Electrically Switchable Magnetic Molecules: Inducing a Magnetic Coupling by Means of an External Electric Field in a Mixed-Valence Polyoxovanadate Cluster

Electric control of spin transitions at the atomic scale

Electric control of spins has been a longstanding goal in the field of solid state physics due to the potential for increased efficiency in information processing. This efficiency can be optimized by transferring spintronics to the atomic scale. We present electric control of spin resonance transitions in single TiH molecules by employing electron spin resonance scanning tunneling microscopy (ESR-STM). We find strong bias voltage dependent shifts in the ESR signal of about ten times its line width. We attribute this to the electric field in the tunnel junction, which induces a displacement of the spin system changing the g-factor and the effective magnetic field of the tip. We demonstrate direct electric control of the spin transitions in coupled TiH dimers. Our findings open up new avenues for fast coherent control of coupled spin systems and expands on the understanding of spin electric coupling.

Hybrid Molecular Magnets with Lanthanide- and Countercation-Mediated Interfacial Electron Transfer between Phthalocyanine and Polyoxovanadate

A series of {V₁₂}-nuclearity polyoxovanadate cages covalently functionalized with one or sandwiched by two phthalocyaninato (Pc) lanthanide (Ln) moieties via V-O-Ln bonds were prepared and fully characterized for paramagnetic Ln = Sm^III-Er^III and diamagnetic Ln = Lu^III, including Y^III. The LnPc-functionalized {V₁₂O₃₂} cages with fully oxidized vanadium centers in the ground state were isolated as (nBu₄N)₃[HV₁₂O₃₂Cl(LnPc)] and (nBu₄N)₂[HV₁₂O₃₂Cl(LnPc)₂] compounds. As corroborated by a combined experimental (EPR, DC and AC SQUID, laser photolysis transient absorption spectroscopy, and electrochemistry) and computational (DFT, MD, and model Hamiltonian approach) methods, the compounds feature intra- and intermolecular electron transfer that is responsible for a partial reduction at V(3d) centers from V^V to V^IV in the solid state and at high sample concentrations. The effects are generally Ln dependent and are clearly demonstrated for the (nBu₄N)₃[HV₁₂O₃₂Cl(LnPc)] representative with Ln = Lu^III or Dy^III. Intramolecular charge transfer takes place for Ln = Lu^III and occurs from a Pc ligand via the Ln center to the {V₁₂O₃₂} core of the same molecule, whereas for Ln = Dy^III, only intermolecular charge transfer is allowed, which is realized from Pc in one molecule to the {V₁₂O₃₂} core of another molecule usually via the nBu₄N⁺ countercation. For all Ln but Dy^III, two of these phenomena may be present in different proportions. Besides, it is demonstrated that (nBu₄N)₃[HV₁₂O₃₂Cl(DyPc)] is a field-induced single molecule magnet with a maximal relaxation time of the order 10^-3 s. The obtained results open up the way to further exploration and fine-tuning of these three modular molecular nanocomposites regarding tailoring and control of their Ln-dependent charge-separated states (induced by intramolecular transfer) and relaxation dynamics as well as of electron hopping between molecules. This should enable us to realize ultra-sensitive polyoxometalate powered quasi-superconductors, sensors, and data storage/processing materials for quantum technologies and neuromorphic computing.

Structurally-New Hexadecanuclear Ni-Containing Silicotungstate with Catalytic Hydrogen Generation Activity

A structurally-new, carbon-free hexadecanuclear Ni-containing silicotungstate, [Ni₁₆(H₂O)₁₅(OH)₉(PO₄)₄(SiW₉O₃₄)₃]^19-, has been facilely synthesized using a one-pot, solution-based synthetic method systematically characterized by single-crystal X-ray diffraction and several other techniques. The resulting complex works as a noble-metal-free catalyst for visible-light-driven catalytic generation of hydrogen, by coupling with a [Ir(coumarin)₂(dtbbpy)][PF₆] photosensitizer and a triethanolamine (TEOA) sacrificial electron donor. Under minimally optimized conditions, a turnover number (TON) of 842 was achieved for TBA-Ni₁₆P₄(SiW₉)₃-catalyzed hydrogen evolution system. The structural stability of TBA-Ni₁₆P₄(SiW₉)₃ catalyst under photocatalytic conditions was evaluated by the mercury-poisoning test, FT-IR, and DLS measurements. The photocatalytic mechanism was elucidated by both time-solved luminescence decay and static emission quenching measurements.

Organic Mixed-Valence Compounds and the Overhauser Effect in Insulating Solids

Recent experiments have shown that the organic free radical 1,3-bisdiphenylene-2-phenylallyl (BDPA) can induce an Overhauser effect dynamic nuclear polarization in insulating solids, a feat previously considered not to be possible. Here, we establish that this peculiar ability of the BDPA radical stems from its mixed-valence nature and the ensuing intramolecular charge transfer. Using state-of-the-art DMRGSCF calculations, we confirm the class II mixed-valence nature of BDPA with the characteristic double-well potential energy surface, and we investigate the mechanism of the consequent electron hopping. A two-component vibronic Hamiltonian is then employed to compute the rate of electron hopping from a quantum dynamical time-propagation of the density matrix. The predicted hyperfine coupling oscillations indeed fall within the frequency range required for an Overhauser effect. The paradigm of mixed-valence compounds as a mining source opens many possibilities for the development and fine tuning of novel polarizing agents.

Computational study of the staircase molecular conductivity of polyoxovanadates adsorbed on Au(111)

This computational study presents the molecular conduction properties of polyoxovanadates V₆O₁₉ (Lindqvist-type) and V₁₈O₄₂, as possible successors of the materials currently in use in complementary metal–oxide semiconductor (CMOS) technology.

New pronounced progress in the synthesis of group 5 polyoxometalates

This highlight summarizes new developments made in group 5 polyoxometalate science of high nuclearity clusters with focus on synthetic approaches.

Controlled one pot synthesis of polyoxofluorovanadate molecular hybrids exhibiting peroxidase like activity

V^V/IV mixed-valence polyoxofluorovanadate clusters have been synthesized through one pot preparation process. The trigonal bipyramidal coordinated vanadium atoms mimic the structure of the active site and activity of the vanadium peroxidases.

Decoding the role of encapsulated ions in the electronic and magnetic properties of mixed-valence polyoxovanadate capsules {X@V22O54} (X = ClO4-, SCN-, VO2F2-): a combined theoretical approach

The electronic structure and magnetism of mixed-valence, host-guest polyoxovanadates {X@VO₅₄} with diamagnetic (X =) ClO₄^- (T_d, 1) and SCN^- (C_∞v, 2) template anions are assessed by means of two theoretical methods: density functional theory and effective Hamiltonian calculations. The results are compared to those obtained for another member of this family with X = VO₂F₂^- (C_2v, 3) (see P. Kozłowski et al., Phys. Chem. Chem. Phys., 2017, 19, 29767-29771), for which complementary data are also acquired. It is demonstrated that the X guest anions strongly influence the electronic and magnetic properties of the system, leading to various valence states of vanadium and modifying V-O-V exchange interactions. Our findings are concordant with and elucidate the available experimental data (see K. Y. Monakhov et al., Chem. - Eur. J., 2015, 21, 2387-2397).

Vanadyl dithiolate single molecule transistors: the next spintronic frontier?

On the road towards quantum devices, chemistry can offer elementary pieces with a built-in function, like [TbPc2]- which functions as a molecular transistor for nuclear spin detection. We argue that a large class of molecules have similar potential. In particular, we review the recent progress regarding highly coherent spin qubits based on vanadium dithiolate complexes. We propose their use as single molecule transistors to read and control a triple nuclear spin qubit, which could enable a low-current nuclear spin detection scheme by means of a spin valve effect.

Design and Assembly of Covalently Functionalised Polyoxofluorovanadate Molecular Hybrids

Mixed-valent polyoxometalate (POM) clusters are one of the most interesting host species, showing a wide range of structural features and properties. The facile preparation and functionalisation of a mixed-valent polyoxofluorovanadates is reported, where two electrons are trapped to antipodal sites of the clusters. The first members of this family of clusters with the general formula, [V^V₁₂ V^IV₂ O₁₆ (μ-O)₁₀ (μ₃ -O)₁₀ (μ₃ -F)₂ (L)₂ ]^6- , where L: py=pyridine (1); pyr=pyrazine (2); im=imidazole (3), are unique organic-inorganic hybrids with the addition of a N-donor ligand at either end of the polyoxofluorovanadate. The composition and connectivity of 1-3 were characterised by single-crystal X-ray diffraction and electrospray ionisation mass spectrometry. Electron paramagnetic resonance spectroscopy revealed that the two well-separated V^IV ions in each cluster are fully uncoupled with J=0, giving a degenerate singlet-triplet ground state. This attenuation of the exchange interaction is probed with density functional theoretical calculations that reveal that the inclusion of the fluoride ion in the cluster produces a bond pathway biased toward destructive interference between competing ferromagnetic and antiferromagnetic interactions. These robust molecular materials are the ideal combination of desirable electronic properties, with an organic handle with which they can be integrated into spintronic circuitry for molecular devices.

Reconciling the valence state with magnetism in mixed-valent polyoxometalates: the case of a {VO2F2@V22O54} cluster

The electronic structure and magnetism of the recently synthesised mixed-valent {V^VO₂F₂@VO₅₄} (1) host-guest polyoxovanadate envisaged as a potential building block of a molecule-based quantum computer are analysed using density functional theory (DFT) and effective Hamiltonian calculations. The form of the t-J like effective Hamiltonian has been inspired by the acquired DFT data, and the valence state used in DFT calculations has been suggested by the fits to the experimental magnetic data with the effective Hamiltonian. This self-consistent approach breaks through the magnetochemical limitations of vanadium-oxo cluster 1, giving results fully concordant with the experiment and allowing us to determine the valence state of 1, which contrary to other members of this host-guest family appears to feature 9 valence electrons.

Electrically switchable magnetic exchange in the vibronic model of linear mixed valence triferrocenium complex

A vibronic model for the electric field control of antiferromagnetic exchange is developed for the linear mixed-valence triferrocenium complex Fe(iii)–Fe(ii)–Fe(iii), which is proposed as possible molecular candidate for the implementation of a quantum logic gate.

The role of the multiconfigurational character of nitronyl-nitroxide in the singlet–triplet energy gap of its diradicals

CAS(2,2) reference may not be sufficient for the computation of singlet–triplet energy gap by DDCI.

Microwave-assisted synthesis of organically functionalized hexa-molybdovanadates

The microwave-assisted reaction of (TBA)₄[β-Mo₈O₂₄] and (TBA)₃[H₃V₁₀O₂₈] with pentaerythritol or tris(hydroxymethyl)aminomethane yields polyanions with the general formula (TBA)₂[V₃Mo₃O₁₆(O₃–R)] (R: C₅H₈OH – 1; R: C₄H₆NH₂ – 3). Post-synthetic esterification of 1 yields the acylated derivative 2, with all compounds being characterized in the solid and solution state.

Redox-Induced Gating of the Exchange Interactions in a Single Organic Diradical

Embedding a magnetic electroactive molecule in a three-terminal junction allows for the fast and local electric field control of magnetic properties desirable in spintronic devices and quantum gates. Here, we provide an example of this control through the reversible and stable charging of a single all-organic neutral diradical molecule. By means of inelastic electron tunnel spectroscopy we show that the added electron occupies a molecular orbital distinct from those containing the two radical electrons, forming a spin system with three antiferromagnetically coupled spins. Changing the redox state of the molecule therefore switches on and off a parallel exchange path between the two radical spins through the added electron. This electrically controlled gating of the intramolecular magnetic interactions constitutes an essential ingredient of a single-molecule [Formula: see text] quantum gate.

Single ion magnets based on lanthanoid polyoxomolybdate complexes

Organic solubility of these POMs enhances the chemical processability into molecular spintronic devices.

Sequential single-crystal-to-single-crystal transformations promoted by gradual thermal dehydration in a porous metavanadate hybrid

The porous hybrid metavanadate [{Cu(cyclam)}(VO₃)₂]·5H₂O undergoes a series of sequential and reversible transformations upon thermally-triggered gradual dehydration that have been monitored by single-crystal X-ray diffraction.