Here we report on the strong magneto-chiral dichroism (MChD) detected through visible and near-infrared light absorption up to 5.0 T on {Er5Ni6} metal clusters obtained by reaction of enantiopure chiral ligands and NiII and ErIII precursors. Single-crystal diffraction analysis reveals that these compounds are 3d-4f heterometallic clusters, showing helical chirality. MChD spectroscopy reveals a high gMChD dissymmetry factor of ca. 0.24 T-1 (T = 4.0 K, B = 1.0 T) for the 4I13/2 â 4I15/2 magnetic-dipole allowed electronic transition of the ErIII centers. This record value is 1 or 2 orders of magnitude higher than that of the d-d electronic transitions of the NiII ions and the others f-f electric-dipole induced transitions of the ErIII centers. These findings clearly show the key role that magnetic-dipole allowed transitions have in the rational design of chiral lanthanide systems showing strong MChD.
Here we report magneto-chiral dichroism (MChD) detected through visible and near-infrared light absorption of a chiral dysprosium(III) coordination polymer. The two enantiomers of [DyIII(H6(py)2)(hfac)3]n [H6(py)2 = 2,15-bis(4-pyridyl)ethynylcarbo[6]helicene; hfac- = 1,1,1,5,5,5-hexafluoroacetylacetonate], where the chirality is provided by a functionalized helicene ligand, were structurally, spectroscopically, and magnetically investigated. Magnetic measurements reveal a slow relaxation of the magnetization, with differences between enantiopure and racemic systems rationalized on the basis of theoretical calculations. When the enantiopure complexes are irradiated with unpolarized light in a magnetic field, they exhibit multiple MChD signals associated with the f-f electronic transitions of DyIII, thus providing the coexistence of MChD-active absorptions and single-molecule-magnet (SMM) behavior. These findings clearly show the potential that rationally designed chiral SMMs have in enabling the optical readout of magnetic memory through MChD.
Because the combination of chiral and magnetic properties is becoming more and more attractive for magneto-chiral phenomena, we here aim at exploring the induction of chirality to achiral magnetic molecules as a strategy for the preparation of magneto-chiral objects. To this end, we have associated free base- and metallo-porphyrins with silica nano helices, using a variety of elaboration methods, and have studied them mainly by electronic natural circular dichroism (NCD) and magnetic circular dichroism (MCD) spectroscopies. While electrostatic or covalent surface grafting uniformly yielded very low induced CD (ICD) for the four assayed porphyrins, a moderate response was observed when the porphyrins were incorporated into the interior of the double-walled helices, likely due to the association of the molecules with the chirally-organized gemini surfactant. A generally stronger, but more variable, ICD was observed when the molecules were drop casted onto the helices immobilised on a quartz plate, likely due to the different capacities of the porphyrins to aggregate into chiral assemblies. Electronic spectroscopy, electron microscopy and IR spectroscopy were used to interpret the patterns of aggregation and their influence on ICD and MCD. No enhancement of MCD was observed as a result of association with the nanohelices except in the case of the free base, 5,10,15,20-tetra-(4-sulfonatophenyl)porphyrin (TPPS). This nanocomposite demonstrated a large ICD in the Soret region and a large MCD in the Q-region due to J-aggregation. However, no induced MChD was observed, possibly due to the spectral mismatch between the ICD and MCD peaks.
The combination of physical properties sensitive to molecular chirality in a single system allows the observation of fascinating phenomena such as magneto-chiral dichroism (MChD) and circularly polarized luminescence (CPL) having potential applications for optical data readout and display technology. Homochiral monodimensional coordination polymers of YbIII were designed from a 2,15-bis-ethynyl-hexahelicenic scaffold decorated with two terminal 4-pyridyl units. Thanks to the coordination of the chiral organic chromophore to Yb(hfac)3 units (hfac- =1,1,1,5,5,5-hexafluoroacetylaconate), efficient NIR-CPL activity is observed. Moreover, the specific crystal field around the YbIII induces a strong magnetic anisotropy which leads to a single-molecule magnet (SMM) behaviour and a remarkable room temperature MChD. The MChD-structural correlation is supported by computational investigations.
Here, we report the molecular self-assembly of hydroxido-bridged {Ln5Ni6} ((Ln3+ = Dy3+, Y3+) metal clusters by the reaction of enantiopure chiral ligands, namely, (R/S)-(2-hydroxy-3-methoxybenzyl)-serine), with NiII and LnIII precursors. Single-crystal diffraction analysis reveals that these compounds are isostructural sandwich-like 3d-4f heterometallic clusters showing helical chirality. Direct current magnetic measurements on {Dy5Ni6} indicates ferromagnetic coupling between DyIII and NiII centers, whereas those on {Y5Ni6} denote that the NiII centers are antiferromagnetically coupled and/or magnetically anisotropic. Magneto-chiral dichroism (MChD) measurements on {Dy5Ni6} and its comparison to that of {Y5Ni6} provide the first experimental observation of intense multimetal site MChD signals in the visible-near-infrared region. Moreover, the comparison of MChD with natural and magnetic circular dichroism spectra unambiguously demonstrate for the first time that the MChD signals associated with the NiII d-d transitions are mostly driven by natural optical activity and those associated with the DyIII f-f transitions are driven by magnetic optical activity.
Lanthanoid Series Elements , Organometallic Compounds , Crystallography, X-Ray , Lanthanoid Series Elements/chemistry , Magnetic Phenomena , Magnetics , Organometallic Compounds/chemistry
Molecular electronic spins are good candidates as qubits since they are characterized by a large tunability of their electronic and magnetic properties through a rational chemical design. Coordination compounds of light transition metals are promising systems for spin-based quantum information technologies, thanks to their long spin coherence times up to room temperature. Our work aims at presenting an in-depth study on how the spin-phonon coupling in vanadyl-acetylacetonate, [VO(acac)2], can change as a function of temperature using terahertz time-domain spectroscopy and density functional theory (DFT) calculations. Powder THz spectra were recorded between 10 and 300 K. The temperature dependence of vibrational frequencies was then accounted for in the periodic DFT calculations using unit-cell parameters measured at two different temperatures and the optimized ones, as usually reported in the literature. In this way, it was possible to calculate the observed THz anharmonic frequency shift with high accuracy. The overall differences in the spin-phonon coupling magnitudes as a function of temperature were also highlighted showing that the computed trends have to be ascribed to the anisotropic variation of cell parameters.
We show that [VO(TPP)] (vanadyl tetraphenylporphyrinate) is a promising system to implement quantum computation algorithms based on encoding information in multi-level (qudit) units. Indeed, it embeds a nuclear spin 7/2 coupled to an electronic spin 1/2 by hyperfine interaction. This qubit-qudit unit can be exploited to implement quantum error correction and quantum simulation algorithms. Through a combined theoretical and broadband nuclear magnetic resonance study, we demonstrate that the elementary operations of such algorithms can be efficiently implemented on the nuclear spin qudit. Manipulation of the nuclear qudit can be achieved by resonant radio-frequency pulses, thanks to the remarkably long coherence times and the effective quadrupolar coupling induced by the strong hyperfine interaction. This approach may open new perspectives for developing new molecular qubit-qudit systems.
The interplay between chirality and magnetic fields gives rise to a cross effect referred to as magneto-chiral anisotropy (MChA), which can manifest itself in different physical properties of chiral magnetized materials. The first experimental demonstration of MChA was by optical means with visible light. Further optical manifestations of MChA have been evidenced across most of the electromagnetic spectrum, from terahertz to X-rays. Moreover, exploiting the versatility of molecular chemistry toward chiral magnetic systems, many efforts have been made to identify the microscopic origins of optical MChA, necessary to advance the effect toward technological applications. In parallel, the replacement of light by electric current has allowed the observation of nonreciprocal electrical charge transport in both molecular and inorganic conductors as a result of electrical MChA (eMChA). MChA in other domains such as sound propagation, photochemistry, and electrochemistry are still in their infancy, with only a few experimental demonstrations, and offer wide perspectives for further studies with potentially large impact, like the understanding of the homochirality of life. After a general introduction to MChA, we give a complete review of all these phenomena, particularly during the last decade.
We report here a comprehensive characterization of a 3d organometallic complex, [V(Cp)2Cl2] (Cp = cyclopentadienyl), which can be considered as a prototypical multilevel nuclear qudit (nuclear spin I = 7/2) hyperfine coupled to an electronic qubit (electronic spin S = 1/2). By combining complementary magnetic resonant techniques, such as pulsed electron paramagnetic resonance (EPR) and broadband nuclear magnetic resonance (NMR), we extensively characterize its Spin Hamiltonian parameters and its electronic and nuclear spin dynamics. Moreover, we demonstrate the possibility to manipulate the qubit-qudit multilevel structure by resonant microwave and radiofrequency pulses, driving coherent Rabi oscillations between targeted electronuclear states. The obtained results demonstrate that this simple complex is a promising candidate for quantum computing applications.
Here we report the first experimental observation of magneto-chiral dichroism (MChD) detected through light absorption in an enantiopure lanthanide complex. The P and M enantiomers of [YbIII((X)-L)(hfac)3] (X = P, M; L = 3-(2-pyridyl)-4-aza[6]-helicene; hfac = 1,1,1,5,5,5-hexafluoroacetylacetonate), where the chirality is held by the helicene-based ligand, were studied in the near-infrared spectral window. When irradiated with unpolarized light in a magnetic field, these chiral complexes exhibit a strong MChD signal (gMChD ca. 0.12 T-1) associated with the 2F5/2 â 2F7/2 electronic transition of YbIII. The low temperature absorption and MChD spectra reveal a fine structure associated with crystal field splitting and vibronic coupling. The temperature dependence of the main dichroic signal detected up to 150 K allowed, for the first time, the disentanglement of the two main microscopic contributions to the dichroic signal predicted by the MChD theory. These findings pave the way toward probing MChD in chiral lanthanide-based single-molecule magnets.
It is not known whether the current territorial organization for acute revascularization treatments in ischemic stroke patients guarantees similar time to treatment and functional outcomes among different levels of institutional stroke care. We aimed to assess the impact of time to treatment on functional outcomes in ischemic stroke patients who received intravenous thrombolysis (IVT) alone, bridging (IVT plus thrombectomy), or primary thrombectomy in level 1 and level 2 Stroke Units (SUs) in Triveneto, a geographical macroarea in Northeast of Italy. We conducted an analysis of data prospectively collected from 512 consecutive ischemic stroke patients who received IVT and/or mechanical thrombectomy in 25 SUs from September 17th to December 9th 2018. The favorable outcome measures were mRS score 0-1 and 0-2 at 3 months. The unfavorable outcome measures were mRS score 3-5 and death at 3 months. We estimated separately the possible association of each variable for time to treatment (onset-to-door, door-to-needle, onset-to-needle, door-to-groin puncture, needle-to-groin puncture, and onset-to-groin puncture) with 3-month outcome measures by calculating the odds ratios (ORs) with two-sided 95% confidence intervals (CI) after adjustment for pre-defined variables and variables with a probability value ≤ 0.10 in the univariate analysis for each outcome measure. Distribution of acute revascularization treatments was different between level 1 and level 2 SUs (p < 0.001). Among 182 patients admitted to level 1 SUs (n = 16), treatments were IVT alone in 164 (90.1%), bridging in 12 (6.6%), and primary thrombectomy in 6 (3.3%) patients. Among 330 patients admitted to level 2 SUs (n = 9), treatments were IVT alone in 219 (66.4%), bridging in 74 (22.4%), and primary thrombectomy in 37 (11.2%) patients. Rates of excellent outcome (51.4% vs 45.9%), favorable outcome (60.1% vs 58.7%), unfavorable outcome (33.3% vs 33.8%), and death (9.8% vs 11.3%) at 3 months were similar between level 1 and 2 SUs. No significant association was found between time to IVT alone (onset-to-door, door-to-needle, and onset-to-needle) and functional outcomes. After adjustment, door-to-needle time ≤ 60 min (OR 4.005, 95% CI 1.232-13.016), shorter door-to-groin time (OR 0.991, 95% CI 0.983-0.999), shorter needle-to-groin time (OR 0.986, 95% CI 0.975-0.997), and shorter onset-to-groin time (OR 0.994, 95% CI 0.988-1.000) were associated with mRS 0-1. Shorter door-to-groin time (OR 0.991, 95% CI 0.984-0.998), door-to-groin time ≤ 90 min (OR 12.146, 95% CI 2.193-67.280), shorter needle-to-groin time (OR 0.983, 95% CI 0.972-0.995), and shorter onset-to-groin time (OR 0.993, 95% CI 0.987-0.999) were associated with mRS 0-2. Longer door-to-groin time (OR 1.007, 95% CI 1.001-1.014) and longer needle-to-groin time (OR 1.019, 95% CI 1.005-1.034) were associated with mRS 3-5, while door-to-groin time ≤ 90 min (OR 0.229, 95% CI 0.065-0.808) was inversely associated with mRS 3-5. Longer onset-to-needle time (OR 1.025, 95% CI 1.002-1.048) was associated with death. Times to treatment influenced the 3-month outcomes in patients treated with thrombectomy (bridging or primary). A revision of the current territorial organization for acute stroke treatments in Triveneto is needed to reduce transfer time and to increase the proportion of patients transferred from a level 1 SU to a level 2 SU to perform thrombectomy.
Ischemic Stroke/therapy , Thrombectomy/methods , Thrombolytic Therapy/methods , Aged , Aged, 80 and over , Female , Humans , Ischemic Stroke/epidemiology , Italy/epidemiology , Male , Middle Aged , Prospective Studies , Treatment Outcome
The selection of molecular spin qubits with a long coherence time, Tm, is a central task for implementing molecule-based quantum technologies. Even if a sufficiently long Tm can be achieved through an efficient synthetic strategy and ad hoc experimental measurement procedures, many factors contributing to the loss of coherence still need to be thoroughly investigated and understood. Vibrational properties and nuclear spins of hydrogens are two of them. The former plays a paramount role, but a detailed theoretical investigation aimed at studying their effects on the spin dynamics of molecular complexes such as the benchmark phthalocyanine (Pc) is still missing, whereas the effect of the latter deserves to be examined in detail for such a class of compounds. In this work, we adopted a combined theoretical and experimental approach to investigate the relaxation properties of classical [Cu(Pc)] and a CuII complex based on the ligand tetrakis(thiadiazole)porphyrazine (H2TTDPz), characterized by a hydrogen-free molecular structure. Systematic calculations of molecular vibrations exemplify the effect of normal modes on the spin-lattice relaxation process, unveiling a different contribution to T1 depending on the symmetry of normal modes. Moreover, we observed that an appreciable Tm enhancement could be achieved by removing hydrogens from the ligand.
Magnetochiral dichroism (MChD) is a nonreciprocal manifestation of light-matter interaction that can be observed in chiral magnetized systems. It features a differential absorption of unpolarized light depending on the relative orientation of the magnetic field and the light wavevector and on the absolute configuration of the system. The relevance of this effect for optical readout of magnetic data calls for a complete understanding of the microscopic parameters driving MChD with an easy-accessible and nondamaging light source, such as visible light. For this purpose, here we report on MChD detected with visible light on a chiral magnetic helix formulated as [MnIII(cyclam)(SO4)]ClO4·H2O (cyclam = 1,4,8,11-tetraazacyclotetradecane) featuring antiferromagnetically coupled anisotropic MnIII ions. Alternate current susceptibility measurements revealed the existence of a single-chain magnet behavior hidden below the canted antiferromagnetism (TN = 5.8 K) already evidenced by direct current magnetometry. A detailed analysis of the optical absorption gives access to the value of the zero-field splitting parameter D (2.9 cm-1), which quantifies the magnetic anisotropy of the MnIII centers. Below the magnetic ordering temperature of the material, the MChD spectra exhibit intense absolute configuration dependent MChD signals reaching record values of ca. 12% of the absorbed intensity for the two electronic transitions most influenced by the spin-orbit coupling of the MnIII ion. These findings set a clear route toward the design and preparation of highly MChD-responsive molecular materials.
Spin crossover complexes are among the most studied classes of molecular switches and have attracted considerable attention for their potential technological use as active units in multifunctional devices. A fundamental step toward their practical implementation is the integration in macroscopic devices adopting hybrid vertical architectures. First, the physical properties of technological interest shown by these materials in the bulk phase have to be retained once they are deposited on a solid surface. Herein, we describe the study of a hybrid molecular inorganic junction embedding the spin crossover complex [Fe(qnal)2] (qnal = quinoline-naphthaldehyde) as an active switchable thin film sandwiched within energy-optimized metallic electrodes. In these junctions, developed and characterized with the support of state of the art techniques including synchrotron Mössbauer source (SMS) spectroscopy and focused-ion beam scanning transmission electron microscopy, we observed that the spin state conversion of the Fe(II)-based spin crossover film is associated with a transition from a space charge-limited current (SCLC) transport mechanism with shallow traps to a SCLC mechanism characterized by the presence of an exponential distribution of traps concomitant with the spin transition temperature.
Magneto-chiral dichroism (MChD) is a non-reciprocal manifestation of light-matter interaction that can be observed in chiral systems possessing a magnetization, either spontaneous or induced by an external magnetic field. It features a differential absorption or emission of unpolarized light that depends on the relative orientation of the magnetization with respect to the direction of the light propagation vector and on the absolute configuration of the system. Molecular chemistry is the best-suited route towards systems combining chirality and magnetism. Nowadays, investigation of MChD is still in its infancy although this effect might play a fundamental role in technological applications, such as optical readout of magnetic data with unpolarized light. With this Minireview, the authors provide a precise description of this unconventional effect, recall the main results obtained so far and, highlighting new challenges, underline the opportunities opened to molecular chemists interested in investigating this fascinating effect with implications in chemistry and beyond.
Here we report on magneto-chiral dichroism (MChD) detected with visible light on the chiral Prussian Blue Analogue [MnII(X-pnH)(H2O)][CrIII(CN)6]·H2O (X = S, R; pn = 1,2-propanediamine). Single crystals suitable for magneto-optical measurements were grown starting from enantiopure chiral ligands. X-ray diffraction and magnetic measurements confirmed the 2D-layered structure of the material, its absolute configuration, and its ferrimagnetic ordered state below a critical temperature TC of 38 K. Absorption and MChD spectra were measured between 450 and 900 nm from room temperature down to 4 K. At 4 K the electronic spectrum features spin-allowed and spin-forbidden transitions of CrIII centers, spin-forbidden transitions of the MnII centers, and metal-to-metal charge transfer bands. The MChD spectra below the magnetic ordering temperature exhibit intense absolute configuration-dependent MChD signals. The temperature dependence of these signals closely follows the material magnetization. Under a magnetic field of 0.46 T, the most intense contribution to MChD represents 2.6% T-1 of the absorbed intensity, one of the highest values observed to date.
Implementation of modern Quantum Technologies might benefit from the remarkable quantum properties shown by molecular spin systems. In this Perspective, we highlight the role that molecular chemistry can have in the current second quantum revolution, i.e., the use of quantum physics principles to create new quantum technologies, in this specific case by means of molecular components. Herein, we briefly review the current status of the field by identifying the key advances recently made by the molecular chemistry community, such as for example the design of molecular spin qubits with long spin coherence and the realization of multiqubit architectures for quantum gates implementation. With a critical eye to the current state-of-the-art, we also highlight the main challenges needed for the further advancement of the field toward quantum technologies development.
Paramagnetic molecules can show long spin-coherence times, which make them good candidates as quantum bits (qubits). Reducing the efficiency of the spin-phonon interaction is the primary challenge toward achieving long coherence times over a wide temperature range in soft molecular lattices. The lack of a microscopic understanding about the role of vibrations in spin relaxation strongly undermines the possibility of chemically designing better-performing molecular qubits. Here we report a first-principles characterization of the main mechanism contributing to the spin-phonon coupling for a class of vanadium(IV) molecular qubits. Post-Hartree-Fock and density functional theory methods are used to determine the effect of both intermolecular and intramolecular vibrations on modulation of the Zeeman energy for four molecules showing different coordination geometries and ligands. This comparative study provides the first insight into the role played by coordination geometry and ligand-field strength in determining the spin-lattice relaxation time of molecular qubits, opening an avenue to the rational design of new compounds.
Intravenous thrombolysis (IVT) is the treatment of choice for most patients with acute ischemic stroke. According to the recently updated guidelines, IVT should be administered in absence of absolute exclusion criteria. We aimed to assess the proportion of ischemic strokes potentially eligible and actually treated with IVT, and to explore the reasons for not administering IVT. We prospectively collected and analyzed data from 1184 consecutive ischemic stroke patients admitted to the 22 Stroke Units (SUs) of the Veneto region from September 18th to December 10th 2017. Patients were treated with IVT according to the current Italian guidelines. For untreated patients, the reasons for not administering IVT were reported by each center in a predefined model including absolute and/or relative exclusion criteria and other possible reasons. Out of 841 (71%) patients who presented within 4.5 h of stroke onset, 704 (59%) had no other absolute exclusion criteria and were therefore potentially eligible for IVT according to the current guidelines. However, only 323 (27%) patients were eventually treated with IVT. Among 861 (73%) untreated patients, 480 had at least one absolute exclusion criterion, 283 only relative exclusion criteria, 56 only other reasons, and 42 a combination of relative exclusion criteria and other reasons. Our study showed that only 46% (323/704) of the potentially eligible patients were actually treated with IVT in the SUs of the Veneto region. All healthcare professionals involved in the acute stroke pathway should make an effort to bridge this gap between eligibility and reality.
Stroke/drug therapy , Thrombolytic Therapy/methods , Administration, Intravenous , Aged , Brain Ischemia , Female , Health Personnel/education , Humans , Italy , Male , Middle Aged , Practice Guidelines as Topic
Treatment of N,N'-bis(2-aminophenyl)oxalamide (bapoxH6, 1) with ethyl oxalyl chloride in THF afforded oxamide-N,N'-bis(o-phenylene oxamic acid ethyl ester) (L1H4Et2, 2), which was converted to 3 (oxamide-(o-phenylene oxamic acid ethyl ester)(o-phenylene-N1-methyloxalamide); L2H5EtMe) and 4 (oxamide-N,N'-bis(o-phenylene-N1-methyloxalamide); L3H6Me2) by the addition of appropriate equivalents of MeNH2. Successive treatment of 2-4 with six equivalents of [nBu4N]OH and two equivalents of CuII salt resulted in the formation of the binuclear complexes [nBu4N]2[Cu2(L1)] (5), [nBu4N]2[Cu2(L2Me)] (6) and [nBu4N]2[Cu2(L3Me2)] (7). Upon addition of one equivalent of [Cu(pmdta)(NO3)2] (pmdta = N,N,N',N'',N''-pentamethyldiethylenetriamine) to 5-7, the trinuclear complexes [Cu3(L1)(pmdta)] (8), [Cu3(L2Me)(pmdta)] (9) and [Cu3(L3Me2)(pmdta)] (10) were obtained, while the addition of two equivalents of [Cu(pmdta)(NO3)2] gave rise to the tetranuclear complexes [Cu4(L1)(pmdta)2](NO3)2 (11), [Cu4(L2Me)(pmdta)2](NO3)2 (12) and [Cu4(L3Me2)(pmdta)2](NO3)2 (13). The identities of compounds 2-4 were established by elemental analyses, NMR and IR spectroscopy, and ESI-MS measurements. For the multinuclear complexes 5-13, elemental analysis and IR spectroscopy were applied to confirm their identities. Furthermore, the solid-state structures of 5-8 and 11-13 were determined by single crystal X-ray diffraction studies. The magnetic behavior of 5-8 and 11-13 was studied by direct current susceptibility measurements as a function of temperature. For the binuclear complexes 5-7, exceptionally large antiferromagnetic exchange interactions with J1,2 values of -378, -397 and -419 cm-1 were determined. Astonishingly, the tendency of these series of magnetic exchange interactions can be smoothly associated with the d-d transitions of 5-7 measured through UV-Vis spectroscopy. The J1,2 value of 8 amounts to -507 cm-1, while for the tetranuclear complexes 11-13, this value is significantly smaller and amounts to -294, -292 and -370 cm-1. The second antiferromagnetic exchange interactions J2,3 and J1,4 are equal due to inversion symmetry and are -100, -135, -80 and -108 cm-1 for 8 and 11-13, respectively, in the expected range. Magneto-structural correlations are used to discuss the variable magnetic exchange interactions of all here reported multinuclear complexes.
