The structural, electronic and thermodynamic properties of the designed p-benzoquinone based dicationic ionic liquids: insight from DFT–GD3 and QTAIM†

Abstract

In this work, the impact of various anions on the physicochemical properties of the designed p-benzoquinone-based dicationic ionic liquids [BTAD][A1–8]₂ ([BTAD]²⁺ = [p-C₆O₂(N₃H₂)₂]²⁺ and A1–8 = [CH₃CO₂]⁻, [CF₃CO₂]⁻, [N(CN)₂]⁻, [CF₃SO₃]⁻, [ClO₄]⁻, [BF₄]⁻, [NTf₂]⁻ and [PF₆]⁻) was investigated at the M06-2X/6-31++G(d,p) level of theory in the gas phase and solvent media. Besides, dispersion-corrected M06-2X-GD3, B2PLYP-GD3 and mPW2PLYP-GD2 functionals were employed to calculate the corrected interaction energies. The thermodynamic interaction energies in gas and solvent media, structural parameters, electrostatic potential maps, natural charge of atoms, charge transfer (CT), electron density properties, potentials of the anodic and cathodic limits (V_AL and V_CL), electrochemical windows (ECW), acidity (ΔpK_a1 and ΔpK_a2) and reduced gradient density plots (RGD) were examined. Based on the corrected interaction energies, the stability order of [BTAD][A1–8]₂ complexes at all levels of theory is [BTAD][CH₃CO₂]₂ > [BTAD][CF₃CO₂]₂ > [BTAD][N(CN)₂]₂ > [BTAD][CF₃SO₃]₂ > [BTAD][ClO₄]₂ > [BTAD][BF₄]₂ > [BTAD][NTf₂]₂ > [BTAD][PF₆]₂. The calculated ECW of [BTAD][A3–8]₂ is in the range of 4.5 to 7.5 V, demonstrating that these ILs can be promising candidates for the substitution of currently used electrolyte solutions based on organic molecular solvents in electrochemical devices.