Keggin-type polyoxometalate 1 : 1 complexes of Pb(II) and Bi(III): experimental, theoretical and luminescence studies

Bi3+ and Pb2+ uptake by a monolacunary Keggin-type [PW11O39]7- anion leads to the formation of [PW11O39Bi]4- and [PW11O39Pb]5- complexes with a stereochemically active lone pair at the incorporated heterometal. The two complexes were isolated as (TBA)4[PW11O39Bi] (1) and (TBA)5[PW11O39Pb] (2) and characterized by 31P and 183W NMR spectroscopy, high-resolution electrospray mass-spectrometry (HR-ESI-MS) and cyclic voltammetry (CV). EXAFS and XANES data confirm the unchanged oxidation state and ψ-square pyramidal geometry of Bi3+ and Pb2+ in 1 and 2. DFT calculations were used in order to (i) confirm the absence of ligands attached to the heterometal sites in both complexes and localize the lone pair, and (ii) assign all signals in the 183W NMR spectra. Complexes 1 and 2 demonstrate photoluminescence (PL). A reversible change in the PL spectra of both complexes in the presence of water vapor has been detected. On the contrary, PL data for sandwich-type ((CH3)4N)4K3[H4(PW11O39)2Bi]·25H2O (3) do not show sensitivity to water vapor.

"Host in Host" Supramolecular Core-Shell Type Systems Based on Giant Ring-Shaped Polyoxometalates

Herein, we show how the chaotropic effect arising from reduced molybdate ions in acidified aqueous solution is able to amplify drastically weak supramolecular interactions. Time-resolved Small Angle X-ray Scattering (SAXS) analysis suggests that molybdenum-blue oligomeric species form huge aggregates in the presence of γ-cyclodextrin (γ-CD) which results in the fast formation of nanoscopic {Mo₁₅₄ }-based host-guest species, while X-ray diffraction analysis reveals that the ending-point of the scenario results in an unprecedented three-component well-ordered core-shell-like motif. A similar arrangement was found by using preformed hexarhenium chalcogenide-type cluster [Re₆ Te₈ (CN)₆ ]^4- as exogenous guest. This seminal work brings better understanding of the self-assembly processes in general and gives new opportunities for practical applications in the design of complex multicomponent materials via the simplicity of the non-covalent chemistry.

Tubular polyoxoanion [(SeMo6O21)2(C2O4)3]10− and its transformations

Tubular [(SeMo₆O₂₁)₂(C₂O₄)₃]¹⁰⁻ polyoxoanion can be assembled from Na₂MoO₄/SeO₂/H₂C₂O₄ system. TBABr precipitates complexes of [Mo₆O₁₉]²⁻ and [β-Mo₈O₂₆Na₂(NO₃)]³⁻ from its aqueous solution. Speciation of [β-Mo₈O₂₆]⁴⁻ and [Mo₆O₁₉]²⁻ has been studied.

Unusual π–π interactions directed by the [{(C6H6)Ru}2W8O30(OH)2]6− hybrid anion

The [{(C₆H₆)Ru}₂W₈O₃₀(OH)₂]⁶⁻ hybrid anion as a new type of π–π stacking induced building block and methanol oxidation precatalyst.

Interactions of aromatic rings in the crystal structures of hybrid polyoxometalates and Ru clusters

Computational analysis for π–π interaction energies of {(arene)Ru}2+ containing complexes and relative group 5 hybrid polyoxometalates reveals different frameworks. Some perspectives on πOF materials processing and crystal engineering were discussed.

Solvatomorphs of (Bu4N)2[{Ag(N2-py)}2Mo8O26]: structure, colouration and phase transition

(Bu4N)2[β-{Ag(N2-py)}2Mo8O26] demonstrates monomer/polymer dualism and a colouration phenomenon. The polymeric phase reveals a Ag assisted phase transition. Such complexes can act as precursors for catalytically active materials.

Coordination capacity of Keggin anions as polytopic ligands: case study of [VNb12O40]15

Reaction of Na9H4[VNb12O40{NbO(CO3)}2] with [(C6H6)RuCl2]2 (molar ratio {VNb12} : {(C6H6)Ru} = 1 : 4) in aqueous solution gives a mixture of [α-{(C6H6)Ru}4VNb12O40]7- and [α-{(C6H6)Ru}3VNb12O40]9-. Direct acetone diffusion into mother liquor leads to crystallization of Na6H[α-{(C6H6)Ru}4VNb12O40]·41.25H2O (1), characterized by single crystal X-ray diffraction (SCXRD). This anion has four organometallic fragments coordinated to the α-Keggin type [VNb12O40]15- backbone in different manner. Three {(C6H6)Ru}2+ groups cap triangular faces and one group a rectangular face of [VNb12O40]15-. Equilibrated mixture of [α-{(C6H6)Ru}4VNb12O40]7- and [α-{(C6H6)Ru}3VNb12O40]9- was studied by 1H DOSY NMR, HPLC-ICP-AES and HPLC-ESI-MS combined techniques. Direct chromatographic separation of these complexes results in unexpected transformation of both species into [α-{(C6H6)Ru}5VNb12O40]5-, isolated and characterized as Na5[α-{(C6H6)Ru}5VNb12O40]·16H2O (2). This anion contains five coordinated organometallic groups occupying both triangular and rectangular faces.

Proton motion inside [(DMF)2H]2[W6Cl14]: structural, Raman and luminescence studies

Protonation of DMF by (H₇O₃)₂[W₆Cl₁₄] results in the appearance of strongly proton coupled [(DMF)₂H]⁺ dimers. Such units are captured as the cationic part of [(DMF)₂H]₂[W₆Cl₁₄] (1). The proton behavior in such dimers was studied for the first time with single crystal X-ray diffraction (XRD) and ¹H MAS NMR, Raman and photoluminescence (PL) spectroscopic techniques. The experimental data reveal the presence of two types of [(DMF)₂H]⁺ dimers in 1 (cisoidal and transoidal, with respect to the mutual orientations of their C-O groups) which differ in terms of the degree to which they interact with the cluster anions as the temperature decreases. At room temperature all the OO distances in the [(DMF)₂H]⁺ dimers are very short (2.375 Å) and almost equal. ¹H MAS NMR spectra show a resonance line at 18.7 ppm which is very close to that observed in sodium hydrogen maleate with a strong hydrogen bond belonging to a single-well potential of proton motion. The temperature decrease leads to the differentiation of [(DMF)₂H]⁺ dimers due to the elongation of the OO distance in one pair while keeping a practically constant OO distance in the second pair. The analysis of the cation-anion interactions reveals a strong difference between these two types of dimers which results from the shifting of one DMF molecule toward a terminal Cl^- ligand of the cluster anion. The DFT calculations were used to show the difference in OH⁺O stretches for two different dimers. Moreover, we have found the PL of such dimeric units in the solid state. The temperature screening of the PL behavior demonstrates two types of luminescent centers at low temperatures which coalesce at 298 K. The proton motion in the hydrogen bond was studied using Raman spectroscopy, which was beneficial to monitor the complex behavior over a very broad temperature range from 5 to 298 K. According to the Raman data, we are dealing with a symmetric double-well potential for the hydrogen bond at room temperature, which becomes a broad single well potential below 110 K for the [(DMF)₂H]⁺ cation with a longer OO distance (the cisoidal isomer) and below 60 K for the [(DMF)₂H]⁺ cation with a shorter OO distance (the transoidal isomer).

Cyclodextrin-Assisted Hierarchical Aggregation of Dawson-type Polyoxometalate in the Presence of {Re6Se8} Based Clusters

The association of metallic clusters (CLUS) and polyoxometalates (POM) into hierarchical architectures is achieved using γ-cyclodextrin (γ-CD) as a supramolecular connector. The new self-assembled systems, so-called CLUSPOM, are formed from Dawson-type polyoxometalate [P₂W₁₈O₆₂]^6- and electron-rich rhenium clusters. It is worth noting that a cluster-based cation [{Re₆Se₈}(H₂O)₆]²⁺ on one hand and a cluster-based anion on the other hand [{Re₆Se₈}(CN)₆]^4- can be associated with the anionic POM. In the absence of the supramolecular connector, a "CLUSPOM salt" was obtained from aqueous solution of the cationic cluster and the polyoxometalate. In this solid, the arrangement between the polymetallic building blocks is mainly governed by long-range Coulombic interactions. In the presence of γ-CD, the Dawson anion and the cationic cluster are assembled differently, forming a hierarchical supramolecular solid, K₂[{Re₆Se₈}(H₂O)₆]₂{[P₂W₁₈O₆₂]@2γ-CD}·42H₂O, where the organic macrocycle acts as a ditopic linker between the inorganic building blocks. In such an edifice, the short-range molecular recognition dominates the long-range Coulombic interactions leading to a specific three-dimensional organization. Interestingly, the assembling of anionic POM [P₂W₁₈O₆₂]^6- with the anionic rhenium cluster [{Re₆Se₈}(CN)₆]^4- is also achieved with γ-CD despite the repulsive forces between the nanosized anions. The resulting solid, K₁₀{[{Re₆Se₈}(CN)₆]@2γ-CD}[P₂W₁₈O₆₂]·33H₂O, is built from 1:2 inclusion complexes {[{Re₆Se₈}(CN)₆]@2γ-CD}^4- linked by a POM unit interacting with the exterior wall of the organic macrocycle. Multinuclear NMR and small-angle X-ray scattering investigations support supramolecular preorganization in aqueous solution prior to crystallization.

Memory devices based on novel alkyl viologen halobismuthate(iii) complexes

Four novel halobismuthate(iii) complexes with alkyl viologen cations: (R2Viol)2[Bi2X10] (R = n-butyl, n-pentyl, X = Cl, Br) have been synthesized. Both chloride complexes revealed photochromic behavior and were successfully utilized for the fabrication of OFET-based memory devices with high switching coefficients and good write-read-erase cycling stability.

From Specific γ-CD/[Nb6 Cl12 (H2 O)6 ]2+ Recognition to Biological Activity Tuning

Specific molecular recognition of γ-cyclodextrin (γ-CD) by the cationic hexanuclear niobium [Nb₆ Cl₁₂ (H₂ O)₆ ]²⁺ cluster complex in aqueous solutions results in a 1:1 supramolecular assembly {[Nb₆ Cl₁₂ (H₂ O)₆ ]@γ-CD}²⁺ . NMR spectroscopy, isothermal titration calorimetry (ITC), and ESI-MS were used to study the interaction between the inorganic cluster and the organic macrocycle. Such molecular association affects the biological activity of [Nb₆ Cl₁₂ (H₂ O)₆ ]²⁺ , decreasing its cytotoxicity despite enhanced cellular uptake. The 1:1 stoichiometry is maintained in solution over a large window of the reagents' ratio, but crystallization by slow evaporation produces a 1:2 host-guest complex [Nb₆ Cl₁₂ (H₂ O)₆ @(γ-CD)₂ ]Cl₂ ⋅20 H₂ O featuring the cluster encapsulated between two molecules of γ-CD. The 1:2 complex was characterized by XRD, elemental analysis, IR spectroscopy, and thermogravimetric analysis (TGA). Quantum chemical calculations were performed to model host-guest interaction.

Self-Assembly of Ag+/[PW11NbO40]4- Complexes in Nonaqueous Solutions

Self-assembly between Ag⁺ and [PW₁₁NbO₄₀]^4- in N- and O-donor solvents (nitriles and amides) has been studied. In the case of dimethylformamide (DMF), formation of a yellow [Ag₄(DMF)₁₂][PW₁₁NbO₄₀] (1a) metastable phase and a colorless [Ag₄(DMF)₁₀][PW₁₁NbO₄₀] (1) stable phase was observed. In acetonitrile (CH₃CN), the product was [Ag(CH₃CN)₄]₂{[Ag(CH₃CN)₃]₂[PW₁₁NbO₄₀]} (2a). By contrast, [SiW₁₂O₄₀]^4- of the same size and charge as [PW₁₁NbO₄₀]^4- produces [Ag(CH₃CN)₃]₄[SiW₁₂O₄₀] (3a). Partial desolvation of 2a and 3a leads to Ag₄[PW₁₁NbO₄₀]·7.5CH₃CN (2) and Ag₄[SiW₁₂O₄₀]·7.5CH₃CN (3), respectively. The CH₃CN molecules in the structure of 2 are labile, and this compound was used as the starting material to study solvent-exchange processes in N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMA), diethylformamide (DEF), and benzonitrile (PhCN) solutions. These solvent reactions yield [Ag(DMA)₄][Ag₃(DMA)₆][PW₁₁NbO₄₀] (4), [Ag₂(NMP)₄(CH₃CN)]₂[PW₁₁NbO₄₀]·1.3NMP (5a), [Ag₂(NMP)₅]₂[PW₁₁NbO₄₀] (5b), Ag₄[PW₁₁NbO₄₀]·9.5DEF (6), and [Ag(PhCN)₄]₂[{Ag(PhCN)₃}₂PW₁₁NbO₄₀] (7). All products were isolated and characterized by single-crystal X-ray diffraction (except for 2 and 3), IR, elemental analysis, and thermogravimetric analysis techniques. The O-donor solvents favor polynuclear, solvent-bridged cationic aggregates. In the case of DMF, DMA, and DEF discrete, tri- and tetranuclear polycations are observed, while in the case of NMP, the formation of infinite polycationic structures takes place. By contrast, the N-donor solvents (CH₃CN and PhCN) favor mononuclear cations, which can exist either as distorted tetrahedral, isolated [Ag(Solv)₄]⁺ cations or as pseudotriangular {Ag(Solv)₃}⁺ units, additionally coordinated to a polyoxometalate. Screening of the luminescent properties for solid samples of 1-7 revealed that only 5a/5b and 7 are emissive. In particular, the sample containing 5a and 5b demonstrates long-lived phosphorescence with a 30 ms lifetime.

[{AgL}2Mo8O26]n– complexes: a combined experimental and theoretical study

Two sets of silver–molybdate complexes with L = XR₃ (X = P, As, Sb; R₃ = Ph₃, Ph₂Py) and functionalized pyridine-based ligands have been studied with different techniques.

Chlorotellurate(iv) supramolecular associates with “trapped” Br2: features of non-covalent halogen⋯halogen interactions in crystalline phases

Reactions of chlorotellurates(iv) and Br₂ afford formation of supramolecular complexes Cat₂{[TeCl₆](Br₂)} (Cat = Me₃N⁺ (1), PyH⁺ (2), 4-MePyH⁺ (3) and 1-MePy⁺ (4)) where dibromine fragments are “trapped” by [TeCl₆]³⁻via Br⋯Cl halogen bonding.

Reactions of [Ru(NO)Cl5]2- with pseudotrilacunary {XW9O33}9- (X = AsIII, SbIII) anions

Reactions of [Ru(NO)Cl₅]^2- with pseudotrivacant B-α-[XW₉O₃₃]^9- (X = As^III, Sb^III) at 160 °C result in the rearrangement of polyoxometalate backbones into {XM₁₈} structures. In the case of arsenic, oxidation of As^III to As^V takes place with the formation of a mixture of plenary and monosubstituted Dawson [As₂W₁₈O₆₂]^6- and [As₂W₁₇Ru(NO)O₆₁]^7- anions, of which the latter was isolated as Me₂NH₂⁺ (DMA-1a and DMA-1b) and Bu₄N⁺ (Bu₄N-1) salts and fully characterized. Both α₁ and α₂ isomers of [As₂W₁₇Ru(NO)O₆₁]^7- were present in the reaction mixture; pure [α₂-As₂W₁₇Ru(NO)O₆₁]^7- was isolated as the Bu₄N⁺ salt. In the case of antimony, [SbW₉O₃₃]^9- is converted into a mixture of [SbW₁₈O₆₀]^9- and [SbW₁₇{Ru(NO)}O₅₉]^10-. The formation of trisubstituted [SbW₁₅{Ru(NO)}₃O₅₇]^12- as a minor byproduct was detected by HPLC-ICP-AES. The monosubstituted [SbW₁₇{Ru(NO)}O₅₉]^10- anion was isolated as DMAH⁺ (DMA-2) and mixed inorganic cation (CsKNa-2) salts and characterized by XRD, HPLC-ICP-AES, EA and TGA techniques. X-ray analysis shows the presence of the {Ru(NO)}-group in the 6-membered ("equatorial") belt of the Sb-free hemisphere. The experimental findings were confirmed and interpreted by means of quantum chemical calculations.