New graphite lamellar compounds

Abstract

Solutions of lithium or sodium in hexamethylphosphoramide react with graphite to give ternary lamellar compounds, with “ideal” formulas Li( S) C 32 and Na( S) C 27 respectively, where ( S) represents a molecule of solvent. Since the solutions of the alkali metals are relatively unstable, the reaction must be carried out with complete exclusion of oxygen and water-vapor. X-ray diffraction studies (Debye-Scherrer) show that both compounds are first-stage, with the following parameters: Li(S)C 32: a = 19,68 A ̊ , c = 30,48 A ̊ , c a = 1.548 Na(S)C 27: a = 12,73 A ̊ , c = 15,24 A ̊ , c a = 1.19 . In both cases, the c parameter is a multiple of 7.62 Å; this probably represents the distance between two successive carbon planes, but the final value of c is determined by the helicoidal rotation of successive planes around the hexagonal axis. Although it has not yet been possible to ascribe unambiguous positions to the solvent molecules, it seems that the P-O bond of hexamethylphosphoramide lies perpendicular to the carbon planes. Both compounds show a fairly intense electron spin resonance signal. Spin densities (measured at 280 MHz) are: Li( S) C 32, 2.1 10 22 spin/mole; Na( S) C 27, 7.0 10 22 spin/mole. If the unpaired spins are solely due to unionized metal atoms, the average ionization is 96.5 and 85%, respectively for Li and Na. These values confirm the hypothesis that the species between the graphite planes in lamellar compounds is nearly completely ionized, whenever this ionization is possible.