Oxidative Intercalation of Graphite by Fluoroanionic Species

Abstract

Whether oxidative intercalation of graphite by fluoroanions can occur may be estimated from the electron affinity, Ε (-ΔΗ298 in kcal mol -1 ), of the oxidizing half reaction. For first-stage salts with MF6-guests, Ε must exceed 120 kcal mol -1 . The values of E(e -+ 3 /2 MF5 --> MF6-+ 1 /2 MF3) for AsF5 and PF5 (125 and 87 kcal mol -1 , respectively) account for the spontaneous intercalation of graphite by AsF5 and the failure of PF5 to do so. Spontaneous intercalation by PF5 + F2 occurs because E(e -+ PF5 + 1 /2 F2 --> PF6-) = 165 kcal mol -1 . The thermodynamic nature of the barrier to intercalation is dem onstrated by the reduction of CxPF6 salts by PF3: CxPF6 + 1 /2PF3 --> xC + 3/2 PF5. Chlorine with certain fluoroacids can also bring about intercalation of fluoroanions. Polarizable neutral molecules, by improving the lattice energetics of graphite salts, may also be spontaneously intercalated (e.g., C14AsF6 + 1 /2AsF5 --> C14AsF 6· 1/2ASF5). When high positive charge at carbon occurs, F -is trans ferred from the fluoroanion to the carbon and novel graphite fluor ides (e.g., C1. 3F) are formed. ^flL OST OF THE REACTANTS THAT BRING ABOUT INTERCALATION of graphite are either strong oxidants or reductants such as nitric acid or alkali metal (1-3). The oxidation or reduction of the graphite that accompanies the in tercalation was clearly shown by Ubbelohde and co-workers (4-6) to be

Editors’ Choice—Mechanistic Elucidation of Anion Intercalation into Graphite from Binary-Mixed Highly Concentrated Electrolytes via Complementary 19F MAS NMR and XRD Studies

“…− or SbF 6 − , also intercalation of AsF 5 /SbF 5 and AsF 3 /SbF 3 species into graphite has been reported. [72][73][74] However, in our work, no other species like PF 5 or other fluorophosphates could be identified in the charged graphite electrodes, which is in accordance to earlier reports. [44][45][46] Furthermore, no significant stage dependence of the 19 F chemical shift is observed, even though highly oxidizing potentials of ≈5 V vs Li|Li + are reached for the stage 1-GICs.…”

Room Temperature Syntheses of AuF6- and PtF6- Salts, Ag+AuF6-, Ag2+PtF62-, and Ag2+PdF62-, and an Estimate for E(MF6-) [M = Pt, Pd]

“…This stability of AuF 6 - is in agreement with the large electron affinity, E (AuF 6 ), calculated by Miyoshi and Sakai of 9.56 eV. The higher nuclear charge of gold must be the most important factor in the greater oxidation resistance of AuF 6 - relative to PtF 6 - the ionization potential of which − (= E (PtF 6 )) is ∼ 8 eV, but the more favorable exchange energy of the dt 2g 6 configuration of Au(V) relative to the dt 2g 5 configuration of Pt(V) must also contribute. The tighter binding of all electrons in AuF 6 - versus PtF 6 - is seen in the smaller effective volume of the former (see Table ).…”

“…The salts have similar unit cells 6,16,47 and stability with respect to dissociation. In harmony with these similarities the electron affinity of RuF 6 should be close to that of PtF 6 [34][35][36] which is ∼8 eV. It might have been expected, therefore, that the second electron affinity would also have nearly the same value for both ions.…”

Weakly Coordinating Anions HA2-Generated from Oxoanions A-and Their Conjugate Acids. Coordination Equilibria, Ionic Conductivities, and the Structures of {Cu2(H(CH3SO3)2)4}nand [Cu(CO)(H(CF3CO2)2)]2

“…30 kcal/mol (e.g., H(CH 3 CO 2 ) 2 - , 29.3 kcal/mol) . Although this is considerably lower than the gas-phase enthalpies of F - dissociation from BF 4 - (92(6) kcal mol -1 ), PF 6 - (101(8) kcal mol -1 ), and even HF 2 - (39(1) kcal mol -1 ), the fragmentation of a particular HA 2 - anion into HA and A - may be sufficiently endothermic to afford stable complexes in some cases.…”