Isolation and X-ray Structure of a Dialkylbismuth(III) Iodo "Nanosquare": Breaking the Polymeric Mold of R2BiX.

We report the synthesis, X-ray structure, and solution behavior of a "nanosquare" formed by four repeating (iPr2BiI) units. The title complex [iPr2BiI]4 (1) formed spontaneously as the major product from the reaction of iPr3Bi with MI2 (M = Mn, Co, Fe). Complex 1 was then more directly synthesized via bromination of iPr3Bi to form (iPr2BiBr), followed by iodide substitution. The X-ray structure of 1 exhibited acute Bi-I-Bi bonds (∼85-95°) that enabled formation of the hollow square motif. Synthetic control experiments with R2BiX (R = iPr, Bn; X = I, Br) revealed that the identities of both the halide and bismuth R group are determinants for square formation: the bromo-substituted [iPr2BiBr]n (2) and benzyl-substituted [Bn2BiI]n (3) variants formed only polymers as determined by X-ray crystallography. Density functional theory calculations revealed nearly pure p-orbital-based bonding molecular orbitals on both iodide and bismuth, facilitating the ∼90°/180° bonding motifs.