The Structure of [HSi9](3-) in the Solid State and Its Unexpected Highly Dynamic Behavior in Solution

摘要

We report on the first unambiguous detection of the elusive [HSi9](3-) anion in solutions of liquid ammonia by various Si-29 and H-1 NMR experiments including chemical exchange saturation transfer (CEST). The characteristic multiplicity patterns of both the Si-29 and H-1 resonances together with CEST and a partially reduced H-1,Si-29 coupling constant indicate the presence of a highly dynamic Si-8 entity and a Si-H moiety with slow proton hopping. Theoretical calculations corroborate both reorganization of Si-8 on the picosecond timescale via low vibrational modes and proton hopping. In addition, in a single-crystal X-ray study of (K(DB[18]crown-6))(K([2.2.2]crypt))(2)[HSi9]center dot 8.5 NH3, the Hatom was unequivocally localized at one vertex of the basal square of the monocapped square-antiprismatic cluster. Thus experimental studies and theoretical considerations provide unprecedented insight into both the structure and the dynamic behavior of these cluster anions, which hitherto had been considered to be rigid.