Aqua-(2,9-dimethyl-1,10-phenanthroline-κN,N')diformato-κO,O';κO-nickel(II) monohydrate.

The asymmetric unit of the title compound, [Ni(HCO(2))(2)(C(14)H(12)N(2))(H(2)O)]·H(2)O, contains a mononuclear complex mol-ecule hydrogen bonded to a lattice water mol-ecule. The Ni(II) atom exhibits a distorted octa-hedral coordination geometry formed by the N atoms from a 2,9-dimethyl-1,10-phenanthroline ligand, two O atoms of a chelating formate anion, one aqua O atom and one O atom of a coordinating formate anion. The mol-ecules are assembled into chains extending along [100] through by O-H⋯O hydrogen bonds. The supra-molecular chains are further linked into layers parallel to (011) by weak π-π packing inter-actions [centroid-centroid separation = 3.768 (2) Å]. The resulting layers are stacked to meet the requirement of close-packing patterns.