Magneto-chiral dichroism is a non-reciprocal--that is, directional--effect observed in magnetized chiral systems, featuring an unbalanced absorption of unpolarized light depending on the direction of ...the magnetization. Despite the fundamental interest in a phenomenon breaking both parity and time-reversal symmetries, magneto-chiral dichroism is one of the least investigated aspects of light-matter interaction most likely because of the weakness of the effect in most reported experiments. Here we have exploited the element selectivity of hard X-ray radiation to investigate the magneto-chiral properties of enantiopure crystals of two isostructural molecular helicoidal chains comprising either cobalt(II) or manganese(II) ions. A strong magneto-chiral dichroism, with Kuhn asymmetry of the order of a few per cent, has been observed in the cobalt chains system, whereas it is practically absent for the manganese derivative. The spectral features of the X-ray magneto-chiral dichroism signal differ significantly from the natural and magnetic dichroic contributions and have been rationalized here using the multipolar expansion of matter-radiation interaction.
The unique properties of graphene, transition-metal dichalcogenides and other two-dimensional (2D) materials have boosted interest in layered coordination solids. In particular, 2D materials that ...behave as both conductors and magnets could find applications in quantum magnetoelectronics and spintronics. Here, we report the synthesis of CrCl2(pyrazine)2, an air-stable layered solid, by reaction of CrCl2 with pyrazine (pyz). This compound displays a ferrimagnetic order below ∼55 K, reflecting the presence of strong magnetic interactions. Electrical conductivity measurements demonstrate that CrCl2(pyz)2 reaches a conductivity of 32 mS cm–1 at room temperature, which operates through a 2D hopping-based transport mechanism. These properties are induced by the redox-activity of the pyrazine ligand, which leads to a smearing of the Cr 3d and pyrazine π states. We suggest that the combination of redox-active ligands and reducing paramagnetic metal ions represents a general approach towards tuneable 2D materials that consist of charge-neutral layers and exhibit both long-range magnetic order and high electronic conductivity.
Acquiring spatial control of nanoscopic metal clusters is central to their function as efficient multi-electron catalysts. However, dispersing metal clusters on surfaces or in porous hosts is ...accompanied by an intrinsic heterogeneity that hampers detailed understanding of the chemical structure and its relation to reactivities. Tethering pre-assembled molecular metal clusters into polymeric, crystalline 2D or 3D networks constitutes an unproven approach to realizing ordered arrays of chemically well-defined metal clusters. Herein, we report the facile synthesis of a {Pd
} cluster-based organometallic framework from a molecular triangulo-Pd
(CNXyl)
(Xyl = xylyl; Pd
) cluster under chemically mild conditions. The formally zero-valent Pd
cluster readily engages in a complete ligand exchange when exposed to a similar, ditopic isocyanide ligand, resulting in polymerization into a 2D coordination network (Pd
-MOF). The structure of Pd
-MOF could be unambiguously determined by continuous rotation 3D electron diffraction (3D-ED) experiments to a resolution of ~1.0 Å (>99% completeness), showcasing the applicability of 3D-ED to nanocrystalline, organometallic polymers. Pd
-MOF displays Pd
cluster nodes, which possess significant thermal and aerobic stability, and activity towards hydrogenation catalysis. Importantly, the realization of Pd
-MOF paves the way for the exploitation of metal clusters as building blocks for rigidly interlocked metal nanoparticles at the molecular limit.
Abstract
Electronic synergy between metal ions and organic linkers is a key to engineering molecule-based materials with a high electrical conductivity and, ultimately, metallicity. To enhance ...conductivity in metal-organic solids, chemists aim to bring the electrochemical potentials of the constituent metal ions and bridging organic ligands closer in a quest to obtain metal-
d
and ligand-
π
admixed frontier bands. Herein, we demonstrate the critical role of the metal ion in tuning the electronic ground state of such materials. While VCl
2
(pyrazine)
2
is an electrical insulator, TiCl
2
(pyrazine)
2
displays the highest room-temperature electronic conductivity (5.3 S cm
–1
) for any metal-organic solid involving octahedrally coordinated metal ions. Notably, TiCl
2
(pyrazine)
2
exhibits Pauli paramagnetism consistent with the specific heat, supporting the existence of a Fermi liquid state (i.e., a correlated metal). This result widens perspectives for designing molecule-based systems with strong metal-ligand covalency and electronic correlations.
Magnetochiral dichroism (MΧD) originates in the coupling of local electric fields and magnetic moments in systems where a simultaneous break of space parity and time-reversal symmetries occurs. This ...magnetoelectric coupling, displayed by chiral magnetic materials, can be exploited to manipulate the magnetic moment of molecular materials at the single molecule level. We demonstrate herein the first experimental observation of X-ray magnetochiral dichroism in enantiopure chiral trigonal single crystals of a chiral mononuclear paramagnetic lanthanide coordination complex, namely, holmium oxydiacetate, at the Ho L
3
-edge. The observed magnetochiral effect is opposite for the two enantiomers and is rationalised on the basis of a multipolar expansion of the matter-radiation interaction. These results demonstrate that 4f-5d hybridization in chiral lanthanoid coordination complexes is at the origin of magnetochiral dichroism, an effect that could be exploited for addressing of their magnetic moment at the single molecule level.
Magnetochiral Dichroism of chiral mononuclear lanthanoid complexes is for the first time detected by X-ray absorption measurements on single crystals of Holmium oxydiacetate, at the Ho L
3
-edge. The effect is of opposite sign for the two enantiomers.
Iridates from the molecular side Pedersen, Kasper S; Bendix, Jesper; Tressaud, Alain ...
Nature communications,
07/2016, Letnik:
7, Številka:
1
Journal Article
Recenzirano
Odprti dostop
New exotic phenomena have recently been discovered in oxides of paramagnetic Ir(4+) ions, widely known as 'iridates'. Their remarkable properties originate from concerted effects of the crystal ...field, magnetic interactions and strong spin-orbit coupling, characteristic of 5d metal ions. Despite numerous experimental reports, the electronic structure of these materials is still challenging to elucidate, and not attainable in the isolated, but chemically inaccessible, IrO6(8-) species (the simplest molecular analogue of the elementary {IrO6}(8-) fragment present in all iridates). Here, we introduce an alternative approach to circumvent this problem by substituting the oxide ions in IrO6(8-) by isoelectronic fluorides to form the fluorido-iridate: IrF6(2-). This molecular species has the same electronic ground state as the {IrO6}(8-) fragment, and thus emerges as an ideal model for iridates. These results may open perspectives for using fluorido-iridates as building-blocks for electronic and magnetic quantum materials synthesized by soft chemistry routes.
Abstract
The recent discovery of superconductivity in paramagnetic UTe
2
turns spotlight on a serious candidate for spin-triplet state. To draw a complete picture of the superconducting state in UTe
...2
precise knowledge of the electronic properties of the 5
f
states of Uranium is missing. We report on x-ray absorption and magnetic circular dichroism experiments performed at the U
M
4,5
edges at 2.7 K. At ambient pressure the 5
f
electron count is found to be in-between 2.6 and 2.8. Partial delocalization of the 5
f
electrons is further confirmed by the reduced value of the U orbital to spin magnetic moment ratio. The 5
f
count is reduced by as large as 7 percent at the transition to a magnetically ordered state at P
c
≈ 1.5 GPa. At pressures above 4 GPa, the 5
f
count increases back towards U
3+
in the tetragonal phase. The observed “valence instabilities” and their interplay with magnetism seem to be important ingredients to understand the electronic structure in UTe
2
in different phases.
A simple procedure based on anion exchange was employed for the enantiomeric resolution of the extended metal atom chain (EMAC) Co
(dpa)
(MeCN)
. Use of the chiral salt (NBu
)
As
(tartrate)
, (Λ-
or ...Δ-
), resulted in the selective crystallization of the EMAC enantiomers as Δ-Co
(dpa)
(MeCN)
(NBu
)
Λ-As
(tartarte)
, (Δ-
) and Λ-Co
(dpa)
(MeCN)
(NBu
)
Δ-As
(tartrate)
(Λ-
), respectively, in the
42
2 space group, whereas a racemic mixture of
yielded Co
(dpa)
(MeCN)
As
(tartrate)
·2MeCN (
-
), which crystallized in the
2/
space group. The local electronic and magnetic structure of the EMAC enantiomers was studied, exploiting a variety of dichroisms in single crystals. A strong linear dichroism at the Co K-edge was observed in the orthoaxial configuration, whereas it vanished in the axial orientation, thus spectroscopically confirming the
crystal symmetry. Compounds Δ-
and Λ-
are shown to be enantiopure materials as evidenced by mirror-image natural circular dichroism spectra in the UV/vis in solution and in the X-ray range at the Co K-edge in single crystals. The surprising absence of detectable X-ray magnetic circular dichroism or X-ray magnetochiral dichroism signals at the Co K-edge, even at low temperature (3 K) and a high magnetic field (17 T), is ascribed to a strongly delocalized spin density on the tricobalt core.
Valence change memories are novel data storage devices in which the resistance is determined by a reversible redox reaction triggered by voltage. The oxygen content and mobility within the active ...materials of these devices play a crucial role in their performance. Therefore, materials which present fast oxygen migration properties and can accommodate variable oxygen stoichiometry are promising candidates. In this work, the perovskite La0.5Sr0.5MnO3‐δ (LSM50) as memristive material is studied, which presents a more facile oxygen vacancy formation and faster oxygen migration compared to other strontium‐substituted manganites. For the first time reproducible resistive switching is reported in epitaxial LSM50‐based devices with active Ti electrodes, which show large operating window and stable multilevel states. Based on the structural, chemical, and electrical results, a simple phenomenological description of the resistive switching phenomena taking place in these novel LSM50‐based memristive devices is proposed.
For the first time, resistive switching in epitaxial La0.5Sr0.5MnO3‐δ (LSM50) with analog characteristics, gradual resistance changes, and good retention, suitable for neuromorphic computing applications is reported. Compared to other Sr poorer LSM compositions, LSM50 can create oxygen vacancies more easily, which improves device performance, i.e., larger resistance windows at lower operating voltage.
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