Hierarchic supramolecular interactions within assemblies in solution and in the crystal of 2,3,6,7-tetrasubstituted 5,5′-(anthracene-9,10-diyl)bis[pyrimidin-2-amines]

The title compounds 6 and 7 were synthesized in good yield (Schemes I and 2), and their mode of assembly was studied both in solution, for the tetrakis(decyloxy) derivative 6, and in the crystal, for the tetramethoxy analogue 7. The pyrimidin-2-amine moieties of 6 and 7 can engage in three different supramolecular interactions: i) metal ligation via one of the pyrimidine N-atoms, ii) cooperative double H-bonding via the NH2 group, and iii) pi-pi-stacking interactions. In solution, coordination of the central Zn-atom within the soluble porphyrinatozinc complex 19 leads to significant changes in the NMR and absorption spectra of 6. In the absence of metal ligation, the next strongest interaction is H-bonding which can operate in nonpolar or moderately polar solvents. In these cases, however, no stacking interaction or inclusion compounds could be put into evidence in the case of 6 by absorption, fluorescence, or NMR spectroscopies. The pi-stacking interactions were only observed in the crystal of 7 in conjunction with double H-bonding. Slightly disordered DMSO molecules are also H-bonded to the NH2 groups of 7, perturbing the expected packing. The present study illustrates some of the challenges inherent to directing hierarchical assembly processes in the solid state.