Na₅[CN₂]₂[CN], (Li, Na)₅[CN₂]₂[CN], and K₂[CN₂]: Carbodiimides from High‐Pressure Synthesis

Abstract

Abstract The first alkali metal carbodiimide cyanides Na 5 [CN 2 ] 2 [CN] and (Li, Na) 5 [CN 2 ] 2 [CN] were obtained from reaction of carbon with nitrogen gas pressure of 7 MPa in sodium melts without orwith admixture of Li 3 N, respectively. The crystal structures wererefined from single‐crystal X‐ray diffraction (Na 5 [CN 2 ] 2 [CN]: a = 7.201(2) Å, c = 6.605(4) Å, I 4/ mmm , R 1 = 0.028, wR 2 = 0.079; (Li 1.40 Na 3.60(3) ) 5 [CN 2 ] 2 [CN]: a = 7.0034(3) Å, Im $\bar{3}$ m , R 1 = 0.038, wR 2 = 0.084). Whereas in Na 5 [CN 2 ] 2 [CN] a fully ordered arrangement of the anions is realized, in (Li, Na) 5 [CN 2 ] 2 [CN] both the alkali metal cations and the anions are disordered, with some site preference of lithium and sodium, leading to an increase of space group symmetry from I 4/ mmm for the pure sodium compound to Im $\bar{3}$ m for the mixed Li/Na phase. Ammonothermal synthesis at 90 MPa leads to crystal growth of carbodiimide K 2 [CN 2 ] ( a = 5.762(1) Å , b = 5.669(1) Å ,c = 5.756(1) Å , β = 108.78(3)°, C 2/ m ) crystals in the cold zone of an autoclave. The crystal structure was analyzed and compared to the carbodiimide cyanides.