Crystal structure, intermolecular interactions and NLO properties for imidazolium hydrogen sulfate ionic liquid

Abstract

Crystal structure, intermolecular interactions and nonlinear optical behavior for the ionic liquid imidazolium hydrogen sulfate (ImHS) were presented in the current paper for the first time. This was achieved applying a combined experimental (single crystal X-ray diffraction) and theoretical (Quantum theory of atoms in molecules (QTAM), Hirshfeld surface (HS), natural bond orbital (NBO) analysis) method. The quantum chemical calculations were conducted via density functional theory at B3LYP/6–311++G(2d,2p) level. Important nonlinear optical parameters such as dipole moment (μ), polarizability (α), anisotropy of polarizability (∆α) and first-order hyperpolarizability (β) are calculated at B3LYP/6–311++G(2d,2p) level of theory as well.It was shown that fragments with different molecular geometry present in the ImHS structure. Formation of hydrogen bonds (O···H) between the imidazolium cation and hydrogen sulfate anion stabilizes the ImHS structure. It was confirmed by means of QTAM, HS and NBO, where intensive electron density distribution between aromatic ring and inorganic anion due to O···H interactions was registered. Pronounced charge transfers between imidazolium cycle and hydrogen sulfate anion were found to be responsible for highly polarizable nature of ImHS, registered as high values for μ, α and β. Based on these, the studied ionic liquid was denoted as a good nonlinear optical material.