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[Display omitted] • The critical design features of Parashift and ParaCEST MRI probes for molecular imaging are outlined. • The difficulties, advantages, and opportunities presented with d-block paramagnetic centres are discussed. • The current proof-of-concept responsive transition metal Parashift and ParaCEST systems are summarised within the review. • The current challenges and prospects of Parashift and ParaCEST probes for in vivo imaging are evaluated. The development of ParaCEST and Parashift agents presents opportunities for MRI molecular imaging agents (rather than simple contrast agents) for mapping physiological/biological/chemical environments. Long-term toxicity concerns and questions over sustainability are steering the MRI contrast agent community towards gadolinium-free alternatives, and thus Parashift and ParaCEST research is turning to d -block chemistry. Macrocyclic coordination chemistry is exploited in the judicious design of Parashift/ParaCEST molecular probes for in vivo imaging, to impart water stability as well as solubility, stabilisation of metal oxidation and spin states with anisotropic magnetic susceptibilities (for large hyperfine shifts and suitable paramagnetic relaxation rate enhancements), and optimised exchange dynamics of labile protons for CEST agents. Whilst the current exogenous transition metal Parashift and ParaCEST agents are still in their infancy, in vitro studies demonstrate their potential for in vivo applications. The development of responsive Parashift/ParaCEST agents is also summarised in this review; the mapping of temperature and pH is possible, whilst the prospect of imaging redox potentials and metal ion concentrations is under investigation with proof-of-concept studies. In vivo imaging with transition metal Parashift and/or ParaCEST probes is yet to be established, but studies with lanthanide-based systems demonstrate the possibilities as the chemistry of this field advances, and the role of endogenous MRI contrast due to paramagnetic metal ions is discussed. [ABSTRACT FROM AUTHOR]

Ternary transition metal borides (TTMBs) will break materials application limitation in harsh service environments, owing to their structure versatility and high component tunable ability. Herein, we reported a solid solution boride CrFeB synthesized by high pressure and high temperature method. CrFeB yields an asymptotic hardness of 14.2 GPa and thermal stability temperature is up to 1250 K. DC magnetic susceptibility measurements revealed that there is a separation between zero-field cooled and field cooled curve at around 5 K, which indicated the spin glass behavior for CrFeB. Temperature dependence AC susceptibility analysis gives further evidence that the freezing temperature increases with frequency following Vogel-Fulcher law. On the basis of XPS results and first-principle calculations, we speculate that the complex magnetic behaviors may derive from the short-range magnetic exchange of same occupation sites two metal atoms. Cr and Fe atoms tend to have opposite magnetic moments in these short-range exchange behaviors. The intrinsic magnetic disorder and short-range frustration lead to spin random freezing of CrFeB at low temperatures, which conforms to typical spin glass characteristics. These results will contribute to understanding the complex magnetism behavior of CrFeB and provides a new idea to design multifunctional TTMBs. [Display omitted] • Novel ternary solid solution boride CrFeB was fabricated by high pressure and high temperature method. • CrFeB exhibits high hardness, excellent antioxidant capacity and spin-glass behavior at low temperature. • The short-range magnetic exchange and long-range random occupancy of two metals lead to the spin glass behavior for CrFeB. • Regulating the interactions between metal components will help optimize the performance of multicomponent metal borides. [ABSTRACT FROM AUTHOR]

Rectification of spin currents is investigated theoretically in a normal‐metal/ferromagnetic‐insulator/normal‐metal heterostructure. The ferromagnetic insulator is assumed to have an anisotropic parameter of Δ > 1, and thus it is gapped. In the presence of a magnetic field along the z‐direction, the ground state becomes the one with all spins pointing upward (in the z‐direction). When a spin‐up polarized current is incident from the left metal, it is suppressed due to spin blockade; however, the spin‐down polarized current can pass through the insulator easily. Thus rectification of spin currents can be realized and it is found that the rectification coefficient can be up to ≈10 (or even higher) in the limit of low temperature or large energy gap. It can be further improved when the spin system is asymmetrically coupled with the metals. The results could be useful in spintronics based on magnetic insulators. [ABSTRACT FROM AUTHOR]

Recently, "host–guest chemistry" aspects of material science have received much attention, particularly in relation to moderating the functions of materials. In particular, magnetic properties involving the "magnetic ordering" and "spin crossover" of host–guest metal complex systems have been actively investigated in terms of their host–guest chemistry. That is, systems in which the magnetic properties are sensitive to perturbation by the uptake of guests (which thus act as chemical stimuli). Such guests (solvents, gases and organic molecules) very often influence the structures of both discrete metallosupramolecular assemblies as well as those of coordination polymers/metal‐organic frameworks (CPs/MOFs), providing a means for fine‐tuning their magnetic behavior, including the switching of their spin states. In this minireview, we report recent progress in the development and investigation of magnetic materials of both the CP and MOF categories as well as of discrete complexes whose properties are modulated by guests. [ABSTRACT FROM AUTHOR]

The effect of high pressure on the electronic characteristics of CoO is analyzed in the framework of the multielectron model of transition metal oxides. The specific features of spin crossover for d7 terms of Co2+ are compared to those characteristic of d5 and d6 configurations. A pressure-induced transition between antiferromagnetic and ferromagnetic states at the spin crossover point is predicted. A model is proposed to describe the pressure-induced variation of the electrical resistance exhibiting a stepwise change by eight orders of magnitude at the structural transition point observed at 43 GPa and the subsequent metallization above 133 GPa. [ABSTRACT FROM AUTHOR]

In recent years, X‐ray emission spectroscopy (XES) in the Kβ (3p‐1s) and valence‐to‐core (valence‐1s) regions has been increasingly used to study metal active sites in (bio)inorganic chemistry and catalysis, providing information about the metal spin state, oxidation state and the identity of coordinated ligands. However, to date this technique has been limited almost exclusively to first‐row transition metals. In this work, we present an extension of Kβ XES (in both the 4p‐1s and valence‐to‐1s [or VtC] regions) to the second transition row by performing a detailed experimental and theoretical analysis of the molybdenum emission lines. It is demonstrated in this work that Kβ2 lines are dominated by spin state effects, while VtC XES of a 4d transition metal provides access to metal oxidation state and ligand identity. An extension of Mo Kβ XES to nitrogenase‐relevant model complexes shows that the method is sufficiently sensitive to act as a spectator probe for redox events that are localized at the Fe atoms. Mo VtC XES thus has promise for future applications to nitrogenase, as well as a range of other Mo‐containing biological cofactors. Further, the clear assignment of the origins of Mo VtC XES features opens up the possibility of applying this method to a wide range of second‐row transition metals, thus providing chemists with a site‐specific tool for the elucidation of 4d transition metal electronic structure. [ABSTRACT FROM AUTHOR]

The structural and electronic properties of solid coordination compounds are of great interest in a wide variety of applications. The sensitivity of solid-state NMR to local structural environments in the presence of a transition metal with unpaired spins is demonstrated through 13C and 1H MAS NMR spectra of tris(acetylacetonato)manganese (III), Mn(acac) 3. The spectral assignment is established using a combination of density-functional theory and experimental NMR methods. An analysis of the spin-density distribution throughout the ligands as probed by NMR provides an understanding of the molecular electronic structure. The paramagnetic interaction enhances the spectral resolution and offers the possibility of using these spectra as structural fingerprints. The unique character of Mn(acac) 3 to manifest various degrees of Jahn-Teller distortions allows for a discussion of the relation between the electron occupancy, crystal structure, and 13C NMR peak shifts. Image 1 • NMR can probe ligand chemical environments near a paramagnetic metal center. • NMR is a sensitive probe of electronic structure due to Jahn-Teller distortions. • The presence of unpaired electrons amplifies the 13C shift range ten-fold. • 1H MAS NMR can be used as a fingerprint to distinguish amongst polymorphs. [ABSTRACT FROM AUTHOR]

By first principles method, we have determined the geometric configuration of K/Ba-codoped phenanthrene based on the formation energy calculations, and systematically investigated its electronic and magnetic properties. There are two bands crossing Fermi energy which mainly result from the LUMO+1 orbitals of two phenanthrene molecules in a unit cell, and the cylinder-like Fermi surface along the Γ - Z direction reflects the two-dimension character of metallic conduction of K/Ba-codoped phenanthrene. Compared to K-doped phenanthrene, K/Ba-codoping can donate more electrons to molecule to modify the electronic structure, while the intercalation of dopants does not result in the large distortion of molecule. (KBa)1phenanthrene is a magnetic metal with the spin moment of 0.32 μB per each molecule, and unexpectedly, the spins gather in one edge of molecule rather than a uniform distribution on the whole molecule. Our results demonstrate that codoping of monovalent and bivalent metals is an effective approach to modulate the electronic properties of metal-doped hydrocarbons. [ABSTRACT FROM AUTHOR]

The accumulation of amyloid-β (Aβ) aggregates is found in the brains of Alzheimer's disease patients. Thus, numerous efforts have been made to develop chemical reagents capable of targeting Aβ peptides and controlling their aggregation. In particular, tunable coordination and photophysical properties of transition metal complexes, with variable oxidation and spin states on the metal centers, can be utilized to probe Aβ aggregates and alter their aggregation profiles. In this review, we illustrate some rational strategies for designing photoactivatable metal complexes as chemical sensors for Aβ peptides or modulators against their aggregation pathways, with some examples. This review describes some examples of photoactivatable metal complexes that can probe and modulate amyloid-β peptides, with an emphasis on design approaches. [Display omitted] • Chemical reagents for amyloid-β (Aβ) are needed for elucidating the amyloid pathology. • Photoactivatable metal complexes are designed to probe Aβ peptides. • Aβ aggregation is controlled by metal complexes with photoillumination. [ABSTRACT FROM AUTHOR]

A rapid increase of human population in the last years stimulates a search for alternative renewable and environmentally friendly energy resources. Hydrogen energy becomes one of the most promising candidates to replace the largely consumed fossil fuels. The first crucial step in the process of obtaining the hydrogen energy is an efficient storage of hydrogen gas. Modified graphene nanomaterials have already proved their capability as adsorbents of gas molecules. An affinity to bind, and subsequently store, hydrogen molecules is investigated using density functional theory (DFT) for the series of graphene quantum dots (GQDs) doped with different transition metals. Overall, considering the calculated binding energies and bonding distances, the Fe-doped GQD is the most promising material for H 2 capture, with storage capacity limited to three H 2 molecules on one Fe atom. Further potential candidates for effective H 2 adsorption are Mn-, and Cr-doped GQDs. Our calculations suggest that an induced change of their spin states may significantly enhance their H 2 adsorption ability. Such a change of spin state would be more easily accomplished in the case of Mn-doped GQD, having the doublet and quartet spin state energetically closer to each other (ca. 16.5 kJ mol−1). • H 2 adsorption ability of the GQDs doped with various transition metals is theoretically investigated. • The Fe-doped GQDs are the most promising materials for H 2 capture. • An induced change of the spin state may improve the H 2 adsorption ability of Mn-, and Cr-doped GQDs. • The storage capacity of one transition metal dopant atom is limited to three H 2 molecules. [ABSTRACT FROM AUTHOR]

[Display omitted] • Transition metal dioxide anions effectively react with SO 2 in the gas phase. • CuO 2 − and ZnO 2 − oxidate SO 2 to SO 4 − by double oxygen transfer. • CoO 2 − and NiO 2 − consecutively ligate two SO 2 molecules. • Ligation of H 2 O to ZnO 2 − changes the reactivity to single oxygen transfer to form SO 3 −. • Spin density on the metal plays a special role in addressing the reactivity. The reactivity of transition metal dioxide anions of cobalt, nickel, copper and zinc with sulfur dioxide has been investigated in the gas phase by mass spectrometric techniques and theoretical calculations. Dioxide anions of the late transition metals Cu and Zn promote an unprecedented fast and efficient oxidation to the sulfate radical anion through a double oxygen transfer, whereas the earlier transition metals Ni and Co only undergo the addition of two SO 2 molecules. The ligation of a water molecule to ZnO 2 − switches the reaction path to a single oxygen anion transfer, forming SO 3 −. [ABSTRACT FROM AUTHOR]

[Display omitted] • A combination between solid state and molecular orbital DFT calculations. • Using NBO analysis in comparison with solid state charges. • Considerable shifts in plasmon peaks for some metal-graphene systems in visible region. • Useful data for prediction of plasmonic properties for larger systems. • Requirement for development of new theories for plasmonics through adsorption phenomena. In this study, plasmonic properties of transition metal atoms (Sc-Zn, Pd, Pt) adsorbed on various sites of graphene sheets were investigated before and after CO adsorption by density functional theory (DFT). To this aim, Electron Energy Loss Spectroscopy (EELS) of these systems were obtained by periodic DFT. The results indicated that the highest in-plane plasmon peaks undergo blue shifts after CO adsorption, in such a way that Co–graphene system demonstrates the highest blue shift of 2.42 eV from Visible to UV region. Also, out-of-plane plasmons do not exhibit significant sensitivity to CO adsorption. For deeper understanding of electronic structure of metal-graphene systems, appropriate molecular models were considered, and natural bond orbital (NBO) analysis applied. Comparison of solid-state net charges with the NBO charges showed that CO adsorption has more non-local characteristics, while the metal atom adsorption on bare graphene surface has more local nature. Moreover, Jahn–Teller distortion of metal adatom strongly depends on the net charges of nearest-neighbor C atoms on the surface. In addition, spin distribution on metal 3d orbitals plays a role to some extent. These results can be useful for experimental researchers who want to construct the sensors and optical devices based on metal-graphene interactions. [ABSTRACT FROM AUTHOR]

The electron structure of [MCl 4 ] q complexes, q = 0, −1 and −2, of the 1st row transition metals in various spin states was evaluated using MP2 and 15 DFT functionals. The changes of the physical oxidation state and of the calculated d-electron population at the central atom are equal. [Display omitted] The structures of [MCl 4 ] q complexes, q = 0, −1 and −2, of the 1st row transition metals in various spin states were optimized at MP2/6-311G* level of theory. Their electron structure was evaluated by the Mulliken population analysis and alternatively by the Natural population analysis at MP2 and DFT levels of theory using 15 functionals. For constant charge q of the complex the changes of the physical oxidation states based on [Ar]d n occupations and of the calculated d-electron population dx at the central atom are equal. Their increase with the negative charge q of the complex can be concluded as well. The transition metal complexes with 'innocent' ligands can be used for scaling the analogous complexes with 'non-innocent' ligands by estimating their physical oxidation states. [ABSTRACT FROM AUTHOR]

The electronic structures and magnetic properties of square-octagonal bismuthene embedded with 3 d transition elements were studied systematically by the first-principles calculations. The formation energies of all the cases are negative, indicating the feasibility and practicability for these doped monolayer bismuthene. No considerable spin splitting appears in Sc-, Co-, and Zn-doped compounds. After doping, Sc- and Co-doped compounds are semiconductors while Zn-doped compound is metal. Ti-, V-, Cr-, Mn-, Fe-, Ni-, and Cu-doped systems behave as magnetic semiconductors. Among them, Cu-doped system exhibits both desirable spin gapless and bipolar magnetic semiconducting characteristics. In addition, Fe-doped system is a wonderful candidate for realizing quantum anomalous Hall insulating state. Image 1 • Sc- and Co-doped square-octagonal bismuthene are nonmagnetic semiconductors. • Zn-doped square-octagonal bismuthene is nonmagnetic metal. • Fe-doped square-octagonal bismuthene is a ferromagnetic Chern insulator for realizing quantum anomalous Hall insulating state. • Cu-doped square-octagonal bismuthene is either spin gapless or bipolar magnetic semiconductor. [ABSTRACT FROM AUTHOR]