Tetraiododiborane(4) (B₂ I₄ ) is a Polymer Based on sp³ Boron in the Solid State

Herein we present the first solid-state structures of tetraiododiborane(4) (B₂ I₄ ), which was long believed to exist in all phases as discrete molecules with planar, tricoordinate boron atoms, like the lighter tetrahalodiboranes(4) B₂ F₄ , B₂ Cl₄ , and B₂ Br₄ . Single-crystal X-ray diffraction, solid-state NMR, and IR measurements indicate that B₂ I₄ in fact exists as two different polymeric forms in the solid state, both of which feature boron atoms in tetrahedral environments. DFT calculations are used to simulate the IR spectra of the solution and solid-state structures, and these are compared with the experimental spectra.