Using Coordination Chemistry to Control "Click" Reactions: The Selective Formation of Asymmetrically Ligated Polyoxometalates.

The Cu(I)-catalyzed azide-alkyne cycloaddition reaction between (NBu)[VO((OCH)CCHN)] and 3-ethynylpyridine led to the formation of products capable of forming poorly soluble coordination compounds with transition metal ions such as Cu(I) and Zn(II). The formation of these poorly soluble phases is an important feature that was used to determine the course of reactions, allowing the selective preparation of symmetric bis-pyridyltriazolyl and asymmetric monopyridyltriazolyl derivatives with relatively high yields and high substrate conversions. The asymmetric compound (NBu)[VO((OCH)CCH-NCH-CHN)((OCH)CCHN)] (V) was utilized in the subsequent "click" postfunctionalization reaction with 1,4-diethynylbenzene, resulting in a covalently bound V-V dimer.

Reversible Optical Switching of Polyoxovanadates and Their Communication via Photoexcited States.

The 2-bit Lindqvist-type polyoxometalate (POM) [VO((OCH)CCHN)] with a diamagnetic {VO} core and azide termini shows six fully oxidized V centers in solution as well as the solid state, according to V NMR spectroscopy. Under UV irradiation, it exhibits reversible switching between its ground S state and the energetically higher lying states in acetonitrile and water solutions. TD-DFT calculations demonstrate that this process is mainly initialized by excitation from the S to S state.

Synthesis and structures of cobalt-expanded zirconium- and cerium-oxo clusters as precursors for mixed-metal oxide thin films.

Transforming current complementary metal-oxide-semiconductor (CMOS) technology to fabricate memory chips and microprocessors into environmentally friendlier electronics requires the development of new approaches to resource- and energy-efficient electron transport and switching materials. Metal and multi-metal oxide layers play a key role in high-end technical applications. However, these layers are commonly produced through high-energy and high-temperature procedures.

Bioorthogonal chemistry of polyoxometalates - challenges and prospects.

Bioorthogonal chemistry has enabled scientists to carry out controlled chemical processes in high yields while minimizing hazardous effects. Its extension to the field of polyoxometalates (POMs) could open up new possibilities and new applications in molecular electronics, sensing and catalysis, including inside living cells. However, this comes with many challenges that need to be addressed to effectively implement and exploit bioorthogonal reactions in the chemistry of POMs.

Oxovanadium electronics for in-memory, neuromorphic, and quantum computing applications.

Vanadium is a critical raw material. In the nearby future, it may, however, become one of the key elements of computer devices based on two-dimensional arrays of spin qubits for quantum information processing or charge- and resistance-based data memory cells for non-volatile in-memory and neuromorphic computing. The research and development (R&D) of vanadium-containing electronic materials and methods for their responsible fabrication underpins the transition to innovative hybrid semiconductors for energy- and resource-efficient memory and information processing technologies.

Multistate switching of scanning tunnelling microscopy machined polyoxovanadate-dysprosium-phthalocyanine nanopatterns on graphite.

We demonstrate the first formation of stable, multistate switchable monolayers of polyoxometalates (POMs), which can be electronically triggered to higher charged states with increased conductance in the current-voltage profile at room temperature. These responsive two-dimensional monolayers are based on a fully oxidised dodecavanadate cage (POV12) equipped with Dy(III)-doped phthalocyanine (Pc) macrocycles adopting the face-on orientation on highly oriented pyrolytic graphite (HOPG). The layers can be lithographically processed by the tip of a scanning tunnelling microscope (STM) to machine patterns with diameters ranging from 30 to 150 nm.

Increasing the redox switching capacity of Lindqvist-type hexavanadates by organogold post-functionalisation.

The covalent attachment of organogold(I) moieties to the Lindqvist-type polyoxovanadate results in a measurable charge re-distribution across the formed Au-{V6}-Au linkages. Scanning probe microscopy studies of these hybrid compounds on the Au(111) surface demonstrate the increase in the number of switching states with stepwise increase in molecular conductance, compared with unfunctionalised hexavanadates.

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

A series of {V}-nuclearity polyoxovanadate cages covalently functionalized with one or sandwiched by two phthalocyaninato (Pc) lanthanide (Ln) moieties V-O-Ln bonds were prepared and fully characterized for paramagnetic Ln = Sm-Er and diamagnetic Ln = Lu, including Y. The LnPc-functionalized {VO} cages with fully oxidized vanadium centers in the ground state were isolated as (BuN)[HVOCl(LnPc)] and (BuN)[HVOCl(LnPc)] 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 to V in the solid state and at high sample concentrations.

What is the maximum charge uptake of Lindqvist-type polyoxovanadates in organic-inorganic heterostructures?

One of the striking characteristics of the tris(alkoxo)-ligated Lindqvist-type polyoxovanadates [VV6O{(OCH)CR}] in highest oxidation state in solution is the ease of their chemical post-functionalization the R group. On surfaces it is their conductivity as a function of individual V(3d) redox states. In both cases, the structural stability of the fully-oxidized dianion is enabled by charge-balancing counterions.

Synthesis and crystal structure of a one-dimensional chain-like strontium(II) coordination polymer built of -methyldi-ethano-lamine and isobutyrate ligands.

The one-dimensional coordination polymer () [Sr(ib)(Hmda)] (Hib = isobutyric acid, CHO, and Hmda = -methyldi-ethano-lamine, CHNO), namely, -poly[[(-methyldi-ethano-lamine-κ ,,')strontium(II)]-di-μ-isobutyrato-κ ,':;κ :,'], was prepared by the one-pot aerobic reaction of [ZrO(OH)(ib)(HO)]·3Hib with Sr(NO) and Hmda in the presence of MnCl and EtN in aceto-nitrile. The use of MnCl is key to the isolation of as high-quality colorless crystals in good yield. The mol-ecular solid-state structure of was determined by single-crystal X-ray diffraction.

Synthesis and Characterisation of Luminescent [Cr L(μ-carboxylato)] Complexes with High-Spin S=3 Ground States (L=N S donor ligand).

The synthesis, structure, magnetic, and photophysical properties of two dinuclear, luminescent, mixed-ligand [Cr L(O CR)] complexes (R=CH (1), Ph (2)) of a 24-membered binucleating hexa-aza-dithiophenolate macrocycle (L) are presented. X-ray crystallographic analysis reveals an edge-sharing bioctahedral N Cr(μ-SR) (μ -O CR)CrN core structure with μ -bridging carboxylate groups. A ferromagnetic superexchange interaction between the electron spins of the Cr ions leads to a high-spin (S=3) ground state.

Insights from Adsorption and Electron Modification Studies of Polyoxometalates on Surfaces for Molecular Memory Applications.

This Account highlights recent experimental and theoretical work focusing on the development of polyoxometalates (POMs) as possible active switching units in what may be called "molecule-based memory cells". Herein, we critically discuss how multiply charged vanadium-containing POMs, which exhibit stable metal-oxo bonds and are characterized by the excellent ability to change their redox states without significant structural distortions of the central polyoxoanion core, can be immobilized best and how they may work optimally at appropriate surfaces. Furthermore, we critically discuss important issues and challenges on the long way toward POM-based nanoelectronics.

Expansion of Zirconium Oxide Clusters by 3d/4f Ions.

Two series of charge-neutral coordination clusters featuring quasi-isostructural metal oxide cores, isolated as [ZrFeLnO(ib)(bda)(NO)]·MeCN (Ln = La (), Ce (), Pr (), and Nd (); ib = isobutyrate; Hbda = -butyldiethanolamine) and [ZrFeLnO(ib)(mda)(NO)]·MeCN (Ln = La (), Ce (), Pr (), and Nd (); Hmda = -methyldiethanolamine), were obtained via one-pot reactions of [FeO(ib)(HO)]NO as a critical precursor, Ln(NO)·6HO (Ln = La, Ce, Pr, and Nd), the respective aminoalcohol, and [ZrO(OH)(ib)(HO)]·3Hib in an acetonitrile solution. The coordination clusters in - feature {ZrO} cores that are structurally expanded by two 4f (Ln) and two 3d (Fe) metal ions, each individually coordinated to one of the eight oxide centers of {ZrO}, producing a metal skeleton where the 3d/4f positions cap four of the triangular faces of the central Zr octahedron. The coordination clusters differ in the chosen aminoalcohol coligands, -butyldiethanolamine or -methyldiethanolamine, which lead to a different isobutyrate coordination pattern in the two series, while the {FeLnZrO} core structure remains virtually unaffected.

Synthesis, Structure, and Surface Adsorption Characteristics of a Polynuclear Mn-Yb Complex.

The controlled adsorption of polynuclear coordination compounds with specific structural and electronic characteristics on surfaces is crucial for the prospective implementation of molecule-surface interfaces into practical electronic devices. From this perspective, a neutral 3d,4f-coordination cluster [MnMnYbO(OH)(L·SMe)(OOCMe)]·2MeCN·3EtOH (·2MeCN·3EtOH), where L·SMe is a Schiff base, has been synthesized and fully characterized and its adsorption on two different solid substrates, gold and graphite, has been studied. The mixed-valence compound with a bilayered metal core structure and the structurally exposed thioether groups exhibits a substantially different surface bonding to metallic gold and semimetallic graphite substrates.

Insertion of V Ions into the Polyoxotungstate Archetype {AsW}.

A new polyoxometalate compound consisting of the 39-tungsto-4-arsenate(III) unit with four incorporated V ions, isolated as (NH)[(VO)(VO(HO))(AsWO)(AsWV(OH)O)(WO)]·48HO (-), was synthesized and fully characterized. SQUID magnetometry shows three weakly coupled V centers with an antiferromagnetic exchange interaction and one isolated V ion as a spin-/ Curie paramagnet. UV-vis spectroscopy indicates that the structure remains intact in aqueous solution for at least 24 h.

TiO /PtTi(111) surface-directed formation of electronically responsive supramolecular assemblies of tungsten oxide clusters.

Highly ordered titanium oxide films grown on a PtTi(111) alloy surface were utilized for the controlled immobilization and tip-induced electric field-triggered electronic manipulation of nanoscopic WO clusters. Depending on the operating conditions, two different stable oxide phases, z'-TiO and w'-TiO , were produced. These phases show a strong effect on the adsorption characteristics and reactivity of WO clusters, which are formed as a result of thermal evaporation of WO powder on the complex TiO /PtTi(111) surfaces under ultra-high vacuum conditions.

{PVW}-Polyoxometalates Functionalized with Phthalocyaninato Y and Yb Moieties.

A tris(alkoxo)pyridine-augmented Wells-Dawson polyoxometalate (BuN)[] (WD = PVWO(OCH)C, Py = CHN) was functionalized with phthalocyaninato metal moieties ( where M = Y or Yb and Pc = CHN) to afford (BuN)[H()] compounds. High-resolution mass spectrometry was used to detect and identify the hybrid assembly. The magnetism studies reveal substantial differences between M = Yb (monomeric, single-ion paramagnetism) and M = Y (containing dimers, radical character).

Hexavanadate-Organogold(I) Hybrid Compounds: Synthesis by the Azide-Alkyne Cycloaddition and Density Functional Theory Study of an Intriguing Electron Density Distribution.

The fully oxidized Lindqvist-type hexavanadate compounds decorated by phosphine-derivatized Au(I) moieties oriented in a fashion (-BuN)[VO{(OCH)CCH(NCCH)AuP(CHOMe)}] () and (-BuN)[VO{(OCH)CCHOCH(CNH)AuP(CHOMe)}] () have been prepared by azide-alkyne cycloaddition reactions and characterized by various techniques, including NMR, IR, and UV/vis spectroscopy and electrospray ionization mass spectrometry. Electronic structure calculations unveil the potential of these model hybrid junctions for application in controlled charge-transport experiments on substrate surfaces.

Conductive Self-Assembled Monolayers of Paramagnetic {Co } and { } Coordination Clusters on Gold Surfaces.

Two polynuclear cobalt(II,III) complexes, [Co(N)(--bda)(bza·SMe)] () and [Co(N)(--bda)(bza·SMe)(MeOH)]Cl (), where Hbza·SMe = 4-(methylthio)benzoic acid and --Hbda = --butyldiethanolamine, were synthesized and fully characterized by various techniques. Compound exhibits an unusual, approximately -symmetric {Co } core of two isosceles Co triangles with perpendicularly oriented planes, sharing a central, high-spin Co ion residing in a distorted tetrahedral coordination environment. This central Co ion is connected to four outer, octahedrally coordinated low-spin Co ions oxo bridges.

Self-assembled monolayers of polyoxovanadates with phthalocyaninato lanthanide moieties on gold surfaces.

The two first representatives of phthalocyaninato (Pc) lanthanide-ligated polyoxovanadate cages {[V12O32(Cl)](LnPc)n}n-5 (n = 1 or 2, Ln = Yb3+) were synthesised and fully characterised. These magnetic complexes form two-dimensional self-assembled monolayers exhibiting electrical conductivity on gold substrate surfaces, as assessed by using an EGaIn tip.

Polyoxometalates as components of supramolecular assemblies.

The non-covalent interaction of polyoxometalates (POMs) with inorganic- or organic-based moieties affords hybrid assemblies with specific physicochemical properties that are of high interest for both fundamental and applied studies, including the discovery of conceptually new compounds and unveiling the impact of their intra-supramolecular relationships on the fields of catalysis, molecular electronics, energy storage and medicine. This minireview summarises the recent advances in the synthetic strategies towards the formation of such non-covalent POM-loaded assemblies, shedding light on their key properties and the currently investigated applications. Four main emerging categories according to the nature of the conjugate are described: (i) POMs in metal-organic frameworks, (ii) POMs merged with cationic metal complexes, (iii) architectures generated with solely POM units and (iv) POMs assembled with organic molecular networks.

How Does the Redox State of Polyoxovanadates Influence the Collective Behavior in Solution? A Case Study with [I@VO] ( q = 3, 5, 7, 11, and 13).

A series of stable reduction-oxidation states of the cagelike [I@V VO] polyoxovanadate (POV) with x = 8, 10, 12, 16, and 18 were studied with density functional theory and molecular dynamics to gain insight into the structural and electron distribution characteristics of these metal-oxo clusters and to analyze the charge/redox-dependent assemblage processes in water and acetonitrile (MeCN) solutions. The calculations show that the interplay between the POV redox state (molecular charge) and the solvent polarity, countercation size, and hydrophilicity (or hydrophobicity) controls the POV agglomeration phenomena, which substantially differ between aqueous and MeCN media. In MeCN, agglomeration is more pronounced for intermediate-charged POVs, whereas in water, the lowest-charged POVs and organic countercations tend to agglomerate into a microphase.

Supramolecular Construction of Cyanide-Bridged Re Diimine Multichromophores.

The reactions of labile [Re(diimine)(CO)(HO)] precursors (diimine = 2,2'-bipyridine, bpy; 1,10-phenanthroline, phen) with dicyanoargentate anion produce the dirhenium cyanide-bridged compounds [{Re(diimine)(CO)}CN)] (1 and 2). Substitution of the axial carbonyl ligands in 2 for triphenylphosphine gives the derivative [{Re(phen)(CO)(PPh)}CN] (3), while the employment of a neutral metalloligand [Au(PPh)(CN)] affords heterobimetallic complex [{Re(phen)(CO)}NCAu(PPh)] (4). Furthermore, the utilization of [Au(CN)], [Pt(CN)], and [Fe(CN)] cyanometallates leads to the higher nuclearity aggregates [{Re(diimine)(CO)NC} M] (M = Au, x = 2, 5 and 6; Pt, x = 4, 7 and 8; Fe, x = 6, 9 and 10).

Interplay between the amphipathic polyoxometalate interactions in solution and at solid-liquid interfaces: a toolbox for the technical application.

The far-reaching interplay between the speciation of polyoxometalates (POMs) in the liquid phase and the POM adsorption characteristics on substrate surfaces yet remains to be understood. The significance of this interplay is however paramount because it indicates the degree of technical applicability of solvent-processable POM molecules. Herein, we target this fundamentally important issue, shedding light on the "POM-counterion-solvent" and "POM-counterion-solvent-substrate" processes.

Addressing Multiple Resistive States of Polyoxovanadates: Conductivity as a Function of Individual Molecular Redox States.

The sustainable development of IT-systems requires a quest for novel concepts to address further miniaturization, performance improvement, and energy efficiency of devices. The realization of these goals cannot be achieved without an appropriate functional material. Herein, we target the technologically important electron modification using single polyoxometalate (POM) molecules envisaged as smart successors of materials that are implemented in today's complementary metal-oxide-semiconductor (CMOS) technology.