Cation and Anion Transfer in Quinuclidinium Hexafluorophosphate Plastic Crystal: Role of Constituent Ions and the Crystalline Structure

Abstract

This research demonstrates the cation and anion transfer of an organic ionic plastic crystal (OIPC), quinuclidinium hexafluorophosphate ([HQ]­PF6), in the pure state and mixtures doped with lithium or chloride ions. The pure material and the mixtures show relatively simple thermal behaviors. Powder X-ray diffraction determined a cubic crystal structure, a common feature of OIPCs, in the high-temperature phase of the pure material. Solid-state nuclear resonance spectra of the pure material reveal rotation-assisted ion mobility and the presence of the plastic crystal phase. The ionic conductivity of the mixtures doped with lithium ions and chloride ions increases significantly. Arrhenius conduction behaviors are observed in both the pure material and ion-doped mixtures, with effective activation energies of ∼60–110 kJ mol–1. Ionic conductivity also implies that ions transfer either through the bulk crystal or via grain boundaries. This is the first time that the cation and anion transfer in a quinuclidinium-based OIPC is reported, and the anion (here Cl–) is transferred in plastic crystal systems where solid solutions are likely formed. Different ion conduction behaviors of the pure and doped materials are closely associated with shapes and relative sizes of constituent ions. The results provide useful information to improve the understanding of structure–property relationships in OIPCs.

Transfer of Machine Learning Fairness across Domains

“…The transfer learning here corresponds to preserving fairness for a single sensitive attribute but over different tasks. However, Lan and Huan [17] found empirically that fairness does not transfer well to a new domain. They found that as accuracy increased in the transfer process, fairness decreases in the new domain.…”

“…In these cases, a proxy of the sensitive attribute have been used [14], or researchers need very sample-efficient techniques [1,4]. For distant proxies, researchers have asked how well fairness transfers across attributes [17]. Here the sensitive attribute differs in the source and target domains.…”

Defect-Assisted High Anion Conductivity in Diethyldimethylammonium d-Camphorsulfonate Plastic Crystal: A Size Effect of Target Ions

“…The drying of the pure material and doped mixtures was performed as reported previously . In brief, the samples were dried thoroughly under a vacuum for at least 48 h at 50–70 °C.…”

“…Then, the pellet was fixed between two stainless steel electrodes of a homemade conductance cell and isolated from air using several silicone-rubber flat gaskets. A self-designed aluminum barrel was used for heating and cooling the conductance cell assembly, as reported previously . The temperature of the sample was measured using a K-type thermocouple with an accuracy of 0.5 °C.…”

8-Quinolinyl Oxazoline: Ligand Exploration in Enantioselective Ni-Catalyzed Reductive Carbamoyl-Alkylation of Alkene to Access the Chiral Oxindoles

“…Subsequently, the Wang group reported a Ni-catalyzed asymmetric reductive carboacylation of pendant alkene enabled by an elaborated t Bu-4-morpholinylPyrox ligand, providing various chiral oxindoles derivatives in up to 80% yield and up to 89% ee. 15 Nevertheless, the most commonly used chiral ligands in current reductive cross-coupling reactions limit to the well-developed scaffolds. In 2020, we disclosed an 8-quinolinyl imidazoline (8-Quinim) enabled Ni-catalyzed carbamoyl-alkylation of unactivated alkene for the unprecedented synthesis of chiral nonaromatic heterocycles, in which 8-Quinox ligand performed inferiorly in enantioselectivity control.…”