Syntheses, characterization and crystal structures of fourdesigned host–guest compounds of the compositions [{CuIIL1}2⊂(H3N(ethylene)NH3)](NO3)2 (1), [{CuIIL1}2⊂(H3N(propylene)NH3)](NO3)2 (2), [{CuIIL1}2⊂(H3N(butylene)NH3)](NO3)2 (3) and [{CuIIL2}2⊂(H3N(ethylene)NH3)](NO3)2 (4) are described in this investigation [H2L1 = N,N′‐ethylenebis(3‐methoxysalicylaldimine); H2L2 = N,N′‐ethylenebis(3‐ethoxysalicylaldimine); ethylene = (CH2)2; propylene = (CH2)3; butylene = (CH2)4]. Compounds 2 and 3 crystallize in the orthorhombic Pcab and monoclinic C2/c systems, respectively, while the space group of compounds 1 and 4 is triclinic P$\bar {1}$. In all of these four compounds 1–4, the two +NH3 sites of the [H3N(CH2)nNH3]2+ dication (n = 2–4) behave as guests in the O4 compartment of two [CuIIL1/L2] moieties through bifurcated N–H···O(phenoxo) and N–H···O(methoxy/ethoxy) hydrogen‐bonding interactions. Evidently, two mononuclear copper(II) moieties are interlinked by bridging supramolecular synthons, resulting in the formation of a supramolecular dimer in the title compounds. From the extent of displacement of the N atoms of [H3N(CH2)nNH3]2+ from the least‐squares O(phenoxo)2O(methoxy/ethoxy)2 plane, it is clear that [CuIIL1] is a better host than [CuIIL2] for the diprotonated diamine guests. Comparison of the inclusion of water and diprotonated diamines in [CuIIL1/L2] is also described in the present investigation. Interestingly, of the two guest species, water and diprotonated diamines, [CuIIL2] prefers the former and [CuIIL1] prefers the latter.