S1 Supplementary Information Attractive Strain - The Disadvantages of Rigid Multiple H-bond Donors and Acceptors. A Theoretical Analysis of the Hydrogen-Bonding Interactions in Heterodimers of Tetraazaanthracenedione with Pyridylureas Antonio Oliva, Juan Bertran and J. J. Dannenberg Departament de Quimica, Unitat de Quimica Fisica, Uniersitat Autonoma, 08193 Bellaterra (Barcelona), Spain; Department of Chemistry, City University of New York - Hunter College and the Graduate School, 695 Park Avenue, New York NY 10021; Institute of Computational Chemistry and Department of Chemistry, University of Girona, 17071 Girona (Catalonia), Spain