A new polynucleating oxime-containing Schiff base ligand, 2-hydroxyimino-N'-[1-(2-pyridyl)ethylidene]propanohydrazone (Hpop), has been synthesized and fully characterized. pH potentiometric, electrospray ionization mass spectrometric, and spectrophotometric studies of complex formation in H2O/DMSO solution confirmed the preference for polynuclear complexes with 3d metal ions. Single-crystal X-ray diffraction analyses of [Ni-4(pop)(4)(HCOO)(4)]center dot 7H(2)O (1), [Cu-4(pop-H)(4)(HCOOH)(4)] center dot H2O (2), and [Cu-4(pop-H)(4)(H2O)(4)] center dot 9H(2)O (3) indicated the presence of a [2 x 2] molecular grid structure in all three compounds but distinct configurations of the cores: a head-to-tail ligand arrangement with overall S-4 symmetry of the grid in the Cu2+ complexes as opposed to a head-to-head ligand arrangement with (noncrystallographic) O-2 grid symmetry for the Ni2+ complex. A cryomagnetic study of 3 revealed intramolecular ferromagnetic exchange between copper ions in the grid, while in 1, antiferromagnetic interactions between the metal ions were observed.