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The magnetic behavior of the polyanion [Fe3(μ-L)6(H2O)6]6– (L2– = (1,2,4-triazol-4-yl)ethanedisulfonate) as the corresponding dimethylammonium salt shows memory effect above room temperature, with a dynamic thermal hysteresis cycle over 90 K and temperature-induced excited spin state trapping (TIESST) phenomena at the highest temperatures reported. Taking advantage of the polyanionic nature of this tri- metallic complex, we were able to substitute the dimethylammonium cations by the monovalent heavy alkali metal cesium. This methathesis yielded the salt Cs6[Fe3(μ-L)6(H2O)6], with different molecular packing that increases the number and strength of cation–anion interactions, including a more robust H-bonded network. In this phase, the spin transition still occurs above room temperature, but it is more abrupt and narrow (≈50 K wide hysteresis). Despite these differences, TIESST is observed with almost identical characteristic temperature (TTIESST = 240 K) than in the parent compound, which is an additional experimental evidence supporting the molecular origin of the TIESST behavior in these materials.