First Characterization of the Ammine−Ammonium Complex [{NH4(NH3)4}2(μ-NH3)2]2+ in the Crystal Structure of [NH4(NH3)4][B(C6H5)4]·NH3 and the [NH4(NH3)4]+ Complex in [NH4(NH3)4][Ca(NH3)7]As3S6·2NH3 and [NH4(NH3)4][Ba(NH3)8]As3S6·NH3

The compound [NH4(NH3)4][B(C6H5)4]·NH3 (1) was prepared by the reaction of NaB(C6H5)4 with a proton-charged ion-exchange resin in liquid ammonia. [NH4(NH3)4][Ca(NH3)7]As3S6·2NH3 (2) and [NH4(NH3)4][Ba(NH3)8]As3S6·NH3 (3) were synthesized by reduction of As4S4 with Ca and Ba in liquid ammonia. All ammoniates were characterized by low-temperature single-crystal X-ray structure analysis. They were found to contain the ammine−ammonium complex with the maximal possible number of coordinating ammonia molecules, the [NH4(NH3)4]+ ion. 1 contains a special dimer, the [{NH4(NH3)4}2(μ-NH3)2]2+ ion, which is formed by two [NH4(NH3)4]+ ions linked by two ammonia molecules. The H3N−H···N hydrogen bonds in all three compounds range from 1.82 to 2.20 Å (DHA = Donor-H···Acceptor angles: 156−178°). In 2 and 3, additional H2N−H···S bonds to the thioanions are observed, ranging between 2.49 and 3.00 Å (DHA angles: 120−175°). Two parallel phenyl rings of the [B(C6H5)4]- anion in 1 form a π···π hydrogen bond (C···C distance, 3.38 Å; DHA angles, 82°), leading to a dimeric [B(C6H5)4]2 2- ion.