The influence of nuclear spin on the magnetic hysteresis of a single‐molecule is evidenced. Isotopically enriched DyIII complexes are synthesized and an isotopic dependence of their magnetic ...relaxation is observed. This approach is coupled with tuning of the molecular environment through dilution in an amorphous or an isomorphous diamagnetic matrix. The combination of these approaches leads to a dramatic enhancement of the magnetic memory of the molecule. This general recipe can be efficient for rational optimization of single‐molecule magnets (SMMs), and provides an important step for their integration into molecule‐based devices.
DIY magnetism: The quantum tunneling in a mononuclear Dy‐based complex, which already behaves as a single‐molecule magnet (SMM), can be drastically reduced, improving the capability of the molecule to store magnetic information. This improvement is brought about by using isotopes of DyIII without a nuclear magnetic moment, thus suppressing the hyperfine interaction, and by dilution of the SMM in a diamagnetic matrix, thus cancelling the internal field.
We report persistent chiral organic mono- and diradical cations based on bicarbazole molecular design with an unprecedented stability dependence on the type of chirality, namely, axial versus ...helical. An unusual chemical stability was observed for sterically unprotected axial bicarbazole radical in comparison with monocarbazole and helical bicarbazole ones. Such results were experimentally and theoretically investigated, revealing an inversion in energy of the singly occupied molecular orbital (SOMO) and the highest (doubly) occupied molecular orbital (HOMO) in both axial and helical bicarbazole monoradicals along with a subtle difference of electronic coupling between the two carbazole units, which is modulated by their relative dihedral angle and related to the type of chirality. Such findings allowed us to explore in depth the SOMO–HOMO inversion (SHI) in chiral radical molecular systems and provide new insights regarding its impact on the stability of organic radicals. Finally, these specific electronic properties allowed us to prepare a persistent, intrinsically chiral, diradical which notably displayed near-infrared electronic circular dichroism responses up to 1100 nm and almost degenerate singlet–triplet ground states with weak antiferromagnetic interactions evaluated by magnetometry experiments.
The reaction between the ((E)-N′-(2-hydroxy-3-methoxybenzylidene)pyrazine-2-carbohydrazide) (H2opch) ligand and the metallo-precursor Dy(hfac)3·2H2O led to the formation of an homometallic ...coordination complex with the formula Dy2(hfac)3(H2O)(Hopch)2Dy(hfac)4 (1). In presence of both Dy(hfac)3 2H2O and the Fe(II) salt, the heterobimetallic tetranuclear FeDy3(hfac)8(H2O)2(opch)2 (2) was isolated, while the addition of the co-ligand 1,2-Bis(2-hydroxy-3-methoxybenzylidene) hydrazine (H2bmh) led to the formation of two heterobimetallic tetranuclear complexes with the formula Fe3Dy(hfac)6(opch)2(H2bmh) C6H14 (3) C6H14 and Fe2Dy2(hfac)7(opch)2(H2bmh) 0.5C7H16 (4) 0.5C7H16. Single crystal X-ray diffraction and dc magnetic investigation demonstrated that 3 and 4 involved the iron center in the +II and +III oxidation states. Dynamic magnetic measurements highlighted the single-molecule magnet behavior of 1 and 2 in a zero applied dc field primarily due to the ferromagnetic interactions taking place in these compounds.
The anionic hydroxyethyl-substituted gold dithiolene complex NEt4Au(EtOH-thiazdt)2 is synthesized and further oxidized to the neutral radical species Au(EtOH-thiazdt)2• through ...electrocrystallization. Single-crystal X-ray diffraction studies highlight the existence of the two cis and trans isomers for the monoanionic complex, with involvement of the hydroxy group in intermolecular O–H···S hydrogen-bonding interactions. The neutral radical complex, Au(EtOH-thiazdt)2•, is isostructural with its known ethyl analogue, namely, Au(Et-thiazdt)2•. It exhibits a semiconducting behavior (σRT = 0.05–0.07 S cm–1) at room temperature and ambient pressure with an activation energy of 0.14 eV. Comparison of the crystal structures and transport and magnetic properties with those of the prototypical Au(Et-thiazdt)2• single-component conductor shows that the replacement of ethyl by a slightly bulkier hydroxyethyl substituent affects only weakly the overlap interactions, complemented here by added O–H···S hydrogen-bonding interactions.
We report a new molecular design to afford persistent chiral organic open-shell systems with configurational stability and an inversion in energy of the singly occupied molecular orbital (SOMO) and ...the highest doubly occupied molecular orbital (HOMO) for both mono- and diradical states. The unpaired electron delocalization within the designed extended helical π-conjugated systems is a crucial factor to reach chemical stabilities, which is not obtained using the classical steric protection approach. The unique features of the obtained helical monoradicals allow an exploration of the chiral intramolecular electron transfer (IET) process in solvents of different polarity by means of optical and chiroptical spectroscopies, resulting in an unprecedented electronic circular dichroism (ECD) sign inversion for the radical transitions. We also characterized the corresponding helical diradicals, which show near-infrared electronic circular dichroism at wavelengths up to 1100 nm and an antiferromagnetic coupling between the spins, with an estimated singlet–triplet gap (ΔE ST) of about −1.2 kcal mol–1. The study also revealed an intriguing double SOMO–HOMO inversion (SHI) electronic configuration for these diradicals, providing new insight regarding the peculiar energetic ordering of radical orbitals and the impact on the corresponding (chiral) optoelectronic properties.
The rational design of molecular chains made of 4f ions and substituted 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical is presented. The reaction of Ln(hfac)3·2H2O (hfac– = ...hexafluoroacetylacetonate) and the 4-cyano-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO-CN) radical affords air- and moisture-stable isostructural molecular chains of the formula Ln(hfac)3TEMPO-CN n for Ln = GdIII and TbIII, whereas zero-dimensional complexes of the formula Dy(hfac)3(TEMPO-CN)2Dy(hfac)3(H2O)22 are obtained for Ln = DyIII. To the best of our knowledge, the Gd derivative, Gd-TEMPO-CN, shows one of the strongest antiferromagnetic (AF) couplings for Gd–radical pairs ever reported with J Gd–rad/k B = −21.18 K, 14.72 cm–1 (H = −JS rad S Gd spin Hamiltonian convention). The TbIII derivative, Tb-TEMPO-CN, also shows strong Tb–radical AF coupling, which has been rationalized using the ab initio CASSCF approach (J Tb–rad = −23.02 K, −16.7 cm–1) and confirmed by luminescence measurements. Tb-TEMPO-CN shows remarkable properties for a Tb–radical-based single-molecule magnet (U eff = 69.3 ± 1 K; τ0 = 1.3 × 10–7 s) and two different relaxation processes triggered by interchain magnetic coupling.
Abstract
An approach to supervised classification and regression of superconductive materials is proposed which builds on the DeepSet technology. This enables us to provide the chemical constituents ...of the examined compounds as an input to the algorithm, while avoiding artefacts that could originate from the chosen ordering in the list. The performance of the method are successfully challenged for both classification (tag a given material as superconducting) and regression (quantifying the associated critical temperature). We then searched through the International Mineralogical Association list with the trained neural network. Among the obtained superconducting candidates, three materials were selected to undergo a thorough experimental characterization. Superconductivity has been indeed confirmed for the synthetic analogue of michenerite, PdBiTe, and observed for the first time in monchetundraite, Pd
2
NiTe
2
, at critical temperatures in good agreement with the theory predictions. This latter is the first certified superconducting material to be identified by artificial intelligence methodologies.
Powder samples and single crystals of Li2InMo3O8 were obtained by solid state reaction. The structure was determined by single-crystal X-ray diffraction (771 independent reflections for 33 refinable, ...R1=0.0158 and wR2=0.0354). Li2InMo3O8 is isomorphous with Li2SnMo3O8 and crystallizes in the hexagonal space group P63mc with unit-cell parameters a=5.7931(2)Å, c=10.4681(4)Å and Z=2. The crystal structure consists of distorted hexagonal-close-packed oxygen layers with stacking sequence abac along 001 and that are held together by alternating lithium–indium and molybdenum layers. The Li+ and In3+ ions occupy, respectively, tetrahedral and octahedral sites in the ratio 2:1. The Mo atoms occupy octahedral sites and form strongly bonded triangular clusters involving three MoO6 octahedra that are each shared along two edges, constituting a Mo3O13 unit. The variations of the Mo–Mo and Mo–O bond lengths according to the number of electrons per Mo3 cluster are discussed. The trivalent oxidation state of the indium leads to one unpaired electron per Mo3 and thus gives rise to a paramagnetic spin behavior with an effective magnetic moment of 1.5μB per Mo3 cluster. The magnetic susceptibility vs. temperature curve also shows a maximum at 25K arising probably from an antiferromagnetic ordering between the Mo3 clusters.
We present here the synthesis, the crystal structure, and the magnetic properties of the new quaternary compound Li2InMo3O8 containing magnetic Mo3O13 units with one unpaired electron. Display omitted
•The new quaternary reduced molybdenum oxide containing Mo3 clusters, Li2InMo3O8, was synthesized by solid state reaction.•Single-crystal X-ray study.•One unpaired electron per Mo3 cluster leading to a paramagnetic spin behavior with an effective magnetic moment of 1.5μB per Mo3 cluster.•Magnetic susceptibility measurements show a maximum at 25K arising probably from an antiferromagnetic ordering between the Mo3 clusters.
Stable bulk glasses from the quaternary system Cu-As-Te-Se are investigated for thermoelectric applications. These materials exhibit a low thermal conductivity Kappa similar to 0.3 W K super(-1) m ...super(-1) which is appealing for raising the thermoelectric figure of merit ZT. The addition of small amounts of selenium within the telluride amorphous matrix plays two fundamental roles. First, the increased disorder associated with the size mismatch improves glass-formation and widens the glass-formation domain, and second, it increases phonon scattering and slightly decreases the thermal conductivity. Furthermore, the addition of copper up to 32% dramatically increases the electrical conductivity without notably affecting the thermal conductivity. This permits us to obtain bulk glass samples with promising thermoelectric properties, which could be manufactured through conventional low-cost glass casting methods. While addition of copper permits the increase of electrical conductivity by more than six orders of magnitude, another three orders of magnitude are required to obtain thermoelectric materials with competitive ZT. Nevertheless, predicted values of ZT > 1.2 are estimated which would constitute some of the highest reported figure of merit for a bulk solid at room temperature. The effect of glass annealing on thermoelectric properties is also discussed.
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