Aromatic radical cation formation on the intracrystal surfaces of transition metal layer lattice silicates

Abstract

Publication costs assisted by Michigan State UniversityThe adsorption of selected aromatic molecules on the intracrystal surfaces of Fe(II1) and VQ2+ exchange forms of a layer lattice silicate (hectorite) has been studied by ir, uv-visible, and esr spectroscopy. In addition to aromatic radical cation formation, type I1 species, which exhibit an intense charge-transfer band in the ir region and vibrational frequencies that are substantially shifted relative to the parent molecule, are formed with benzene on the Fe(II1) exchange form and with anisole and thiophene on both Fe(II1) and V02+ exchange forms. The complexes are identical with those previously observed on Cu(I1) layer lattice silicates. It is suggested that the type I1 species are associated radical cations formed by electron transfer from the parent molecule to the metal ion. Toluene radical cation formation is accompanied by polymerization, and the polymer apparently inhibits radical cation association. IntroductionIn an earlier report1 from these laboratories it was shown that the chemisorption of benzene on the interlamellar surfaces of copper(I1) montmorillonite under dehydrating conditions results in the formation of two distinct species distinguishable by infrared spectroscopy: a greenyellow type I complex containing a planar C6H6 ring, and

Reaction of Benzene with Cu(II)- and Fe(III)-Exchanged Hectorites

“…Freshly prepared Cu(II)-and Fe(III)-exchanged hectorite films give EPR spectra similar to those described in the literature (Rupert, 1973;Pinnavaia et al, 1974). After allowing these films to react with benzene between 65 ~ and 100~ the resonance due to the metal was reduced and a new single-line resonance was observed.…”

“…The reaction of benzene with Cu(II)-and Fe(III)-exchanged smectites was reported by Mortland et al (1971), Rupert (1973), and Pinnavaia et al (1974). They demonstrated that chemisorption of benzene by clay under dehydrating conditions produced two chemical species distinguishable by their color, electron paramagnetic resonance (EPR), and infrared (IR) spectra.…”

“…The g,value and linewidth data suggest strong similarities. Both the Cu(II)-and Fe(III)-exchanged hectorite films reacted with benzene under the conditions described by Rupert (1973) and Pinnavaia et al (1974) to produce type I and type II complexes, in contrast to these films, films prepared using the sealed-tube technique showed no tendency to change from a burgundy color on exposure to the atmosphere or to water. Examination of the free radical signal after film exposure to the atmosphere showed striking differences.…”

“…A burgundy type II species has a single-line EPR spectrum apparently due to :organic free radicals and an IR spectrum which suggests the presence of an organic species having less aromatic character than benzene. Pinnavaia et al (1974) found that the two species are reversibly interconvertable by the addition or removal of small amounts of water, with the type II species dominating under more anhydrous conditions. From EPR studies of benzene and other arene reactions in Cu(II)-exchanged montmorillonite, Rupert (1973) suggested that the reaction forming the type II species involved electron transfer from benzene to Cu(II) and that Heisenberg or chemical-exchange phenomena involving the benzene cations and/or neutral benzene molecules produced a single, exchange-narrowed EPR line.…”

Integrated investigations on the adsorption mechanisms of fulvic and humic acids on three clay minerals

“…3 and 5, Table 1). Previous works suggested that the phenomenon in which Fe 3+ induced selective adsorption of aromatic moieties of NOM was probably due to the electron transfer mechanism [37,38]. In this study electron transfer was directly evidenced by the XPS spectra of iron cation (Fig.…”