Lewis-base adducts of main group 1 metal compounds: X. Lithium bromide and iodide complexes with acetonitrile (1:2, 1:4 respectively)

Although only sparingly soluble in acetonitrile, lithium(I) bromide and iodide crystallize as acetonitrile adducts, structurally characterized as LiX/MeCN 1:2 and 1:4 respectively by single-crystal structure determinations. The bromide is a μ, μ′-dibromo-bridged dimer, [(MeCN)₂LiBr₂Li(NCMe)₂)] (monoclinic, P2₁n, a 7·624(2), b 12·612(2), c 8·047(3) Å, ß 98·94(3)°, Z 2 dimers; R 0·038 for N_o 1081 ‘observed’ reflections); Li-Br, N 2·534(7), 2·492(8); 2·031(9), 2·047(8) Å respectively, with Li ⋯ Li, 3·17(1); Br⋯Br, 3·8989(9) Å respectively. The iodide is ionic, [Li(NCMe)4]⁺I^- (orthorhombic, P2₁22₁, a 20·66(1), b 12·208(6), c 8·429(5) Å, Z 6; R 0·062 for N_o 866).