Ureidobenzotriazine Multiple H-Bonding Arrays:  The Importance of Geometrical Details on the Stability of H-Bonds

A 3-ureidobenzo-1,2,4-triazine 1-<i>N-</i>oxide (<b>1</b>) was synthesized successfully. The derivative displays an acceptor−donor−acceptor−acceptor (ADAA) hydrogen-bonding motif in CDCl₃ and DMSO-<i>d</i><i>₆</i> solution as well as in the solid state. Although moderately strong association of <b>1</b> was observed with DAD motifs, nonspecific binding is observed with ureidopyridines featuring a complementary DADD array. Density functional calculations of conformations <b>1a</b> and <b>1b</b> together with two complexes revealed the clearly nonplanar geometry of the multiply hydrogen-bonded complex, in which some bonds are significantly longer (3.2 Å) than is optimal for H-bonds. As a result, only very small free energies of association were calculated, in line with the experimentally observed absence of specific assembly of the components.