PNNL

Abstract

We report a rare family of pyridine-coordinated iodobismuthate(III) salts supported by alkyltriphenylphosphonium and tetraphenylphosphonium cations. Reactions of BiI3 with Ph3PR+I- (R = Me, Et, nPr, nBu, Ph) in neat pyridine, followed by crystallization, yield structurally tunable bismuth-halide-pyridine anions dictated by reagent stoichiometry. Combination of BiI3 and Ph3PR+I- in 2:1 ratio produced [Ph3PR]2[BiI5Py], 1 (R = Me, Et, nPr, Ph), while combination in 1:1 ratio resulted in three compounds: [Ph3PR][cis-BiI4Py2], 2 (R = nPr, Ph), [Ph3PR][trans-BiI4Py2], 3 (R = Me, Et, Ph), and [Ph3PR]2[transoid-Bi2I8Py2], 4 (R = Me, Et, nPr, nBu, Ph). In many cases, the compounds were isolated as Py or Et2O solvates, and in some cases multiple degrees of solvation or polymorphism were encountered. Hirshfeld analysis of 1-4 showed the major anion-cation/anion/solvent interactions to be H…I, H…H, and C…H. Diffuse reflectance measurements of representative compounds, all of which were yellow-orange to red-orange, revealed bandgaps in the range of 1.9-2.2 eV where density-of-states KS-DFT calculations attribute the absorption to metal-centered charge transfer within the anionic unit. NLMO and QTAIM analyses further indicate predominantly ionic Bi(III)–I/pyridine bonding with robust inner-sphere coordination that is insensitive to outer-sphere perturbations.