In the two title complexes of cinnamaldehyde salicyloylhydrazone [or 2-hydroxy-N'-(3-phenylprop-2-enylidene)benzohydrazide], [Ni(C(16)H(13)N(2)O(2))(2)(CH(4)O)(2)], (I), and [Ni(C(16)H(13)N(2)O(2))(2)(C(5)H(5)N)(2)], (II), the Ni(II) atoms lie on crystallographic inversion centres and have distorted octahedral geometries. The equatorial plane is defined by two carbonyl O atoms and two hydrazine N atoms of two bidentate trans-oriented salicyloylhydrazone ligands. The axial positions are occupied by two O atoms from two coordinated methanol molecules in (I) and by two N atoms from two coordinated pyridine molecules in (II). There is an extended chain structure in (I) resulting from intermolecular O-H...O hydrogen bonds between coordinated methanol molecules and phenol O atoms, while (II) comprises discrete molecules. Complex (I) also exhibits weak pi-pi stacking interactions, and intramolecular O-H...N hydrogen bonds are present in both (I) and (II). The salicyloylhydrazone ligands in (I) and (II) are coordinated to the metal atom through the carbohydrazide O and N(2) atoms, not via the phenol O atom. We have established a link between the reagents used and the nuclearity of the complex formed: the ligand produced by condensation between salicylhydrazide and an aldehyde leads to mononuclear complexes, while replacing the aldehyde in the reaction by a ketone leads to multinuclear complexes.