Binary Group 15 Polyazides. Structural Characterization of [Bi(N3)4]−, [Bi(N3)5]2–, [bipy·Bi(N3)5]2–, [Bi(N3)6]3–, bipy·As(N3)3, bipy·Sb(N3)3, and [(bipy)2·Bi(N3)3]2 and on the Lone Pair Activation of Valence Electrons

The binary group 15 polyazides As(N3)3, Sb(N3)3, and Bi(N3)3 were stabilized by either anion or donor−acceptor adduct formation. Crystal structures are reported for [Bi(N3)4]–, [Bi(N3)5]2–, [bipy·Bi(N3)5]2–, [Bi(N3)6]3–, bipy·As(N3)3, bipy·Sb(N3)3, and [(bipy)2·Bi(N3)3]2. The lone valence electron pair on the central atom of these pnictogen(+III) compounds can be either sterically active or inactive. The [Bi(N3)5]2– anion possesses a sterically active lone pair and a monomeric pseudo-octahedral structure with a coordination number of 6, whereas its 2,2′-bipyridine adduct exhibits a pseudo-monocapped trigonal prismatic structure with CN 7 and a sterically inactive lone pair. Because of the high oxidizing power of Bi(+V), reactions aimed at Bi(N3)5 and [Bi(N3)6]– resulted in the reduction to bismuth(+III) compounds by [N3]–. The powder X-ray diffraction pattern of Bi(N3)3 was recorded at 298 K and is distinct from that calculated for Sb(N3)3 from its single-crystal data at 223 K. The [(bipy)2·Bi(N3)3]2 adduct is dimeric and derived from two BiN8 square antiprisms sharing an edge consisting of two μ1,1-bridging N3 ligands and with bismuth having CN 8 and a sterically inactive lone pair. The novel bipy·As(N3)3 and bipy·Sb(N3)3 adducts are monomeric and isostructural and contain a sterically active lone pair on their central atom and a CN of 6. A systematic quantum chemical analysis of the structures of these polyazides suggests that the M06-2X density functional is well suited for the prediction of the steric activity of lone pairs in main-group chemistry. Furthermore, it was found that the solid-state structures can strongly differ from those of the free gas-phase species or those in solutions and that lone pairs that are sterically inactive in a chemical surrounding can become activated in the free isolated species.