Hydrogen bonding in dimers of tritolyl and tritosylurea derivatives of triphenylmethanes

Abstract

The crystal structure of the homodimer formed by the tritolylurea 3a proves the existence of a belt of six bifurcated hydrogen bonds between both NH and the OC groups of the adjacent urea residues. For the tritosylurea 3b, four additional three-center hydrogen bonds, also involving the SO₂ oxygen, are found in the crystalline state. Molecular dynamics simulations in a chloroform box confirm these patterns of the hydrogen bonds and the resulting elongation of the dimer 3b·3b in comparison to 3a·3a. The calculated complexation energies for the three dimeric combinations are nearly identical in agreement with the simultaneous formation of heterodimer 3a·3b in a mixture of 3a and 3b.