Bi2(NCN)3, the first binary pnictogen carbodiimide, and its ammonia derivative Bi2(NCN)3·NH3 have been prepared via nonaqueous liquid-state low-temperature ammonolysis. The crystal structure of Bi2(NCN)3·NH3 in space group Cc solved via single-crystal X-ray diffraction corresponds to a two-dimensional-like motif with layers of NCN2- alternating with honeycomb-like layers of edge-sharing distorted BiN6 octahedra, half of which are also coordinated by molecular ammonia occupying the octahedral holes. By contrast, Bi2(NCN)3 adopts a higher-symmetric C2/c structure with a single Bi position and stronger distortion but empty octahedral voids. In both cases, Bi3+ and its 6s2 lone pair are well mirrored by antibonding Bi-N interactions below the Fermi level. Density functional theory calculations reveal an exothermic reaction for the intercalation of NH3 into Bi2(NCN)3, consistent with the preferential formation of Bi2(NCN)3·NH3 in the presence of ammonia. A Bärnighausen tree shows both compounds to be hettotypic derivatives of the R3̅c M2(NCN)3 corundum structure that express highly distorted hexagonal-close-packed layers of NCN2- in order to accommodate the aspherical Bi3+ cations. Although Bi2(NCN)3 does not resemble the isovalent Bi2Se3 in forming two-dimensional layers and a topological insulator, theory suggests a driving force for the spontaneous formation of Bi2Se3/Bi2(NCN)3 sandwiches and a conducting surface state arising within the uppermost Bi2(NCN)3 layer.