Bis(9-aminoacridinium) bis(pyridine-2,6-dicarboxylato)zincate(II) trihydrate

In the title compound, (C13H11N2)2[Zn(C7H3NO4)2]·3H2O, the ZnII ion is six-coordinated with the N4O2 donor set being a distorted octahedron through two almost perpendicular (r.m.s. deviation of ligand atoms from the mean plane is 0.057 Å) tridentate pyridine-2,6-dicarboxylate ligands [dihedral angle between the ligands = 86.06 (4)°]. The charge is compensated by two 9-aminoacridinium cations protonated on the ring N atom. A variety of intermolecular contacts, such as ion–ion, N—H⋯O and O—H⋯O hydrogen bonds, and π–π stacking [centroid–centroid distances = 3.4907 (9)–4.1128 (8) Å], between cations and between anions, play important roles in the formation of the three-dimensional network.


Experimental
Crystal data (C 13  H atoms treated by a mixture of independent and constrained refinement Á max = 0.23 e Å À3 Á min = À0.33 e Å À3 Table 1 Hydrogen-bond geometry (Å , ). Among different derivatives of pyridinedicarboxylate, pyridine-2,6-dicarboxylic acid (pydcH 2 ), also called dipicolinic acid (H 2 pdic), has been widely considered because of its high symmetry and bioactive properties. The most common coordination mode of (pydc) 2is as a tridentate ligand via N and two carboxylate groups that can be coordinated to a metal in a meridional fashion (Eshtiagh-Hosseini, Mirzaei, Yousefi et al., 2011;Park et al., 2007).
In this contribution, we have synthesized and characterized a new coordination compound with (pydc) 2coordinated to Zn II and protonated 9-aminoacridine as the cation which is formulated as (9aaH) 2 [Zn(pydc) 2 ].3H 2 O.
The asymmetric unit of the title compound comprises a dianionic complex, [Zn(pydc) 2 ] 2-, two 9aaH + cations and three water molecules (Fig. 1). In the anionic complex, Zn II is six-coordinated via two (pydc) 2ions with the ZnN 2 O 4 donor set in a distorted octahedral geometry. The two (pydc) 2moieties are almost perpendicular to each other (the angle between the mean ligand planes (rms deviation of ligand atoms from the mean plane is 0.057 Å) intersecting at Zn1 is 86.62 (2)°).
Bond lengths and angles are comparable with those in similar structures (Tabatabaee et al., 2009;MacDonald et al., 2000;Aghabozorg et al., 2008;Harrison et al., 2006). Recently, our group reported a similar compound with Mn(II) as a metal center which has the same stochiometery as the title compound (Eshtiagh-Hosseini, Mirzaei, Eydizadeh et al., 2011). Binding of the H 2 O molecules to the anionic complex and the 9aaH + cations occur via N-H···O and O-H···O hydrogen bonds creating two different motifs with graph sets R 4 2 (8) and R 3 3 (9) (Fig. 2). In Fig. 3, a packing diagram of the title compound viewed down the b axis is shown in which a variety of intermolecular contacts can be observed. The most significant additional interactions are π-π stacking between (pydc) 2ligands in adjacent anions and between sets of 9aaH + cations (Fig. 3).

Experimental
To 5 mL of an aqeous solution of pydcH 2 (0.026 g, 0.15 mmol), 5 mL of a methanolic solution of 9aa (0.030 g,0.15 mmol) was added dropwise. Then, powdered ZnCl 2 .2H 2 O (0.011 g, 0.075 mmol) was added and the resulting solution was heated and stirred for 3 hrs at 60°C. Yellow crystals were obtained by slow evaporation of the solvent at room temperature after 3 days.

Refinement
A full-matrix least-squares refinement implemented in the SHELXL97 (Sheldrick, 2008) was used. All non-H atoms were refined anisotropically. The H atoms were positioned geometrically and allowed to ride on their parent atoms, with C-H = 0.93 Å and 0.97 Å for C and 0.86 Å for N atom and U iso (H) = 1.2 U eq (C,N). The H atoms of water were located in difference map and refined with the following restraints: O-H = 0.95 (2) Å and H···H = 1.50 (4) Å (total of 9 restraints were used).

Figure 1
An ORTEP view of the asymmetric unit of the title compound with numbering of the non-hydrogen atoms (probability  The chain formed by the anionic complex and the water molecules. Zinc ions are depicted as spheres of arbitrary radii.