The arrangement of paraquat bound by vermiculite and montmorillonite

Abstract

The exchange complex produced by paraquat (1,1′-dimethyl-4,4′-bipyridinium dichloride) and Llano vermiculite formed a close-packed layer of uniformly oriented cations whose tilted pyridinium rings were situated over and partly keyed into the hexagonal holes between the surface oxygen atoms of the vermiculite. Other vermiculites behaved similarly, but in paraquat-montmorillonite, the rings were flat. Paraquat-vermiculite and montmorillonite had basal spacings of 14.1 and 12.4 Å when air dry and 12.8 and 12.4 Å, respectively, after heating at 80°C. From polarized infrared spectra obtained by total attenuated reflectance, the long axes of the organic cations are shown to be parallel to the basal surfaces of both silicate minerals. Vibrations corresponding to directions across the pyridinium rings are 35–37° for paraquat-vermiculite and flat to the surface for paraquat-montmorillonite. The bands associated with the cross vibrations are split when the pyridinium rings key into the surface. X-Ray diffraction photographs of flakes of paraquat-vermiculite show reflections between those of the host vermiculite lattice. A model is given of the packing of the organic cations on the surface of vermiculite and the effects of varying charge density and water content are discussed.