The magnetism of a series of tetranuclear complexes of the [Fe4IIL4]8+ [2x2]-grid-type was investigated, revealing the occurrence of spin transition behavior within this class of compounds. The phenomenon depends directly on the nature of the substituent R(1) in the 2-position on the central pyrimidine group of the ligand L. All Fe(II) ions in compounds with R(1) substituents favoring strong ligand fields (R(1)=H; OH) remain completely in the diamagnetic low-spin state. Only complexes bearing R(1) substituents attenuating the ligand field by steric (and to a lesser extent electronic) effects (R(1)=Me; Ph) exhibit spin transition behavior triggered by temperature. In general, gradual and incomplete transitions without hysteresis were observed for magnetically active complexes. The systems described provide approaches to the development of (supra)molecular spintronics.