(2-Amino-7-methyl-4-oxidopteridine-6-carboxylato-κ3 O 4,N 5,O 6)(ethane-1,2-diamine-κ2 N,N′)(1H-imidazole-κN 3)nickel(II) dihydrate

In the title complex, [Ni(C8H5N5O3)(C2H8N2)(C3N2H4)]·2H2O, a tridentate 2-amino-7-methyl-4-oxidopteridine-6-carboxylate (pterin) ligand, a bidentate ancillary ethane-1,2-diamine (en) ligand and a monodentate 1H-imidazole (im) ligand complete a distorted octahedral geometry around the NiII atom. The pterin ligand forms two chelate rings. Both the en and im ligands are arranged nearly orthogonally relative to the pterin ligand [dihedral angles between the mean planes of the en and pterin ligands and of the im and pterin ligands are 84.62 (9) and 85.14 (9)°, respectively]. N—H⋯N, N—H⋯O, O—H⋯N and O—H⋯O hydrogen bonds link the complex molecules and lattice water molecules into a three-dimensional network.

The molecular structure ( Fig. 1) (Crispini et al., 2005). This factor is responsible to a large extent for the observed distortion here from regular octahedral geometry.
Accordingly, the O1-Ni1-O3 axis shows maximum deviation [153.37 (5)°] from linearity. Again, closest approach to linearity [174.10 (7)°] is observed for the N7-Ni1-N8 axis, which is associated with both the im and en ligands. Here each such ligand tries to achieve near orthogonality with respect to the pterin ligand [dihedral angles between the mean planes of the en and pterin ligands and of the im and pterin ligands are 84.62 (9) and 85.14 (9)°, respectively], for minimizing the steric repulsion. In line with the earlier observations on related copper complexes (Odani et al., 1992), the pyrazine ring N atom (N1) is located in the equatorial plane. The corresponding short Ni1-N1 distance [1.9787 (16) Å] indicates dπ-pπ interaction between the pterin ring and the Ni II atom (d 8 ), with further assistance from the nearby πdonating phenolate and carboxylate O atoms (Kohzuma et al., 1988). The pterin ligand is coordinated in its binegative  (Baisya & Roy, 2013;Beddoes et al., 1993;Russell et al., 1992).
In the crystal, intermolecular N-H···N, N-H···O, O-H···N and O-H···O hydrogen bonds (Table 1) link the complex molecules and lattice water molecules into a three-dimensional network (Fig 2). The lattice water molecules play a decisive role for the crystal packing.

Refinement
The H atoms were all located in a difference map, but those attached to C atoms were repositioned geometrically. The H atoms were initially refined with soft restrains on bond lengths and angles to regularize their geometry ( with rigiding constrains (Cooper et al., 2010).

Figure 2
The crystal packing diagram of the title compound, viewed along the a axis. Dotted lines indicate hydrogen bonds.