Hexadecacobalt(II)-Containing Polyoxometalate-Based Single-Molecule Magnet

Unprecedented high-nuclear transition-metal-cluster-substituted heteropolyoxoniobates: synthesis by {V8 } ring insertion into the POM matrix and antitumor activities

Reactions of hexaniobate with vanadate in the presence of Ni(2+) , Zn(2+) , or Cu(2+) have furnished three high-nuclear vanadium cluster-substituted heteropolyoxoniobates (HPNs): {Ni(en)3 }5 H{V(V) Nb8 V(IV) 8 O44 }⋅9 H2 O (1), (H2 en)Na2 [{Zn(en)2 (Hen)}{Zn(en)2 (H2 O)}2 {PNb8 V(IV) 8 O44 }]⋅11 H2 O (2), and Na{Cu(en)2 }3 {[Cu(en)2 ]2 [PNb8 V(IV) 8 O44 ]}⋅11 H2 O (3) (en=1,2-diaminoethane). Their structures have been determined and characterized by single-crystal X-ray diffraction analysis, thermogravimetric analysis (TGA), and elemental analysis. Structural analysis has revealed that compounds 1-3 contain similar {V8 }-substituted [X(V) Nb8 V(IV) 8 O44 ](11-) (X=P, V) clusters, obtained by inserting a {V8 } ring into tetravacant HPN [XNb8 O36 ](27-) . To the best of our knowledge, compounds 1-3 represent the first high-nuclear vanadium cluster-substituted HPNs, and compound 1 is the largest vanadoniobate cluster yet obtained in HPN chemistry. Nickel and zinc cations have been introduced into HPNs for the first time, which might promise a more diverse set of structures in this family. Antitumor studies have indicated that compounds 1 and 2 exhibit high activity against human gastric cancer SGC-7901 cells, SC-1680 cells, and MG-63 cells.

Design and construction of a thermotropic liquid crystal material based on high-nuclear transition-metal cluster-containing polyoxometalates

DODA⁺ was used as a surfactant to react with polyoxoanion [Ni₉(OH)₃(H₂O)₆(HPO₄)₂(PW₉O₃₄)₃]¹⁶⁻, resulting in an organic–inorganic hybrid complex SEP-1, the first liquid crystal materials based on high-nuclear transition-metal cluster-substituted polyoxoanions.

Assembly of heterobimetallic NiII–LnIII (LnIII = DyIII, TbIII, GdIII, HoIII, ErIII, YIII) complexes using a ferrocene ligand: slow relaxation of the magnetization in DyIII, TbIII and HoIII analogues

Structure and characterization of a new family of dinuclear 3d–4f heterobimetallic complexes [LNi(H₂O)(μ-OAc)Ln(NO₃)₂]·CH₃CN; {Ln = Dy^III (1), Tb^III (2), Ho^III (3), Gd^III (4), Er^III (5), Y^III (6)} using a ferrocene-based compartmental ligand H₂L.

Nona-copper(II)-containing 18-tungsto-8-arsenate(III) exhibits antitumor activity

The nona-Cu(II)-containing tungstoarsenate(III) [H4{Cu(II)9As(III)6O15(H2O)6}(α-As(III)W9O33)2](8-) (1a) has been synthesized and characterized. Polyanion 1a comprises a unique, cylindrical {Cu(II)9As(III)6O15(H2O)6}(6+) cluster, which forms a large central cavity and is capped on either end by an [α-As(III)W9O33](9-) capping group. It exhibits remarkable activity against K562 leukaemia cells, as well as induces HepG2 cell apoptosis and autophagy.

A polyoxometalate-based single-molecule magnet with a mixed-valent {Mn(IV)2Mn(III)6Mn(II)4} core

A polyoxometalate (POM)-based {Mn(IV)2Mn(III)6Mn(II)4} complex with single-molecule magnet (SMM) behaviour was prepared, exhibiting the largest known Mn nuclearity and the most Mn valence states in the POM-based SMM family.

Rhombus-shaped tetranuclear [Ln4] complexes [Ln = Dy(III) and Ho(III)]: synthesis, structure, and SMM behavior

The reaction of a new hexadentate Schiff base hydrazide ligand (LH3) with rare earth(III) chloride salts in the presence of triethylamine as the base afforded two planar tetranuclear neutral complexes: [{(LH)2Dy4}(μ2-O)4](H2O)8·2CH3OH·8H2O (1) and [{(LH)2Ho4}(μ2-O)4](H2O)8·6CH3OH·4H2O (2). These neutral complexes possess a structure in which all of the lanthanide ions and the donor atoms of the ligand remain in a perfect plane. Each doubly deprotonated ligand holds two Ln(III) ions in its two distinct chelating coordination pockets to form [LH(Ln)2](4+) units. Two such units are connected by four [μ2-O](2-) ligands to form a planar tetranuclear assembly with an Ln(III)4 core that possesses a rhombus-shaped structure. Detailed static and dynamic magnetic analysis of 1 and 2 revealed single-molecule magnet (SMM) behavior for complex 1. A peculiar feature of the χM" versus temperature curve is that two peaks that are frequency-dependent are revealed, indicating the occurrence of two relaxation processes that lead to two energy barriers (16.8 and 54.2 K) and time constants (τ0 = 1.4 × 10(-6) s, τ0 = 7.2 × 10(-7) s). This was related to the presence of two distinct geometrical sites for Dy(III) in complex 1.

Magnetic polyoxometalates: from molecular magnetism to molecular spintronics and quantum computing

In this review we discuss the relevance of polyoxometalate (POM) chemistry to provide model objects in molecular magnetism. We present several potential applications in nanomagnetism, in particular, in molecular spintronics and quantum computing.

Polyoxometalate-decorated nanoparticles

Polyoxometalate cluster anions (POMs) control formation and morphology, and serve as protecting ligands, for structurally and compositionally diverse nanostructures. While numerous examples of POM-protected metal(0) nanoparticle syntheses and reactions can now be found in the literature, the use of POMs to prepare nano-scale analogs of binary inorganic materials, such as metal-oxides, sulfides and halides, is a relatively recent development. The first part of this critical review summarizes the use of POMs as protecting ligands for metal(0) nanoparticles, as well as their use as templates for the preparation of new inorganic materials. Here, key findings that reveal general trends are given additional emphasis. In the second part of the review, new information concerning the structure of POM-protected metal(0) nanoparticles is systematically developed. This information, obtained by the combined use of cryogenic transmission microscopy (cryo-TEM) and UV-vis spectroscopy, provides a new perspective on the formation and structure of POM-decorated nanoparticles, and on the rational design of catalytic and other functional POM-based nano-assemblies.

Functionalization and post-functionalization: a step towards polyoxometalate-based materials

Polyoxometalates (POMs) have remarkable properties and a great deal of potential to meet contemporary societal demands regarding health, environment, energy and information technologies. However, implementation of POMs in various functional architectures, devices or materials requires a processing step. Most developments have considered the exchange of POM counterions in an electrostatically driven approach: immobilization of POMs on electrodes and other surfaces including oxides, embedding in polymers, incorporation into Layer-by-Layer assemblies or Langmuir-Blodgett films and hierarchical self-assembly of surfactant-encapsulated POMs have thus been thoroughly investigated. Meanwhile, the field of organic-inorganic POM hybrids has expanded and offers the opportunity to explore the covalent approach for the organization or immobilization of POMs. In this critical review, we focus on the use of POM hybrids in selected fields of applications such as catalysis, energy conversion and molecular nanosciences and we endeavor to discuss the impact of the covalent approach compared to the electrostatic one. The synthesis of organic-inorganic POM hybrids starting from bare POMs, that is the direct functionalization of POMs, is well documented and reliable and efficient synthetic procedures are available. However, as the complexity of the targeted functional system increases a multi-step strategy relying on the post-functionalization of preformed hybrid POM platforms could prove more appealing. In the second part of this review, we thus survey the synthetic methodologies of post-functionalization of POMs and critically discuss the opportunities it offers compared to direct functionalization.

Controlled association of single-molecule magnets (SMMs) into coordination networks: towards a new generation of magnetic materials

The field of molecular magnetism has rapidly expanded since the discovery of single-molecule magnets (SMMs) at the beginning of the 1990s. Numerous SMMs have been studied and a broad community currently works on these systems to improve their magnetic characteristics. However, it has also become an important strategy to diversify a part of our research activity toward the organization of these magnetic molecules in order to move closer to future applications. One of the possible ways is to utilize SMMs as molecular building blocks and assemble them with the help of coordination chemistry. This strategy presents a significant challenge since the intrinsic magnetic properties of the parent SMMs can be modified, which consequently also provides a unique opportunity to investigate new behaviours at the frontier between SMMs and classical bulk magnets. Furthermore, the design of systems with "enhanced" SMM properties or magnet behaviour is theoretically possible by choosing coordinating linkers that could favour an effective ferromagnetic arrangement of the SMMs. In this perspective article, we will give an overview of the known networks based on SMMs with an emphasis on the synthetic strategies, magnetic properties, and finally possible routes to a new generation of molecular magnetic materials.

Strategic design and refinement of Lewis acid-base catalysis by rare-earth-metal-containing polyoxometalates

Efficient polyoxometalate (POM)-based Lewis acid-base catalysts of the rare-earth-metal-containing POMs (TBA(6)RE-POM, RE = Y(3+), Nd(3+), Eu(3+), Gd(3+), Tb(3+), or Dy(3+)) were designed and synthesized by reactions of TBA(4)H(4)[γ-SiW(10)O(36)] (TBA = tetra-n-butylammonium) with RE(acac)(3) (acac = acetylacetonato). TBA(6)RE-POM consisted of two silicotungstate units pillared by two rare-earth-metal cations. Nucleophilic oxygen-enriched surfaces of negatively charged POMs and the incorporated rare-earth-metal cations could work as Lewis bases and Lewis acids, respectively. Consequently, cyanosilylation of carbonyl compounds with trimethylsilyl cyanide ((TMS)CN) was efficiently promoted in the presence of the rare-earth-metal-containing POMs via the simultaneous activation of coupling partners on the same POM molecules. POMs with larger metal cations showed higher catalytic activities for cyanosilylation because of the higher activation ability of C═O bonds (higher Lewis acidities) and sterically less hindered Lewis acid sites. Among the POM catalysts examined, the neodymium-containing POM showed remarkable catalytic performance for cyanosilylation of various kinds of structurally diverse ketones and aldehydes, giving the corresponding cyanohydrin trimethylsilyl ethers in high yields (13 substrates, 94-99%). In particular, the turnover frequency (714,000 h(-1)) and the turnover number (23,800) for the cyanosilylation of n-hexanal were of the highest level among those of previously reported catalysts.

DFT study of ionic peapod structures from single-walled carbon nanotubes and Lindqvist tungstates

DFT investigations have been carried out on encapsulation of Lindqvist-type W(6)O(19)(2-) anion inside hydrogenated (n,n) armchair single-walled carbon nanotubes (h-CNTs) with n = 8, 9, 10 to understand the confinement effect of the CNTs on the rotation of W(6)O(19)(2-). The energy-decomposition analysis (EDA) of interaction between W(6)O(19)(2-) and CNTs shows that with the increase of confinement effect from n = 8, 9, to 10, the destabilizing ΔE(Pauli) plays a more important role in the relative orientation of W(6)O(19)(2-) inside CNTs. For W(6)O(19)(2-)@(9,9) h-CNT, the most stable orientation appears at the y/z angle 45°/36°. The confinement effect reduces significantly the energy gap of W(6)O(19)(2-)@(n,n) h-CNT (n = 8, 9, 10) compared with free W(6)O(19)(2-). Electron transfer from the W(6)O(19)(2-) to CNT is observed.