Abstract: | The title compound, (2,6‐diacetylpyridine bis{2‐(hydroxyimino)propanoyl]hydrazone}(2−))nickel(II) dimethyl sulfoxide solvate monohydrate, Ni(C15H17N7O4)]·C2H6OS·H2O, represents the first example of square‐planar N4 coordination via N atoms with four different functions, namely amide, azomethine, hydroxyimino and pyridine. The coordination polyhedron of the central Ni atom has a slightly distorted square‐planar geometry. The 2,6‐diacetylpyridine bis{2‐(hydroxyimino)propanoyl]hydrazone} ligand forms one six‐ and two five‐membered chelate rings, and a pseudo‐chelate ring through an intramolecular hydrogen bond with an amide group as donor and a deprotonated hydroxyimino group as acceptor, resulting in a pseudomacrocyclic arrangement. |