The nanosized self-assemblies {[{Ln^III}{H₂O⊂Cr^III₃Ln^III₆}]₂(H₂O)} (Ln = Dy, 1 and Tb, 2) based on new 3d–4f mixed-metal coordination topologies are formed via extensive intramolecular hydrogen bonding that is directed by enclosed water molecules. Compounds 1 and 2 show single-molecule magnet characteristics manifested by hysteresis loops up to 1.6 K (U_eff = 8.3 cm⁻¹) and 1 K (U_eff = 3.4 cm⁻¹), respectively.