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 ((Pr2BiI)-Pr-i) units. The title complex [(Pr2BiI)-Pr-i](4). (1) formed spontaneously as the major product from the reaction of (Pr3Bi)-Pr-i with MI2 (M = Mn, Co, Fe). Complex 1 was then more directly synthesized via bromination of (Pr3Bi)-Pr-i to form ((Pr2BiBr)-Pr-i), followed by iodide substitution. The X-ray structure of 1 exhibited acute Bi-I-Bi bonds (similar to 85-95 degrees) that enabled formation of the hollow square motif. Synthetic control experiments with R2BiX (R = Pr-i, Bn; X = I, Br) revealed that the identities of both the halide and bismuth R group are determinants for square formation: the bromo-substituted [(Pr2BiBr)-Pr-i](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 similar to 90 degrees/180 degrees bonding motifs.