Crystals grown from a solution containing equimolar portions of barbital (3) and N,N’-bis(4-tert-butylphenyl)-melamine (4) in toluene/isopropyl alcohol (1:1 v/v) comprise a cyclic CA(3).M(3) "rosette" (5). The six molecules in this supramolecular motif are held together by 18 hydrogen bonds. Characterization of solutions of equimolar mixtures of 3 and 4 in chloroform by H-1 NMR spectroscopy, gel permeation chromatography, and vapor pressure osmometry demonstrates that the same cyclic CA(3).M(3) rosette (5) is also the most probable structure, when [3] = [4] > 4 mM. H-1 NMR exchange experiments confirm that the CA(3).M(3) rosette (5) is qualitatively much less stable in chloroform solution than the supramolecular aggregate hub(M)(3):3barbital (1) that is preorganized for self-assembly by a covalent tris(melamine) derivative. Complexes formed between 4 and different isocyanurates indicate that intermolecular interactions, as a consequence of the steric bulk of the substituents on these derivatives, favor the formation of the cyclic CA(3).M(3) rosette over competing linear hydrogen-bonded motifs. There is inferential evidence for formation of a complex of modest stability with composition CA.M(2) when 2[3] = [4].