  Spiroborate anions based inorganic electrolytes and ionic liquids (ILs) have
fascinating electrochemical and tribological properties, and have received
widespread attention in industrial applications. Molecular chiralities of
spiroborate anions have a significant effect on microstructures and macroscopic
functionalities of these ionic materials in applications, and thus deserve a
fundamental understanding. In current work, we performed quantum chemistry
calculations to address binding strength and coordination structures of chiral
bis(mandelato)borate ([BMB]) anions with representative alkali metal ions, as
well as electronic properties of alkali metal ion-[BMB] ion pair complexes. The
optimized [BMB] conformers are categorized into V-shaped, bent, and twisted
structures with varied electrostatic potential contours, conformational
energies, and distinct alkali metal ion-[BMB] binding structures. Alkali metal
ions have additional associations with phenyl groups in V-shaped [BMB]
conformers owing to preferential cation-$\pi$ interactions. Furthermore,
effects of molecular chiralities of [BMB] anions on thermodynamics and
microstructural properties of tetraalkylphosphonium [BMB] ILs were studied by
performing extensive atomistic interactions. Oxygen atoms in [BMB] anions have
competitive hydrogen bonding interactions with hydrogen atoms in cations
depending on molecular chiralities and steric hindrance effects of [BMB]
anions. However, molecular chiralities of [BMB] anions have negligible effect
on liquid densities of tetraalkylphosphonium [BMB] ILs and spatial
distributions of boron atoms in anions around phosphorous atoms in cations.
Enlarging tetraalkylphosphonium cation sizes leads to enhanced cation-anion
hydrogen bonding and Coulombic interactions due to enhanced segregation of
polar groups in apolar networks in heterogeneous IL matrices.
