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.