Synthesis, Crystal Structure, Symmetry Relationships, and Electronic Structure of Bismuth Carbodiimide Bi₂(NCN)₃ and Its Ammonia Adduct Bi₂(NCN)₃·NH₃

Abstract

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.

Computational Design and Theoretical Properties of WC3N6, an H-Free Melaminate and Potential Multifunctional Material

“…Besides binary C 3 N 4 , carbon–nitrogen-based complex anions such as carbodiimide − NCN 2– , guanidinate , CN 3 5– , or ortho-nitrido carbonate CN 4 8– also allow to generate three-dimensional materials in combination with (transition) metal cations, and these may be regarded as complex salts offering rich structural diversity and physicochemical properties. Molecular melamine, C 3 H 6 N 6 , the trimer of molecular cyanamide, H 2 NCN, plays a special role not only because it may be used for making g-C 3 N 4 (see above) but also due to the fact that it allows for deprotonation to prepare metal melaminate salts, − yet another way to arrive at high-performance photocatalysts.…”

The [NCN]2– Carbodiimide Complex Anion and Its Compounds–A “Divalent Nitride” Unit for Nitridocarbonates in Materials and Applications

“…97 DFT is seemingly incapable to correctly model the ground state. Indeed, further studies involving muon-spin relaxation, 13 C nuclear magnetic resonance, and electron-spin resonance studies revealed the absence of classical magnetic ordering to the lowest temperatures but a large enhancement of spin correlations and unexpected inhomogeneous magnetism below 80 K. 97 Upon including 63,65 Cu nuclear quadrupole resonance, the magnetic ground state of the Cu 2+ (S = 1/2) spins appear as being frozen and disordered. 98 This is especially evident from temperature-dependent 13 C NMR spectra which show superposition of two low-temperature components.…”

“…The introduction of cations that lie outside of this “Goldilocks Zone” or alternatively those with specific coordination preferences lead to crystal structures with a greater orientational dispersion of NCN 2– . A telling example of this is seen for Ln 2 (NCN) 3 binaries which adopt [corundum]-derived structures ( R c ) with Ln N 6 octahedra for smaller lanthanides ( Ln = Tm–Lu), but then switch to a monoclinic ( C 2/ c ) variant with Ln N 7 polyhedra for larger lanthanides ( Ln = Y, Pr–Er). , Furthermore, the introduction of metal cations with stereochemically active lone pairs, such as Pb 2+ , Sn 2+ and Bi 3+ , results in metal nitrocarbonates with far more irregular polyhedra and lower symmetry crystal structures that express a range of intriguing properties. − …”

Crystallization of the Fundamental Tetracyanamidometallates Li4[Si(CN2)4] and Li4[Ge(CN2)4] from Polymeric Li‐T‐(NCN)‐I Precursors (T=Si, Ge)

“…Metal dinitridocarbonates, more commonly referred as carbodiimides (N=C=N) 2À or cyanamides (NÀ C�N) 2À are already developed with various metals of the periodic table, and the number of new compounds is still growing. Representative pseudo-binary members are characterized as M(CN 2 ) and M 2 (CN 2 ) 3 with M being a main group metal (e. g. Ca, [7] In, [8] Sn, [6] or Bi [9] ), a transition metal (e. g. Zr, Hf, [10,11] Cr, [12] Mn, [13] Fe, [14] Co, Ni [15] or Zn [16] ), or a rare-earth (RE) [1] metal. An attractive but less-common field of compounds within the chemistry of (NÀ C�N) 2À ions are tetracyanamidometallate compounds, evidenced by the [T(NCN) 4 ] nÀ ion, in which T represents a main group element such as Si, [17,18,19] Ge, [20] Al [21,22] or Ga. [23] The compounds ARE[Si(NCN) 4 ] (A = K, Rb, Cs; RE = rare earth) were reported to exhibit outstanding optical properties (photoluminescence and/or second harmonic generation = SHG) and to behave stable in air.…”

“…Metal dinitridocarbonates, more commonly referred as carbodiimides (N=C=N) 2− or cyanamides (N−C≡N) 2− are already developed with various metals of the periodic table, and the number of new compounds is still growing. Representative pseudo‐binary members are characterized as M (CN 2 ) and M 2 (CN 2 ) 3 with M being a main group metal (e. g. Ca, [7] In, [8] Sn, [6] or Bi [9] ), a transition metal (e. g. Zr, Hf, [10,11] Cr, [12] Mn, [13] Fe, [14] Co, Ni [15] or Zn [16] ), or a rare‐earth ( RE ) [1] metal.…”