The system graphite-MnCl 2-AlCl 3 Kinetics, structure and mechanism of formation

Abstract

Graphite-MnCl 2-AlCl 3 intercalation compounds have been prepared via MnCl 2-AlCl 3 complexes. First stage compounds are eventually formed at both 325 and 500°C; products formed at the lower reaction temperature are richer in Mn (C 5.95MnCl 2(AlCl 3) 0.21) than those at 500° (C 7.15MnCl 2(AlCl 2.5) 0.3). At 325° the mechanism is a quasi-selective intercalation of AlCl 3 to the second stage followed by insertion of MnCl 2 to a mixed stage I compound, and finally an isostage Mn enrichment with Al depletion. At 500°, insertion proceeds differently. Rate limiting reactions at each temperature are proposed. Powder X-ray diffractograms give I c = 9.51 A ̊ for Mn-rich first stage compounds. Comparison of calculated and observed (00 l) structure factors gives an Mn-Cl spacing of 1.46 Å as in the pure dichloride. Analysis of ( hkl) positions and the (10 l) and (11 l) intensities of the inserted MnCl 2 indicate an intercalant superlattice with a 0 = 3.69 A ̊ and c 0 = 3 × I c = 28.53 A ̊ . First stage compounds prepared at 500° are considerably less ordered. Results obtained at 325° are especially significant in that 1. (1) this represents the lowest temperature at which dichlorides have been intercalated to rich stages, and 2. (2) long-range (i.e. 3-dimensional) ordering has been documented in a dichloride intercalation compound for the first time, and is sensitive to reaction temperature.