Probing the local structure of Prussian blue electrodes by 113Cd NMR spectroscopy

Isostructural Synthesis of Iron-Based Prussian Blue Analogs for Sodium-Ion Batteries

Rechargeable sodium ion batteries (SIBs) have promising applications in large-scale energy storage systems. Iron-based Prussian blue analogs (PBAs) are considered as potential cathodes owing to their rigid open framework, low-cost, and simple synthesis. However, it is still a challenge to increase the sodium content in the structure of PBAs and thus suppress the generation of defects in the structure. Herein, a series of isostructural PBAs samples are synthesized and the isostructural evolution of PBAs from cubic to monoclinic after modifying the conditions is witnessed. Accompanied by, the increased sodium content and crystallinity are discovered in PBAs structure. The as-obtained sodium iron hexacyanoferrate (Na1.75 Fe[Fe(CN)6 ]0.9743 ·2.76H2 O) exhibits high charge capacity of 150 mAh g-1 at 0.1 C (17 mA g-1 ) and excellent rate performance (74 mAh g-1 at 50 C (8500 mA g-1 )). Moreover, their highly reversible Na+ ions intercalation/de-intercalation mechanism is verified by in situ Raman and Powder X-ray diffraction (PXRD) techniques. More importantly, the Na1.75 Fe[Fe(CN)6 ]0.9743 ·2.76H2 O sample can be directly assembled in a full cell with hard carbon (HC) anode and shows excellent electrochemical performances. Finally, the relationship between PBAs structure and electrochemical performance is summarized and prospected.

Molecular Magnetic Materials Based on {Co III (Tp*)(CN) 3 } − Cyanidometallate: Combined Magnetic, Structural and 59 Co NMR Study

The cyanidocobaltate of formula fac‐PPh₄[Co^III(^Me2Tp)(CN)₃] ⋅ CH₃CN (1) has been used as a metalloligand to prepare polynuclear magnetic complexes (^Me2Tp=hydrotris(3,5‐dimethylpyrazol‐1‐yl)borate). The association of 1 with in situ prepared [Fe^II(bik)₂(MeCN)₂](OTf)₂ (bik=bis(1‐methylimidazol‐2‐yl)ketone) leads to a molecular square of formula {[Co^III{(^Me2Tp)}(CN)₃]₂[Fe^II(bik)₂]₂}(OTf)₂ ⋅ 4MeCN ⋅ 2H₂O (2), whereas the self‐assembly of 1 with preformed cluster [Co^II₂(OH₂)(piv)₄(Hpiv)₄] in MeCN leads to the two‐dimensional network of formula {[Co^II₂(piv)₃]₂[Co^III(^Me2Tp)(CN)₃]₂ ⋅ 2CH₃CN}_∞ (3). These compounds were structurally characterized via single crystal X‐ray analysis and their spectroscopic (FTIR, UV‐Vis and ⁵⁹Co NMR) properties and magnetic behaviours were also investigated. Bulk magnetic susceptibility measurements reveal that 1 is diamagnetic and 3 is paramagnetic throughout the explored temperature range, whereas 2 exhibits sharp spin transition centered at ca. 292 K. Compound 2 also exhibits photomagnetic effects at low temperature, selective light irradiations allowing to promote reversibly and repeatedly low‐spin⇔high‐spin conversion. Besides, the diamagnetic nature of the Co(III) building block allows us studying these compounds by means of ⁵⁹Co NMR spectroscopy. Herein, a ⁵⁹Co chemical shift has been used as a magnetic probe to corroborate experimental magnetic data obtained from bulk magnetic susceptibility measurements. An influence of the magnetic state of the neighbouring atoms is observed on the ⁵⁹Co NMR signals. Moreover, for the very first time, ⁵⁹Co NMR technique has been successfully introduced to investigate molecular materials with distinct magnetic properties.

A DFT/ZORA Study of Cadmium Magnetic Shielding Tensors: Analysis of Relativistic Effects and Electronic-State Approximations

Theoretical considerations are discussed for the accurate prediction of cadmium magnetic shielding tensors using relativistic density functional theory (DFT). Comparison is made between calculations that model the extended lattice of the cadmium-containing solids using periodic boundary conditions and pseudopotentials with calculations that use clusters of atoms. The all-electron cluster-based calculations afford an opportunity to examine the importance of (i) relativistic effects on cadmium magnetic shielding tensors, as introduced through the ZORA Hamiltonian at either the scalar (SC) or spin-orbit (SO) levels and (ii) variation in the class of the DFT approximation. Twenty-three combinations of pseudopotentials or all-electron methods, DFT functionals, and relativistic treatments are assessed for the prediction of the principal components of the magnetic shielding tensors of 30 cadmium sites. We find that the inclusion of SO coupling can increase the cadmium magnetic shielding by as much as ca. 1100 ppm for a certain principal values; these effects are most pronounced for cadmium sites featuring bonds to other heavy atoms such as cadmium, iodine, or selenium. The best agreement with experimental values is found at the ZORA SO level in combination with a hybrid DFT method featuring a large admixture of Hartree-Fock exchange such as BH&HLYP. Finally, a theoretical examination is presented of the magnetic shielding tensor of the Cd(I) site in Cd₂(AlCl₄)₂.

A [FeIII(Tp)(CN)3]− scorpionate-based complex as a building block for designing ion storage hosts (Tp: hydrotrispyrazolylborate)

Using a scorpionate-based complex as a building block, a new cyanide-based molecular material was investigated as a lithium-ion storage host.

M, Osiry H, Ramos-Sánchez G, González I. Electronic density distribution of Mn–N bonds by a tuning effect through partial replacement of Mn by Co or Ni in a sodium-rich hexacyanoferrate and its influence on the stability as a cathode for Na-ion batteries

This study evaluates the effect of equimolar substitution of manganese by cobalt or nickel in hexacyanoferrate open frameworks as electrode for Na-ion batteries.