Simultaneous Formation of Arsenic Nitride Chalcogenides As ₃ NS ₃ and As ₃ NSe ₃ and Arsenic–Chalcogen Zintl Anions by Ammonothermal Reactions

Reactions of elemental As, Mn, and chalcogen (S or Se) in liquid ammonia, either at 55°C or under supercritical conditions at 150°C, yield by using sulfur [Mn(NH 3 ) 6 ](As 4 S 6 )·NH 3 as yellow crystals and as minority phase red, hexagonal plate‐shaped crystals of the arsenic nitride sulfide As 3 NS 3 . Using selenium, yellow [Mn(NH 3 ) 6 ](As 2 Se 6 ) and black As 3 NSe 3 are formed. All compounds were characterized by energy dispersive X‐ray spectroscopy analyses and crystal structure determinations. (As 4 S 6 ) 2– and (As 2 Se 6 ) 2– are known polyanionic Zintl ions. (As 4 S 6 ) 2– adopts a new trans ‐type conformation. Raman spectra of the cis and trans conformers are calculated and compared with the experimental spectrum. As 3 NS 3 and As 3 NSe 3 crystallize isotypically in the hexagonal space group P 6 3 / m . The crystal structure is built of planar NAs 3 moieties of perfect equilateral shape. The NAs 3 groups are stacked and connected via As–S–As and As‐Se‐As bridges to 1‐D strands, which are arranged in the crystal to form a hexagonal rod packing. Each six strands form a 7 Å wide channel, in which NH 3 solvent molecules can reversibly be incorporated. (DFT) Density functional theory calculations reveal the single bond character between As and N. As 3 NSe 3 turns out as slightly less ionic than As 3 NS 3 . The band gap is calculated to 3.23 eV (M → M transition) for As 3 NS 3 . A much smaller and indirect band gap of 2.20 eV (K → M) emerges for As 3 NSe 3 , despite the structural similarities.