A COMPARISON OF THE HYDROGEN-BOND ACCEPTOR PROPERTIES OF DIMETHYLAMINO AND IMINOPHOSPHORANE GROUPS IN O-PHENYLENEDIAMINE DERIVATIVES

The crystal structures of o-Y,Z-benzene hydrobromide and hydrohexafluo rophosphate salts have been determined by X-ray analysis; Y = Z = NMe2 for compounds I-III; Y = NMe2, Z = NPPh3 for IV-V and Y = Z = NPPh3 f or VI-VII. The main peculiarity of these structures is the hydrogen bo nd interactions of the ''extra proton'' which are responsible for the conformation of the cation. The nature of hydrogen interactions, inter molecular, intramolecular and bifurcated, depends on the anion and on the Y,Z substituents. The effects of protonation on bond distances and angles are clearly indicated. The N+-H...N intermolecular bonds exhib it N...N values in the 2.584(3)-2.719(5) angstrom range, the shortest contact corresponds to a bis-iminophosphorane derivative. Semiempirica l calculations at AM1 level have been carried out for 1,2-bis(dimethyl amino)benzene and its monoprotonated cation (I-III). The shape and siz e of the anion, that of the guest molecule and those of corresponding holes have been analyzed by means of the quotients between their plana r specific inertial moments of volume and surface. A C-13-NMR study of these compounds shows dynamic processes of proton transfer which corr espond to some of the structures found in the solid state.