2. "Hydrogen-Bonded Tapes Based on Symmetrically Substituted Diketopiperazines: A Robust Structural Motif for the Engineering of Molecular Solids", Palacin, S., Chin, D. N., Simanek, E. E., MacDonald, J. C., Whitesides, G. M., McBride, M. T. and Palmore, G. T. R., J. Am. Chem. Soc., 1997, 119, 11807-11