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

Abstract

The binary group 15 polyazides As(N(3))(3), Sb(N(3))(3), and Bi(N(3))(3) were stabilized by either anion or donor-acceptor adduct formation. Crystal structures are reported for [Bi(N(3))(4)](-), [Bi(N(3))(5)](2-), [bipy·Bi(N(3))(5)](2-), [Bi(N(3))(6)](3-), bipy·As(N(3))(3), bipy·Sb(N(3))(3), and [(bipy)(2)·Bi(N(3))(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(N(3))(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(N(3))(5) and [Bi(N(3))(6)](-) resulted in the reduction to bismuth(+III) compounds by [N(3)](-). The powder X-ray diffraction pattern of Bi(N(3))(3) was recorded at 298 K and is distinct from that calculated for Sb(N(3))(3) from its single-crystal data at 223 K. The [(bipy)(2)·Bi(N(3))(3)](2) adduct is dimeric and derived from two BiN(8) square antiprisms sharing an edge consisting of two μ(1,1)-bridging N(3) ligands and with bismuth having CN 8 and a sterically inactive lone pair. The novel bipy·As(N(3))(3) and bipy·Sb(N(3))(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.