X-ray diffraction and spectroscopic verification of dimerization in hexasubstituted para-nitrosophenols

It has been established earlier that the brilliant-green solution of the potassium salt of 2,6-diethoxycarbonyl-3,5-dimethyl-4-nitrosophenol (С14H16KNO6) - (I) when treated with an acid yields a white precipitate of 2,6-diethoxycarbonyl-3,5-dimethyl-4-nitrosophenol, presumably (С14H17NO6)2 - (II). The crystal structures of both compounds have been determined and dimer formation has been confirmed by X-ray powder diffraction. Modeling of the structures with 22 and 42 non-hydrogen atoms was carried out by the Monte-Carlo technique applying “rigid” and “soft” constraints. The Rietveld method was used for the structure refinement. The layers parallel to the plane (10-1) are distinguished in structure (I). The distance between the layers is equal to 9.28 Å. The interlayer space is filled by ethoxygroups. In the layer the zigzag chains of potassium cations are located at the distance 9.38 Å from each other, with the organic anions being embedded between them. The π-conjugation between phenol- and nitroso-groups is observed in the anions (С14H16NO6)−, resulting in a flat ion. Potassium cations have irregular sevenfold coordination. The π-system of the nitroso-group participates in the potassium coordination. Dimerization in structure (II) is due to the interaction of the nitrogen atoms of the nitroso-groups, d(N-N) = 1.29 Å. The planes of the benzene rings form an angle of 23°. The absence of the π-conjugation makes the molecule flexible, which at the molecule packing into a crystal is subjected to the requirement of the closest packing with the loss of the possible center of symmetry. The results of the X-ray diffraction studies are consistent with the evidence of the IR and 1H NMR spectroscopy.