Non‐Globular Organic Ionic Plastic Crystal Containing a Crown‐Ether Moiety – Tuning Its Behaviour Using Sodium Salts

Abstract

Organic ionic plastic crystals (OIPCs) are a class of soft materials showing positional order while still allowing orientational freedom. Due to their motional freedom in the solid state, they possess plasticity, non-flammability and high ionic conductivity. OIPC behavior is typically exhibited by 'simple' globular molecules allowing molecular rotation, whereas the interactions that govern the formation of OIPC phases in complex nonglobular molecules are less understood. To better understand these interactions, a new family of non-globular OIPCs containing a 15-crown-5 ether moiety was synthetized and character-ized. The 15C5BA molecule prepared does not exhibit the sought-after behavior because of its non-globular nature and strong intermolecular H-bonds that restrict orientational motion. However, the OIPC behavior was successfully obtained through complexation of the crown-ether moiety with sodium salts containing chaotropic anions. Those anions weaken the interactions between the molecules, allowing rotational freedom and tuning of the thermal and morphological properties of the OIPC.

On the impact of the type of anion on the properties of solid-state electrolytes

“…The size of the 15-crown-5 moiety and the ion-dipole interactions of the polyether segments with Na + allow for its preferential complexation with sodium over other alkali metal ions [21]. The successful synthesis was confirmed by 1 H NMR, FT-IR and Maldi-TOF analysis as reported in our previous work [20].…”

“…The synthesis of the 15C5BA monomer was performed according to previously reported literature [20]. The preparation of the 15C5BA monomer was performed as follows.…”

“…15-crown-5 ether moiety containing monomer was chosen for its Na + selectivity and synthetized according to literature [20]. The size of the 15-crown-5 moiety and the ion-dipole interactions of the polyether segments with Na + allow for its preferential complexation with sodium over other alkali metal ions [21].…”

“…This behaviour suggests the formation of a different type of interaction arising between the amides in the polymer matrix and the sodium salts. This is due to the breaking of the H-bonds and the formation of intermolecular interactions with the anions (I − , SCN − , BF 4 − ) due to their chaotropic character [20]. The polymer complexed with NaPF 6 does not experience the breaking of the H-bonds between the amides due to the non-coordinating character of PF 6 − [22][23][24].…”

“…2, blue and green curves) compared to the other polymers prepared. This is attributed to the weakening of the H-bonds between the amidic functionalities of the 15C5BA polymer and to the formation of new interactions with the counterions of the sodium salts (I − , SCN − ) [20]. The presence of H-bonds in the structure of a molecule is indeed known to increase the thermal stability of the system compared to a situation in which there is no interaction [30].…”