Supramolecular Architecture of Chloranilate Salts with Organic Cations: π-stacking vs. Hydrogen Bonding

Four novel salts of chloranilic acid (H2CA; 3,6-dichloro-2,5-dihydroxy-1,4-quinone) with organic cations pyridinium (Hpy+), piperazinediium (H2ppz2+), 4,4\u27-bipyridinediium (H2bpy2+) and 1,10-phenanthrolinium (Hphen+) were prepared and structurally characterised: (Hpy)2CA (1), (H2ppz)CA (2), (H2bpy)CA·4H2O (3) and (Hphen)HCA·MeOH (4). Supramolecular architecture is based on extensive hydrogen bonding and π-stacking. The central motive is chloranilate dianion which acts as an acceptor of two bifurcated hydrogen bonds. Topology and dimensionality of hydrogen bonded networks can be tuned by use of different cations: thus discrete motives, 1D chains and 2D layers were observed. Three different types of π-stacks are present: aromatic stacks, quinoid stacks and stacks of alternating quinoid and aromatic rings. This work is licensed under a Creative Commons Attribution 4.0 International License

Robust Macroscopic Polarization of Block Copolymer-Templated Mesoporous Perovskite-Type Thin-Film Ferroelectrics

Ferroelectrics play an important role in various applications, from electronics to mechanics, optics, and biomedicine. Here, the preparation of a series of block copolymer–templated mesostructured (lead‐free) oxide ferroelectrics is described. Distorted perovskite LiNbO$_3$, LiTaO$_3$, and solid solution LiNbO$_3$–LiTaO$_3$ are produced as single‐phase thin films of good quality by the dip‐coating method using an evaporation‐induced self‐assembly process. They are investigated by a combination of electron microscopy, X‐ray diffraction and scattering, X‐ray photoelectron spectroscopy, and time‐of‐flight secondary ion mass spectrometry. Thermal treatment at ≥600 °C is required to initiate crystallization. Both the pore ordering and thermal stability increase with increasing tantalum content. Ferroelectric testing through dynamic and remanent polarization experiments at ambient conditions confirm the uniformity and purity of the LiNbO$_3$ thin‐film system. Results from positive‐up and negative‐down test measurements reveal a stable switching polarization of 2 µC cm$^{−2}$, with a coercive field of 50 kV cm$^{−1}$. Taken together, the lithium niobium and tantalum oxides prepared in the work are rare examples of sol–gel derived perovskite‐type materials with an ordered mesoporous morphology. Because of the spontaneous electrical polarization observed for LiNbO$_3$, such block copolymer–templated thin films might pave the way for the development of a new class of 3D nanocomposite ferroics

Synthesis, structural characterization and magnetic properties of ordered mesoporous Pr1−xCaxMnO3Pr_{1−x}Ca_{x}MnO_{3} thin films

Mixed-valence manganese oxides with a perovskite structure are promising candidates for next-generation electronic devices, among others, because of the combination of ferromagnetism with other technologically important properties. Herein we report the block copolymer-templating synthesis, structural characterization and magnetic properties of thermally stable thin films of cubic mesoporous praseodymium calcium manganite (PCMO), Pr1−xCaxMnO3 with x ≈ 0.3. This novel sol–gel derived material is one of the rare examples of a complex mixed-metal oxide with both uniform and ordered nanoscale porosity. Calcination in air at 750 °C produces the desired crystallinity without compromising the pore-solid architecture. The data acquired from superconductive quantum interference device magnetometry confirm the phase purity and high degree of crystallinity. Below around 115 K, the films show clear signs of ferromagnetic behavior, with large low-temperature coercivity. Collectively, the results unequivocally demonstrate the quality of the polymer-templated mesostructured PCMO thin films, whose unique morphology makes them attractive for a variety of applications and further provides an opportunity for designing tailored and multifunctional (host/guest) nanocomposites