Comprehensive Research Organization for Science and Society

Three-dimensional covalent organic frameworks (3D COFs) are promising crystalline porous materials, but the elucidation of their structure remains challenging, particularly for those featuring spiroborate linkages. Herein, we report the synthesis of a 3D single-crystalline COF (scCOF) with nbo topology, constructed from a rigid square-planar monomer, tetracyclopentatetraphenylene (TCTP), and spiroborate linkages. Theoretical calculations revealed that the TCTP core possesses higher rigidity than phthalocyanine, effectively suppressing structural fluctuations during framework formation. The structure of the resulting TCTP-COF was successfully determined using microcrystal electron diffraction (MicroED), revealing a non-interpenetrated cubic framework with space group Im-3m. TCTP-COF exhibits high crystallinity, thermal stability up to 320 °C, and permanent porosity with a Brunauer–Emmett–Teller surface area of 1360 m2·g–1. To the best of our knowledge, this work represents the first structural determination of a spiroborate-linked 3D scCOF using electron diffraction methods, providing a new design strategy for expanding the chemical space of highly ordered 3D COF architectures.

This work successfully demonstrated the crystal structure determination of large π-conjugated molecules using Micro-crystal Electron Diffraction（MicroED）. The poorly soluble tweezer-shaped molecules were synthesized, and their crystal structures were determined directly from the reaction vessels to MicroED, bypassing sample purification steps such as column chromatography and recrystallization. MicroED would be a powerful analytical tool for determining the structures of molecules and their assemblies for microcrystals, such as poorly soluble compounds, rare natural products, mechanochemical products, and membrane proteins. In this paper, we also report on the establishment of the MicroED techniques in Okazaki, detailing the preliminary experiments conducted for system startup, which included sample preparation, sample loading, calibration, data measurement, and data reduction.

Polarized neutron reflectometry (PNR) analyzes surface and interfacial structures of materials. For the SHARAKU reflectometer at the Materials and Life Science Experimental Facility in the Japan Proton Accelerator Research Complex, precise measurements under weak magnetic fields, which are critical for modern spintronics, have long been challenging. To address this issue, we developed a precise weak-field sample environment equipped with a newly designed coil system. The magnetic field at the sample position can be applied within the surface/interface plane, either in the scattering plane (horizontal configuration) or perpendicular to it (vertical configuration). The horizontal configuration achieved high polarization efficiency across a stable field range, whereas the vertical configuration enabled the experiments to cross zero into negative fields. We demonstrated the instrument’s capability by resolving the remanent magnetic structure of an Fe film. Its applicability to soft matter was proven through analysis of a cellulose thin film with roughness using magnetic contrast variation PNR. In this case, precise weak-field control is essential to tune the magnetic contrast from the reference layer beneath the soft film. These results establish the system as a versatile platform for future PNR and polarized off-specular scattering experiments across a wide range of materials.

The Hall effect is one of the most fundamental but elusive phenomena in condensed matter physics due to the rich variety of underlying mechanisms. Here we report an exceptionally large Hall effect in a frustrated magnet GdCu2 with high conductivity. The Hall conductivity at the base temperature is as high as the order of 104–105 Ω−1 cm−1 and shows abrupt sign changes under magnetic fields. Remarkably, the giant Hall effect is rapidly suppressed as the longitudinal conductivity is lowered upon increasing temperature or introducing tiny amount of quenched disorder. Our systematic transport measurements combined with neutron scattering measurements, ab initio band calculations and spin model calculations indicate that the unusual Hall effect can be understood in terms of spin-splitting induced emergence/disappearance of Fermi pockets as well as skew scattering from spin-chiral cluster fluctuations in a field-polarized state. The present study demonstrates complex interplay among magnetization, spin-dependent electronic structure, and spin fluctuations in producing the giant Hall effect in highly conductive frustrated magnets with a distorted triangular lattice.