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

A 3-ureidobenzo-1,2,4-triazine 1-N-oxide (1) was synthesized successfully. The derivative displays an
acceptor−donor−acceptor−acceptor (ADAA) hydrogen-bonding motif in CDCl3 and DMSO-d6 solution
as well as in the solid state. Although moderately strong association of 1 was observed with DAD motifs,
nonspecific binding is observed with ureidopyridines featuring a complementary DADD array. Density
functional calculations of conformations 1a and 1b 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.