Synthesis and structures of lithium salts of two cluster iodoarsenate(III)s and a periodohexaantimonate(III)

Treatment of the lithium β-diketiminate Li{N(C₆H₃-2,6)C(Me)}₂CH] with an equivalent portion of arsenic(III) iodide unexpectedly afforded Li(thf)₄]₂As₈I₂₆] (1) in modest yield. Another new cluster anion featured in Li(thf)₄]₂Li(thf)₆]As₇I₂₄]·1.5(thf) (2) was obtained in excellent yield from lithium iodide and four equivalents of AsI₃ in thf. Using the same stoichiometry and solvent, but with SbI₃ in place of AsI₃, furnished in good yield Li(thf)₄]₄Sb₆I₂₂]·2(thf) (3). The structures of the new crystalline orange (1, 3) or orange/red (2) salts was established by single crystal X-ray diffraction. Each anion of 1-3 may be factorised into respectively (AsI₂)₆(AsI)₂(μ₂-I)₁₀(μ₅-I)₂]²⁻ (1), {(AsI₂)(μ₂-I)(μ₃-I)}₆As]³⁻ (2) and (SbI₃)₂(SbI₂)₂(SbI)₂(μ₂-I)₆(μ₃-I)₄]⁴⁻ (3). Each As atom in 2 and each Sb atom in 3 is the centre of a six-coordinate distorted octahedron, while the arsenic atoms in 1 have either four- or six-coordinate environments.