N-Hydroxyurea dimers: A matrix isolation and theoretical study

• Two types of N-hydroxyurea (HU)2 dimers are trapped in argon matrices.
• The dimers are stabilized by a strong OH⋯O bond.
• There is an additional weak interaction NH⋯O or NH2⋯O in dimers, respectively.
• The most stable centrosymmetric structures are not identified in matrices.

The dimerization of N-hydroxyurea (NH2CONHOH) has been investigated by FTIR matrix isolation spectroscopy and DFT(B3LYP)/6-311++G(2d,2p) calculations. The analysis of NH2CONHOH/Ar matrix spectra and comparison with theoretical ones reveal the formation of two types of dimers with a strong OH⋯O hydrogen bond. There is an additional weak interaction between the oxygen atom of the OH group of the proton donor molecule and the NH or NH2 group of the proton acceptor in both dimers, respectively. The identified structures correspond to local minima on the PES. The formation of the less stable structures not the most stable ones indicates that the creation of N-hydroxyurea dimers is related to the dipole-dipole interaction at the initial stage of the dimerization process, which favours generation of polar dimers.