Smallest acyclic tricationic molecule containing a Bis(phosphine)-stabilized low-valent triantimony-based Unit.

Mukherjee, Nilanjana; Peerless, Benjamin; Nadurata, Vincent L; Kumar, Vikas; Sangole, Mayur P; Singh, Kirandeep; Wiedemann, Haakon T A; Kay, Christopher W M et al. · Nat Commun · 2026

basic_science · Level V

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Abstract

Element-element bonded multiply charged cationic species are well known as dimers or small cyclic oligomers in the condensed phase. However, the smallest acyclic version, a trinuclear unit possessing greater than a monocationic charge, has remained elusive. Here we introduce a bis(phosphine) supported low valent triantimony-based tricationic compound as a new entrant in this field. Structural elucidation and electronic understanding reveal a W-shaped tricationic unit comprising of a three-center four-electron sigma-bonded triantimony moiety that is terminally capped by bis(phosphine) ligands, with the central antimony atom having two lone pairs of electrons. The unique counter trianion [Sb(O)<sub>2</sub>(OTf)<sub>4</sub>]<sup>3-</sup> (OTf = CF<sub>3</sub>SO<sub>3</sub>) possesses reactive polar Sb<sup>δ+</sup>-O<sup>δ-</sup> bonds, the structure of which is determined from single crystal X-ray diffraction analysis. The ensemble of reactive molecular fragments found in this highly charged antimony-based compound makes it thermally unstable. Nonetheless, this fully characterized fleeting species shows a diverse reactivity profile, advancing the isolation of various novel antimony compounds, including the formation of a distinct low-valent antimony-cobalt carbonyl cluster.