AUTHOR=Pei Han-Wen , Li Bin , Laaksonen Aatto , Wang Yong-Lei 

TITLE=How Molecular Chiralities of Bis(mandelato)borate Anions Affect Their Binding Structures With Alkali Metal Ions and Microstructural Properties in Tetraalkylphosphonium Ionic Liquids

JOURNAL=Frontiers in Chemistry

VOLUME=Volume 8 - 2020

YEAR=2020

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2020.00065

DOI=10.3389/fchem.2020.00065

ISSN=2296-2646

ABSTRACT=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.
The optimized [BMB] conformers are categorized into V-shaped, bent, and twisted anion 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 intermolecular hydrogen bonding and Coulombic interactions due to enhanced segregation of polar groups in apolar networks in heterogeneous IL matrices.