Two bis(tridentate) Schiff base ligands H2L(x) were used to construct three 2×2 grid-type tetranuclear Fe(II) complexes 1-3 to obtain polynuclear spin-crossover materials. Magnetic susceptibility measurements show that the spin states of the complexes are related to the substituents of H2L(x), and that spin transition occurs only in complexes 1 and 2, which are derived from a bulky ligand, whereas complex 3 is diamagnetic. The transition temperatures of complexes 1 and 2 are close to room temperature and are dependent on counteranions. The spin transition of complex 1 can be reversibly tuned by the dehydration and hydration process.

Supramolecular strategy was employed to achieve the highest nuclearity Co(II) cluster exhibiting spin-crossover (SCO) behavior. Magnetic susceptibility characterization of the Co4(II) complex shows that two different spin-transition processes occur. The SCO behavior is directed by the partially deprotonated polydentate ligand, which favors the structural distortion required by the spin transition.