Vibronic coupling, the interaction between molecular vibrations and electronic states, is a fundamental effect that profoundly affects chemical processes. In the case of molecular magnetic materials, ...vibronic, or spin-phonon, coupling leads to magnetic relaxation, which equates to loss of magnetic memory and loss of phase coherence in molecular magnets and qubits, respectively. The study of vibronic coupling is challenging, and most experimental evidence is indirect. Here we employ far-infrared magnetospectroscopy to directly probe vibronic transitions in Yb(trensal) (where H
trensal = 2,2,2-tris(salicylideneimino)trimethylamine). We find intense signals near electronic states, which we show arise due to an "envelope effect" in the vibronic coupling Hamiltonian, which we calculate fully ab initio to simulate the spectra. We subsequently show that vibronic coupling is strongest for vibrational modes that simultaneously distort the first coordination sphere and break the C
symmetry of the molecule. With this knowledge, vibrational modes could be identified and engineered to shift their energy towards or away from particular electronic states to alter their impact. Hence, these findings provide new insights towards developing general guidelines for the control of vibronic coupling in molecules.
Toward Molecular 4f Single-Ion Magnet Qubits Pedersen, Kasper S; Ariciu, Ana-Maria; McAdams, Simon ...
Journal of the American Chemical Society,
05/2016, Letnik:
138, Številka:
18
Journal Article
Recenzirano
Quantum coherence is detected in the 4f single-ion magnet (SIM) Yb(trensal), by isotope selective pulsed EPR spectroscopy on an oriented single crystal. At X-band, the spin–lattice relaxation (T 1) ...and phase memory (T m) times are found to be independent of the nuclei bearing, or not, a nuclear spin. The observation of Rabi oscillations of the spin echo demonstrates the possibility to coherently manipulate the system for more than 70 rotations. This renders Yb(trensal), a sublimable and chemically modifiable SIM, an excellent candidate for quantum information processing.
We present the in-depth determination of the magnetic properties and electronic structure of the luminescent and volatile dysprosium-based single molecule magnet Dy
(bpm)(fod)
(Hfod = ...6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione, bpm = 2,2'-bipyrimidine).
calculations were used to obtain a global picture of the electronic structure and to predict possible single molecule magnet behaviour, confirmed by experiments. The orientation of the susceptibility tensor was determined by means of cantilever torque magnetometry. An experimental determination of the electronic structure of the lanthanide ion was obtained combining Luminescence, Far Infrared and Magnetic Circular Dichroism spectroscopies. Fitting these energies to the full single ion plus crystal field Hamiltonian allowed determination of the eigenstates and crystal field parameters of a lanthanide complex without symmetry idealization. We then discuss the impact of a stepwise symmetry idealization on the modelling of the experimental data. This result is particularly important in view of the misleading outcomes that are often obtained when the symmetry of lanthanide complexes is idealized.
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.
The term “frustration” in the context of magnetism was originally used by P. W. Anderson and quickly adopted for application to the description of spin glasses and later to very special lattice ...types, such as the kagomé. The original use of the term was to describe systems with competing antiferromagnetic interactions and is important in current condensed matter physics in areas such as the description of emergent magnetic monopoles in spin ice. Within molecular magnetism, at least two very different definitions of frustration are used. Here we report the synthesis and characterization of unusual nine-metal rings, using magnetic measurements and inelastic neutron scattering, supported by density functional theory calculations. These compounds show different electronic/magnetic structures caused by frustration, and the findings lead us to propose a classification for frustration within molecular magnets that encompasses and clarifies all previous definitions.
The use of kinetically robust chromium(III) fluorido complexes as synthons for mixed 3d-4f clusters is reported. The tendency toward linear {CrIII–F–LnIII} units dictates the cluster topology. ...Specifically, we show that reaction of cis-CrIIIF2(NN)2NO3 (NN = 1,10-phenanthroline (“phen”) or 2,2′-bipyridine (“bpy”)) with Ln(NO3)3·xH2O produces isostructural series of molecular {Ln2Cr2} squares (1–9) with linear fluoride bridges. In a parallel fashion, fac-CrIIIF3L, where L = N,N′,N″-trimethyl-1,4,7-triazacyclononane (“Me3tacn”), reacts with Nd(NO3)3·6H2O to form a fluoride-centered penta-nuclear complex and fac-CrIIIF3L′, with L′ = 1,1,1-tris-((methylamino)methylethane) (“Me3tame”), reacts with Ln(hfac)3(H2O)2 (hfacH = 1,1,1,5,5,5-hexafluoroacetylacetone) to yield an isostructural series of {Ln3Cr2} (10–14) trigonal bipyramids with no central ligand. The formation of the latter is accompanied by a partial solvolysis of the Cr(III) precursor but without formation of insoluble LnF3. The magnetic properties of the gadolinium containing clusters allow quantification of fluoride-mediated, antiferromagnetic Gd–Cr exchange interactions of magnitude between 0.14 cm–1 and 0.71 cm–1 (Ĥ = J 12 Ŝ 1·Ŝ 2 formalism) and vanishingly small J Gd–Gd of 0.06(0) cm–1. The large spin and small anisotropy together with weak exchange interactions in the {Gd3Cr2} (11) cluster give rise to a very large magneto-caloric effect of −ΔS m = 28.7 J kg–1 K–1 (μ0 H = 90 to 0 kOe).
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.
The central MnII ions in a series of calix4arene‐stabilised butterflies can be sequentially replaced with LnIII ions, maintaining the structural integrity of the molecule but transforming its ...magnetic properties. The replacement of MnII for GdIII allows for the examination of the transferability of spin‐Hamiltonian parameters within the family as well as permitting their reliable determination. The introduction of the 4f ions results in weaker intramolecular magnetic exchange, an increase in the number of low‐lying excited states, and an increase in magnetisation relaxation, highlighting the importance of exchange over single‐ion anisotropy for the observation of SMM behaviour in this family of complexes. The presence of the TMII/III(TBC4)(OH)(solvent) metalloligand (TM=transition metal, TBC=p‐tBu‐calix4arene) suggests that magnetic calixnarene building blocks can be employed to encapsulate a range of different “guests” within structurally robust “hosts”.
The central MnII ions in a series of calix4arene‐supported butterflies can be sequentially replaced with LnIII ions, systematically transforming the magnetic properties. This study highlights: 1) the importance of exchange over single‐ion anisotropy for the observation of SMM behaviour in this family of complexes, and 2) the potential of using metalloligands to encapsulate a range of different ‘guests’ within structurally robust ‘hosts’.
A tetranuclear 2 × 2 grid-like manganese(III) Schiff base complex, Mn4 , has been synthesized and characterized by single-crystal X-ray crystallography. Direct-current magnetization measurements ...were performed on the system and proved to be insufficient for an accurate magnetic model to be deduced. Combined inelastic neutron scattering (INS) and electron paramagnetic resonance (EPR) experiments provided the necessary information in order to successfully model the magnetic properties of Mn4 . The resulting model takes into account both the magnitude and the relative orientations of the single-ion anisotropy tensors.
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