Bis(5-methyl-pyrazine-2-carboxyl-ato-κ²N,O)nickel(II).

In the title complex, [Ni(C6H5O2N2)2], the Ni(II) atom is situated on an inversion centre and is coordinated in a square-planar geometry by four O atoms and two N atoms of the chelating ligands.

Diaqua-bis-(5-methyl-pyrazine-2-carboxyl-ato-κN,O)cobalt(II) dihydrate.

In the title complex, [Co(C(6)H(5)N(2)O(2))(2)(H(2)O)(2)]·2H(2)O, the coordination geometry of the Co(2+) cation is distorted octa-hedral, with two N atoms and two O atoms from two 5-methyl-pyrazine-2-carboxyl-ate ligands in the equatorial plane. The two remaining coordination sites are occupied by two water mol-ecules. In addition, there are two uncoordinated water mol-ecules in the asymmetric unit. The crystal structure is stabilized by a network of O-H⋯O and O-H⋯N hydrogen-bonding inter-actions, forming a three-dimensional structure.