Two structurally related bis(imidoylamidine or 1,3,5-triazapentadiene)nickel(II) compounds [Ni{HN=C(3-py)NC-(3-py)=NH](2)}center dot H2O center dot MeOH (1) and [Ni{HN=C(3-py)N(H)C(3-py)=NH}(2)]Cl-2 (2) with symmetrical 3- pyridyl (3-py) substituents have been prepared by direct 2-butanone oxime mediated transformation of 3-cyanopyridine in the presence of Ni(MeCO2)(2)center dot 4H(2)O or NiCl2 center dot 2H(2)O, respectively. Compounds I and 2 have been characterized by elemental analyses, IR, H-1 and C-13{H-1} NMR spectroscopy, and FAB(+) mass spectrometry, while their slow recrystallization in air from organic solvents revealed a high affinity for water and resulted in the formation of the derived compounds [Ni{HN=C(3-py)NC(3-py)=NH}(2)]center dot 6H(2)O (1) and [Ni{HN=C(3-py)N(H)(0.5)C-(3-py)=NH}(2)]Cl center dot 2H(2)O (2'). Single-crystal X-ray diffraction analyses allowed the identification of discrete hexameric water or hybrid water-chloride clusters hosted by the crystal matrixes of V and 2', respectively. Both the (H2O)6 and [(H2O)(4)(Cl)(2)](2-) clusters possess similar geometries and consist of cyclic planar tetranuclear (H2O)(4) or [(H2O)(2)(Cl)(2)](2-) cores with two dangling water molecules. These water associates occupy voids in the crystal cells and display extensive H-bonding interactions with monomeric nickel-organic units, thus playing a key role in the formation of 3D hydrogen-bonded supramolecular assemblies.