catena-Poly[diacridinium [zinc(II)-di-μ-pyrazine-2,3-dicarboxylato-κ3 N 1,O 2:O 3;O 3:N 1,O 2]]

The crystal structure of the title compound, {(C13H10N)2[Zn(C6H2N2O4)2]}n, consists of polymeric Zn complex anions and discrete acridinium cations. The Zn cation, located on an inversion center, is N,O-chelated by two pyrazine-2,3-dicarboxylate (pyzdc) anions in the basal plane, and is further coordinated by two carboxylate O atoms from adjacent pyzdc anions in the axial directions with a longer Zn—O bond distance, forming a distorted ZnN2O4 coordination geometry. The pyzdc anions bridge the Zn cations, forming polymeric chains running along the crystallographic b axis. The acridinium cations are linked to the complex chains via N—H⋯O and C—H⋯O hydrogen bonding. Significant π–π stacking between parallel acridinium ring systems is observed in the crystal structure, face-to-face distances being 3.311 (3) and 3.267 (4) Å.

Data collection: SMART (Bruker, 1998); cell refinement: SAINT-Plus (Bruker, 1998); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL. Comment H 2 pyzdc has proved to be well suited for the construction of multidimensional frameworks due to the presence of two adjacent carboxylate groups (O donor atoms) as substituents on the N-heterocyclic pyrazine ring (N donor atoms). In this paper, we report the hydrothermal synthesis, crystal and molecular structure of a pyrazinecarboxylate-based Zn atom supramolecular coordination compound as a novel inorganic polymer, for the first time. The hydrothermal reaction between H 2 pyzdc, acr, and zinc nitrate tetra-hydrate, resulted in the formation of {(C 13 H 10 N) 2 [Zn(C 6 H 2 N 2 O 4 ) 2 ]} n . This inorganic polymeric compound consists of an anionic complex, [Zn(pyzdc) 2 ] 2-, counter-ions, (acrH) + molecules. In the title inorganic polymeric compound, two COOH protons have been transferred to non-coordinated pyridine rings of acr moieties. The central Zn1 atom is six-coordinated by N1 and O1 atoms in the equatorial plane from two (pyzdc) 2ligands and by two O4 atoms in the axial positions (Fig. 1). The coordination environment around the Zn atom may be considered as slightly distorted octahedral. The anionic complex lies on a crystallographic center of symmetry. The mean Zn-N and Zn-O bond lengths are 2.093 (2) and 2.138 (17) Å, respectively. In the structure of the title inorganic polymeric compound, (acrH) + cations and [Zn(pyzdc) 2 ] 2anions are linked together by classical N3-H3B···O3 and non-classical C13-H13···O2 and C16-H16···O3 hydrogen bonds. In the crystal structure of the title polymeric compound, the spaces between [Zn(pyzdc) 2 ] 2fragments are filled with layers of (acrH) + cations. Indeed, the arrangement of anionic layers to each other resulted in the making of suitable spaces for entering cationic parts. As a essential factor extensive π-π stacking interactions between parallel aromatic rings of the acridinium ions,(acrH) + , with face-to-face distances of 3.311 (3) and 3.267 (4) Å, caused to further stabilization of crystalline network.
It should be noted that most of the molecular structures consisting up dicarboxylate ligands incorporate water molecules of hydration which may lead to formation kind of (H 2 O) n clusters (Review article by Aghabozorg et al. 2010a). The used reaction conditions such as hydrothermal synthesis versus just normal synthesis in aqueous conditions play basic roles in this regard. Additionally, if water molecules are present, it may prevent polymerization because it will coordinate to the metal center and so, used dicarboxylate ligand can not play chelate role for connecting metal centers to each other.
For example, herein, we have obtained an inorganic polymer because of applying hydrothermal condition. But, recently published work of our research group (Aghabozorg et al. 2010b) show that the reaction of cobalt(II) nitrate hexa-hydrate, acr, and H 2 pyzdc in aqueous solution and routine condition resulted in the formation of (acrH) 2 [Co(pyzdc) 2 (H 2 O) 2 ]. 6H 2 O crystals as monomeric structure.

Experimental
A mixture of H 2 pyzdc (0.83 mmol, 140 mg), acridine (1.67 mmol, 300 mg), and Zn(NO 3 ) 2 .4H 2 O (0.27 mmol, 80 mg) in distilled water (12 ml) was placed in a Teflon-lined stainless steel vessel, heated to 423 K for 4 days, and then cooled to supplementary materials sup-2 room temperature over 12 h. Red block crystals were obtained after five months by slow evaporation of solvent with a yield of approximate 55% based on Zn.
Refinement N-bonded H atom was located in a difference Fourier map and refined with a distance restraint. Other H atoms were placed in calculated positions and refined in a riding mode. U iso (H) = 1.2 U eq (C,N). Fig. 1. A part of the title polymeric compound, thermal ellipsoids are shown at the 50% probability level. Symmetry code:

Figures
Crystal data (C 13

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 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 (Å 2 )
x y z U iso */U eq Zn1