Elusive Zintl Ions [ µ HSi4]3- and [Si5]2- in Liquid Ammonia: Protonation States, Sites, and Bonding Situation by NMR and Theory.

Elusive Zintl Ions [µ HSi4]3- and [Si5]2- in Liquid Ammonia: Protonation States, Sites, and Bonding Situation by NMR and Theory. Angew Chem Int Ed Engl. 2019 Jan 08;: Authors: Hastreiter F, Lorenz C, Hioe J, Gärtner S, Nanjundappa L, Korber N, Gschwind RM Abstract They are detected! The existence of the elusive and stunning [µ HSi4]3- anion in liquid ammonia solutions could unambiguously be proven by diverse 1H and 29Si NMR experiments. Both, NMR and Quantum Chemical Calculations reveal that the hydrogen atom bridges two silicon atoms of the [Si4]4- cluster contrary to expectations that it is located at one vertex silicon atom of the tetrahedron. Additionally, for the first time [Si5]2- was detected and characterized in liquid ammonia by NMR. Theoretical calculations indicate that the formation of [µ HSi4]3- can be explained by high charge density and the increase of electron delocalization in [µ HSi4]3- compared to [Si4]4- providing additional driving force for protonation. Furthermore, the calculation showed that [Si5]2- is resistant to protonation owing to strong charge delocalization, which is significantly reduced upon protonation. Thus, NMR and calculations reveal three silicides in liquid ammonia being unprotonated [Si5]2-, terminally protonated [HSi9]3- or bridged protonated [µ HSi4]3-. The protonation trend can be roughly predicted by the difference in charge delocalization of the parent compound and the product, which...
Source: Angewandte Chemie - Category: Chemistry Authors: Tags: Angew Chem Int Ed Engl Source Type: research
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