Reactions of Beryllium Halides in Liquid Ammonia: The Tetraammineberyllium Cation [Be(NH3)4]2+, its Hydrolysis Products, and the Action of Be2+ as a Fluoride-Ion Acceptor

The first structural characterization of the text‐book tetraammineberyllium(II) cation [Be(NH3)4]2+, obtained in the compounds [Be(NH3)4]2Cl4⋅17NH3 and [Be(NH3)4]Cl2, is reported. Through NMR spectroscopic and quantum chemical studies, its hydrolysis products in liquid ammonia were identified. These are the dinuclear [Be2(μ‐OH)(NH3)6]3+ and the cyclic [Be2(μ‐OH)2(NH3)4]2+ and [Be3(μ‐OH)3(NH3)6]3+ cations. The latter species was isolated as the compound [Be3(μ‐OH)3(NH3)6]Cl3⋅7NH3. NMR analysis of solutions of BeF2 in liquid ammonia showed that the [BeF2(NH3)2] molecule was the only dissolved species. It acts as a strong fluoride‐ion acceptor and forms the [BeF3(NH3)]− anion in the compound [N2H7][BeF3(NH3)]. The compounds presented herein were characterized by single‐crystal X‐ray structure analysis, 9Be, 17O, and 19F NMR, IR, and Raman spectroscopy, deuteration studies, and quantum chemical calculations. The extension of beryllium chemistry to the ammine system shows similarities but also decisive differences to the aquo system. Beryllium unraveled! The chemistry of BeF2 and BeCl2 in liquid ammonia has been unraveled. The [Be(NH3)4]2+ cation has been structurally elucidated for the first time (see figure). Its hydrolysis products were found to be the open‐chain cation [Be2(μ‐OH)(NH3)6]3+ and the cyclic cations [Be2(μ‐OH)2(NH3)4]2+ and [Be3(μ‐OH)3(NH3)6]3+. [BeF2(NH3)2] is the only dissolved species in liquid ammonia. This compound can be used as a fluoride‐ion acceptor and forms [N2H7][BeF3(NH3)].