pH-controlled construction of lanthanide clusters from lacunary polyoxometalate with single-molecule magnet behavior

Cerium-Encapsulated SbIII-SeIV-Templating Polyoxotungstate for Electrochemically Sensing Human Multidrug Resistance Gene Segment

A tower-like SbIII-SeIV-templating polyoxotungstate [H2N(CH3)2]12Na7H3[Ce0.5/Na0.5(H2O)5]2[SbSe2W21O75]2·50H2O (1) was synthesized, whose skeleton is assembled from two prolonged lacunary Dawson [SbSe2W21O75]13- units and two [Ce0.5/Na0.5(H2O)5]2+ linkers. The uncommon [SbSe2W21O75]13- unit can be viewed as a combination of one [SeW6O21]2- group grafted onto a trivacant Dawson [SbSeW15O54]11- subunit. The conductive composite 1-Au@rGO containing 1, gold nanoparticles, and reduced graphene oxide (rGO) was conveniently prepared, using which the 1-Au@rGO-based electrochemical genosensor was constructed for detecting human multidrug resistance gene segment. This work enriches structural types of dual-heteroatom-inserted polyoxometalates and promotes the application of polyoxometalates in genosensors.

[α-AsW9O33]9- bridged hexagonal clusters of Ln(III) showing field induced SMM behavior: experimental and theoretical insight

Polyoxometalates (POM), as inorganic polydentate oxygen donors, provide binding opportunities for oxophilic lanthanide metal centers to construct novel Ln-substituted POM materials with exciting structures and attractive properties. Herein, we have reported four arsenotungstate [α-AsW₉O₃₃]^9- based lanthanide-containing polyoxometalates [Cs_xK_36-x{Ln₆(H₂O)₁₂(α-AsW₉O₃₃)₆}]·yH₂O (Ln = Er (1), Gd (2), Ho (3), and Tb (4)), which are synthesized in an alkaline medium. Complexes 1-3 are the dimeric structures of [Ln₃(H₂O)₆(α-AsW₉O₃₃)₃]^18- polyanions, whereas complex 4 is a hexamer of the polyanion [Tb (H₂O)₂(α-AsW₉O₃₃)]^6- as a building unit. In all the complexes, [α-AsW₉O₃₃]^9- units are staggered up and down and give rise to the chair conformation, where one [α-AsW₉O₃₃]^9- unit bridges two Ln(III) centers through four μ₂-oxygen and two terminal oxygen atoms, resulting in the hexagonal arrangement of lanthanides. The dynamic magnetic measurement indicates that only complex 1 exhibits slow relaxation of magnetization with an applied dc field (1500 Oe). To gain insight into the slow relaxation of magnetization in complex 1, the ligand-field parameters and the splitting of the ground-state multiplet of the Er(III) ions have been estimated. The ab initio calculation results confirm that the ground state wave function of these molecules (1, 3, and 4) is mainly composed of a mixture of m_J states, and the non-axial crystal field (CF) terms are more predominant than the axial CF term. The solid-state fluorescence spectra of 1-4 reveal that the photoexcitation O → M ligand-to-metal charge-transfer (LMCT) of arsenotungstate fragments is effectively quenched due to the spatial coordination environment around the Ln(III) ion.

Recent Advances of Ti/Zr-Substituted Polyoxometalates: From Structural Diversity to Functional Applications

Polyoxometalates (POMs), a large family of anionic polynuclear metal-oxo clusters, have received considerable research attention due to their structural versatility and diverse physicochemical properties. Lacunary POMs are key building blocks for the syntheses of functional POMs due to their highly active multidentate O-donor sites. In this review, we have addressed the structural diversities of Ti/Zr-substituted POMs based on the polymerization number of POM building blocks and the number of Ti and Zr centers. The synthetic strategies and relevant catalytic applications of some representative Ti/Zr-substituted POMs have been discussed in detail. Finally, the outlook on the future development of this area is also prospected.

Roles of Organic Fragments in Redirecting Crystal/Molecular Structures of Inorganic-Organic Hybrids Based on Lacunary Keggin-Type Polyoxometalates

Lacunary polyoxometalates (LPOMs) are key precursors for the synthesis of functional POMs. To date, reviews dedicated to behavioral studies of LPOMs often comprise the role of metal ions, including transition metal (TM) and rare earth (RE) ions, in extending and stability of high-nuclearity clusters. In contrast, the role of organic ligands in the structures and properties of lacunary-based hybrids has remained less explored. In this review, we focus on the role of organic fragments in the self-assembling process of POM-based architectures and discuss relationships between the nature and structure of organic ligand and properties such as the topology of hybrid inorganic–organic material in RE and TM-RE heterometallic derivatives of lacunary Keggin-type POMs. The effects of organic fragment in mixed ligand hybrids are also briefly reviewed.

Cation-Directed Synthetic Strategy Using 4f Tungstoantimonates as Nonlacunary Precursors for the Generation of 3d-4f Clusters

The first synthetic pathway using a series of four nonlacunary 4f-heterometal-substituted polyoxotungstate clusters Na₂₁[(Ln(H₂O)(OH)₂(CH₃COO))₃(WO₄)(SbW₉O₃₃)₃]·nH₂O (NaLnSbW₉; Ln = Tb^III, Dy^III, Ho^III, Er^III, Y^III) as precursors for the directed preparation of nine new 3d–4f heterometallic tungstoantimonates K₅Na₁₂H₃[TM(H₂O)Ln₃(H₂O)₅(W₃O₁₁)(SbW₉O₃₃)₃]·nH₂O (KTMLnSbW₉; TM = Co^II, Ni^II; Ln = Tb^III, Dy^III, Ho^III, Er^III, Y^III) has been developed. Systematic studies revealed an increased K content in the aqueous acidic reaction mixture to be the key step in the cation-directed preparation of 3d–4f compounds; among those, the Co-containing members represent the first examples of KCoLnSbW₉ (Ln = Tb^III, Dy^III, Ho^III, Er^III, Y^III) heterometallic tungstoantimonates exhibiting the SbW₉ building block. All 13 compounds have been characterized thoroughly in the solid state by powder and single-crystal X-ray diffraction (XRD), revealing a cyclic trimeric polyoxometalate architecture with three SbW₉ units encapsulating a planar triangle of Ln^III ions in the case of NaLnSbW₉ and a heterometallic core of one TM^II and three Ln^III for KTMLnSbW₉ (TM = Co^II, Ni^II; Ln = Tb^III, Dy^III, Ho^III, Er^III, Y^III). The results obtained by XRD are supplemented by complementary characterization methods in the solid state such as IR spectroscopy, thermogravimetric analysis, and elemental analysis as well as in solution by UV–vis spectroscopy. Detailed magnetic studies on the representative compounds KTMDySbW₉ (TM = Co^II, Ni^II) and KCoYSbW₉ of the series revealed field-induced slow magnetic relaxation.

The first step-by-step synthetic protocol using preformed 4f tungstoantimonate clusters as nonlacunary precursors for the controlled preparation and thorough characterization of a family of nine new 3d−4f heterometallic polyoxometalates [TM(H₂O)Ln₃(H₂O)₅(W₃O₁₁)(SbW₉O₃₃)₃]^20- (KTMLnSbW₉) (TM = Co^II, Ni^II; Ln = Tb^III, Dy^III, Ho^III, Er^III, Y^III) is reported. Magnetic studies on the Dy^III-containing representatives [TM(H₂O)Dy₃(H₂O)₅(W₃O₁₁)(SbW₉O₃₃)₃]²⁰⁻ (TM = Co^II, Ni^II) show single-molecule-magnet behavior.

Ionic strength effect on regulating the synthetic assembly of polyoxometalate clusters with slow magnetic relaxation behavior

Three novel polyoxometalate (POM) clusters of K10Na10[Dy3(H2O)6Ni(H2O)(W3O11)(B-α-SbW9O33)3]·(H2O)45 (1), (NH4)5K4Na8[Dy3(H2O)6SbV(H2O)(W3O11)(B-α-SbW9O33)3]·(H2O)50 (2), and (NH4)9Na[Ni2(H2O)6(WO2)2(B-β-SbW9O33)2]·(H2O)24 (3) were successfully obtained using the same precursor under different ionic strength conditions. Structural analysis showed that compounds 1-3 possess discrepant structural characteristics in 1 M KCl, 1 M NH4Cl, and saturated NH4Cl, respectively. Among them, 2 is the first reported lanthanide cluster including both Sb3+ and Sb5+ in POM derivatives. Furthermore, the analysis of ac magnetic data proved that 1 and 2 embodied dramatic field-induced slow magnetic relaxation, and the effective barrier of 2 was estimated as Ueff/KB = 21.10 K based on the Orbach process. It was found that the structure and magnetic properties of POM materials can be regulated using an effective and satisfactory ionic strength-controlled strategy.