Synthesis and Structural Characterization of Antimony Polyazides

High-pressure and high-temperature synthesis of crystalline Sb3 N5

A chemical reaction between Sb and N2 was induced under high-pressure (32-35 GPa) and high-temperature (1600-2200 K) conditions, generated by a laser heated diamond anvil cell. The reaction product was identified by single crystal synchrotron X-ray diffraction at 35 GPa and room temperature as crystalline antimony nitride with Sb3 N5 stoichiometry and structure belonging to orthorhombic space group Cmc21 . Only Sb-N bonds are present in the covalent bonding framework, with two types of Sb atoms respectively forming SbN6 distorted octahedra and trigonal prisms and three types of N atoms forming NSb4 distorted tetrahedra and NSb3 trigonal pyramids. Taking into account two longer Sb-N distances, the SbN6 trigonal prisms can be depicted as SbN8 square antiprisms and the NSb3 trigonal pyramids as NSb4 distorted tetrahedra. The Sb3 N5 structure can be described as an ordered stacking in the bc plane of bi- layers of SbN6 octahedra alternated to monolayers of SbN6 trigonal prisms (SbN8 square antiprisms). The discovery of Sb3 N5 finally represents the long sought-after experimental evidence for Sb to form a crystalline nitride, providing new insights about fundamental aspects of pnictogens chemistry and opening new perspectives for the high-pressure chemistry of pnictogen nitrides and the synthesis of an entire class of new materials.

Labile Low-Valent Tin Azides: Syntheses, Structural Characterization, and Thermal Properties

The first two examples of the class of tetracoordinate low-valent, mixed-ligand tin azido complexes, Sn(N₃)₂(L)₂, are shown to form upon reaction of SnCl₂ with NaN₃ and SnF₂ with Me₃SiN₃ in either pyridine or 4-picoline (2, L = py; 3, L = pic). These adducts of Sn(N₃)₂ are shock- and friction-insensitive and stable at r.t. under an atmosphere of pyridine or picoline, respectively. A new, fast, and efficient method for the preparation of Sn(N₃)₂ (1) directly from SnF₂, and by the stepwise de-coordination of py from 2 at r.t., is reported that yields 1 in microcrystalline form, permitting powder X-ray diffraction studies. Reaction of 1 with a nonbulky cationic H-bond donor forms the salt-like compound {C(NH₂)₃}Sn(N₃)₃ (4) which is comparably stable despite its high nitrogen content (55%) and the absence of bulky weakly coordinating cations that are conventionally deemed essential in related systems of homoleptic azido metallates. The spectroscopic and crystallographic characterization of the polyazides 1-4 provides insight into azide-based H-bonded networks and unravels the previously unknown structure of 1 as an important lighter binary azide homologue of Pb(N₃)₂. The atomic coordinates for 1 and 2-4 were derived from powder and single crystal XRD data, respectively; those for 1 are consistent with predictions made by DFT-D calculations under periodic boundary conditions.