Crystal structure of tetraaquabis(3,5-diamino-4H-1,2,4-triazol-1-ium)cobalt(II) bis[bis(pyridine-2,6-dicarboxylato)cobaltate(II)] dihydrate

The asymmetric unit of the title compound, [Co(C2H6N5)2(H2O)4][Co(C7H3NO4)2]2·2H2O, features 1.5 CoII ions (one anionic complex and one half cationic complex) and one water molecule. In the cationic complex, the CoII atom is located on an inversion centre and is coordinated by two triazolium cations and four water molecules, adopting an octahedral geometry where the N atoms of the two triazolium cations occupy the axial positions and the O atoms of the four water molecules the equatorial positions. The two triazole ligands are parallel offset (with a distance of 1.38 Å between their planes). In the anionic complex, the CoII ion is six-coordinated by two N and four O atoms of the two pyridine-2,6-dicarboxylate anions, exhibiting a slightly distorted octahedral coordination geometry in which the mean plane of the two pyridine-2,6-dicarboxylate anions are almost perpendicular to each other, making a dihedral angle of 85.87 (2)°. In the crystal, molecules are linked into a three-dimensional network via C—H⋯O, C—H⋯N, O—H⋯O and N—H⋯O hydrogen bonds.

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick 2008); program(s) used to refine structure: SHELXL2013 (Sheldrick, 2015); molecular graphics: SHELXTL (Sheldrick 2008); software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009  Among different multidentate species, compounds bearing carboxylate functions are widely studied ligands for producing stable transition metals coordination polymers and supramolecular architectures, mostly because of the versatile ligating abilities of the -COO moieties and also due to the enhanced affinity of these metal ions towards such O donors. There have been a number of successful attempts at utilizing proton transfer from carboxylic acids to both heterocyclic and substituted amine nitrogens (Moghimi et al., 2002;Moghimi et al., 2005;Moghimi et al., 2007;Aghabozorg et al., 2008;Aghabozorg et al., 2009;Tabatabaee et al., 2009, Pasdar et al., 2011, Yousuf et al., 2011b. Dicarboxylic acids possess a good potential to be used as proton donors in the synthesis of proton transfer compounds. In continuation of our work, we report herein the trinuclear complex of Co II with pyridine-2,6-dicarboxylic acid as proton donor and 3,5-diamino-1,2,4triazole as proton acceptor.

S2. Structural commentary
The asymmetric unit consits of half whole repeating unit of the title compound ( Fig. 1) and is composed of 1.5 Co II ions (one anionic complex and one half cationic complex) and one water molecule. In the cationic complex, the Co II atom (Co2) is located on an inversion centre and is coordinated by two triazolium cations and four water molecules, adopting an octahedral geometry where the N atoms of the two triazolium cations (N3 & N3A) occupy the axial positions (Co-N = 2.2016 (7) Å) and the O atoms of the four water molecules (O2W, O2WA, O3W & O3WA) occupy the equatorial positions (Co-O = 2.0590 (7) -2.1080 (7) Å). Atoms with suffix A were generated by the symmetry operation -x, -y, -z.
The two triazole ligands are parallel offset (with a distance of 1.377 Å between the exact parallel planes). The angle between the Co-N bond and the centroid of the triazole plane is 158.56°. The bond distances are comparable with those reported for similar complexes Prasad & Rajasekharan, 2007;Colak et al., 2009). In the anionic complex, the Co II ion (Co1) is six-coordinated by two N (Co-N = 2.0273 (9) -2.0308 (9) Å) and four O (Co-O = 2.1471 (7) -2.2223 (7) Å) atoms of the two pyridine-2,6-dicarboxylate anions, exhibiting a slightly distorted octahedral coordination geometry where the mean plane of the two pyridine-2,6-dicarboxylate anions (maximum deviation = 0.0851 (9) Å at C7) are almost perpendicular to each other with a dihedral angle of 85.87 (2)°.

S4. Synthesis and crystallization
An aqueous solution (10 ml) containing 0.5mmol (0.0496 g) of 3,5-diamino-1,2,4-triazole was added to a hot and stirring aqueous solution (20 ml) containing 1mmol (0.167 g) of pyridine-2,6-dicarboxylic acid and 1mmol (0.238 g) of CoCl 2 .6H 2 O. The resulting pink solution was stirred for 30 min and allowed to stand at room temperature. Crystals formed after 3 days but single crystals suitable for X-ray analysis were separated after one month.

S5. Refinement details
N-and O-bound H atoms were located from the difference Fourier map and were refined freely [N-H = 0.79 (2) to 0.92 (2) Å; O-H = 0.79 (2) to 0.86 (2) Å]. The remaining H atoms were calculated geometrically and were refined using a riding model with U iso = 1.2 U eq (C), with the bond lengths of C-H being 0.95 Å.

Figure 1
The molecular structure of the title compound with atom labels and 50% probability displacement ellipsoids. Atoms with suffix A were generated by the symmetry operation -x, -y, -z.