(2-Amino-7-methyl-4-oxidopteridine-6-carboxyl-ato-κ(3)O(4),N(5),O(6))aqua-(ethane-1,2-diamine-κ(2)N,N')nickel(II) dihydrate.

The Ni(II) atom in the title complex, [Ni(C(8)H(5)N(5)O(3))(C(2)H(8)N(2))(H(2)O)]·2H(2)O, is six-coordinated in a distorted octa-hedral geometry by a tridentate 2-amino-7-methyl-4-oxidopteridine-6-carboxyl-ate (pterin) ligand, a bidentate ancillary ethane-1,2-diamine (en) ligand and a water mol-ecule. The pterin ligand forms two chelate rings. The en and pterin ligands are arranged nearly orthogonally [dihedral angle between the mean plane of the en mol-ecule and the pterin ring = 77.1 (1)°]. N-H⋯O, O-H⋯N and O-H⋯O hydrogen bonds link the complex mol-ecules and lattice water mol-ecules into a three-dimensional network. π-π inter-actions are observed between the pyrazine and pyrimidine rings [centroid-centroid distance = 3.437 (2) Å].