Based on isostructurality between crystals formed upon combining the dicationic tecton 2 with either M3FeIII(CN)6 or M4FeII(CN)6 (M = Cs), a rare example of an H-bonded mixed valence Fe(II)–Fe(III) solid solution ((Cs223-[FeII(CN)6]2)0.83(23-[FeIII(CN)6]2)0.17)) and curious necklace-like composite crystals were generated.