“Wheeling Templates” in Molecular Oxothiomolybdate Rings: Syntheses, Structures, and Dynamics

Record Aluminum Molecular Rings for Optical Limiting and Nonlinear Optics

Crystalline cluster materials, a class of functional motif aggregations, provide a great opportunity for tuning the properties stemming from the flexible and accurate variation of inorganic and organic compositions. In this study, we demonstrate the effects of functional ligand and ring size regulation on the structures and third-order nonlinear optical (NLO) properties. Revealed by the single-crystal X-ray analysis results, aluminum molecular ring expansion is achieved by 2×9 and 3×6 strategies. In terms of the given organic shells, we further tuned the aluminum molecular ring sizes from 3.0 nm to 1.7 nm. The picosecond Z-scan measurements results revealed that the third-order NLO performances do not only depend on the general conjugate interactions but are also related to hydrogen bonding, polarizability, and ring sizes. The large nonlinear absorption coefficient and onset prove that the observed samples are promising candidates for the field of nonlinear optics.

Isolated molybdenum-based microporous POMs for selective adsorption of gases

Dodecanuclear, icosanuclear and octanuclear porous MOF-like POMs materials [MoV12O12(μ2-O)4(μ3-O)12(Htrz)4(trz)4]∙nH2O (n = 22, 1; n = 92, 2; Htrz = 1H-1,2,3-triazole), [MoV8O8(μ2-O)12(Htrz)8]½∙[MoV12O12(μ2-O)4(μ3-O)12(Htrz)4(trz)4]∙44H2O (3), and [MoV8O8(μ2-O)12(Htrz)8]·62H2O (4) have been obtained and well...

The role of mono- and dicarboxylic acids in the building of oxomolybdates containing {MoO4}, {Mo2O5}, {Mo2O6}, {Mo3O8}, {Mo5O17}, {Mo5O18}, {Mo8O26}, and {SiMo12O40} units

We describe the impact of mono- and dicarboxylic acids on the formation of polyoxomolybdates of different nuclearities, such as {Mo5O17}, {Mo5O18}, {Mo8O26}, and {SiMo12O40}.

Spontaneous formation of a chiral (Mo2O2S2)2+-based cluster driven by dimeric {Te2O6}-based templates

Utilization of tellurite anion as template, led to the formation of unprecedented oxothiometalate based building blocks and the spontaneous manifestation of chirality.

Utilization of [Mo₂S₂O₂(H₂O)₆]²⁺ and a tellurite anion led to the formation of three new clusters, 1–3, with unique structural features. The tellurite anion not only templated the formation of [(Mo₂O₂S₂)₄(TeO₃)(OH)₉]^3–1 and [(Mo₂O₂S₂)₁₂(TeO₃)₄(TeO₄)₂ (OH)₁₈]^10–3, but also the in situ generation of two different types of dimeric {Te₂O₆} based moieties induced the spontaneous assembly of the chiral [(Mo₂O₂S₂)₁₀(TeO₃)(Te₂O₆)₂(OH)₁₈]^8– anionic cluster, 2.

Construction of a new binding manner in carboxylic acid-functionalized phosphomolybdates

A new binding manner of C–N–Mo bonds was constructed in carboxylic acid-functionalized phosphomolybdates, and the polyanion was present as a hexamer.

Tellurite-Squarate Driven Assembly of a New Family of Nanoscale Clusters Based on (Mo2 O2 S2 )2

The preparation and characterization of a new family of four polyoxothiometalate (POTM) clusters are reported, with varying size and complexity, based upon the dimeric [Mo2 O2 S2 (H2 O)6 ]2+ cation with the general formula (NMe4 )a Kb [(Mo2 O2 S2 )c (TeO4 )d (C4 O4 )e (OH)f ] where a,b,c,d,e,f={1,7,14,2,4,10}=1, {Mo28 Te2 }; {2,26,36,12,10,48}=2, {Mo72 Te12 }; {0,11,15,3,3,21}=3, {Mo30 Te3 }; {2,6,12,2,4,16}=4, {Mo24 Te2 }. The incorporation of tellurite anions allowed the fine tuning of the templating and bridging of the available building blocks, leading to new topologies of increased complexity. The structural diversity of this family of compounds ranges from the highly symmetrical cross-shaped {Mo24 Te2 } to the stacked ring structure of {Mo72 Te12 }, which is the largest tellurium-containing POTM cluster reported so far. Also a detailed experimental analysis revealed that the pH isolation window extends from acidic to basic values. ESI-MS analyses not only confirmed the stability of this family in solution but also revealed the stability of the observed virtual building blocks.

Wheel-to-rhomboid isomerization as well as nitrene transfer catalysis of ruthenium-thiolate wheels

A unique ruthenium-thiolate molecular rhomboid ([square tilted open])-[Ru(SAr)₂(CO)₂]₈, which consists of eight octahedra linked by alternate face- and vertex-sharing, was produced by isomerization of the molecular wheel (○)-[Ru(SAr)₂(CO)₂]₈ at elevated temperature. The use of a (○)-[Ru(SAr)₂(CO)₂]₆ wheel for catalytic aziridination of alkenes via nitrene transfer is also described.

Syntheses, structural diversities and characterization of a series of coordination polymers with two isomeric oxadiazol-pyridine ligands

In this work two positional-isomeric oxadiazol-pyridine ligands 3-(5-methyl-1,3,4-oxadiazol-2-yl)pyridine (L₁) and 4-(5-methyl-1,3,4-oxadiazol-2-yl)pyridine (L₂) have been designed and synthesized.

Controlled assembly of hybrid architectures based on carboxylic acid ligands and [(O3PCH2PO3)Mo6O22]12−

Polyanion 2a with a reverse symmetrical “crown-type” structure is composed of two {(HO₃PCH₂PO₃)Mo₆O₁₈(CH₃CO₂)₂} subunits and a linking bridge.

Self assembly of carboxylate/alcoholate functionalized ring-shape phosphomolybdates

Carboxylate and alcoholate ligands were covalently attached to a [HPMo₆O₂₁]²⁻ cluster to generate a series of inorganic–organic hybrid phosphomolybdates.

Controlled assembly of inorganic-organic frameworks based on [SeMo6O21]4- polyanion

The chemical system based on [SeMo6O21](4-) polyanion and carboxylate ligand has been investigated. According to the inherent nature of organic groups, a series of selenomolybdates with three architectures have been isolated through rational and deliberate synthetic routes by stereospecific addition of different carboxylic acids. Such an approach is potentially interesting for {SeMo6} cluster, which exhibits a high surface nucleophilicity and is capable of being functionalized by covalently bound carboxylic acids. Investigation of the assemblies reveals that carboxylic acids have good flexibility and conformational freedom, representing the powerful chemical tools to control the polyanion assembly processes.

A flow-system array for the discovery and scale up of inorganic clusters

The batch synthesis of inorganic clusters can be both time consuming and limited by a lack of reproducibility. Flow-system approaches, now common in organic synthesis, have not been utilized widely for the synthesis of clusters. Herein we combine an automated flow process with multiple batch crystallizations for the screening and scale up of syntheses of polyoxometalates and manganese-based single-molecule magnets. Scale up of the synthesis of these architectures was achieved by programming a multiple-pump reactor system to vary reaction conditions sequentially, and thus explore a larger parameter space in a shorter time than conventionally possible. Also, the potential for using the array as a discovery tool is demonstrated. Successful conditions for product isolation were identified easily from the array of reactions, and a direct route to 'scale up' was then immediately available simply by continuous application of these flow conditions. In all cases, large quantities of phase-pure material were obtained and the time taken for the discovery, repetition and scale up decreased.

Dynamic properties of a hexadecamolybdenum wheel: studies in solution and density functional theory calculations

Variable temperature (1)H NMR studies of the host-guest complex [Mo(16)O(16)S(16)(OH)(16)(H(2)O)(4)(PDA)(2)](4-) (1 ; PDA(2-) = phenylenediacetate) previously carried out in D(2)O have revealed a complex behavior in solution, involving a gliding motion of both parallel phenyl rings of the PDA(2-) ligands. In the present work, we present new NMR spectra carried out in the aprotic solvent CD(3)CN, which allow the observation of the proton signals associated with the bridging hydroxo groups of the inorganic host. The new spectra provide detailed information about the concerted reorganization of the guest components, that is, PDA(2-) and water molecules. The existence of an equilibrium between two distinct isomers differing in the linking mode between the inorganic host and the two equivalent PDA(2-) ligands is evidenced. This equilibrium appears strongly dependent upon the temperature, leading to a complete inversion of the distribution between 300 and 226 K. The thermodynamic data related to the isomerization reaction have been determined (Delta(r)H = -50.5 kJ mol(-1) and Delta(r)S = -215 J mol(-1) K(-1)). Furthermore, at low temperature, one of the isomers exists in two conformations, only differing in the H-bond network involving the inner water molecules. Density functional theory calculations were carried out to push ahead the interpretations obtained from experiment, identify the isomers of 1, and specify the role and the positions of the guest water molecules. Among the various structures that have been calculated for 1, three fall in a narrow energy range and should correspond to the species characterized by variable-temperature (1)H NMR experiments in CD(3)CN. Finally, this study shows how the internal disposition of the ligands affects the ellipticity of the Mo(16) ring which varies from one isomer to the other in the 0.73-1 range and highlights solvation of the ring as one of the key parameters for the conformational design of these flexible host-guest systems.

High-Dimensional Assembly Depending on Polyoxoanion Templates, Metal Ion Coordination Geometries, and a Flexible Bis(imidazole) Ligand

By introducing the flexible 1,1'-(1,4-butanediyl)bis(imidazole) (bbi) ligand into the polyoxovanadate system, five novel polyoxoanion-templated architectures based on [As(8)V(14)O(42)](4-) and [V(16)O(38)Cl](6-) building blocks were obtained: [M(bbi)(2)](2)[As(8)V(14)O(42)(H(2)O)] [M = Co (1), Ni (2), and Zn (3)], [Cu(bbi)](4)[As(8)V(14)O(42)(H(2)O)] (4), and [Cu(bbi)](6)[V(16)O(38)Cl] (5). Compounds 1-3 are isostructural, and they exhibit a binodal (4,6)-connected 2D structure with Schläfli symbol (3(4) x 4(2))(3(4) x 4(4) x 5(4) x 6(3))(2), in which the polyoxoanion induces a closed four-membered circuit of M(4)(bbi)(4). Compound 4 exhibits an interesting 3D framework constructed from tetradentate [As(8)V(14)O(42)](4-) cluster anions and cationic ladderlike double chains. There exists a bigger M(8)(bbi)(6)O(2) circuit in 4. The 3D extended structure of 5 is composed of heptadentate [V(16)O(38)Cl](6-) anions and flexural cationic chains; the latter consists of six Cu(bbi) segments arranged alternately. It presents the largest 24-membered circuit of M(24)(bbi)(24) so far observed made of bbi molecules and transition-metal cations. Investigation of their structural relations shows the important template role of the polyoxoanions and the synergetic interactions among the polyoxoanions, transition-metal ions, and flexible ligand in the assembly process. The magnetic properties of compounds 1-3 were also studied.

Structure, Formation, and Dynamics of Mo12 and Mo16 Oxothiomolybdenum Rings Containing Terephtalate Derivatives

The influence of rigid or semirigid dicarboxylate anions, terephtalate (TerP(2-)), isophtalate (IsoP(2-)), and phenylenediacetate (PDA(2-)) on the self-condensation process of the [Mo(2)O(2)S(2)](2+) dioxothio cation has been investigated. Three new molybdenum rings, [Mo(12)O(12)S(12)(OH)(12)(TerP)](2-) ([Mo(12)TerP](2-)), [Mo(16)O(16)S(16)(OH)(16)(H(2)O)(4)(PDA)(2)](4-) ([Mo(16)(PDA)(2)](4-)), and [Mo(16)O(16)S(16)(OH)(16)(H(2)O)(2)(IsoP)(2)](4-) ([Mo(16)(IsoP)(2)](4-)) have been isolated and unambiguously characterized in the solid state by single-crystal X-ray studies and in solution by various NMR methods and especially by diffusion-correlated NMR ((1)H DOSY) spectroscopy, which was shown to be a powerful tool for the characterization and speciation of templated molybdenum ring systems in solution. Characterization by FT-IR and elemental analysis are also reported. The dynamic and thermodynamic properties of both the sixteen-membered rings were studied in aqueous medium. Specific and distinct behaviors were revealed for each system. The IsoP(2-)/[Mo(2)O(2)S(2)](2+) system gave rise to equilibrium, involving mono-templated [Mo(12)IsoP](2-) and bis-templated [Mo(16)(IsoP)(2)](4-) ions. Thermodynamic parameters have been determined and showed that the driving-force for the formation of the [Mo(16)(IsoP)(2)](4-) is entropically governed. However, whatever the conditions (temperature, proportion of reactants), the PDA(2-)/[Mo(2)O(2)S(2)](2+) system led only to a single compound, the [Mo(16)(PDA)(2)](4-) ion. The latter exhibits dynamic behavior, consistent with the gliding of both the stacked aromatic groups. Stability and dynamics of both Mo(16) rings was related to weak hydrophobic or pi-pi stacking inter-template interactions and inner hydrogen-bond network occurring within the [Mo(16)(IsoP)(2)](4-) and [Mo(16)(PDA)(2)](4-) ions.

Syntheses and Characterizations of Palladium-Based Molecular Triangle/Square Compounds and Hybrid Composites with Polyoxometalates

Syntheses and characterizations of a Pd-based molecular triangle and square and hybrid composites with polyoxometalates are examined. The equilibrium between the Pd-based molecular triangle [(en*)Pd(4,4'-bpy)]3(NO3)6 and square [(en*)Pd(4,4'-bpy)]4(NO3)8 largely depends on the solvents, and both compounds have successfully been isolated: [(en*)Pd(4,4'-bpy)]3(NO3)6.3.5DMSO, monoclinic Cc (No. 9), a = 19.8210(2) A, b = 34.3667(5) A, c = 27.5484(4) A, beta = 89.9420(10) degrees , V = 18765.5(4) A3; [(en*)Pd(4,4'-bpy)]4(NO3)8, monoclinic C2/c (No. 15), a = 45.6921(16) A, b = 8.7721(8) A, c = 36.719(3) A, beta = 126.509(2) degrees , V = 11829.4(14) A3. The reactions of the Pd-based molecular triangle/square with [W6O19]2-, [W10O32]4-, and [alpha-SiW12O40]4- form [[(en*)Pd(4,4'-bpy)]4[ supersetW6O19]][W6O19]3, [[(en*)Pd(4,4'-bpy)]4[ supersetW6O19]](NO3)6, [[(en*)Pd(4,4'-bpy)]4[ supersetW10O32]][W10O32], [(en*)Pd(4,4'-bpy)]4[W10O32]2, and [(en*)Pd(4,4'-bpy)]4[alpha-SiW12O40]2. The molecular square does not encapsulate the largest [alpha-SiW12O40]4-, but it does encapsulate [W6O19]2- and [W10O32]4-. The isolation of [W6O19]2- and [alpha-SiW12O40]4- from the mixture by use of the molecular square is possible by utilizing the quite different solubility of [[(en*)Pd(4,4'-bpy)]4[ supersetW6O19]](NO3)6 and [(en*)Pd(4,4'-bpy)]4[alpha-SiW12O40]2 formed in DMSO. The size-selective encapsulation property of supramolecules may open the new way to rationalize isolation methods of the useful polyoxometalates.

Polyoxometalate clusters, nanostructures and materials: From self assembly to designer materials and devices

Polyoxometalates represent a diverse range of molecular clusters with an almost unmatched range of physical properties and the ability to form structures that can bridge several length scales. The new building block principles that have been discovered are beginning to allow the design of complex clusters with desired properties and structures and several structural types and novel physical properties are examined. In this critical review the synthetic and design approaches to the many polyoxometalate cluster types are presented encompassing all the sub-types of polyoxometalates including, isopolyoxometalates, heteropolyoxometalates, and reduced molybdenum blue systems. As well as the fundamental structure and bonding aspects, the final section is devoted to discussing these clusters in the context of contemporary and emerging interdisciplinary interests from areas as diverse as anti-viral agents, biological ion transport models, and materials science.

Host–guest adaptability within oxothiomolybdenum wheels: structures, studies in solution and DFT calculations

The formation of host-guest cyclic architectures, built up through the self-condensation process of [Mo(2)O(2)S(2)](2+) oxothiocations around linear dicarboxylate ions such as adipate (Adip(2-)), suberate (Sub(2-)) and azelaate (Azel(2-)) anions is reported. The complexes [Mo(12)Adip](2-), [Mo(12)Sub](2-) and [Mo(14)Azel](2-) have been characterized in the solid state by X-ray diffraction and in solution by (1)H NMR in different solvents (D(2)O, DMF, DMSO and CD(3)CN). The host-guest dynamics appear to be dependent on the nature of the system and are mainly governed by mutual adaptability between the host and the guest. (1)H NMR DOSY experiments show systematic differences, either positive or negative between the experimental and calculated molecular weights which appear to be correlated with the charge of the anion. The relative stabilities of the twelve-membered rings containing the Adip(2-), Pim(2-) (pimelate) or Sub(2-) anions were determined experimentally and decrease according to the order [Mo(12)Adip](2-) > [Mo(12)Pim](2-) > [Mo(12)Sub](2-). The host-guest adaptability depends on the length of the carbon chain and gives rise to selective encapsulation processes. Finally, theoretical DFT investigations in the gas phase yielded conformations whose symmetry and geometrical parameters proved consistent with X-ray structures and (1)H NMR spectra recorded in DMSO or DMF. Energy calculation highlights the high flexibility of the ring showing that only 3.1 kJ mol(-1) accompanies the conformational change from circular to elliptical. The host-guest bond energy (Delta E) calculated for the Mo(12)-based clusters is consistent with the experimental stability scale, major variations being due to some constraints undergone by the central alkyl chain.