Physical Chemistry Chemical Physics

Asakura, Daisuke; Sudayama, Takaaki; Nanba, Yusuke; Hosono, Eiji; Kiuchi, Hisao; Yamazoe, Kosuke; Miyawaki, Jun; Harada, Yoshihisa; Yamada, Atsuo; Wang, Ru-Pan; de Groot, Frank M. F.

doi: 10.1039/d4cp03759fpmid: 39692579

To understand the electronic-structure change of LiCoO2, a widely used cathode material in Li-ion batteries, during charge–discharge, we performed ex situ soft X-ray absorption spectroscopy (XAS) and resonant soft X-ray emission spectroscopy (RXES) of the Co L3 edge in combination with charge-transfer multiplet calculations. The RXES profile significantly changed for the charged state at 4.2 V vs. Li/Li+, corresponding to the oxidation reaction from a Co3+ low-spin state for the initial state, while the XAS profile exhibited small changes. For the 4.2-V charged state, we confirmed that approximately half of the initial Co3+ ions were oxidized to Co4+ ions. The multiplet calculation of the RXES results revealed that the Co4+ state has a negative charge-transfer energy and the d6L̲ state (L̲ is a ligand hole) is the most stable. Therefore, the O 2p hole created by the strong charge-transfer effect plays a major role in the redox reaction of LiCoO2.

Nieuwland, Celine; van Dam, Angelina N.; Bickelhaupt, F. Matthias; Fonseca Guerra, Célia

doi: 10.1039/d4cp04042bpmid: 39660363

The hydrogen-bond donor strength of ureas, widely used in hydrogen-bond donor catalysis, molecular recognition, and self-assembly, can be enhanced by increasing the size of the chalcogen X in the C00000000000000000000000000000000111111110000000011111111000000000000000000000000X bond from O to S to Se and by introducing more electron-withdrawing substituents because both modifications increase the positive charge on the NH groups which become better hydrogen-bond donors. However, in 1,3-diaryl X-ureas, a steric mechanism disrupts the positive additivity of these two tuning factors, as revealed by our quantum-chemical analyses. This leads to an enhanced hydrogen-bond donor strength, despite a lower NH acidity, for 1,3-diaryl substituted O-ureas compared to the S- and Se-urea analogs. In addition, we provide a strategy to overcome this steric limitation using a predistorted urea-type hydrogen-bond donor featuring group 14 elements in the CX bond so that the hydrogen-bond donor strength of X-urea derivatives bearing two aryl substituents can be enhanced upon varying X down group 14.

Tarannum, Ibtesham; Singh, Saurabh Kumar

doi: 10.1039/d4cp03016hpmid: 39373561

Organometallic sandwich complexes of Dy(iii) ion are ubiquitous for designing high-temperature single-ion magnets with blocking temperatures close to the liquid nitrogen boiling point. Magnetic bistability at the molecular level makes them potential candidates for nano-scale information storage materials. In the present contribution, we have thoroughly investigated the electronic structure, bonding, covalency, and magnetic anisotropy of inorganic dysprosocene complexes with a general formula of [Dy(E4)2]− (where E = N, P, As, CH) using state-of-the-art scalar relativistic density functional theory (SR-DFT), and a multiconfigurational complete active space self-consistent field (CASSCF) method with the N-electron valence perturbation theory (NEVPT2). Geometry optimization calculations predict stabilization of the [Dy(E4)2]− complexes with a linear geometry and D4h local symmetry Dy(iii) ion in [Dy(N4)2]− (1) and [Dy(P4)2]− (2) complexes, while a bent geometry has been observed for the [Dy(As4)2]− (3), [Dy(P2(CH)2)2]− (4), and [Dy(As2(CH)2)2]− (5) complexes. Energy decomposition analysis (EDA) and natural bonding orbital (NBO) calculations reveal sizable 5d–ligand covalency followed by 6s/6p and weak 4f–ligand covalency in complexes 1–5. Both the natural localized molecular orbitals (NLMOs) at the DFT level and ab initio-based ligand field theory (AILFT) at the NEVPT2 level of theory predict an increase in the Dy–ligand covalency as we move from N to As. Spin-Hamiltonian parameter analysis of complexes 1–5 reveals stabilization of the mJ |±15/2〉 as the ground state with highly axial g values (gxx ∼ gyy ∼ 0 and gzz ∼ 20) and the barrier height of 2902, 1214, 1104, 1845, and 1509 K for 1–5, respectively. The Orbach effective demagnetization barrier (Ueff) for complexes 1–5 ranges between 2416–1175 K, with a record Ueff value of 2416 K observed for 1. In addition, we have explored the role of heavy element effects on the magnetic anisotropy by turning off the spin–orbit coupling of the pnictogens (N, P, and As), and our calculations clearly predict that heavy atoms in the first coordination sphere help in increasing the barrier height for magnetic relaxation. Heavy elements like P and As significantly enhance the SOC contributions, thereby providing a platform for designing and optimizing Dy(iii) complexes with tailored magnetic behaviors.

Feng, Chiwen; Liang, Yanwei; Sun, Jiaying; Wang, Renhai; Sun, Huaijun; Dong, Huafeng

doi: 10.1039/d4cp03879gpmid: 39744971

The combination of data science and materials informatics has significantly propelled the advancement of multi-component compound synthesis research. This study employs atomic-level data to predict miscibility in binary compounds using machine learning, demonstrating the feasibility of such predictions. We have integrated experimental data from the Materials Project (MP) database and the Inorganic Crystal Structure Database (ICSD), covering 2346 binary systems. We applied a random forest classification model to train the constructed dataset and analyze the key factors affecting the miscibility of binary systems and their significance while predicting binary systems with high synthetic potential. By employing advanced genetic algorithms on the Co–Eu system, we discovered three novel thermodynamically stable phases, CoEu8, Co3Eu2, and CoEu. This research offers valuable theoretical insights to guide experimental synthesis endeavors in binary and complex material systems.