The Ternary Post‐transition Metal Carbodiimide SrZn(NCN)₂

Abstract

SrZn(NCN)2, the first example of a ternary post‐transition metal carbodiimide, was prepared by a solid‐state metathesis reaction. The crystal structure was solved from PXRD data and found to adopt the orthorhombic (Cmcm) BaZnSO structure, a high symmetry modification of that expressed by the oxide analogue SrZnO2. Locally, SrZn(NCN)2 features ZnN4 tetrahedra and SrN6 trigonal prisms similar to those in quarternary LiSr2M(NCN)4 (M = Al3+ and Ga3+) phases, however, the overall topologies are distinct with single chains in the former and double chains in the latter. Electronic structure calculations indicate an indirect bandgap of about 2.95 eV in SrZn(NCN)2, slightly lower than the experimentally observed bandgap of 3.4 eV in SrZnO2 and consistent with a greater degree of covalency. The structural similarities between SrZn(NCN)2 and oxychalcogenide analogues highlight the pseudochalcogenide character of NCN2– and suggest that the title compound may serve as a template for accessing novel ternary carbodiimides featuring tetrahedrally coordinated transition metals.

Synthesis and Characterisation of the Nitridocuprate(I) Nitride Carbodiimide (Sr6N)[CuN2][CN2]2

“…The symmetric, asymmetric, and deformation vibrational frequencies agree well with what has been previously observed for [CN 2 ] 2– anions via Raman spectroscopy , , . The splitting at roughly 2000 cm –1 is typically seen for cyanamides, but is also seen in multi‐cationic carbodiimides . A vibrational frequency is observed at 743 cm –1 , which belongs to a C=N double bond, and would suggest the presence of carbodiimide rather than cyanamide ions is more probable.…”

“…[5,11,42] The splitting at roughly 2000 cm -1 is typically seen for cyanamides, but is also seen in multi-cationic carbodiimides. [46] A vibrational frequency is observed at 743 cm -1 , which belongs to a C=N double bond, and would suggest the presence of carbodiimide rather than cyanamide ions is more probable.…”

Synthesis, Crystal Structure, and Chemical-Bonding Analysis of BaZn(NCN)2

“…The crystal structure of BaZn(NCN)2 is well described as a two-dimensional network of ZnN4 tetrahedra ( Figure 5) sharing edges through N(1)-C(2)-N(4) units and vertices through N(2)-C(1)-N(3) units, with Ba 2+ cations in the interlayer voids (Figure 1). The ZnN4 tetrahedra are comprised of four distinct Zn-N bond lengths (Figure 2), with an average Zn-N bond distance of 2.080(8) Å comparable to those in SrZn(NCN)2 (dZn-N = 2.059(4) Å) and ZnNCN (dZn-N = 2.009(2) Å) [14,25], which also feature ZnN4 tetrahedra. Meanwhile, Ba 2+ adopts an eight-fold coordination of nitrogen atoms, quite distinct from the irregular six-coordinate twisted trigonal prismatic environment observed in BaNCN [26], with Ba-N distances between 2.650(7) and 3.015(7) Å ( Figure 2), and with an average Ba-N bond length dBa-N = 2.886(7) Å, similar to those observed in LiBa2Al(NCN)4 (dBa(1)-N = 2.889 (8) and dBa(2)-N = 2.918(8) Å) [19].…”

“…The crystal structure of BaZn(NCN) 2 is well described as a two-dimensional network of ZnN 4 tetrahedra ( Figure 5 [14,25], which also feature ZnN 4 tetrahedra. Meanwhile, Ba 2+ adopts an eight-fold coordination of nitrogen atoms, quite distinct from the irregular six-coordinate twisted trigonal prismatic environment observed in BaNCN [26], with Ba-N distances between 2.650(7) and 3.015 [19].…”

“…Very recently, we have come close in this endeavor with the preparation of SrZn(NCN) 2 [14], the first example of a ternary post-transition metal carbodiimide, which was targeted with inspiration from LiSr 2 M(NCN) 4 (M = Al 3+ and Ga 3+ ) phases [15,16]. SrZn(NCN) 2 adopts the versatile BaZnOS structure which, in oxychalcogenide analogues, can incorporate a range of different tetrahedrally coordinated divalent transition metals [17,18].…”