catena-Poly[[bis­­(1-ethyl-1H-imidazole-κN³)copper(II)]-μ-oxalato-κ⁴O¹,O²:O^1′,O^2′]

The title compound, [Cu(C₂O₄)(C₅H₈N₂)₂]_n, is composed of one-dimensional linear chains running parallel to the a axis. In the chain, trans-[Cu(imidazole)₂]²⁺ units are sequentially bridged by bis-bidentate oxalate ligands, resulting in an octa­hedral CuO₄N₂ donor set. The Cu⋯Cu separation through the oxalate bridge is 5.620 (5) Å. Both the Cu atoms and the C—C bond of the oxalate bridge are bis­ected by inversion centres.

Related literature

For general background on ferroelectric organic compounds with framework structures, see: Fu et al. (2009); Ye et al. (2006); Zhang et al. (2008, 2010).

Experimental

Crystal data

• [Cu(C₂O₄)(C₅H₈N₂)₂]

• M_r = 343.83

• Monoclinic, P 2₁ /n

• a = 5.6200 (11) Å

• b = 8.8577 (18) Å

• c = 14.481 (3) Å

• β = 96.55 (3)°

• V = 716.2 (2) ų

• Z = 2

• Mo Kα radiation

• μ = 1.55 mm⁻¹

• T = 293 K

• 0.30 × 0.25 × 0.20 mm

Data collection

• Rigaku SCXmini diffractometer

• Absorption correction: multi-scan (CrystalClear; Rigaku, 2005) T_min = 0.635, T_max = 0.734

• 7300 measured reflections

• 1653 independent reflections

• 1267 reflections with I > 2σ(I)

• R_int = 0.062

Refinement

• R[F² > 2σ(F²)] = 0.040

• wR(F²) = 0.092

• S = 1.05

• 1653 reflections

• 98 parameters

• H-atom parameters constrained

• Δρ_max = 0.48 e Å⁻³

• Δρ_min = −0.33 e Å⁻³

Data collection: CrystalClear (Rigaku, 2005); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97.

Supporting information

S1. Comment

As part of our ongoing study of potential ferroelectric materials we have determined the structure of the present copper complex and examined its dielectric behaviour with temperature. This is the usual method for detecting these materials (Fu et al., 2009; Ye et al., 2006; Zhang et al., 2008; Zhang et al., 2010). Unfortunately, the dielectric constant for the title compound, Cu[C₅H₈N]₂C₂O₄, (I) does not show any behavior indicating the onset of a ferroelectric phase change over the range 80 K to 298 K (m.p.319–329).

The Cu atoms are located on crystallographic inversion centers, and are coordinated to four oxygen atoms of two bridging oxalato ligands, also bisected by inversion centres, and two endocyclic nitrogen atoms from two crystallograhically related imidazole molecules, resulting in octahedral MO₄N₂ donor sets. Fig. 2 suggests the way in which oxalato-bridged chains build up. The Cu — Cu intrachain separation is 5.620 (5) Å.

Related literature

For general background on ferroelectric organic frameworks, see: Fu et al. (2009); Ye et al. (2006); Zhang et al. (2008, 2010).

S2. Experimental

A mixture of 1-ethyl imidazole (1.9 g, 20 mmol), cupric oxalate (1.5 g, 10 mmol) in water was stirred for several days at ambient temperature; blue block crystals were obtained on standing.

S3. Refinement

All H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with C—H = 0.93–0.96 Å, and with Uĩso(H) = 1.2 Uĩso(C) or 1.5 Uĩso(C) for ethy H atoms..

Computing details

Data collection: CrystalClear (Rigaku, 2005); cell refinement: CrystalClear (Rigaku, 2005); data reduction: CrystalClear (Rigaku, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. Ellipsoid plot of (I), ( 50% probability level). Symmetry codes A: -x, 1-y, 1-z. B: 1-x, 1-y, 1-z. C: -1+x, y, z.
	Fig. 2. Packing diagram of the title compound showing the way in which chains are built up.

catena-Poly[[bis(1-ethyl-1Himidazole-κN³)copper(II)]- µ-oxalato-κ⁴O¹,O²:O^1',O^2']

Crystal data

[Cu(C2O4)(C5H8N2)2]	F(000) = 354
Mr = 343.83	Dx = 1.594 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 1653 reflections
a = 5.6200 (11) Å	θ = 2.3–27.5°
b = 8.8577 (18) Å	µ = 1.55 mm^−1
c = 14.481 (3) Å	T = 293 K
β = 96.55 (3)°	Block, blue
V = 716.2 (2) Å^3	0.30 × 0.25 × 0.20 mm
Z = 2

Data collection

Rigaku SCXmini diffractometer	1267 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.062
Graphite monochromator	θmax = 27.5°, θmin = 3.7°
ω scans	h = −7→7
Absorption correction: multi-scan (CrystalClear; Rigaku, 2005)	k = −11→11
Tmin = 0.635, Tmax = 0.734	l = −18→18
7300 measured reflections	2 standard reflections every 150 reflections
1653 independent reflections	intensity decay: none

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)] = 0.040	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.092	H-atom parameters constrained
S = 1.05	w = 1/[σ^2(Fo^2) + (0.0361P)^2 + 0.3394P] where P = (Fo^2 + 2Fc^2)/3
1653 reflections	(Δ/σ)max < 0.001
98 parameters	Δρmax = 0.48 e Å^−3
0 restraints	Δρmin = −0.33 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
Cu1	0.0000	0.5000	0.5000	0.02341 (16)
C1	0.0677 (5)	0.4366 (4)	0.3025 (2)	0.0326 (7)
H1	0.1452	0.3463	0.3194	0.039*
C2	−0.1151 (5)	0.6469 (4)	0.3090 (2)	0.0365 (7)
H2	−0.1900	0.7304	0.3318	0.044*
C3	−0.0853 (6)	0.6229 (4)	0.2184 (2)	0.0397 (8)
H3	−0.1337	0.6861	0.1685	0.048*
C4	0.1083 (6)	0.4132 (4)	0.1331 (2)	0.0439 (8)
H4A	−0.0227	0.4136	0.0833	0.053*
H4B	0.1477	0.3088	0.1482	0.053*
C5	0.3213 (7)	0.4885 (4)	0.0999 (3)	0.0534 (9)
H5A	0.2801	0.5899	0.0809	0.080*
H5B	0.3701	0.4333	0.0482	0.080*
H5C	0.4505	0.4906	0.1494	0.080*
C6	0.4839 (4)	0.4123 (3)	0.49195 (17)	0.0210 (5)
N1	−0.0177 (4)	0.5292 (3)	0.36168 (15)	0.0282 (6)
N2	0.0296 (4)	0.4876 (3)	0.21516 (16)	0.0339 (6)
O1	0.3372 (3)	0.6619 (2)	0.52150 (13)	0.0291 (5)
O2	0.2754 (3)	0.3599 (2)	0.49398 (12)	0.0259 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.0188 (2)	0.0301 (3)	0.0218 (2)	0.0016 (2)	0.00409 (16)	−0.0002 (2)
C1	0.0357 (16)	0.0345 (16)	0.0279 (16)	0.0039 (14)	0.0056 (13)	0.0016 (13)
C2	0.0367 (16)	0.0403 (18)	0.0333 (16)	0.0065 (14)	0.0067 (13)	0.0027 (14)
C3	0.0414 (17)	0.0478 (19)	0.0291 (16)	0.0012 (16)	0.0010 (13)	0.0095 (15)
C4	0.050 (2)	0.056 (2)	0.0266 (16)	−0.0079 (17)	0.0082 (14)	−0.0087 (15)
C5	0.063 (2)	0.050 (2)	0.052 (2)	−0.0054 (19)	0.0277 (19)	0.0000 (18)
C6	0.0211 (12)	0.0244 (14)	0.0172 (12)	0.0034 (12)	0.0008 (10)	0.0010 (11)
N1	0.0265 (12)	0.0336 (15)	0.0248 (12)	0.0027 (10)	0.0048 (10)	0.0015 (10)
N2	0.0358 (13)	0.0422 (15)	0.0238 (12)	−0.0023 (12)	0.0042 (10)	−0.0010 (11)
O1	0.0235 (9)	0.0270 (11)	0.0374 (11)	0.0020 (8)	0.0069 (8)	−0.0030 (9)
O2	0.0197 (9)	0.0269 (10)	0.0316 (10)	−0.0014 (8)	0.0054 (8)	−0.0003 (9)

Geometric parameters (Å, º)

Cu1—O2	1.9935 (18)	C3—H3	0.9300
Cu1—O2^i	1.9935 (18)	C4—N2	1.470 (4)
Cu1—N1	2.011 (2)	C4—C5	1.497 (4)
Cu1—N1^i	2.011 (2)	C4—H4A	0.9700
Cu1—O1^i	2.3684 (18)	C4—H4B	0.9700
Cu1—O1	2.3684 (19)	C5—H5A	0.9600
C1—N1	1.316 (4)	C5—H5B	0.9600
C1—N2	1.337 (4)	C5—H5C	0.9600
C1—H1	0.9300	C6—O1^ii	1.235 (3)
C2—C3	1.359 (4)	C6—O2	1.264 (3)
C2—N1	1.368 (4)	C6—C6^ii	1.579 (5)
C2—H2	0.9300	O1—C6^ii	1.235 (3)
C3—N2	1.365 (4)
O2—Cu1—O2^i	180.000 (1)	N2—C4—C5	112.7 (3)
O2—Cu1—N1	89.27 (8)	N2—C4—H4A	109.1
O2^i—Cu1—N1	90.73 (8)	C5—C4—H4A	109.1
O2—Cu1—N1^i	90.73 (8)	N2—C4—H4B	109.1
O2^i—Cu1—N1^i	89.27 (8)	C5—C4—H4B	109.1
N1—Cu1—N1^i	180.000 (1)	H4A—C4—H4B	107.8
O2—Cu1—O1^i	103.35 (7)	C4—C5—H5A	109.5
O2^i—Cu1—O1^i	76.65 (7)	C4—C5—H5B	109.5
N1—Cu1—O1^i	89.94 (8)	H5A—C5—H5B	109.5
N1^i—Cu1—O1^i	90.06 (8)	C4—C5—H5C	109.5
O2—Cu1—O1	76.65 (7)	H5A—C5—H5C	109.5
O2^i—Cu1—O1	103.35 (7)	H5B—C5—H5C	109.5
N1—Cu1—O1	90.06 (8)	O1^ii—C6—O2	125.6 (2)
N1^i—Cu1—O1	89.94 (8)	O1^ii—C6—C6^ii	117.7 (3)
O1^i—Cu1—O1	180.00 (7)	O2—C6—C6^ii	116.7 (3)
N1—C1—N2	112.0 (3)	C1—N1—C2	105.3 (2)
N1—C1—H1	124.0	C1—N1—Cu1	126.0 (2)
N2—C1—H1	124.0	C2—N1—Cu1	128.6 (2)
C3—C2—N1	109.5 (3)	C1—N2—C3	106.8 (2)
C3—C2—H2	125.2	C1—N2—C4	125.6 (3)
N1—C2—H2	125.2	C3—N2—C4	127.5 (3)
C2—C3—N2	106.3 (3)	C6^ii—O1—Cu1	108.12 (16)
C2—C3—H3	126.8	C6—O2—Cu1	119.93 (16)
N2—C3—H3	126.8

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