The new nickel(II) coordination polymer poly[diaquanickel(II)-
-(pyrazine-2,3,5,6-tetracarboxylato)-tetraaquanickel(II)], {[{Ni(C
8N
2O
8)(H
2O)
2}Ni(H
2O)
4]}
n, has been synthesized and characterized both spectroscopically and crystallographically, by X-ray powder diffraction analysis. In this two-dimensional coordination polymer, Ni
II ions are bridged by pyrazine-2,3,5,6-tetracarboxylic acid, coordinating in a bis-bidentate manner, so forming one-dimensional polymeric chains. The chains are linked by a second Ni
II ion,
via an O atom of the coordinated carboxylate group, resulting in the formation of a two-dimensional layer-like polymer. The remaining coordination sites of the two independent octahedral Ni
II ions are occupied by water molecules. The layers are connected
via hydrogen bonds involving all six coordinated water molecules.
Supporting information
CCDC reference: 174797
A solution of NiSO4 (1.03 g, 3.92 mmol) in water (20 ml) was added to an
aqueous solution of pyrazine-2,3,5,6-tetracarboxylic acid (0.50 g, 1.95 mmol,
20 ml) at 323 K. The solution was stirred for 5 min at 323 K and then slowly
cooled to room temperature. The light green microcrystalline solid formed was
filtered off after 3 d (yield 0.66 g, 71%). Analysis calculated for
C8H12N2O14Ni2: C 20.12, H 2.53, N 5.87%; found: C 19.42, H 2.54, N
5.73%; IR spectroscopic analysis (KBr, ν, cm-1): 3365 (H2O), 1645 (C═
O), 1443 and 1323 (C═N, C═C).
The indexing procedure (Visser, 1969) revealed a triclinic cell, which was used
for the structure solution. Approximately 400 reflections were extracted from
the powder diffraction pattern for use in direct methods. Two independent
Ni-atom positions, both occupying special positions, and the coordinating N
and O atoms, were located. The structural model was then completed by
difference Fourier techniques. It was not possible to locate the water H
atoms. This model was then used for Rietveld profile refinement. After the
initial refinement of the scale, background and unit cell constants, the
atomic positions were refined with soft constraints for the bond distances
(International Tables for Crystallography, 1995, Vol. C, pp ?-?) and angles,
and with a low weight. In the final cycles of refinement, the shifts in all
the parameters were less than their estimated standard deviations. The final
Rietveld plot is given in Fig. 3.
Data collection: Rigaku/AFC Diffractometer Control Software (Rigaku Corporation, 1995); cell refinement: EXPO (Altomare et al., 1997); data reduction: EXPO; program(s) used to solve structure: EXPO and SHELXL97 (Sheldrick, 1997); program(s) used to refine structure: GSAS (Larson & Von Dreele, 1994); molecular graphics: PLATON (Spek, 2001); software used to prepare material for publication: GSAS.
poly[diaquanickel(II)-µ-(pyrazine-2,3,5,6-tetracarboxylato)-
tetraaquanickel(II)
top
Crystal data top
[Ni(C8N2O8)(H2O)2][Ni(H2O)4] | Z = 1 |
Mr = 477.5 | F(000) = 242 |
Triclinic, P1 | Dx = 2.188 Mg m−3 |
a = 6.9892 (3) Å | Cu Kα radiation, λ = 1.542 Å |
b = 7.169 (4) Å | T = 295 K |
c = 8.2106 (3) Å | Particle morphology: plate-like |
α = 85.922 (3)° | green |
β = 84.242 (4)° | flat sheet, 25 × 25 mm |
γ = 61.818 (3)° | Specimen preparation: Prepared at 295 K |
V = 360.65 (1) Å3 | |
Data collection top
Rigaku model? diffractometer | Data collection mode: reflection |
Radiation source: X-ray tube, rotating anode | Scan method: step |
None monochromator | 2θmin = 10°, 2θmax = 70°, 2θstep = 0.01° |
Specimen mounting: packed powder pellet | |
Refinement top
Refinement on profile intensities | 50 parameters |
Least-squares matrix: full with fixed elements per cycle | 57 constraints |
Rp = 0.065 | H-atom parameters not refined |
Rwp = 0.086 | 1/[y(obs)]1/2 |
Rexp = 0.019 | (Δ/σ)max = 0.01 |
χ2 = 1.690 | Background function: square polynomial |
6000 data points | Preferred orientation correction: none |
Profile function: pseudo-Voigt | |
Crystal data top
[Ni(C8N2O8)(H2O)2][Ni(H2O)4] | β = 84.242 (4)° |
Mr = 477.5 | γ = 61.818 (3)° |
Triclinic, P1 | V = 360.65 (1) Å3 |
a = 6.9892 (3) Å | Z = 1 |
b = 7.169 (4) Å | Cu Kα radiation, λ = 1.542 Å |
c = 8.2106 (3) Å | T = 295 K |
α = 85.922 (3)° | flat sheet, 25 × 25 mm |
Data collection top
Rigaku model? diffractometer | Scan method: step |
Specimen mounting: packed powder pellet | 2θmin = 10°, 2θmax = 70°, 2θstep = 0.01° |
Data collection mode: reflection | |
Refinement top
Rp = 0.065 | 6000 data points |
Rwp = 0.086 | 50 parameters |
Rexp = 0.019 | H-atom parameters not refined |
χ2 = 1.690 | |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
Ni1 | 0.5 | −0.5 | −0.5 | 0.0442 (14)* | |
Ni2 | 0.0 | 0.0 | 0.0 | 0.0442 (14)* | |
O1 | 0.3411 (7) | −0.3757 (10) | −0.2861 (4) | 0.0357 (14)* | |
O2 | −0.0010 (8) | −0.1574 (10) | −0.1899 (6) | 0.0357 (14)* | |
O3 | −0.3159 (13) | −0.3524 (11) | −0.1033 (7) | 0.0357 (14)* | |
O4 | −0.4596 (13) | −0.0776 (11) | −0.2999 (10) | 0.0357 (14)* | |
O5 | 0.3538 (10) | −0.2121 (6) | −0.6071 (8) | 0.0357 (14)* | |
O6 | 0.2786 (7) | −0.2399 (7) | 0.0676 (9) | 0.0357 (14)* | |
O7 | 0.1629 (11) | 0.1344 (11) | −0.1298 (8) | 0.0357 (14)* | |
N1 | 0.2071 (6) | −0.5090 (12) | −0.5042 (7) | 0.0357 (14)* | |
C1 | 0.0512 (9) | −0.4183 (16) | −0.3764 (8) | 0.0357 (14)* | |
C2 | −0.1532 (9) | −0.4034 (16) | −0.3744 (8) | 0.0357 (14)* | |
C3 | 0.1347 (9) | −0.2982 (15) | −0.2850 (14) | 0.0357 (14)* | |
C4 | −0.3290 (17) | −0.2634 (12) | −0.2456 (8) | 0.0357 (14)* | |
Geometric parameters (Å, º) top
Ni1—N1 | 2.082 (1) | Ni2—O6ii | 1.994 (2) |
Ni1—N1i | 2.082 (1) | Ni2—O7 | 2.002 (2) |
Ni1—O1 | 2.002 (2) | Ni2—O7ii | 2.002 (2) |
Ni1—O1i | 2.002 (2) | O3—O6iii | 2.80 (1) |
Ni1—O5 | 2.002 (2) | O3—O6iv | 2.80 (1) |
Ni1—O5i | 2.002 (2) | O4—O5v | 2.56 (1) |
Ni2—O2 | 1.991 (2) | O4—O7iii | 2.64 (1) |
Ni2—O2ii | 1.991 (2) | O5—O6vi | 2.81 (1) |
Ni2—O6 | 1.994 (2) | | |
| | | |
O1—Ni1—N1 | 76.7 (1) | O2ii—Ni2—O6 | 88.1 (1) |
O1i—Ni1—N1 | 103.3 (1) | O2—Ni2—O6 | 91.9 (1) |
O1i—Ni1—N1i | 76.7 (1) | O2ii—Ni2—O6ii | 91.9 (1) |
O1—Ni1—N1i | 103.3 (1) | O2—Ni2—O6ii | 88.1 (1) |
O5—Ni1—N1 | 87.1 (1) | O2ii—Ni2—O7 | 86.5 (1) |
O5i—Ni1—N1i | 87.1 (1) | O2—Ni2—O7 | 93.5 (1) |
O5—Ni1—N1i | 92.9 (1) | O2—Ni2—O7ii | 86.5 (1) |
O5i—Ni1—N1 | 92.9 (1) | O2ii—Ni2—O7ii | 93.5 (1) |
O5—Ni1—O1 | 89.5 (1) | O6—Ni2—O7 | 90.7 (1) |
O5i—Ni1—O1i | 89.5 (1) | O6ii—Ni2—O7 | 89.3 (1) |
O5—Ni1—O1i | 90.5 (1) | O6—Ni2—O7ii | 89.3 (1) |
O5i—Ni1—O1 | 90.5 (1) | O6ii—Ni2—O7ii | 90.7 (1) |
N1i—Ni1—N1 | 180.0 | O2ii—Ni2—O2 | 180.0 |
O1i—Ni1—O1 | 180.0 | O6—Ni2—O6ii | 180.0 |
O5i—Ni1—O5 | 180.0 | O7—Ni2—O7ii | 180.0 |
Symmetry codes: (i) −x+1, −y−1, −z−1; (ii) −x, −y, −z; (iii) x−1, y, z; (iv) −x, −y−1, −z; (v) −x, −y, −z−1; (vi) x, y, z−1. |
Experimental details
Crystal data |
Chemical formula | [Ni(C8N2O8)(H2O)2][Ni(H2O)4] |
Mr | 477.5 |
Crystal system, space group | Triclinic, P1 |
Temperature (K) | 295 |
a, b, c (Å) | 6.9892 (3), 7.169 (4), 8.2106 (3) |
α, β, γ (°) | 85.922 (3), 84.242 (4), 61.818 (3) |
V (Å3) | 360.65 (1) |
Z | 1 |
Radiation type | Cu Kα, λ = 1.542 Å |
Specimen shape, size (mm) | Flat sheet, 25 × 25 |
|
Data collection |
Diffractometer | Rigaku model? diffractometer |
Specimen mounting | Packed powder pellet |
Data collection mode | Reflection |
Scan method | Step |
2θ values (°) | 2θmin = 10 2θmax = 70 2θstep = 0.01 |
|
Refinement |
R factors and goodness of fit | Rp = 0.065, Rwp = 0.086, Rexp = 0.019, χ2 = 1.690 |
No. of data points | 6000 |
No. of parameters | 50 |
No. of restraints | ? |
H-atom treatment | H-atom parameters not refined |
Selected geometric parameters (Å, º) topNi1—N1 | 2.082 (1) | Ni2—O7 | 2.002 (2) |
Ni1—O1 | 2.002 (2) | O3—O6i | 2.80 (1) |
Ni1—O5 | 2.002 (2) | O4—O5ii | 2.56 (1) |
Ni2—O2 | 1.991 (2) | O4—O7i | 2.64 (1) |
Ni2—O6 | 1.994 (2) | O5—O6iii | 2.81 (1) |
| | | |
O1—Ni1—N1 | 76.7 (1) | O2—Ni2—O6 | 91.9 (1) |
O1—Ni1—N1iv | 103.3 (1) | O2—Ni2—O6v | 88.1 (1) |
O5—Ni1—N1 | 87.1 (1) | O2—Ni2—O7 | 93.5 (1) |
O5—Ni1—N1iv | 92.9 (1) | O2—Ni2—O7v | 86.5 (1) |
O5—Ni1—O1 | 89.5 (1) | O6—Ni2—O7 | 90.7 (1) |
O5—Ni1—O1iv | 90.5 (1) | O6—Ni2—O7v | 89.3 (1) |
Symmetry codes: (i) x−1, y, z; (ii) −x, −y, −z−1; (iii) x, y, z−1; (iv) −x+1, −y−1, −z−1; (v) −x, −y, −z. |
Pyrazine-2,3,5,6-tetracarboxylic acid (pztcH4) was first synthesized over 100 years ago (Wolff, 1887, 1893) and an alternative synthesis was later proposed by Chattaway & Humphrey (1929). More recently, it has been used to form coordination polymers with first row transition metals such as iron(II) (Marioni et al., 1986), copper(II) (Graf et al., 1993), manganese(II) (Marioni et al., 1994) and zinc(II) (Marioni et al., 1986). Here, we present the results of the reaction of pztcH4 with NiSO4 to form the title coordination polymer, (I), and describe its analysis and structure determination, carried out using laboratory X-ray powder diffraction. \sch
Compound (I) is a planar two-dimensional polymer (Fig. 1). NiII ions are bridged by the deprotonated ligand pyrazine-2,3,5,6-tetracarboxylic acid (pztc4-, C8N2O8) coordinating in a bis-bidentate manner, so forming one-dimensional polymer chains with coplanar pyrazine rings. The chains are linked by [Ni(H2O)4]2+ units, with atom Ni2 coordinated to atom O2 of the coordinated carboxylate groups in the chains, resulting in the formation of a two-dimensional sheet-like structure. Selected bond distances and angles, and possible hydrogen bond O···O distances, are given in Table 1.
The deprotonated centrosymmetric pztc4- ligand is coordinated to two crystallographically equivalent NiII ions (Ni1) through the two N atoms of the pyrazine ring and two O atoms from two symmetrically opposing carboxylate groups. Water molecules occupy the remaining coordination sites of the octahedral Ni1 ions. The metal ions occupy inversion centres and the ligand possesses Ci symmetry.
The metal-to-metal distance, Ni1···O1—C3—O2···Ni2, is 5.4126 (3) Å, which is shorter than the Ni1-pyrazine-Ni1(1 + x, y, z) distance of 6.989 (1) Å. The Ni1—N1 bond [2.082 (1) Å] is slightly longer, and the Ni2—O2 bond [1.991 (2) Å] slightly shorter, than the same distances in similar NiII complexes with the ligands pyrazine-2,3-dicarboxylic acid (mean Ni—N 2.061 and mean Ni—O 2.060 Å; Mao et al., 1996) and pyrazine-2,5-dicarboxylic acid (Ni—N 2.033 and Ni—O 2.068 Å; Ptasiewicz-Bak et al., 1995). Atom Ni2 of the bridging [Ni(H2O)4]2+ unit forms four short Ni—O bonds [1.991 (2)–1.994 (2) Å] and two long Ni—O bonds [2.002 (5) Å], while for atom Ni1, the Ni—N bonds are longer than the Ni—O distances: 2.082 (2) compared with 2.002 (5) Å.
The two non-coordinated carboxylate groups (atoms C2, O3 and O4) and the coordinated water molecules (atoms O5, O6 and O7) are directed into the interlayer space. The short O···O distances (2.56–2.81 Å; Table 1) suggest possible hydrogen bonding between the layers, which would lead to the formation of a three-dimensional network (Figure 2).
Compound (I) was first synthesized in 1986 (Marioni, 1986) and, based on the elemental analysis, which indicated a metal-to-ligand ratio of 2:1, a binuclear complex was proposed. Thermogravimetric analysis indicated the presence of six water molecules. This result supported the proposition of a binuclear NiII complex containing the pztc4- anion coordinating in a bis-tridentate manner, with the remaining coordination sites of the metal atoms being occupied by water molecules. A single-crystal X-ray analysis was not possible, as the compound was always obtained as a microcrystalline powder. Analysis of the laboratory X-ray powder diffraction data has shown that two chemically independent nickel atoms, Ni1 and Ni2, are found interconnected by a completely deprotonated ligand, pztc4-, to form a two-dimensional coordination polymer. The deprotonated ligand in the Ni-pztc-Ni chains has a formal charge of -4, which is not compensated for by the Ni12+ ions. As has been observed in other metal complexes of pztcH4, the carboxylate groups adjacent to those coordinated to the first metal are rotated by almost 50° out of the plane of the pyrazine ring. These negatively charged chains are then connected by [Ni(H2O)4]2+ ions, resulting in the formation of neutral sheets. This charge compensation behaviour, incorporating [M(H2O)n]2+ units in the structure, has been observed previously in a zinc(II) complex (Hakansson et al., 1993), a series of iron(II) complexes (Laine et al., 1995) and a trinuclear copper(II) complex (Colacio et al., 1993).