Halogenated sodium/lithium monocarba-closo-decaborates: syntheses, characterization, and solid-state ionic conductivity

Abstract

A series of halogenated monocarba-closo-decaborates, M[closo-1-CHB₉H₈-6-X] (M = Na, Li; X = Br, I) and M[closo-1-CHB₉H₄-6,7,8,9,10-I₅] (M = Na, Li) have been synthesized for systematically investigating the influence of halogenation of the monocarba-closo-decaborates on the thermal stability, phase transition and ionic conductivity. The thermal stability of halogenated derivatives is lower than that of the corresponding parent compounds of M[closo-1-CHB₉H₉] (M = Na, Li) with a trend of M[closo-1-CHB₉H₈-6-Br] < M[closo-1-CHB₉H₈-6-I] < M[closo-1-CHB₉H₄-6,7,8,9,10-I₅] (M = Na, Li). Both Na[closo-1-CHB₉H₈-6-Br] and Na[closo-1-CHB₉H₈-6-I] undergo a phase transition before decomposition, which occurred at a higher temperature than that of the parent compound Na[closo-1-CHB₉H₉]. In comparison to the parent compound, all halogenated derivatives show lower ionic conductivities with the trend of M[closo-1-CHB₉H₈-6-Br] > M[closo-1-CHB₉H₈-6-I] > M[closo-1-CHB₉H₄-6,7,8,9,10-I₅] (M = Na, Li). The results are supported by the theoretical calculation results based on ESP, suggesting that the ionic conductivities of halogenated derivatives are mainly influenced by anisotropic electron densities.