Compounds [Rb(18-crown-6)]4As14.6NH3 (1) and [Li(NH3)4]4P14.NH3 (2) were prepared by the reaction of Rb4As6 with SbPh3 and 18-crown-6 and by the reduction of white phosphorus with elemental lithium in liquid ammonia, respectively. Both were characterized by low-temperature single-crystal X-ray structure analysis. They were found to contain the Ci symmetrical Pn14(4-) anion (Pn = P, As), which consists of two nortricyclane-like Pn7-cages connected by a single bond. Molecular complexes of [Rb(18-crown-6)(NH3)]2[Rb(18-crown-6)]2As14 are formed in 1, which are connected to fanfold sheets via N-H...O bonds. The anion is isolated in 2, and N-H...N bonds result in the formation of {[Li(NH3)4](mu-NH3)2[Li(NH3)4]}2+ cationic complexes.
PPh 4 ) 2 HP 7 · 3NH 3 was prepared by the reaction of K 3 P 7 with a proton-charged ion exchange resin in the presence of (PPh 4 )Br in liquid ammonia, and characterized by low temperature X-ray structure analysis. The thermally very unstable compound contains the hydrogenheptaphosphide anion HP 7 2Ϫ , the nortricy-Hydrogen polyphosphides are intermediates between polyphosphanes [1] and polyphosphides [2]. In contrast to the moderately stable, fully protonated polyphosphanes or the equally stable, fully deprotonated polyphosphides, hydrogen polyphosphides tend to form rather unstable solutions, as they disproportionate quickly to yield dihydrogen monophosphide and insoluble higher polyphosphanes. Hydrogen polyphosphides may be prepared by deprotonation of diphosphane(4) with n-butyl lithium, which, according to 31 P-NMR data, yields a number of different anionic species after complicated rearrangement reactions [3Ϫ5], or by the reductive cleavage of white phosphorus P 4 with an excess of alkali metals in liquid ammonia [6]. A more rational approach is the controlled protonation of soluble polyphosphides at low temperatures. After the serendipitous discovery of the first stable hydrogen polyphosphide (PPh 4 )H 2 P 7 [7], our group further developed the latter route by devising several reactions in liquid ammonia. These include the in situ generation of NH 4 Br by the slow reaction of Br 3 Ϫ with NH 3 or the protonation with weakly acidic phosphonium salts [8], as well the use of an ion exchange resin loaded with protons [9]. So far, only compounds containing the anions H 2 P 7Ϫ with a nortricyclane-analogous cage and HP 11 2Ϫ with a trishomocubane-like cage could be isolated. Obviously missing are the alternately protonated anions H 2 P 11 Ϫ and HP 7 2Ϫ . We set out to prepare the latter using ion exchange in liquid ammonia.
The incongruous solvation of polyphosphides and phosphanes or the direct reduction of white phosphorus in liquid ammonia leads to the hydrogen polyphosphides catena-dihydrogen triphosphide, P(3)H(2)(3-), and catena-trihydrogen triphosphide, P(3)H(3)(2-), in the crystalline compounds K(3)(P(3)H(2)).2.3NH(3) (1), Rb(3)(P(3)H(2)).NH(3) (2), [Rb(18-crown-6)](2)(P(3)H(3)).7.5NH(3) (3), and [Cs(18-crown-6)](2)(P(3)H(3)).7NH(3) (4).
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