Bis(2,4,6-triamino-1,3,5-triazin-1-ium) bis(4-hydroxypyridine-2,6-carboxylato)cuprate(II) hexahydrate

In the title compound, (C3H7N6)2[Cu(C7H3NO5)2]·6H2O, the coordination geometry of the CuII atom can be described as distorted octahedral. The equatorial plane is defined by four O atoms from two 4-hydroxypyridine-2,6-dicarboxylate ligands. The axial positions are occupied by the N atoms of the same ligands. There is an extensive three-dimensional hydrogen-bond network reinforcing crystal cohesion.

In the title compound, (C 3 H 7 N 6 ) 2 [Cu(C 7 H 3 NO 5 ) 2 ]Á6H 2 O, the coordination geometry of the Cu II atom can be described as distorted octahedral. The equatorial plane is defined by four O atoms from two 4-hydroxypyridine-2,6-dicarboxylate ligands. The axial positions are occupied by the N atoms of the same ligands. There is an extensive three-dimensional hydrogenbond network reinforcing crystal cohesion.

S1. Comment
Following our research on the synthesis of proton transfer compounds that can function as suitable ligands in the synthesis of metal complexes Aghabozorg, Saadaty et al., 2008), we have obtained the title compound dimelaminium bis(4hydroxypyridine-2,6-carboxylato)cuprate(II) hexahydrated. 4-hydroxypyridine-2,6-carboxylic acid (hypydcH2) was chosen as a proton donor and melamine (tata) as the proton acceptor.
The asymmetric unit of (I) consists of two melaminium (tataH) residues protonated at one ring N atom, two (hypydc) residues coordinating a Cu II ion and six water molecules (Fig. 1). The melaminium cations are essentially planar with the weighted average absolute torsion angle equal to 0.67 (23) for ring A and 1.20 (33)° for ring B. Both rings exhibit a significant distortion from the ideal hexagonal form. The internal C-N-C angle of the protonated N atom (N5A, N5B) is significantly larger than the other two ring C-N-C angles ( Table 1). The angle between the least-squares plane of the two independent cations is 87.97 (12)°. The anions also assemble perpendicularly to each other. The angle between the mean planes of the two independent pyridil rings is 89.51 (12)°. Thus the molecules form a square grid with channels along the b axis (Fig. 2). The Cu II ion is coordinated octahedrally by two ligands of (hypydc). The N atoms of the two independent anions occupy the axial positions while four oxygen atoms form the equatorial plane. There is an extensive network of hydrogen bonds proportionated by the large amount of water molecules. All the water molecules share their hydrogen atoms with another strong acceptor (N,O). The (hypydc) anions have similar H-bonds, but the two independent melaminium cations have different roles in the web of H-bonds. While B molecules only establish H-bonds to neighbouring water or (hypydc) molecules, the A molecules are also joined in dimers (Fig.3, Table 2).

S3. Refinement
All H-atoms could be located in difference Fourier maps. The H atoms of water molecules were refined with an O-H distance restraint of 0.85 (2) Å and U iso (H) = 1.5U eq (O). Short contacts between the H atoms of the water O10 and neighbouring H atoms are observed at the final refinement, an indication that these H atoms are probably disordered. The coordinates of the H atoms of the hydroxyl groups were freely refined with U iso (H) = 1.5U eq (O), the H atoms bonded to the N atoms of the melaminium rings were restrained to have equal N-H distances and U iso (H) = 1.2U eq (N). The supporting information remaining H atoms were placed at calculated positions and refined as riding on their parent atoms with U iso (H) = 1.2U eq (N,C)

Figure 1
ORTEPII (Johnson, 1976) plot of the title compound. Displacement ellipsoids are drawn at the 50% level.

Figure 2
Packing diagram of the title compound. Water molecules were excluded for clarity.

Figure 3
A part of the extensive three-dimensional H-bond network. H-bonds are depicted as dashed lines.

Bis(2,4,6-triamino-1,3,5-triazin-1-ium) bis(4-hydroxypyridine-2,6-carboxylato)cuprate(II) hexahydrate
Crystal data  Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.