
C3—N1—Cu1	125.5 (6)	C12—C11—C10	117.3 (11)
C7—N1—Cu1	116.3 (7)	N2—C12—C11	124.1 (9)
C12—N2—C8	119.8 (8)	C1—O1—Cu1^ii	104.4 (6)
C12—N2—Cu1	126.6 (6)	C1—O2—Cu1	117.8 (6)
C8—N2—Cu1	113.7 (6)	C2—O3—Cu1^ii	116.6 (7)
O1—C1—O2	124.8 (9)	C2—O4—Cu1	106.9 (7)
O1—C1—C2	118.2 (8)

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