catena-Poly[[(3,5-dicarb­oxy­pyrazine-2,6-dicarboxyl­ato-κ3 O 2,N 1,O 6)lithium(I)]-μ-aqua-[triaqua­lithium(I)]-μ-aqua]

Wojciech Starosta; Janusz Leciejewicz

doi:10.1107/S1600536810045903

. 2010 Nov 13;66(Pt 12):m1561–m1562. doi: 10.1107/S1600536810045903

catena-Poly[[(3,5-dicarboxypyrazine-2,6-dicarboxylato-κ³ O ²,N ¹,O ⁶)lithium(I)]-μ-aqua-[triaqualithium(I)]-μ-aqua]

Wojciech Starosta ^a, Janusz Leciejewicz ^a,^*

PMCID: PMC3011810 PMID: 21589251

Abstract

The title coordination polymer, [Li₂(C₈H₂N₂O₈)(H₂O)₅]_n contains two symmetry-independent Li⁺ ions; one is coordinated by five water O atoms, the other by an O,N,O′-tridentate doubly deprotonated pyrazine-2,3,5,6-tetracarboxylate ligand and two water O atoms. Water molecules bridge adjacent Li⁺ ions into ribbons propagating in [100]; an alternative analysis of the structure considers it to contain alternating [Li(C₈H₂N₂O₈)(H₂O)₂]⁻ anions and [Li(H₂O)₃]⁺ cations. In the polymeric model, both lithium ions show distorted trigonal–bipyramidal coordination geometries. Within the ligand, the carboxyl H atoms participate in short, almost symmetric O⋯H⋯O hydrogen bonds in which the non-coordinated carboxylate O atoms are donors and acceptors. In the crystal, the ribbons interact via a network of O—H⋯O hydrogen bonds in which the coordinated water molecules act as donors and ligand carboxylate O atoms as acceptors.

Related literature

For the crystal structures of 3d transition metal complexes with pyrazine-2,3,5,6-tetracarboxylate and water ligands, see: Alfonso et al. (2001 ▶); Graf et al. (1993 ▶); Marioni et al. (1986 ▶); Marioni et al. (1994 ▶). For the structure of a Ca(II) complex, see: Starosta & Leciejewicz (2008 ▶). For the structure of a Li complex with pyrazine-2,3-dicarboxylate and water ligands, see: Tombul et al. (2008 ▶). For a review on metal organic frameworks (MOFs), see: MacGillivray (2010 ▶).

Experimental

Crystal data

[Li₂(C₈H₂N₂O₈)(H₂O)₅]
M _r = 358.08
Monoclinic,
a = 6.8806 (14) Å
b = 11.767 (2) Å
c = 8.8082 (18) Å
β = 103.59 (3)°
V = 693.2 (2) Å³
Z = 2
Mo Kα radiation
μ = 0.16 mm⁻¹
T = 293 K
0.23 × 0.21 × 0.17 mm

Data collection

Kuma KM-4 four-circle diffractometer
Absorption correction: analytical (CrysAlis RED; Oxford Diffraction, 2008) ▶ T _min = 0.971, T _max = 0.975
2291 measured reflections
2136 independent reflections
1459 reflections with I > 2σ(I)
R _int = 0.012
3 standard reflections every 200 reflections intensity decay: 0.5%

Refinement

R[F ² > 2σ(F ²)] = 0.039
wR(F ²) = 0.127
S = 1.03
2136 reflections
148 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.42 e Å⁻³
Δρ_min = −0.32 e Å⁻³

Data collection: KM-4 Software (Kuma, 1996 ▶); cell refinement: KM-4 Software; data reduction: DATAPROC (Kuma, 2001 ▶); 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: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536810045903/hb5710sup1.cif

e-66-m1561-sup1.cif^{(15.7KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810045903/hb5710Isup2.hkl

e-66-m1561-Isup2.hkl^{(105.1KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected bond lengths (Å).

Li1—N1	2.119 (4)
Li1—O4	2.1194 (13)
Li1—O8	1.997 (4)
Li1—O7	2.075 (5)
Li1—O4ⁱ	2.1194 (13)
Li2—O6	1.9412 (12)
Li2—O7	2.385 (4)
Li2—O5	2.052 (4)
Li2—O6ⁱ	1.9412 (12)
Li2—O8ⁱⁱ	2.067 (4)

Open in a new tab

Symmetry codes: (i) Inline graphic ; (ii) .

Table 2. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O6—H61⋯O2ⁱⁱⁱ	0.90 (2)	1.87 (2)	2.7597 (14)	165.4 (19)
O6—H62⋯O4^iv	0.91 (3)	1.91 (3)	2.8129 (14)	173 (2)
O8—H81⋯O2^v	0.86 (2)	1.92 (2)	2.7753 (13)	175.9 (19)
O7—H71⋯O3^iv	0.862 (19)	2.037 (19)	2.8950 (12)	173.8 (17)
O5—H51⋯O1ⁱⁱⁱ	0.903 (19)	2.010 (19)	2.9110 (13)	175.4 (17)
O1—H32⋯O3	1.19 (2)	1.21 (2)	2.3894 (15)	173 (2)

Open in a new tab

Symmetry codes: (iii) Inline graphic ; (iv) ; (v) .

supplementary crystallographic information

Comment

Multidentate organic acids are widely used as ligands in a search for coordination polymers which can find applications in such fields as hydrogen or carbon dioxide storage, catalysis and ion-exchange resins (MacGillivray, 2010). Pyrazine-2,3,5,6-tetracarboxylate ligand is a promising building block in constructing metal-organic frameworks, since it exhibits ten chelating sites: two hetero-ring N atoms and four potentially bidentate carboxylate groups. A formation of a variety of catenated and layered polymeric structures has been reported in compounds of 3 transition metal ions with the title ligand (Marioni et al., 1986; Graf et al., 1993; Marioni et al., 1994; Alfonso et al., 2001). The Ca(II) complex shows a three-dimensional polymeric structure (Starosta & Leciejewicz, 2008). The asymmetric unit cell of a Li(I) complex with the title ligand contains two symmetry independent Li1 and Li2 ions positioned on a mirror plane with y=3/4. Pyrazine-ring N1 and N2 atoms and coordinated water O5, O7, O8 atoms are also positioned on this plane (Fig.1). The Li1 ion is chelated by the N1, O4, O4ⁱ ligand bonding moiety with typical Li—N and Li—O bond distances of 2.119 (4)Å and 2.119 (1) Å, respectively and two bridging aqua O7 and O8 atoms (d_Li1—O7 =2.075 (5)° and d_Li1—O8=1.997 (4) Å). The O4 and O4ⁱ atoms are at opposite apices of a distorted trigonal bipyramid; its equatorial plane is composed of coplanar Li1 ion, hetero-ring N1 atom and the bridging O7 and O8 atoms. Pyrazine-ring atoms are coplanar with r.m.s. of 0.0009 (1) Å; their plane makes an angle of 90° with the equatorial plane. Carboxylic groups C6/O1/O2 and C5/O1/O2 make angles with pyrazine ring of 1.45 (13)° and 4.69 (14)°, respectively. Bond distances and bond angles within the ligand molecule do not differ from those observed in other complexes with the title ligand. A proton situated between carboxylate O3 and O1 atoms, clearly visible on the Fourier map, forms a symmetrical intra-molecular hydrogen bond of 2.389 (2)Å and O3—H32—O1 angle of 173 (3)°. The (2-) charge of the ligand is compensated by the (1+) charge of the Li1 ion. The resulting anion has a charge of (1-). On the other hand, the Li2 ion as coordinated only by aqua O atoms, retains its charge of (1+). The ribbons (Fig. 2) are built of Li(C₈H₂N₂O₈)(H₂O)₂]^1- anions and [Li(H₂O)₄]¹⁺cations bridged by aqua O7 and O8 atoms belonging to coordination spheres of both Li ions. The bridging pathway propagates with Li1—O7—Li2 angle of 111.19 (14)° and Li1—O8—Li2ⁱⁱⁱ angle of 103.81 (16)°. The coordination environment of the Li2 ion is composed of five aqua O atoms, two of them O7 and O8 are bridging it with the Li1 ions. The Li2 ion, O5, O7 and O8 atoms are coplanar and form an equatorial plane of a distorted trigonal bipyramid with O6 and O6ⁱ atoms at opposite apices. Li—O bond distances within this coordination polyhedron are in the range from 1.941 (1)Å to 2.067 (4) Å, the Li2—O7 bridging bond distance amounts to 2.385 (4) Å. Trigonal bipyramidal coordination geometry of a Li(I) ion has been also observed in the structure of its complex with pyrazine-2,3-dicarboxylate and water ligands (Tombul et al. 2008). Coordinated water O atoms are donors in a network of hydrogen bonds to carboxylate O atoms in adjacent ribbons which act as acceptors.

Experimental

50 ml of aqueous solution containing 1 mmol of pyrazine-2,3,5,6-tetracarboxylic acid was added to 50 ml of an aqueous solution containing 4 mmol of lithium hydroxide. The mixture was boiled under reflux for 3 h with conatant stirring, then left to crystallize at room temperature. After a couple of days crystals of (1) were found in the form of colourless blocks. They were dissolved in water and recrystallized three times. The final crystals were washed in metanol and dried in the air.