Bi(III) halometallate ionic liquids: Interactions and speciation.

ABSTRACT

Bismuth containing compounds are of particular interest for optical or photo-luminescent applications in sensing, bio-imaging, telecommunications, and opto-electronics and as components in non-toxic extremely dense liquids. Bismuth(III) halometallates form highly colored novel ionic liquid based solvents for which experimental characterization and fundamental understanding are limited. In this work, Bismuth(III) halometallates incorporating chloride, bromide, and iodide have been studied via density functional theory employing B3LYP-D3BJ/aug-cc-pVDZ. Lone anions, and anions in clusters with sufficient 1-ethyl-3-methyl-imidazolium [C2C1Im]+ counter-cations to balance the charge, have been investigated in the gas- phase, and with polarizable continuum solvation. Evaluation of speciation profiles indicates that dimeric or trimeric anions are prevalent. In contrast to analogous Al systems, anions of higher charge (-2, -3) are present. Speciation profiles are similar, but not identical with respect to the halide. The Bi based anions [BimXn]x- in the gas phase and generalized solvation environment produce multiple low energy conformers; moreover, key structural interaction patterns emerge from an analysis of ion-pair and neutral-cluster structures (BimXn)x-(C2C1Im)x + for x = 1, 2, and 3. Cation-anion interactions are weak; with Coulombic and dispersion forces predominating, anion-π structures are favored, while significant hydrogen bonding does not occur. Anion to cation charge transfer is minimal, but mutual polarization is significant, leading to local positive regions in the anion electrostatic potential surface. The key features of experimental x-ray photoelectron, UV-Vis spectra, and Raman spectra are reproduced, validating the computational results and facilitating rationalization of key features.