Design of Magnetic Polyoxometalates for Molecular Spintronics and as Spin Qubits

Nanoscale Magnetic Arrays through Block Copolymer Templating of Polyoxometalates

Magnetic nanoarrays promise to enable new energy-efficient computations based on spintronics or magnonics. In this work, we present a block copolymer-assisted strategy for fabricating ordered magnetic nanostructures on silicon and permalloy substrates. Block copolymer micelle-like structures were used as a template in which polyoxometalate (POM) clusters could assemble in an opal-like structure. A combination of microscopy and scattering techniques was used to confirm the structural and organizational features of the fabricated materials. The magnetic properties of these materials were investigated by polarized neutron reflectometry, nuclear magnetic resonance, and magnetometry measurements. The data show that a magnetic structural design was achieved and that a thin layer of patterned POMs strongly influenced an underlying permalloy layer. This work demonstrates that the bottom-up pathway is a potentially viable method for patterning magnetic substrates on a sub-100 nm scale, toward the magnetic nanostructures needed for spintronic or magnonic crystal devices.

Bifunctional Sensors Based on Phosphomolybdates for Detection of Inorganic Hexavalent Chromium and Organic Tetracycline

Exploring effective sensors for detecting possible hazards in a water system are greatly significant. This work proposed a strategy for stable and effective bifunctional sensors via incorporating hourglass-type phosphomolybdates into metal-organic fragments to construct a high-dimensional framework. Two hourglass-type phosphomolybdate-based electrochemical sensors toward heavy metal ion Cr(VI) and tetracycline (TC) detection were designed with the formula [Co^II₂(H₂O)₄Na^I₂][Co^II(Hbpe)][Na^I(bpe)_1.5]{Co^II[P^V₄Mo^V₆O₃₁H₆]₂}·9H₂O (1) and [Co^II(H₂O)₄Na^I₃][Co^II(Hbpe)][Co^II(bpe)]{Co^II[P^V₄Mo^V₆O₃₁H₆]₂}·9H₂O (2) [bpe = 1,2-di(4-pyridyl)ethylene]. Structural analysis showed that hybrids 1 and 2 possess three-dimensional POM-supported network features with favorable stability and exhibit reversible redox properties. Experiments found that this kind of hybrids as efficient sensors have excellent electrochemical performance toward Cr(VI) detection with high sensitivities of 0.111 μA·μM^-1 for 1 and 0.141 μA·μM^-1 for 2, fast response time of 1 s, and low detection limits of 30 nM for 1 and 27 nM for 2, which far meet the standard of WHO for drinking water. Moreover, hybrids 1-2 also exhibit fast responses to TC detection with sensitivities of 0.0073 and 0.022 μA·mM^-1 and detection limits of 0.426 and 0.084 mM. This work offers a novel strategy for the purposeful design of efficient POM-based electrochemical sensors for accurate determination of contaminants in a practical water system.

Trigonal Prismatic Coordination of Discrete Rare Earth Ions, Enforced by the Polyoxotungstate [P4 W27 O99 (H2 O)]16

A family of solution‐stable polyanions [Na⊂{Ln^III(H₂O)}{W^VIO(H₂O)}P^V₄W^VI₂₆O₉₈]¹²⁻ (Ln=Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) represent the first examples of polyoxometalates comprising a single lanthanide(III) or yttrium(III) ion in a rare trigonal prismatic O₆ environment. Their synthesis exploits the reactivity of the organophosphonate‐functionalized precursor [P₄W₂₄O₉₂(C₆H₅P^VO)₂]¹⁶⁻ with heterometal ions and yields hydrated potassium or mixed lithium/potassium salts of composition K_xLn_yH_12–x–y[Na⊂{Ln(H₂O)}{WO(H₂O)}P₄W₂₆O₉₈]⋅nH₂O⋅mLiCl (x=8.5–11; y=0–2; n=24–34; m=0–1.5). The Dy, Ho, Er and Yb derivatives are characterized by slow magnetization relaxation.

A Cooperative Photoactive Class-I Hybrid Polyoxometalate With Benzothiadiazole-Imidazolium Cations

An organic–inorganic hybrid species based on the Wells–Dawson polyoxotungstate [P₂W₁₈O₆₂]⁶⁻ and novel fluorescent benzothiadiazole–imidazolium cations, [BTD-4,7-ImH]²⁺, has been synthesized. X-ray crystallographic analysis shows that the inorganic and organic components form a hydrogen-bonded superstructure and that the cations are revealed to be non-equivalent with varying degrees of rotation between the BTD and imidazolium rings due to competition between weak intra- and intermolecular interactions. The UV–vis diffuse reflectance spectra indicate that the hybrid has a band gap of 3.13 eV, while the solid-state fluorescence properties of the cation are quenched in the hybrid material, suggesting the existence of electron transfer between the inorganic and organic components. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies of the polyoxometalate (POM) and BTD-4,7-ImH precursors, estimated through UV–vis absorption spectroscopy and cyclic voltammetry, indicate that electron transfer from the BTD cations to the POM may occur in the excited state.

{VMo9O31[RC(CH2O)3]}6−: the first class of triol ligand covalently-decorated Keggin-type polyoxomolybdates

The first class of triol-ligand covalently-decorated Keggin-type polyoxomolybdates through C–O–Mo bonds were obtained and characterized.

TbO+ in a calcium apatite matrix featuring a triple trigger-type relaxation of magnetization

Tb for Ca substituted hydroxyapatite ceramic samples with composition Ca10-xTbx(PO4)6(OH1-x/2-δ)2, where x = 0.1, 0.5, were synthesized by solid-state reaction at 1300 °C in air, and their crystal structure, vibrational spectra, luminescence, and magnetic properties were studied. Implanting Tb3+ into the calcium apatite crystal lattice results in formation of an effective TbO+ ion which displays a short terbium-oxygen bond of 2.15 Å and a stretching vibration at 534 cm-1. The Tb3+ electronic structure has been revealed by analyzing the luminescence spectra and dc/ac magnetization data. Accordingly, the ground state represents a pseudo doublet with MJ = ±6 and the first exited level is by 112 cm-1 higher in energy. The ion exhibits field induced magnetic bistability with the magnetization reversing over the first exited state. Three paths of magnetization relaxation with field-temperature controlled switching between the paths have been identified.

Manifestation of strong magnetic and giant Raman anisotropy in single crystals of Cu for H substituted strontium hydroxyapatite

The linear [O–Cu–O]⁻ reveals a strong easy axis magnetic anisotropy with a high energy of 4 × 10² cm⁻¹ probed by magnetization measurements and polarized Raman spectroscopy of a single crystal.

Impact of fluoride for hydroxide substitution on the magnetic properties of a Co-based single-ion magnet imbedded in the barium apatite crystal lattice

The atomic group O–Co–O persists in the apatite channel and retains a high energy barrier for magnetization reversal.

Fine tuning of magnetization relaxation parameters of the DyO+ single ion magnet in a hydroxy/fluoro-apatite solid solution

Variation of the crystal environment of DyO⁺ regulates the energy barrier for magnetization reversal and the rate of quantum tunneling of magnetization.

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.

Surfactant-Dependent Charge Transfer between Polyoxometalates and Single-Walled Carbon Nanotubes: A Fluorescence Spectroscopic Study

Hybridizations of redox-active polyoxometalates (POMs) with single-walled carbon nanotubes (SWNTs) have been widely investigated for their diverse applications. For the purpose of constructing high-quality electronic devices, controlling charge transfer within POM/SWNT hybrids is an inevitable issue. As determined by means of fluorescence spectroscopy, electron transfer between SWNTs and a common POM dopant, phosphomolybdic acid (PMo₁₂ ), can be tuned simply by an alteration of nanotube surfactant type from anionic to nonionic. The mechanism is attributed to the influence of surfactant type on the stabilization of the electron donor-acceptor hybrid and effect of surfactant-nanotube interactions. These results will be important to control charge-transport behavior in nanohybrids consisting of carbon nanotubes.