Optoelectronic properties of octahedral molybdenum cluster-based materials at a single crystal level

Octahedral molybdenum (Mo6) clusters constitute suitable building blocks for the design of promising single crystal materials in the field of optoelectronics. Here, we prepared single crystals composed of hydroxo Mo6X8 (X = Br, Cl) cluster complexes interconnected by H-bonding interactions with water molecules and protons. The optoelectronic responses and the absorption and emission spectra of these cluster-based single crystals were acquired upon light irradiation, and they show dependency on the nature of the halogens, with the brominated cluster being the most conductive. A fast photoelectrical response was recorded and it showed remarkable stability after multiple illumination on/off cycles. The results obtained provide relevant information for the development of photonic and optoelectronic devices, sensors and photocatalysts.

Photoinduced electron transfer between a noble-metal-free [Mo6I8Cl6]2- cluster and polyoxometalates

Evidence for photoinduced intermolecular electron transfer from the excited state of the [Mo6I8Cl6]2- electron-rich cluster to polyoxometalates (POMs) is reported. We demonstrate that the global charge density of POMs affects the efficiency of electron transfer. This work paves the way for the rational design of photocatalytic systems using cluster-based complexes as robust noble-metal-free photosensitizers.

Game of Crowns: Na+ Is Coming! Red NIR-Emissive Hybrid Liquid Crystals Containing Discotic Crown Ethers and Na2Mo6X8iCl6 (Xi = Cl or Br)

Molecular or supramolecular materials that can self-organize into columns such as discotic liquid crystals are of interest for several applications in the field of optoelectronics. We show in this work that red near-infrared (NIR)-emissive metal cluster compounds of general formula Na2Mo6X8iCl6 (Xi = Cl or Br) can be readily complexed with discotic liquid crystals containing a crown ether. Three cavity sizes have been tested with crown ethers bearing 4, 5, or 6 oxygen atoms. In all cases, 1:1 complexes were formed, thanks to the well-known supramolecular interactions existing between the Na+ cations of the metal cluster salt and the crown ether derivatives. All obtained hybrids are homogeneous, emit in the red NIR region, and show liquid crystalline properties on a wider temperature range than their precursors. Charge transport properties have been investigated by using a space charge limited current device. Obtained results demonstrate that metal cluster compounds can enhance the charge carrier mobility by 5 orders of magnitude compared to the native discotic organic ligands. Considering that the presented organic crown ether derivatives are not the best candidates to design optoelectronic devices because of their inherently low conductivity, but that similar compounds were developed to design proton conductive porous framework, our results open promising perspectives for the use of metal cluster compounds in devices dedicated to such a field.

Supramolecular Host–Guest Assemblies of [M6Cl14]2–, M = Mo, W, Clusters with γ-Cyclodextrin for the Development of CLUSPOMs

Host–guest assemblies open up opportunities for developing novel functional CLUSPOM multicomponent systems based on transition metal clusters (CLUS), polyoxometalates (POMs) and macrocyclic organic ligands. In water–ethanol solution γ-cyclodextrin (γ-CD) interacts with halide metal clusters [M6Cl14]2– (M = Mo, W) to form sandwich-type structures. The supramolecular association between the clusters and CDs, however, remains weak in solution, and the interactions are not strong enough to prevent the hydrolysis of the inorganic guest. Although analysis of the resulting crystal structures reveals inclusion complexation, 1H NMR experiments in solution show no specific affinity between the two components. The luminescent properties of the host–guest compounds in comparison with the initial cluster complexes are also studied to evaluate the influence of CD.

Gas Phase Reactivity of [Mo6X14]2- Dianions (X = Cl - I)

We investigate collision-induced dissociation (CID) of [Mo₆X₁₄]^2- (X = Cl, Br, I) and the reactivity of fragment ions of these precursors with background gases. Ion mobility measurements and theoretical calculations provide structural information for some of the observed ions. Sequential losses of MoX₂ units dominate the dissociation pathways of [Mo₆Cl₁₄]^2-. Meanwhile, loss of X radicals is the main channel for X = Br and I. Ion mobility measurements and computational investigations indicate minor structural changes in the octahedral Mo₆ unit for [Mo₆I_m]^- (m = 6-13) fragments. We observe that mass spectra obtained using CID substantially vary among mass spectrometers: Specifically, ions with molecular formula [Mo₆X_m(O₂)_n]^- (X = Br and I) are observed as dominant species produced through reactions with O₂ in several mass spectrometers, but also adduct free fragment ions were observed in other instruments, depending on the background conditions. Ion-trap fragmentation combined with theoretical investigations indicates that spontaneous losses of X radicals occur upon binding of O₂ to [Mo₆I_m]^- fragments (m ≤ 12). Theoretical investigations indicate that both oxygen atoms are bound to the vacant sites of the Mo₆ units. This study opens up a new vista to generate and study a large variety of hexanuclear Mo₆X_m(O₂)_n anions.

Flexible and Transparent Luminescent Cellulose-Transition Metal Cluster Composites

Red-NIR luminescent polymers are principally obtained from petroleum-based derivatives in which emitters, usually a critical raw material such as rare-earth or platinum group metal ions, are embedded. Considering the strong ecological impact of their synthesis and the major risk of fossil fuel energy shortage, there is an urgent need to find alternatives. We describe a luminescent nanocomposite based on red-NIR phosphorescent molybdenum nanoclusters, namely Cs₂Mo₆I₈(OCOC₂F₅)₆, embedded in an eco-friendly cellulose biopolymer matrix that is obtained by a simple solvent casting technique. While homogeneity is kept up to 20 wt% of cluster complex doping, annealing hybrids leads to a large increase of their emission efficiency, as demonstrated by quantum yield measurements.

Enhanced NH3 Sensing Performance of Mo Cluster-MoS2 Nanocomposite Thin Films via the Sulfurization of Mo6 Cluster Iodides Precursor

The high-performance defect-rich MoS₂ dominated by sulfur vacancies as well as Mo-rich environments have been extensively studied in many fields, such as nitrogen reduction reactions, hydrogen evolution reactions, as well as sensing devices for NH₃, which are attributed to the under-coordinated Mo atoms playing a significant role as catalytic sites in the defect area. In this study, the Mo cluster-MoS₂ composite was creatively synthesized through a one-step sulfurization process via H₂/H₂S gas flow. The Mo₆ cluster iodides (MIs) coated on the fluorine-doped tin oxide (FTO) glass substrate via the electrophoretic deposition method (i.e., MI@FTO) were used as a precursor to form a thin-film nanocomposite. Investigations into the structure, reaction mechanism, and NH₃ gas sensing performance were carried out in detail. The results indicated that during the gas flowing, the decomposed Mo₆ cluster iodides played the role of template and precursor, forming complicated Mo cluster compounds and eventually producing MoS₂. These Mo cluster-MoS₂ thin-film nanocomposites were fabricated and applied as gas sensors for the first time. It turns out that after the sulfurization process, the response of MI@FTO for NH₃ gas increased three times while showing conversion from p-type to n-type semiconductor, which enhances their possibilities for future device applications.

From Solid-State Cluster Compounds to Functional PMMA-Based Composites with UV and NIR Blocking Properties, and Tuned Hues

New nanocomposite materials with UV-NIR blocking properties and hues ranging from green to brown were prepared by integrating inorganic tantalum octahedral cluster building blocks prepared via solid-state chemistry in a PMMA matrix. After the synthesis by the solid-state chemical reaction of the K₄[{Ta₆Brⁱ₁₂}Br^a₆] ternary halide, built-up from [{Ta₆Brⁱ₁₂}Br^a₆]^4- anionic building blocks, and potassium cations, the potassium cations were replaced by functional organic cations (Kat⁺) bearing a methacrylate function. The resulting intermediate, (Kat)₂[{Ta₆Brⁱ₁₂}Br^a₆], was then incorporated homogeneously by copolymerization with MMA into transparent PMMA matrices to form a brown transparent hybrid composite Ta@PMMA_brown. The color of the composites was tuned by controlling the charge and consequently the oxidation state of the cluster building block. Ta@PMMA_green was obtained through the two-electron reduction of the [{Ta₆Brⁱ₁₂}Br^a₆]^2- building blocks from Ta@PMMA_brown in solution. Indeed, the control of the oxidation state of the Ta₆ cluster inorganic building blocks occurred inside the copolymer, which not only allowed the tuning of the optical properties of the composite in the visible region but also allowed the tuning of its UV and NIR blocking properties.

A Neutral Heteroleptic Molybdenum Cluster trans-[{Mo6I8}(py)2I4]

Despite that the chemistry of octahedral cluster complexes has been actively developed recently, there are still a lot of unexplored areas. For example, to date, only a few halide M6-clusters with N-heterocycles are known. Here, we obtained an apically heteroleptic octahedral iodide molybdenum cluster complex with pyridine ligands—trans-[{Mo6I8}(py)2I4] by the direct substitution of iodide apical ligands of [{Mo6I8}I6]2– in a pyridine solution. The compound co-crystalized with a monosubstituted form [{Mo6I8}(py)I5]– in the ratio of 1:4, and thus, can be described by the formula (pyH)0.2[{Mo6I8}(py)1.8I4.2]·1.8py. The composition was studied using XRPD, elemental analyses, and 1H-NMR and IR spectroscopies. According to the absorption and luminescence data, the partial substitution of apical ligands weakly affects optical properties.

Oxygen-Sensitive Photo- and Radioluminescent Polyurethane Nanoparticles Modified with Octahedral Iodide Tungsten Clusters

The development of cancer treatment techniques able to cure tumors located deep in the body is an urgent task for scientists and physicians. One of the most promising methods is X-ray-induced photodynamic therapy (X-PDT), since X-rays have unlimited penetration through tissues. In this work, octahedral iodide tungsten clusters, combining the properties of a scintillator and photosensitizer, are considered as a key component of nanosized polyurethane (pU) particles in the production of materials promising for X-PDT. Cluster-containing pU nanoparticles obtained here demonstrate bright photo- and X-ray-induced emission in both solid and water dispersion, great efficiency in the generation of singlet oxygen, and high sensitivity regarding photoluminescence intensity in relation to oxygen concentration. Additionally, incorporation of the cluster complex into the pU matrix greatly increases its stability against hydrolysis in water and under X-rays.

A review on functional nanoarchitectonics nanocomposites based on octahedral metal atom clusters (Nb6, Mo6, Ta6, W6, Re6): inorganic 0D and 2D powders and films

This review is dedicated to various functional nanoarchitectonic nanocomposites based on molecular octahedral metal atom clusters (Nb₆, Mo₆, Ta₆, W₆, Re₆). Powder and film nanocomposites with two-dimensional, one-dimensional and zero-dimensional morphologies are presented, as well as film matrices from organic polymers to inorganic layered oxides. The high potential and synergetic effects of these nanocomposites for biotechnology applications, photovoltaic, solar control, catalytic, photonic and sensor applications are demonstrated. This review also provides a basic level of understanding how nanocomposites are characterized and processed using different techniques and methods. The main objective of this review would be to provide guiding significance for the design of new high-performance nanocomposites based on transition metal atom clusters.

Synthesis of novel hexamolybdenum cluster-functionalized copper hydroxide nanocomposites and its catalytic activity for organic molecule degradation

A novel heterogeneous catalytic nanomaterial based on a molybdenum cluster-based halide (MC) and a single-layered copper hydroxynitrate (CHN) was first prepared by colloidal processing under ambient conditions. The results of the elemental composition and crystalline pattern indicated that CHN was comprehensively synthesized with the support of the MC compound. The absorbing characteristic in the ultraviolet and near-infrared regions was promoted by both of the ingredients. The proper chemical interaction between the materials is a crucial reason to modify the structure of the MCs and only a small decrease in the magnetic susceptibility of CHN. The heterogeneous catalytic activity of the obtained MC@CHN material was found to have a high efficiency and excellent reuse when it is activated by hydrogen peroxide (H₂O₂) for the degrading reaction of the organic pollutant at room temperature. A reasonable catalytic mechanism was proposed to explain the distinct role of the copper compound, Mo₆ compound, and H₂O₂ in the production of the radical hydroxyl ion. This novel nanomaterial will be an environmentally promising candidate for dye removal.

Optical property trends in a family of {Mo6I8} aquahydroxo complexes

Luminescence is one of the key properties of octahedral molybdenum cluster complexes and the basis for most areas of their possible practical applications. Nevertheless, the factors affecting the optical properties of the clusters are insufficiently studied and establishing them will allow us to tune both absorption and emission more precisely. In this work, we obtained two new cationic [{Mo6I8}(H2O)4(OH)2](An)2·nH2O (An = NO3-, n = 3; An = OTs-, n = 2, OTs- - p-toluenesulfonate), and two neutral [{Mo6I8}(H2O)2(OH)4]·nH2O (n = 2, 12) aquahydroxo complexes. Due to the similar compositions of the clusters obtained, we determined the influence of crystal packing and ligand environment on the absorption and photo- and radioluminescence properties. Thus, the four-component nature of the cluster emission was established using Gaussian deconvolution of the photoluminescence spectra. It was shown that the influence of both ligand type and crystal density decreases when moving to the red (lower-energy) part of the spectra, with only the first two components located in the blue (higher-energy) part of the spectra being strongly affected. Also, it was found that protonation of two hydroxo ligands leads to a significant decrease in absorption in the visible spectral region.

Near-Infrared Luminescence in Trinuclear Mixed-Metal Chalcogenolate Complexes of the Types [M2Ti(EPh)6(PPh3)2] (M = Cu, Ag; E = S, Se) and [Na(thf)3]2[Ti(SPh)6]

The optical properties of four new trinuclear chalcogenolato bridged metal complexes [Ag₂Ti(SPh)₆(PPh₃)₂], [Na(thf)₃]₂[Ti(SPh)₆], [Cu₂Ti(SePh)₆(PPh₃)₂], and [Ag₂Ti(SePh)₆(PPh₃)₂] have been investigated by absorption and photoluminescence spectroscopy as well as time-dependent density functional theory (TDDFT) calculations and compared to the results published recently for [Cu₂Ti(SPh)₆(PPh₃)₂]. All of these compounds are distinguished by efficient near-infrared luminescence at ∼880-1200 nm in the solid state at low temperatures, which remains quite intense for the copper-titanium complexes at ambient temperature with PL quantum yields of 9.5 and 4.8% at λ_PL = 1090 and 1240 nm for [Cu₂Ti(EPh)₆(PPh₃)₂], E = S, Se, respectively. According to the calculations, a peculiar feature of the lowest-energy electronic transitions in these complexes is their high localization on the metal and chalcogen atoms, with negligible contributions of the "external" ligand groups. Correspondingly, the type of atoms in the M₂TiE₆ (M = Cu, Ag, Na) core structure determines optical properties such as the absorption and emission wavelengths and PL lifetime.

Cyanide Complexes Based on {Mo6I8}4+ and {W6I8}4+ Cluster Cores

Compounds based on new cyanide cluster anions [{Mo₆I₈}(CN)₆]^2–, trans-[{Mo₆I₈}(CN)₄(MeO)₂]^2– and trans-[{W₆I₈}(CN)₂(MeO)₄]²⁻ were synthesized using mechanochemical or solvothermal synthesis. The crystal and electronic structures as well as spectroscopic properties of the anions were investigated. It was found that the new compounds exhibit red luminescence upon excitation by UV light in the solid state and solutions, as other cluster complexes based on {Mo₆I₈}⁴⁺ and {W₆I₈}⁴⁺ cores do. The compounds can be recrystallized from aqueous methanol solutions; besides this, it was shown using NMR and UV-Vis spectroscopy that anions did not undergo hydrolysis in the solutions for a long time. These facts indicate that hydrolytic stabilization of {Mo₆I₈} and {W₆I₈} cluster cores can be achieved by coordination of cyanide ligands.

Zn-Al Layered Double Hydroxide Film Functionalized by a Luminescent Octahedral Molybdenum Cluster: Ultraviolet-Visible Photoconductivity Response

A novel UV-Vis photodetector consisting of an octahedral molybdenum cluster-functionalized Zn₂Al layered double hydroxide (LDH) has been successfully synthesized by co-precipitation and delamination methods under ambient conditions. The electrophoretic deposition process has been used as a low-cost, fast, and effective method to fabricate thin and transparent nanocomposite films containing a dense and regular layered structure. The study provided evidence that the presence of the Mo₆ cluster units between the LDH does not affect the ionic conduction mechanism of the LDH, which linearly depends on the relative humidity and temperature. Moreover, the photocurrent response is remarkably extended to the visible domain. The reproducibility and stabilization of the photocurrent response caused by the Mo₆ cluster-functionalized LDH have been verified upon light excitation at 540 nm. Additionally, it was demonstrated that the films show advantageously strong adherence properties for application requirements.

Octahedral Molybdenum Cluster Complexes with Optimized Properties for Photodynamic Applications

Two new octahedral molybdenum cluster complexes act as an efficient singlet oxygen supplier in the context of the photodynamic therapy of cancer cells under blue-light irradiation. These complexes integrate the {Mo₆I₈}⁴⁺ core with 4'-carboxybenzo-15-crown-5 or cholate apical ligands and were characterized by ¹H NMR, HR ESI-MS, and CHN elemental analysis. Both complexes display high quantum yields of luminescence and singlet oxygen formation in aqueous media associated with a suitable stability against hydrolysis. They are internalized into lysosomes of HeLa cells with no dark toxicity at pharmacologically relevant concentrations and have a strong phototoxic effect under blue-light irradiation, even in the presence of fetal bovine serum. The last feature is essential for further translation to in vivo experiments. Overall, these complexes are attractive molecular photosensitizers toward photodynamic applications.

Terminal Ligand (L) Effects on Zero-Magnetic-Field Splitting in the Excited Triplet States of [{Mo6Br8}L6]2- (L = Aromatic Carboxylates)

We report the emission properties of the octahedral hexamolybdenum(II) bromide-core ({Mo₆Br₈}⁴⁺) clusters having a series of terminal aromatic carboxylate ligands (RCOO), [{Mo₆Br₈}(RCOO)₆]^2-, in solution and crystalline phases. The acid dissociation constant of RCOOH (p K_a(L)) was shown to govern the redox and emission properties of the clusters. Temperature ( T)-controlled emission experiments (3-300 K) demonstrated that the clusters showed large T-dependent emission energies (ν̃^em) and lifetimes (τ^em) because of zero-magnetic-field splitting in the emissive excited triplet (T₁) states. The spin sublevel (Φ _n, n = 1-4) model in the T₁ state of the cluster explained very well the T-dependent emission characteristics (ν̃^em and τ^em), irrespective of the clusters studied. Furthermore, we revealed that the energy difference between the lowest-energy (Φ₁) and energetically upper-lying third (Φ₃) or fourth spin sublevels (Φ₄), Δ E₁₃ or Δ E₁₄, respectively, correlated very well with p K_a( L). The results are discussed in terms of the variation of the effective nuclear charge of the Mo metal center(s) in [{Mo₆Br₈}(RCOO)₆]^2- with that of p K_a(L).

Zero-Magnetic-Field Splitting in the Excited Triplet States of Octahedral Hexanuclear Molybdenum(II) Clusters: [{Mo6X8}Y6]2- (X, Y = Cl, Br, I)

The temperature ( T) dependences of the emissions from the tetra- n-butylammonium salts of [{Mo₆X₈}Y₆]^2- (X, Y = Cl, Br, and I) in optically transparent polyethylene glycol dimethacrylate matrixes were studied in the T range of 3-300 K. [{Mo₆Cl₈}Y₆]^2-, [{Mo₆Br₈}Y₆]^2-, and [{Mo₆I₈}I₆]^2- showed the T-dependent emission characteristics similar to those of other hexanuclear Mo(II), Re(III), and W(II) clusters reported previously, while [{Mo₆I₈}Br₆]^2- and [{Mo₆I₈}Cl₆]^2- exhibited the emission properties different from those of other [{Mo₆X₈}Y₆]^2- clusters. The photophysical behavior of these clusters was explained by the excited triplet state spin-sublevel ( Φ_n, n = 1-4) model irrespective of the nature of X and Y. The zero-magnetic-field splitting energies between the lowest energy (Φ₁) and the higher energy spin sublevels (Φ₄ or Φ₃) caused by the first- or second-order spin-orbit coupling, Δ E₁₄ or Δ E₁₃, were evaluated to be 620-870 or 50-99 cm^-1, respectively. We found the linear correlation between the Δ E₁₄ or Δ E₁₃ value and the fourth power of the atomic number ( Z) of the inner halide X: Δ E₁₄ or Δ E₁₃ vs { Z(X)}⁴ (correlation coefficient: cc = ∼ 0.999). Furthermore, we also found the correlation between Δ E₁₄ or Δ E₁₃ and the ⁹⁵Mo NMR chemical shift of the cluster. These findings gave very important insight into the spin-orbit coupling and zero-magnetic-field splitting in the excited triplet states of transition metal complexes.

Luminescent liquid crystalline hybrid materials by embedding octahedral molybdenum cluster anions with soft organic shells derived from tribenzo[18]crown-6

Crown ethers and their derivatives are versatile building blocks for the design of supramolecular materials. They can be functionalized at will and are well known for their abilities to complex with alkali cations. Here, we show that emissive lanthanide free hybrid materials can be generated by using such building blocks. The organic tribenzo[18]crown-6 central core was functionalized via six-fold Suzuki cross-coupling as a key reaction with three o-terphenyl units which could be converted into their corresponding triphenylenes by the Scholl reaction, leading to novel liquid-crystalline columnar materials. Selected tribenzo[18]crown-6 o-terphenyls could interact with emissive ternary metal cluster compound salts to generate hybrid materials combining the properties of both moieties. Due to synergistic effects and despite the anisometry of the cluster compounds, individual properties such as liquid-crystalline phase stability of the organic part and emission abilities of its inorganic counter-part are enhanced in the hybrid compounds.

Insulated Interlayer for Efficient and Photostable Electron-Transport-Layer-Free Perovskite Solar Cells

Currently, the most efficient perovskite solar cells (PSCs) mainly use planar and mesoporous titanium dioxide (TiO₂) as an electron-transport layer (ETL). However, because of its intrinsic photocatalytic properties, TiO₂ can decompose perovskite absorber and lead to poor stability under solar illumination (ultraviolet light). Herein, a simplified architectural ETL-free PSC with enhanced efficiency and outstanding photostability is produced by the facile deposition of a bathocuproine (BCP) interlayer. Power conversion efficiency of the ETL-free PSC improves from 15.56 to 19.07% after inserting the BCP layer, which is the highest efficiency reported for PSCs involving an ETL-free architecture, versus 19.03% for the n-i-p full device using TiO₂ as an ETL. The BCP interlayer has been demonstrated to have several positive effects on the photovoltaic performances of devices, such as "modulation doping" of the perovskite layer, modification of FTO surface work function, and enhancing the charge-transfer efficiency between FTO and perovskite. Moreover, the BCP-based ETL-free devices exhibit outstanding photostability: the unencapsulated BCP-based ETL-free PSCs retain over 90% of their initial efficiencies after 1000 h of storage in air and maintain 92.2% after 450 h of exposure to full solar irradiation (without a UV filter), compared to only 14.1% in the n-i-p full cells under the same condition.

Optical properties of trinuclear metal chalcogenolate complexes - room temperature NIR fluorescence in [Cu2Ti(SPh)6(PPh3)2]

The optical properties of four isostructural trinuclear chalcogenolato bridged metal complexes [Cu₂Sn(SPh)₆(PPh₃)₂], [Cu₂Sn(SePh)₆(PPh₃)₂], [Ag₂Sn(SPh)₆(PPh₃)₂] and [Cu₂Ti(SPh)₆(PPh₃)₂] have been investigated by absorption and photoluminescence spectroscopy and time-dependent density functional theory (TDDFT) calculations. All copper-tin compounds demonstrate near-infrared (NIR) phosphorescence at ∼900-1100 nm in the solid state at low temperature, which is nearly absent at ambient temperature. Stokes shifts of these emissions are found to be unusually large with values of about 1.5 eV. The copper-titanium complex [Cu₂Ti(SPh)₆(PPh₃)₂] also shows luminescence in the NIR at 1090 nm but with a much faster decay (τ ∼ 10 ns at 150 K) and a much smaller Stokes shift (ca. 0.3 eV). Even at 295 K this fluorescence is found to comprise a quantum yield as high as 9.5%. The experimental electronic absorption spectra well correspond to the spectra simulated from the calculated singlet transitions. In line with the large Stokes shifts of the emission spectra the calculations reveal for the copper-tin complexes strong structural relaxation of the excited triplet states whereas those effects are found to be much smaller in the case of the copper-titanium complex.

The Ouzo effect to selectively assemble molybdenum clusters into nanomarbles or nanocapsules with increased HER activity

Molybdenum clusters assemble spontaneously into nanocapsules or nanomarbles depending on their solubility in a water/THF mixture.

Thermal equilibration between excited states or solvent effects: unveiling the origins of anomalous emissions in heteroleptic Ru(ii) complexes

Thermal equilibration between excited states or solvent effects: unveiling the origins of anti-Kasha emissions in heteroleptic [Ru(H)(CO)(N^N)(tpp)₂]⁺ complexes.

Low dimensional solids based on Mo6 cluster cyanides and Mn2+, Mn3+ or Cd2+ metal ions: crystal chemistry, magnetic and optical properties

Five new cluster compounds based on [Mo₆Brⁱ₈(CN)^a₆]²⁻ and [Mo₆Brⁱ₆Qⁱ₂(CN)^a₆]ⁿ⁻ (Q = S, Se, n = 3, 4) cluster units have been synthesized and characterized.

Mo6 cluster-based compounds for energy conversion applications: comparative study of photoluminescence and cathodoluminescence

We report the photoluminescence (PL) and cathodoluminescence (CL) properties of face-capped [Mo6Xi8La6]2- (X = Cl, Br, I; L = organic or inorganic ligands) cluster units. We show that the emission of Mo6 metal atom clusters depends not only on the nature of X and L ligands bound to the cluster and counter-cations, but also on the excitation source. Seven members of the AxMo6Xi8La6 series (A = Cs+, (n-C4H9)4N+, NH4+) were selected to evaluate the influence of counter-cations and ligands on de-excitation mechanisms responsible for multicomponent emission of cluster units. This study evaluates the ageing of each member of the series, which is crucial for further energy conversion applications (photovoltaic, lighting, water splitting, etc.).

Lattice and Valence Electronic Structures of Crystalline Octahedral Molybdenum Halide Clusters-Based Compounds, Cs2[Mo6X14] (X = Cl, Br, I), Studied by Density Functional Theory Calculations

The electronic and crystal structures of Cs₂[Mo₆X₁₄] (X = Cl, Br, I) cluster-based compounds were investigated by density functional theory (DFT) simulations and experimental methods such as powder X-ray diffraction, ultraviolet-visible spectroscopy, and X-ray photoemission spectroscopy (XPS). The experimentally determined lattice parameters were in good agreement with theoretically optimized ones, indicating the usefulness of DFT calculations for the structural investigation of these clusters. The calculated band gaps of these compounds reproduced those experimentally determined by UV-vis reflectance within an error of a few tenths of an eV. Core-level XPS and effective charge analyses indicated bonding states of the halogens changed according to their sites. The XPS valence spectra were fairly well reproduced by simulations based on the projected electron density of states weighted with cross sections of Al K_α, suggesting that DFT calculations can predict the electronic properties of metal-cluster-based crystals with good accuracy.

Solvent-mediated purification of hexa-molybdenum cluster halide, Cs2[Mo6Cl14] for enhanced optical properties

An octahedral molybdenum cluster compound, Cs₂[Mo₆Cl₁₄], was purified by recrystallization with hydrophilic alcohol solvents for enhancing its luminescence efficiency.

Clustomesogens: Liquid Crystalline Hybrid Nanomaterials Containing Functional Metal Nanoclusters

Inorganic phosphorescent octahedral metal nanoclusters fill the gap between metal complexes and nanoparticles. They are finite groups of metal atoms linked by metal-metal bonds, with an exact composition and structure at the nanometer scale. As their phosphorescence internal quantum efficiency can approach 100%, they represent a very attractive class of molecular building blocks to design hybrid nanomaterials dedicated to light energy conversion, optoelectronic, display, lighting, or theragnostic applications. They are obtained as AnM6X(i)8X(a)6 ternary salt powders (A = alkali cation, M = Mo, Re, W, X(i): halogen inner ligand, X(a) = halogen apical ligand) by high temperature solid state synthesis (750-1200 °C). However, their ceramic-like behavior has largely restricted their use as functional components in the past. Since these last two decades, several groups, including ours, started to tackle the challenge of integrating them in easy-to-process materials. Within this context, we have extensively explored the nanocluster ternary salt specificities to develop a new class of self-organized hybrid organic-inorganic nanomaterials known as clustomesogens. These materials, combine the specific properties of nanoclusters (magnetic, electronic, luminescence) with the anisotropy-related properties of liquid crystals (LCs). This Account covers the research and development of clustomesogens starting from the design concepts and synthesis to their introduction in functional devices. We developed three strategies to build such hybrid super- or supramolecules. In the covalent approach, we capitalized on the apical ligand-metal bond iono-covalent character to graft tailor-made organic LC promoters on the {M6X(i)8}(n+) nanocluster cores. The supramolecular approach relies on the host-guest complexation of the ternary cluster salt alkali cations with functional crown ether macrocycles. We showed that the hybrid LC behavior depends on the macrocycles structural features. Finally, a third strategy, known as the ionic-assembling strategy, exploits the anionic character of the [M6L14](n-) nanocluster units whose charge is counterbalanced by tailor-made organic cations. We first focused on rationalizing the structural-LC behavior relationships of these noncovalent nanostructured materials by using NMR, SAXS, DSC, and POM technics. Depending on the hybrid organic-inorganic volumic fraction, thermotropic layered or nematic phases were observed. In this last case, the nematic phase being the most fluid of all LC phases, we further investigated this class of clustomesogen by introducing them in electro-controlled devices to tune either their photoluminescence or observe polarized emission. We hope this Account will provide useful tools for the development of new materials integrating such bright but still underused inorganic phosphors.

In Situ Generation of Active Molybdenum Octahedral Clusters for Photocatalytic Hydrogen Production from Water

The photocatalytic hydrogen evolution reaction (HER) from water under homogeneous and heterogeneous conditions is explored for the {Mo6 Br(i) 8 }(4+) cluster core based unit starting from (TBA)2 [Mo6 Br(i) 8 F(a) 6 ] (TBA=tetra-n-butylammonium; "i" and "a" refer to the face-capping inner and terminal apical ligand, respectively). The catalytic activity of {Mo6 Br(i) 8 }(4+) is enhanced by the in situ generation of [Mo6 Br(i) 8 F(a) 5 (OH)(a) ](2-) , [Mo6 Br(i) 8 F(a) 3 (OH)(a) 3 ](2-) , and [Mo6 Br(i) 8 (OH)(a) 6 ](2-) , which are identified by ESIMS, luminescence, and NMR techniques. Full substitution of F(-) by OH(-) leads to the formation of (H3 O)2 [Mo6 Br(i) 8 (OH)(a) 6 ]⋅10 H2 O; its structure was determined by single-crystal XRD. The immobilization of the active {Mo6 Br(i) 8 }(4+) onto graphene oxide (GO) surfaces enhances its stability under catalytic conditions. The catalytic activity of the resulting (TBA)2 Mo6 Br(i) 8 @GO material is improved with respect to GO, but is reduced compared to the activity under homogeneous conditions because of changes in the GO semiconducting properties as well as lower activity and/or accessibility of the anchored cluster.

Time-gated luminescence bioimaging with new luminescent nanocolloids based on [Mo6I8(C2F5COO)6]2−metal atom clusters

Functional silica nanoparticles based on metal atom clusters for time gated luminescence biotechnology applications.

Versatility of the ionic assembling method to design highly luminescent PMMA nanocomposites containing [M6Qi8La6]n− octahedral nano-building blocks

Strongly luminescent hybrid nanocomposites were designed by integrating via an ionic technique high content of different transition metal clusters.

Phosphorescent columnar hybrid materials containing polyionic inorganic nanoclusters

Red NIR phosphorescent hybrid materials with columnar liquid crystalline properties show high luminescence thermal stability and sensitivity to their surrounding atmosphere.