While ionic liquids
have proved to be versatile materials for a
wide spectrum of applications, e.g., energy, materials, and medicine,
several challenges remain concerning the rational design of novel
materials. In light of this, a series of four triphenylphosphonium-based
ionic liquids have been synthesized for the first time. These compounds
exhibit high thermal stability with decomposition temperatures up
to 450 °C. Their solid-state structures are characterized by
single-crystal X-ray diffraction and the intermolecular interactions
rigorously analyzed via Hirshfeld surface analysis. It was found
that the unique geometries of the anions used in the study form distinct
interactions with the cations. The interactions in the crystalline
state are correlated with the thermal properties of the four ionic
liquids to rationalize the melting points and phase transitions for
each compound. The observed arrangements of the alkyl chains on the
cations are investigated computationally to gain an understanding
of how rotational freedom may impact the thermal properties of the
compounds. By intention, each IL reported in this work offers a unique
property profile and contributes to the ever-growing ionic liquid
catalog.