Two new tetranuclear iron(II) complexes, [Fe-4(H2LH)(6)](ClO4)(8) (1ClO(4): H2LH = N,N'-bis(imidazole-4-ylmethylidene)-1.4-diaminobenzene) and [Fe-4(H2LMe)(6)](BF4)(8) (2BF(4): H2LMe = N,N'-bis(5-methylimidazole-4-ylmethylidene)-1.4-diaminobenzene), were synthesized from Fe(ClO4 or BF4)(2)center dot 6H(2)O, 1.4-diaminobenzene and 4-formylimidazole or 5-methyl-4-formylimidazole. X-ray analysis revealed that these complexes have a tetrahedral structure with four iron(II) ions at the apexes and the bridging bis(bidentate) ligands on the edges. The internal space of the tetrahedron was filled with the phenylene segments of the bridging ligands. Magnetic susceptibility studies indicated that both 1ClO(4) and 2BF(4) showed gradual but incomplete spin-crossover (SCO) behavior, because the densely packed tetrahedral structure could prevent the contraction of the Fe-N bonds on the highspin to low-spin transition.