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In the structure of the title compound, [Cu(C4O4)(C4H4N2)]n, each copper cation is surrounded by three squarate (3,4-di­hydroxy-3-cyclo­butene-1,2-dioate) anions and two pyrazine ligands, all of which are located in special positions. The copper cation and all atoms of the squarate anion are located on a mirror plane, whereas the pyrazine ligand is located around a mirror plane which is perpendicular to the ring plane. The cations are connected via the squarate anions and the pyrazine ligands, forming sheets parallel to (001).

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270100018722/ln1113sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270100018722/ln1113Isup2.hkl
Contains datablock I

CCDC reference: 162551

Comment top

The structure determination of the title compound is part of a project on the synthesis and characterization of new coordination polymers based on squaric acid derivatives and aromatic diamines using solvothermal methods. There are some copper(II) squarate diamine compounds reported in the literature, but most of them contain additional water molecules coordinated to the copper cations (Bernardinelli et al., 1989; Castro et al., 1990, 1995; Solans et al., 1990; Yaghi et al., 1995). \sch

In the crystal structure of the title compound, (I), the copper cations are coordinated by three oxygen atoms of three squarate anions and two nitrogen atoms of two pyrazine molecules within a slightly distorted tetragonal pyramid with one oxygen atom at the apex of the pyramid (Fig. 1). The Cu—O distances to the oxygen atoms within the quadratic plane are similar whereas the Cu—O distance to the apical oxygen atom, O1, is elongated. The angles around the copper cation within the quadratic plane deviate only slightly from the ideal values, whereas larger deviations are found for the angles in which the oxygen atom O1 is involved. There is one additional, but extremely long Cu—O contact to O4 of 2.732 (3) Å, which should represent only a very weak interaction. However, if this contact is considered in the Cu coordination, the coordination polyhedron around the copper cation is a slightly distorted octahedron.

The copper cations are connected via the pyrazine ligands, which sit across mirror planes, forming nearly linear chains in the direction of the crystallographic b axis. The copper cation is located in the plane of the six-membered ring and the angles C5—N—Cu and C6—N—Cu are about 120 °, which shows that the cations are oriented in the direction of the nitrogen lone-pair. In the squarate anion, only three of the four oxygen atoms are involved in copper coordination. Each anion is surrounded by three copper cations and all lie on the one mirror plane. From this arrangement, double chains are formed in the direction of the crystallographic a axis. Within these chains the copper cations are located in the direction of the oxygen lone pairs. For the oxygen atom O1 which participates in the elongated Cu—O bond, no preferred orientation of the cations in the direction of the oxygen lone pairs is found, which indicates that this must be a weak interaction.

The connection of the copper cations via the pyrazine ligands and the squarate anions leads to sheets parallel to (001). Between the sheets no pronounced interactions can be found.

Related literature top

For related literature, see: Bernardinelli et al. (1989); Castro et al. (1990, 1995); Solans et al. (1990); Yaghi et al. (1995).

Experimental top

Squaric acid (Acros), copper(I) oxide and pyrazine (Acros (molar ratio: 1:1:1) were reacted in water (10 ml) in teflon-lined steel autoclaves at 400 K for 7 d and afterwards cooled down with 3 K min-1. The product was filtered off and washed with deionized water. The precipitate consisted of yellow-green needles of the title compound.

Refinement top

The hydrogen atoms were positioned with idealized geometry and refined using a riding model. In the difference map, one large peak of 1.544 e Å3 is found which is located 1.07 Å from the copper atom. This peak cannot be attributed to absorption effects. This peak always appears even if data from different crystals are used. Careful inspection of reciprocal space plots shows clearly that the selected cell and the selected symmetry is correct.

Computing details top

Data collection: IPDS Program Package (Stoe & Cie, 1998); cell refinement: IPDS Program Package; data reduction: IPDS Program Package; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP in SHELXTLPC (Siemens, 1990); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. View of the copper coordination with labelling and displacement ellipsoids drawn at the 50% probability level (the long Cu—O contact is shown with dotted lines). Symmetry operations: (i) x - 1, y, z; (ii) x, -y + 3/2, z; (iii) x - 1/2, y, -z + 3/2; (iv) x, 1/2 - y, z.
[Figure 2] Fig. 2. Packing diagram of (I) viewed along the b axis.
(I) top
Crystal data top
[Cu(C4O4)(C4H4N2)]F(000) = 508
Mr = 255.67Dx = 2.187 Mg m3
Orthorhombic, PnmaMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2nCell parameters from 8000 reflections
a = 7.3003 (4) Åθ = 3–30°
b = 6.8114 (4) ŵ = 2.81 mm1
c = 15.6135 (11) ÅT = 293 K
V = 776.39 (8) Å3Needle, orange
Z = 40.1 × 0.04 × 0.04 mm
Data collection top
STOE Imaging Plate Diffraction System
diffractometer
1119 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.030
Graphite monochromatorθmax = 30.4°, θmin = 4.3°
ϕ–scansh = 910
8519 measured reflectionsk = 99
1231 independent reflectionsl = 2222
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)] = 0.036Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.099H-atom parameters constrained
S = 1.06 w = 1/[σ2(Fo2) + (0.0578P)2 + 1.4395P]
where P = (Fo2 + 2Fc2)/3
1231 reflections(Δ/σ)max = 0.001
82 parametersΔρmax = 1.54 e Å3
0 restraintsΔρmin = 0.74 e Å3
Crystal data top
[Cu(C4O4)(C4H4N2)]V = 776.39 (8) Å3
Mr = 255.67Z = 4
Orthorhombic, PnmaMo Kα radiation
a = 7.3003 (4) ŵ = 2.81 mm1
b = 6.8114 (4) ÅT = 293 K
c = 15.6135 (11) Å0.1 × 0.04 × 0.04 mm
Data collection top
STOE Imaging Plate Diffraction System
diffractometer
1119 reflections with I > 2σ(I)
8519 measured reflectionsRint = 0.030
1231 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0360 restraints
wR(F2) = 0.099H-atom parameters constrained
S = 1.06Δρmax = 1.54 e Å3
1231 reflectionsΔρmin = 0.74 e Å3
82 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
Cu0.06517 (5)0.75000.67554 (2)0.01391 (14)
C10.6368 (5)0.75000.5845 (2)0.0189 (6)
C20.5129 (5)0.75000.5073 (2)0.0185 (6)
C30.3560 (4)0.75000.56712 (19)0.0148 (5)
C40.4743 (4)0.75000.6393 (2)0.0154 (5)
O10.8044 (4)0.75000.59402 (19)0.0321 (6)
O20.5348 (4)0.75000.42983 (18)0.0337 (7)
O30.1824 (3)0.75000.56144 (14)0.0167 (4)
O40.4280 (3)0.75000.71845 (15)0.0206 (5)
N0.0832 (3)0.4538 (3)0.67893 (12)0.0168 (4)
C50.0377 (4)0.3515 (4)0.60956 (15)0.0262 (5)
H50.00500.41810.55990.031*
C60.1291 (4)0.3522 (3)0.74890 (15)0.0218 (4)
H60.16160.41920.79850.026*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cu0.0177 (2)0.0113 (2)0.0127 (2)0.0000.00232 (12)0.000
C10.0159 (14)0.0216 (14)0.0192 (13)0.0000.0001 (11)0.000
C20.0182 (14)0.0211 (14)0.0163 (13)0.0000.0008 (10)0.000
C30.0137 (13)0.0159 (12)0.0148 (12)0.0000.0007 (9)0.000
C40.0166 (13)0.0142 (12)0.0154 (13)0.0000.0025 (10)0.000
O10.0149 (12)0.0520 (18)0.0295 (13)0.0000.0032 (10)0.000
O20.0315 (15)0.054 (2)0.0156 (11)0.0000.0023 (10)0.000
O30.0139 (10)0.0232 (10)0.0130 (9)0.0000.0004 (7)0.000
O40.0204 (11)0.0285 (12)0.0131 (10)0.0000.0036 (8)0.000
N0.0227 (10)0.0107 (8)0.0170 (8)0.0001 (7)0.0009 (6)0.0007 (6)
C50.0481 (16)0.0154 (10)0.0150 (9)0.0006 (10)0.0051 (9)0.0021 (8)
C60.0336 (12)0.0160 (10)0.0157 (8)0.0006 (9)0.0059 (8)0.0005 (8)
Geometric parameters (Å, º) top
Cu—O4i1.935 (2)C3—O31.271 (4)
Cu—O31.976 (2)C3—C41.420 (4)
Cu—Nii2.022 (2)C4—O41.280 (4)
Cu—N2.022 (2)O1—Cuiv2.290 (3)
Cu—O1iii2.290 (3)O4—Cuv1.935 (2)
C1—O11.233 (4)N—C51.330 (3)
C1—C41.464 (5)N—C61.336 (3)
C1—C21.507 (5)C5—C5vi1.383 (5)
C2—O21.220 (4)C6—C6vi1.392 (4)
C2—C31.478 (4)
O4i—Cu—O3174.48 (10)C3—C2—C187.7 (2)
O4i—Cu—Nii90.65 (5)O3—C3—C4131.4 (3)
O3—Cu—Nii89.74 (5)O3—C3—C2136.8 (3)
O4i—Cu—N90.65 (5)C4—C3—C291.8 (3)
O3—Cu—N89.74 (5)O4—C4—C3127.3 (3)
Nii—Cu—N171.96 (12)O4—C4—C1141.1 (3)
O4i—Cu—O1iii92.59 (11)C3—C4—C191.6 (2)
O3—Cu—O1iii81.89 (10)C1—O1—Cuiv153.2 (3)
Nii—Cu—O1iii93.94 (6)C3—O3—Cu111.6 (2)
N—Cu—O1iii93.94 (6)C4—O4—Cuv133.5 (2)
O1—C1—C4137.2 (3)C5—N—C6117.2 (2)
O1—C1—C2133.8 (3)C5—N—Cu119.02 (16)
C4—C1—C289.0 (3)C6—N—Cu123.68 (15)
O2—C2—C3136.8 (3)N—C5—C5vi121.60 (13)
O2—C2—C1135.6 (3)N—C6—C6vi121.21 (13)
Symmetry codes: (i) x1/2, y, z+3/2; (ii) x, y+3/2, z; (iii) x1, y, z; (iv) x+1, y, z; (v) x+1/2, y, z+3/2; (vi) x, y+1/2, z.

Experimental details

Crystal data
Chemical formula[Cu(C4O4)(C4H4N2)]
Mr255.67
Crystal system, space groupOrthorhombic, Pnma
Temperature (K)293
a, b, c (Å)7.3003 (4), 6.8114 (4), 15.6135 (11)
V3)776.39 (8)
Z4
Radiation typeMo Kα
µ (mm1)2.81
Crystal size (mm)0.1 × 0.04 × 0.04
Data collection
DiffractometerSTOE Imaging Plate Diffraction System
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
8519, 1231, 1119
Rint0.030
(sin θ/λ)max1)0.712
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.036, 0.099, 1.06
No. of reflections1231
No. of parameters82
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)1.54, 0.74

Computer programs: IPDS Program Package (Stoe & Cie, 1998), IPDS Program Package, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), XP in SHELXTLPC (Siemens, 1990), SHELXL97.

Selected geometric parameters (Å, º) top
Cu—O4i1.935 (2)Cu—N2.022 (2)
Cu—O31.976 (2)Cu—O1iii2.290 (3)
Cu—Nii2.022 (2)
O4i—Cu—O3174.48 (10)O4i—Cu—O1iii92.59 (11)
O4i—Cu—N90.65 (5)O3—Cu—O1iii81.89 (10)
O3—Cu—N89.74 (5)N—Cu—O1iii93.94 (6)
Nii—Cu—N171.96 (12)
Symmetry codes: (i) x1/2, y, z+3/2; (ii) x, y+3/2, z; (iii) x1, y, z.
 

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