Hydrogen-bonding was implied between the bipyridinium macrocycle and neutral axle in previously reported X-ray structures. The hydrogen-bond may not be observed here due to chemical exchange line broadening on either the J-coupling, transverse relaxation rate (R2) or chemical shift difference time scales. Alternatively, the dominant structure in solution may differ from that observed in the solid-state Correlation between the hydrogen attached to N d and the protons on the alkyl chain of the urea side chain was also observed. The results are consistent with the preferred configuration described previously (i.e. self-associated pyrimidinol tautomer). Enol proton H b is directly bound to an oxygen and hydrogen-bonded to a carbonyl oxygen atom thus has no observable correlations. H d correlates with N b ; through space communication between orbitals thus indicates intramolecular hydrogen bonding. Proton H c correlates to N a ; whilst an intermolecular hydrogen bond is implied in X-ray crystal structures, coupling arising from intermolecular hydrogen bonding and intramolecular coupling to N a are degenerate.