X-Ray and spectroscopic re-investigation of urotropine–p-nitrophenol complex

Abstract

The product of the reaction between urotropine and p-nitrophenol, reported as a 1:1 adduct that belongs to the triclinic P1 space group, is, in fact, a 1:2 [C6H12N4]·[p-HOC6H4NO2]2·[H2O] hydrate that crystallizes in the monoclinic C2 space group. In the crystal structure, one nitrogen atom of the urotropine moiety is linked by a hydrogen bond to the hydroxyl group of a p-nitrophenol molecule [N⋯O=2.655(7)Å]; the [C6H12N4]·[p-HOC6H4NO2] entities are linked into a linear one-dimensional chain through the lattice water molecule [O⋯N=2.871(8),O⋯O=2.878(7)Å]. The other p-nitrophenol moiety is disordered over two positions across the two-fold axis; its interaction with adjacent water molecules [O⋯O=2.53(1), 2.57(2)Å] holds neighboring chains together. The FTIR spectrum of the complex in the solid indicate the formation of OH⋯N intermolecular hydrogen bond described by an asymmetric double minimum potential and weak Zundel's polarizability. The spectroscopic measurements in solution demonstrate the dissociation of the complex observed in the solid and prove the presence of the 1:1 complexes urotropine–p-nitrophenol. In these complexes no proton transfer from p-nitrophenol to urotropine is observed.