NMR diffusion spectroscopy for the characterization of multicomponent hydrogen-bonded assemblies in solution

NMR diffusion measurements on 10 different multicomponent hydrogen-bonded assemblies, viz. the three single rosettes SR1-SR3 (1₃·2a₃, 1₃·2b₃, 1₃·2c₃) the double rosettes DR1-DR5 (3a₃·2a₆, 3b₃·2b₆, 3c₃·2a₆, 3d₃·2a₆, 3e₃·2a₆), and DR6 (4a₃·1₆), and the tetrarosette TR (5₃·2a₁₂) are described. Some of the above rosettes have been previously identified as well-defined assemblies (viz. SR1, DR1-DR3, and TR) using established characterization techniques (¹H NMR spectroscopy, X-ray diffraction, and MALDI-TOF MS after Ag⁺-labeling). The diffusion coefficients of these assemblies were studied and used as a reference for the identification of three new assemblies (DR4-DR6), the characterization of which could not be established unequivocally using other characterization tools. A good correlation was found between the experimental and calculated diffusion coefficients when DR1 was used as a reference. A relatively good correlation was obtained between the effective hydrolytic radii calculated from the diffusion data and those extracted from gas phase-minimized structures with SR1 and DR2 being exceptions. The diffusion measurements show that assembly DR4 is a thermodynamically stable species, while assemblies DR5 and DR6 are less stable and only present to a minor extent.