Tracing the Jahn‐Teller Distortion of C₆₀ⁿ⁻ in Isostructural Fullerides [M(NH₃)₇]C₆₀ ⋅ NH₃, M=Ba, Sr, K

Abstract

Dedicated to Professor Wolfgang Kaim on the Occasion of his 70th BirthdaySingle crystals of new [Sr(NH 3 ) 7 ]C 60 • NH 3 (compound 1) and [K(NH 3 ) 7 ]C 60 • NH 3 (compound 2) were prepared by extracting mixtures of potassium and C 60 with liquid ammonia, where for the synthesis of 1 solid strontium chloride was added to the extraction mixture. The procedure applied relies on selfcontained continuous evaporation and condensation of ammonia at subcritical conditions in a special, sealed glass vessel, at room temperature (RT). According to single crystal structure analyses on data collected at 123 K, both, 1 and 2, are isostructural with [Ba(NH 3 ) 7 ]C 60 • NH 3 (compound 3). The structure determinations suffer either from systematic twinning (3), or positional disorder for 1 and 2. Crystals of 3, grown and handled throughout at low temperature (123 K), developed large enough twin domains such that an inversion twin type refinement in space group R3m converged properly. For 1 and 2, the crystals of which were grown at RT and subsequently cooled for data collection, refinements of the same structure model were only possible in R-3m while applying split atom positions. For 1 and 3 the accuracy achieved was sufficient to extract a particular bonding distortion pattern for (C 60 ) 2À , which is lifting the degeneracy of the HOMO according to the Jahn-Teller theorem. Independent quantum chemical calculations are lending convincing support to the experimental findings.