The structure of a molecular square assembling from [Pd(en)(NO3)(2)] 3 and 4,4'-bipyridine is confirmed by X-ray crystallography, whereas squares assembling from 3 and larger ligands, py-X-py (py = 4-pyridyl, X = CH=CH, C=C, p-C6H4) are shown to exist in equilibrium with molecular triangles.