A Facile Method for the Synthesis of Binary Tungsten Iodides

The preparation of tungsten iodides in large quantities is a challenge because these compounds are not accessible using an easy synthesis method. A new, remarkably efficient route is based on a halide exchange reaction between WCl₆ and SiI₄. The reaction proceeds at moderate temperatures in a closed glass vessel. The new compounds W₃I₁₂ (W₃I₈?2 I₂) and W₃I₉ (W₃I₈? I₂) containing the novel [W₃I₈] cluster are formed at 120 and 150 °C, and remain stable in air. W₃I₁₂ is an excellent starting material for the synthesis of other metal‐rich tungsten iodides. At increasing temperature these trinuclear clusters undergo self‐reduction until an octahedral tungsten cluster is formed in W₆I₁₂. The synthesis, structure, and an analysis of the bonding of compounds containing this new trinuclear tungsten cluster are presented.     

The Remarkably Robust,Photoactive Tungsten Iodide Cluster [W6I12(NCC6H5)2]

The new heteroleptic tungsten iodide cluster compound [W₆I₁₂(NCC₆H₅)₂] is presented. The synthesis is carried-out from Cs₂W₆I₁₄ and ZnI₂ under solvothermal conditions in benzonitrile solution, yielding red cube-shaped crystals. [W₆I₁₂(NCC₆H₅)₂] represents a heteroleptic [W₆I₈]-type cluster bearing four apical iodides and two benzonitrile ligands. Molecular [W₆I₁₂(NCC₆H₅)₂] clusters form a robust hydrogen bridged crystal structure with high thermal stability and high resistibility against hydrolysis. The electronic structure is analyzed by quantum chemical methods of the calculated electron localization function (ELF) and the band structure. Photoluminescence measurements are performed to verify and describe the photophysical properties of [W₆I₁₂(NCC₆H₅)₂]. Finally, the photocatalytic properties of [W₆I₁₂(NCC₆H₅)₂] are evaluated as a proof-of-concept.     

A twofold interwoven two‐dimensional→two‐dimensional (2‐D→2‐D) cluster–organic network based on the [Cu2I2] cluster and the 4,4′‐(diazenediyl)dipyridine ligand: poly[[μ2‐4,4′‐(diazenediyl)dipyridine]‐μ2‐iodido‐copper(I)]

In the polymeric title compound, [CuI(C₁₀H₈N₄)]_n, the Cu^I atom is in a four‐coordinated tetrahedral geometry, formed by two I atoms and two pyridine N atoms from two different 4,4′‐(diazenediyl)dipyridine (4,4′‐azpy) ligands. Two μ₂‐I atoms link two Cu^I atoms to form a planar rhomboid [Cu₂I₂] cluster located on an inversion centre, where the distance between two Cu^I atoms is 2.7781 (15) Å and the Cu—I bond lengths are 2.6290 (13) and 2.7495 (15) Å. The bridging 4,4′‐azpy ligands connect the [Cu₂I₂] clusters into a two‐dimensional (2‐D) double‐layered grid‐like network [parallel to the (10) plane], with a (4,4)‐connected topology. Two 2‐D grid‐like networks interweave each other by long 4,4′‐azpy bridging ligands to form a dense 2‐D double‐layered network. To the best of our knowledge, this interwoven 2‐D→2‐D network is observed for the first time in [Cu₂I₂]–organic compounds.     

W4Br10 Cluster Intermediates in the Solid State Nucleation of W6Br12

The new adduct W₄Br₁₀ · 2SbBr₃ and the new binary compound W₄Br₁₀ were obtained as products in a reaction cascade in which WBr₆ was reacted with elemental antimony at successively increased temperatures. The crystal structures of both compounds were refined from X‐ray powder diffraction data and their electronic structures were analyzed by MO calculations. The cluster compounds W₄Br₁₀ · 2SbBr₃ and W₄Br₁₀ appear as intermediates in the solid state nucleation of W₆Br₁₂. The overall reaction cascade involves tungsten clusters having tetrahedral (W₄), square pyramidal (W₅) and finally octahedral (W₆) cluster cores.     

Two polymorphs of tetraethylammonium [hydrogen tris(3,5‐dimethylpyrazolyl)borato]di‐μ2‐sulfido‐disulfido(η2‐tetrasulfido)ditungsten(V) with Z′ = 1 and 2

Two polymorphs of the title compound, (C₈H₂₀N)[W₂S₄(S₄)(C₁₅H₂₂BN₆)], have been obtained unexpectedly by attempted recrystallization of a mixed‐metal–sulfur cluster complex from different solvents. The dinuclear complex anion contains W^V in two different coordination environments, one of them distorted octahedral with a tris(pyrazolyl)borate anion, a terminal sulfide and two bridging sulfide ligands, the other distorted square‐pyramidal with a terminal sulfide, two bridging sulfide and a chelating tetrasulfide ligand. The three independent anions in the two polymorphs have essentially the same geometry. The central W₂S₂ ring is a slightly folded rhombus with acute angles at the S atoms, and the WS₄ chelate ring is an envelope with one noncoordinating S atom as the flap. The second polymorph, with Z′ = 2 and pseudo‐inversion symmetry relating the anions of the asymmetric unit, also displays pseudo‐translation features in its layer structure, and all examined crystals were found to be twinned, possibly as a consequence of this structural feature.     

Crystal Structures of Bacterial (6‐4) Photolyase Mutants with Impaired DNA Repair Activity

PhrB from Agrobacterium fabrum is the first prokaryotic photolyase which repairs (6‐4) UV DNA photoproducts. The protein harbors three cofactors: the enzymatically active FAD chromophore, a second chromophore, 6,7‐dimethyl‐8‐ribityllumazine (DMRL) and a cubane‐type Fe‐S cluster. Tyr424 of PhrB is part of the DNA‐binding site and could provide an electron link to the Fe‐S cluster. The PhrB_Y424F mutant showed reduced binding of lesion DNA and loss of DNA repair. The mutant PhrB_I51W is characterized by the loss of the DMRL chromophore, reduced photoreduction and reduced DNA repair capacity. We have determined the crystal structures of both mutants and found that both mutations only affect local protein environments, whereas the overall fold remained unchanged. The crystal structure of PhrB_Y424F revealed a water network extending to His366, which are part of the lesion‐binding site. The crystal structure of PhrB_I51W shows how the bulky Trp leads to structural rearrangements in the DMRL chromophore pocket. Spectral characterizations of PhrB_I51W suggest that DMRL serves as an antenna chromophore for photoreduction and DNA repair in the wild type. The energy transfer from DMRL to FAD could represent a phylogenetically ancient process.     

Alkaline Earth Cluster Compounds AE[W6I14] and the Solvate [Ca(C2H6SO)6][W6I14]

Alkaline earth tungsten iodide clusters AE[W₆I₁₄] with AE = Mg, Ca, Sr, Ba and the solvated compound [Ca(C₂H₆SO)₆][W₆I₁₄] were prepared and structurally characterized. A new synthesis was employed, starting from W₆I₂₂, which is an exceptional compound among binary tungsten iodides because it is soluble in common polar organic solvents. As evidence for the wide range of the applicability of W₆I₂₂, we report the synthesis of the new AE[W₆I₁₄] compounds in comparison to a solid‐state reaction departing from W₃I₁₂.     

(W6I8)Cl4 – A Basic Model Compound for Photophysically Active [(W6I8)L6]2– Clusters?

The heteroleptic cluster compound (W₆I₈)Cl₄ was prepared by thermal conversion of the homoleptic clusters W₆I₁₂ and W₆Cl₁₂ at 700 °C to yield a bright yellow powder. The presence of the smaller chlorido ligands in apical positions of [(W₆I₈)Cl₆]^2– creates nearly spherically clusters showing thermal and chemical inertness. Photoluminescence studies revealed a strong red phosphorescence from excited spin‐triplet states.     

Highly Luminescent Linear Complex Arrays of up to Eight Cuprous Centers

Linearly arranged metal atoms that are embedded in discrete molecules have fascinated scientists across various disciplines for decades; this is attributed to their potential use in microelectronic devices on a submicroscopic scale. Luminescent oligonuclear Group 11 metal complexes are of particular interest for applications in molecular light‐emitting devices. Herein, we describe the synthesis and characterization of a rare, homoleptic, and neutral linearly arranged tetranuclear Cu^I complex that is helically bent, thus representing a molecular coil in the solid state. This tetracuprous arrangement dimerizes into a unique octanuclear assembly bearing a linear array of six Cu^I centers with two additional bridging cuprous ions that constitute a central pseudo‐rhombic Cu^I₄ cluster. The crystal structure determinations of both complexes reveal close d¹⁰???d¹⁰ contacts between all cuprous ions that are adjacent to each other. The dynamic behavior in solution, DFT calculations, and the luminescence properties of these remarkable complexes are also discussed.     

A novel one‐dimensional double‐chain‐like ZnII coordination polymer: poly[bis(1‐benzyl‐1H‐imidazole‐κN3)tris(μ‐cyanido‐κ2C:N)(cyanido‐κC)disilver(I)zinc(II)]

One of most interesting systems of coordination polymers constructed from the first‐row transition metals is the porous Zn^II coordination polymer system, but the numbers of such polymers containing N‐donor linkers are still limited. The title double‐chain‐like Zn^II coordination polymer, [Ag₂Zn(CN)₄(C₁₀H₁₀N₂)₂]_n, presents a one‐dimensional linear coordination polymer structure in which Zn^II ions are linked by bridging anionic dicyanidoargentate(I) units along the crystallographic b axis and each Zn^II ion is additionally coordinated by a terminal dicyanidoargentate(I) unit and two terminal 1‐benzyl‐1H‐imidazole (BZI) ligands, giving a five‐coordinated Zn^II ion. Interestingly, there are strong intermolecular Ag^I…Ag^I interactions between terminal and bridging dicyanidoargentate(I) units and C—H…π interactions between the phenyl rings of BZI ligands of adjacent one‐dimensional linear chains, providing a one‐dimensional linear double‐chain‐like structure. The supramolecular three‐dimensional framework is stabilized by C—H…π interactions between the phenyl rings of BZI ligands and by Ag^I…Ag^I interactions between adjacent double chains. The photoluminescence properties have been studied.     

The new one‐dimensional coordination polymer catena‐poly[[diaquasodium(I)]‐μ‐oxalato‐[diaquairon(III)]‐μ‐oxalato]

The oxalate dianion is one of the most studied ligands and is capable of bridging two or more metal centres and creating inorganic polymers based on the assembly of metal polyhedra with a wide variety of one‐, two‐ or three‐dimensional extended structures. Yellow single crystals of a new mixed‐metal oxalate, namely catena‐poly[[diaquasodium(I)]‐μ‐oxalato‐κ⁴O¹,O²:O^1′,O^2′‐[diaquairon(III)]‐μ‐oxalato‐κ⁴O¹,O²:O^1′,O^2′], [NaFe(C₂O₄)₂(H₂O)₄]_n, have been synthesized and the crystal structure elucidated by X‐ray diffraction analysis. The compound crystallizes in the noncentrosymmetric space group I4₁ (Z = 4). The asymmetric unit contains one Na^I and one Fe^III atom lying on a fourfold symmetry axis, one μ₂‐bridging oxalate ligand and two aqua ligands. Each metal atom is surrounded by two chelating oxalate ligands and two equivalent water molecules. The structure consists of infinite one‐dimensional chains of alternating FeO₄(H₂OW1)₂ and NaO₄(H₂OW2)₂ octahedra, bridged by oxalate ligands, parallel to the [100] and [010] directions, respectively. Because of the cis configuration and the μ₂‐coordination mode of the oxalate ligands, the chains run in a zigzag manner. This arrangement facilitates the formation of hydrogen bonds between neighbouring chains involving the H₂O and oxalate ligands, leading to a two‐dimensional framework. The structure of this new one‐dimensional coordination polymer is shown to be unique among the A^IM^III(C₂O₄)₂(H₂O)_n series. In addition, the absorption bands in the IR and UV–Visible regions and their assignments are in good agreement with the local symmetry of the oxalate ligand and the irregular environment of iron(III). The final product of the thermal decomposition of this precursor is the well‐known ternary oxide NaFeO₂.     

Solvent‐Induced Cluster‐to‐Cluster Transformation of Homoleptic Gold(I) Thiolates between Catenane and Ring‐in‐Ring Structures

Supramolecular ensembles adopting ring‐in‐ring structures are less developed compared with catenanes featuring interlocked rings. While catenanes with inter‐ring closed‐shell metallophilic interactions, such as d¹⁰–d¹⁰ Au^I–Au^I interactions, have been well‐documented, the ring‐in‐ring complexes featuring such metallophilic interactions remain underdeveloped. Herein is described an unprecedented ring‐in‐ring structure of a Au^I‐thiolate Au₁₂ cluster formed by recrystallization of a Au^I‐thiolate Au₁₀ [2]catenane from alkane solvents such as hexane, with use of a bulky dibutylfluorene‐2‐thiolate ligand. The ring‐in‐ring Au^I‐thiolate Au₁₂ cluster features inter‐ring Au^I–Au^I interactions and underwent cluster core change to form the thermodynamically more stable Au₁₀ [2]catenane structure upon dissolving in, or recrystallization from, other solvents such as CH₂Cl₂, CHCl₃, and CH₂Cl₂/MeCN. The cluster‐to‐cluster transformation process was monitored by ¹H NMR and ESI‐MS measurements. Density functional theory (DFT) calculations were performed to provide insight into the mechanism of the “ring‐in‐ring? [2]catenane” interconversions.     

Low-temperature preparation of tungsten halide clusters: Crystal structure of the adduct W<Subscript>5</Subscript>Br<Subscript>12</Subscript> · SbBr<Subscript>3</Subscript>

Single-crystals of a new compound W₅Br₁₂ · SbBr₃ (I) were isolated as a reaction product from the reduction of WBr₆ with elemental antimony at 250°C. The crystal structure was determined by single-crystal X-ray diffraction analysis. The structure contains square-pyramidal tungsten clusters being linked into infinite [(W₅Br₈ⁱ)Br₃^aBr₂^2/a-a] chains through shared W-Br^a-a-W contacts of adjacent clusters. The structure of the adduct I can be viewed as an intercalation compound composed of double-layers of cluster chains alternating with mono-layers of SbBr₃ molecules.     

New Boron‐Centered Mixed‐Halide Zirconium Cluster Phases with a Cubic Structure: NaZr6Cl12–xI2+xB (x È 6) and AII0.5Zr6(Cl, I)14B (AII = Ca,Sr, Ba)

The boron‐centered mixed‐halide zirconium cluster phases were obtained from reactions of appropriate amounts of NaCl or ACl₂ (with A = Ca, Sr, Ba), ZrCl₄, ZrI₄, Zr (powder), and elemental B in sealed tantalum containers at 800–850 °C. Single crystals of NaZr₆Cl_10.94(1)I_3.06B and Sr_0.5Zr₆Cl_11.34(2)I_2.66B have been characterized by X‐ray diffraction at room temperature (cubic, Pa 3, Z = 4, a = 1331.3(1) pm, and a = 1326.2(2) pm, respectively). The Zr₆ octahedra in these phases are centered by boron and three‐dimensionally connected by exo‐iodide atoms which bridge simultaneously three octahedra. Six out of the twelve inner chlorides (one symmetry independent site) which bridge the edges of each octahedron, but are not involved in inter‐cluster bridging (according to AZr₆I^a–a–a_6/2(Cl_12–xI_x)ⁱB), can be completely substituted by iodide. Such a substitution is not possible for the remaining six inner halides on the second symmetry independent site, because the larger iodide atom on this site would experience strong repulsive forces from short anionic contacts. This gives the phase width of NaZr₆Cl_12–xI_2+xB to x È 6. The size of the voids that cover the cations A limits this structure to members with A = Na, Ca, Sr, and Ba. This structure type requires the existence of two differently sized halide types simultaneously.     

W6Cl18: Neue Synthesen,neue Strukturverfeinerung,elektronische Struktur und Magnetismus

W₆Cl₁₈: New Syntheses, New Structure Refinement, Electronic Structure, and Magnetism Pure W₆Cl₁₈ was synthesized after two methods, by oxidizing W₆Cl₁₂ with CCl₄ in an autoclave, and by reaction of W₆Cl₁₂ in a chlorine gas flow. At temperatures above 400 °C and under atmospheric pressure W₆Cl₁₈ transforms into W₆Cl₁₂. The crystal structure of W₆Cl₁₈ was refined after the Rietveld method on X‐ray powder data. The unusual electronic conditions of the 18 electron cluster [W₆Cl₁₂]Cl₆ are compared with those of the electron‐precise 24 electron cluster [W₆Cl₈]Cl₄. The compound exhibits paramagnetic behaviour with two electrons in antibonding energy levels.     

From Cluster to Cluster: Structural Transformation Reactions Among Tungsten Chloride Clusters

Reactions between tungsten halides are discussed along the series of compounds WCl₆ → WCl₄ → W₆Cl₁₂ ↔ W₆Cl₁₈ → [W₆CCl₁₈]ⁿ⁻ ← [W₃Cl₁₃]^u−, focusing on the two closely related tungsten chloride compounds whose structures compromise the well-known octahedro W₆Cl₁₈ cluster and the carbon-centered triprismo W₆CCl₁₈ cluster. Both clusters can be regarded as being built by merging two trigonal [W₃Cl₁₃]^u− units in different ways. Syntheses, structural transformation reactions, and concepts regarding electronic structures are reported.     

Following the Reaction of Heteroanions inside a {W18O56} Polyoxometalate Nanocage by NMR Spectroscopy and Mass Spectrometry

By incorporating phosphorus(III)‐based anions into a polyoxometalate cage, a new type of tungsten‐based unconventional Dawson‐like cluster, [W₁₈O₅₆(HP^IIIO₃)₂(H₂O)₂]^8?, was isolated, in which the reaction of the two phosphite anions [HPO₃]^2? within the {W₁₈O₅₆} cage could be followed spectroscopically. As well as full X‐ray crystallographic analysis, we studied the reactivity of the cluster using both solution‐state NMR spectroscopy and mass spectrometry. These techniques show that the cluster undergoes a structural rearrangement in solution whereby the {HPO₃} moieties dimerize to form a weakly interacting (O₃PH???HPO₃) moiety. In the crystalline state the cluster exhibits a thermally triggered oxidation of the two P^III template moieties to form P^V centers (phosphite to phosphate), commensurate with the transformation of the cage into a Wells–Dawson {W₁₈O₅₄} cluster.     

Chitosan-encapsulated Keggin Anion [Ti2W10PO40]7−. Synthesis, Characterization and Cellular Uptake Studies

The Keggin type polyoxotungstate [Ti₂W₁₀PO₄₀]⁷⁻ forms stable associates with the biopolymer chitosan in the nanometer size range. The cluster compound crystallizes from aqueous solution as K₄H₃[Ti₂W₁₀PO₄₀] · 15H₂O having a tetragonal structure. Both, the cluster compound and the chitosan/[Ti₂W₁₀PO₄₀] associates show a high hydrolytic stability at pH 7.4. The associates formed between the cluster anion [Ti₂W₁₀PO₄₀]⁷⁻ with the polyaminosaccharide chitosan have been characterized by photon correlation spectroscopy, scanning electron microscopy, filtration, centrifugation and zeta potential measurements. The size of the associates formed is in the range of ca. 5×10¹ to 5×10² nm. These particles have a defined stoichiometry with 5–6 cluster anions bound per molecule chitosan. The isoelectric point determined by zeta potential measurements was found for a cluster anion to chitosan molar ratio of 5.5, indicating the charge neutralization between protonated chitosan and [Ti₂W₁₀PO₄₀]⁷⁻ anions. Cellular uptake studies with [Ti₂W₁₀PO₄₀]⁷⁻ using tumor cell lines FaDu (human squamous carcinoma) and HT-29 (human adenocarcinoma) showed that the tungsten amount inside the cells is remarkably enhanced in the presence of chitosan.     

Assembly of Tungsten‐Oxide‐Based Pentagonal Motifs in Solution Leads to Nanoscale {W48}, {W56}, and {W92} Polyoxometalate Clusters

We report an approach to synthesize molecular tungsten‐oxide‐based pentagonal building blocks, in a new {W₂₁O₇₂} unit, and show how this leads to a family of gigantic molecular architectures including [H₁₂W₄₈O₁₆₄]^28? {W₄₈}, [H₂₀W₅₆O₁₉₀]^24? {W₅₆}, and [H₁₂W₉₂O₃₁₁]^58? {W₉₂}. The {W₄₈} and {W₅₆} clusters are both dimeric species incorporating two {W₂₁} units and the {W₅₆} species is the first example of a molecular metal oxide cluster containing a chiral “double‐stranded” motif which is stable in solution as confirmed by mass spectrometry. The {W₉₂} anion having four {W₂₁} units is one of the largest transition metal substituted isopolyoxotungstates known.     

Giant Hollow Heterometallic Polyoxoniobates with Sodalite‐Type Lanthanide–Tungsten–Oxide Cages: Discrete Nanoclusters and Extended Frameworks

The first series of niobium–tungsten–lanthanide (Nb‐W‐Ln) heterometallic polyoxometalates {Ln₁₂W₁₂O₃₆(H₂O)₂₄(Nb₆O₁₉)₁₂} (Ln=Y, La, Sm, Eu, Yb) have been obtained, which are comprised of giant cluster‐in‐cluster‐like ({Ln₁₂W₁₂}‐in‐{Nb₇₂}) structures built from 12 hexaniobate {Nb₆O₁₉} clusters gathered together by a rare 24‐nuclearity sodalite‐type heterometal–oxide cage {Ln₁₂W₁₂O₃₆(H₂O)₂₄}. The Nb‐W‐Ln clusters present the largest multi‐metal polyoxoniobates and a series of rare high‐nuclearity 4d‐5d‐4f multicomponent clusters. Furthermore, the giant Nb‐W‐Ln clusters may be isolated as discrete inorganic alkali salts and can be used as building blocks to form high‐dimensional inorganic–organic hybrid frameworks.