Molecular structure of the complex of N-methylmorpholine betaine with 2,4-dinitrophenol

The 1:1 complex between N-methylmorpholine betaine and 2,4-dinitrophenol, has been characterized by single crystal X-ray analysis and by B3LYP /6-31G(d,p), PM3 and SAM1 calculations. The crystals (monoclinic, space group P21/c) exhibit an interesting property of colour changing-immediately after crystallization they are green, and after approximately 3 h they gradually change the colour into orange. No structural transformation could be connected with this colour change. In the crystal, 2,4-dinitrophenol is engaged in a short O-H⋯O hydrogen bond (O⋯O=2.470(3) Å). The morpholine ring adopts a chair conformation with the equatorial CH3 group and the axial CH2COO·H group. The optimized geometry of the investigated complex at the B3LYP approach is in a good agreement with the crystal structure. Linear correlations have been found between the experimental 1H and 13C chemical shifts and the screening constants computed by the GIAO/B3LYP/6-31G(d,p) method. The signals of protons at positions C(2), C(7) and C(8) depart from this correlation. These protons probably interact with the solvent or other proton acceptors.