Reactions of [SiF4(NH3)2] with Fluorides AF (A = Li-Cs, Tl, NH4) in Liquid NH3: A [NH4(NH3)2]+ Cation and a Thallophilic Interaction in [Tl2(NH3)6]2.

We investigated whether [SiF4(NH3)2] can act as a fluoride-ion acceptor in its reactions with the fluorides AF (A = Li-Cs, Tl, NH4) in anhydrous liquid ammonia (NH3). While LiF and NaF did not react, we obtained the compounds K[SiF5(NH3)], Rb[SiF5(NH3)], and Cs[SiF5(NH3)], as well as [NH4(NH3)2]2[SiF6] and [Tl2(NH3)6][SiF6]·2NH3, from the other starting materials and characterized them by either single-crystal or powder X-ray diffraction. The compound [NH4(NH3)2]2[SiF6] contains the very rarely observed hydrogen-bonded, C2v-symmetric diammine ammonium cation [NH4(NH3)2]+, and the compound [Tl2(NH3)6][SiF6]·2NH3 is an example for an uncommon Tl(I)-Tl(I) interaction. This "thallophilic" interaction was investigated with quantum-chemical methods.