Trimeric Clusters Research Articles

Solvents and Ligands Matter: Structurally Variable Palladium and Nickel Clusters Assembled by Tridentate Selenium- and Tellurium-Containing Schiff Bases

Structurally variable organochalcogen clusters containing palladium(II) and nickel(II) ions were assembled starting from the salicylidene-substituted dichalcogenides (Y-C6H4-N═CH-C6H4-OH)2 ({HLY}2, where Y = Se or Te), and palladium or nickel acetate. The tetrameric palladium clusters contain reduced chalcogenolato ligands {Y-C6H4-N═CH-C6H4-O)}2- ({L'Y}2-, where Y = Se or Te), while the initially formed trimeric nickel clusters contain the intact, coordinated dichalcogenides. The palladium clusters have a general formula of [Pd4(L'Y)4] and represent the first examples of palladium complexes where both a gyrobifastigial and a pseudocubane arrangement of the central Pd4Y4 unit could be established with the same ligand, only depending on the solvents used for crystallization. Reduced density gradient (RDG) considerations based on density functional theory calculations suggest that the commonly referred to stabilizing chalcogen-palladium or palladium-palladium interactions for the two geometric arrangements are weak van der Waals contacts resulting from the contact of two nonbinding lone pairs. In the case of the pseudocubane arrangement, a repulsive steric effect, which is indicated by RDG analysis, is clearly supported by the cuplike distortions detected in the solid-state structure of the compound. In contrast to the reactions with palladium acetate, where the dichalcogenides were cleaved, during similar reactions with nickel acetate, the dichalcogenides remained intact and trimeric clusters of the composition [Ni-μ2-κ2-(Ni{κ5-LY}2)2-μ2-(OAc)2] (Y = Se, Te) were formed. Air oxidation and hydrolysis of [Ni-μ2-κ2-(Ni{κ5-LTe}2)2-μ2-(OAc)2] gave a rare example of a hexanuclear nickel cluster of the composition [Ni2-κ5-(Ni4-κ6-μ6-{(L'Te2O3)(L'TeO2)2}2)-μ2-(H2O)2], which is composed of a well-defined framework consisting of tellurinic anhydride and tellurinate units, which proves the comparably higher oxidation sensitivity of the trinickel dichalcogenide complexes. Electron spray ionization mass spectrometry spectra of both the palladium and nickel clusters indicate that they show fluctional behavior with varying nuclearity in solution and can adopt multiple charge states especially because of the noninnocence of the chalcogen-based ligands. The complexes were fully characterized by spectroscopic methods, elemental analyses, and X-ray diffraction.

Rapid differentiation of simple saccharides based on cluster ions by paper spray tandem mass spectrometry

Simple saccharides have a variety of biological functions, but their structural diversity and inherent structural features pose a major challenge for rapid analysis. In this work, we developed a derivative-free and ion mobility-free method for the rapid analysis of monosaccharides and disaccharides using paper spray tandem mass spectrometry. Trimeric cluster ions consisting of saccharide analytes, ligands and transition metal ions are used as precursor ions. We defined the R-value as the ratio of the intensity of the product ion that loses one molecule of ligand over the intensity of the product ion that loses one molecule of saccharide via collision induced dissociation (CID). The species and conformation of simple saccharides can be easily differentiated by calculating this R-value. With the capability of directly analyzing clinical samples using paper spray ionization, our method can be used to rapidly quantify the molar ratio of galactose to glucose in dried plasma samples to aid in the diagnosis of galactosemia. The analytical strategy provided herein has good potential to be applied to a wide range of saccharide analysis applications in the future.

Ternary zero-dimensional hybrid metal halides with dual emission

Bulk assemblies of zero-dimensional (0D) metal halides with ‘host-guest’ system provide a promising platform for rationally structural tunability and photoluminescence modulation. In this work, we first report a series of ternary 0D metal halides, (bmpy)9[Pb3Cl11](MnCl4)2-2x(SbCl5)2x (bmpy+ = 1-buty-1-methylpyrrolidinium+, C9NH20+), where the organic cation bmpy+ cocrystallizes with [Pb3Cl11]5- trimer clusters, [MnCl4]2− tetrahedra, and [SbCl5]2− pyramids. The emission color of (bmpy)9[Pb3Cl11](MnCl4)2-2x(SbCl5)2x can be easily tuned from green to warm white and finally to orange-red by controlling the excitation wavelength or the [SbCl5]2−/[MnCl4]2− molar ratio, promising its potential for application in multicolor light-emitting devices or even in encrypting multilevel optical codes. This work presents a novel structural modulation strategy to fabricate superior ordered single-crystalline multicomponent materials with multifunctionalities of 0D luminescent metal halides.

Investigation of Formic Acid involved Molecular Clusters with Atmospheric Acidic, Basic and Neutral Species

New particle formation (NPF) is regarded as a main source of tropospheric aerosols. Formic acid (FA) is investigated as a source of NPF by studying its dimer, trimer and tetramer clusters with atmospheric nucleating species like H2O, H2S, MeNH2 and H2O2 employing quantum chemical methods. The structural characteristics, nature of interactions, interaction energies, harmonic vibrational frequencies, thermochemistry at ambient and tropospheric conditions are investigated employing DFT and MP2 methods. Acidic (H2S), basic (MeNH2) and neutral (H2O) nucleating precursors are chosen to study the effect of nature of these species on NPF. Results show that clusters of formic acid with MeNH2 have more stabilising effect than clusters with H2O, H2S and H2O2. The FA-MeNH2 clusters are formed spontaneously at ambient conditions while for others (H2O, H2O2) although the clusters are stable at ambient conditions, yet have positive binding free energy that becomes negative at tropospheric conditions. The cluster formation leads to significant red shifts and increased IR intensities for conventional hydrogen bond donor bond stretching vibrations relative to its monomeric units. For all the nucleating species, stability increases with the growth of clusters.

Immobilization of a trimeric ruthenium cluster in mesoporous chromium terephthalate and its catalytic application.

Molecular trimeric ruthenium carboxylate clusters (Ru3 clusters) have been introduced into the pore channels of mesoporous metal-organic framework chromium terephthalate [MIL-101(Cr)] by employing a facile two-step post-synthetic strategy in which diamine hooks anchored on the framework metal nodes of the MOF are used to covalently immobilize the Ru3 clusters. The catalytic activity of the isolated Ru3 clusters in the pore channels of the MOF was significantly improved compared to the bulk counterpart.

Quantifying Effects of Active Site Proximity on Rates of Methanol Dehydration to Dimethyl Ether over Chabazite Zeolites through Microkinetic Modeling.

Control of the spatial proximity of Brønsted acid sites within the zeolite framework can result in materials with properties that are distinct from materials synthesized through conventional crystallization methods or available from commercial sources. Recent experimental evidence has shown that turnover rates of different acid-catalyzed reactions increase with the fraction of proximal sites in chabazite (CHA) zeolites. The catalytic conversion of oxygenates is an important research area, and the dehydration of methanol to dimethyl ether (DME) is a well-studied reaction as part of methanol-to-olefin chemistry catalyzed by solid acids. Published experimental data have shown that DME formation rates (per acid site) increase systematically with the fraction of proximal acid sites in the six-membered ring of CHA. Here, we probe the effect of acid site proximity in CHA on methanol dehydration rates using electronic structure calculations and microkinetic modeling to identify the primary causes of this chemistry and their relationship to the local structure of the catalyst at the nanoscale. We report a density functional theory-parametrized microkinetic model of methanol dehydration to DME, catalyzed by acidic CHA zeolite with direct comparison to experimental data. Effects of proximal acid sites on reaction rates were captured quantitatively for a range of operating conditions and catalyst compositions, with a focus on total paired acid site concentration and reactant clustering to form higher nuclearity complexes. Next-nearest neighbor paired acid sites were identified as promoting the formation of methanol trimer clusters rather than the inhibiting tetramer or pentamer clusters, resulting in large increases in the rate for DME production due to the lower energy barriers present in the concerted methanol trimer reaction pathway. The model framework developed in this study can be extended to other zeolite materials and reaction chemistries toward the goal of rational design and development of next-generation catalytic materials and chemical processes.

Adsorption and Decomposition of Dimethyl Methylphosphonate on Size-Selected Zirconium Oxide Trimer Clusters

Adsorption and Decomposition of Dimethyl Methylphosphonate on Size-Selected Zirconium Oxide Trimer Clusters

Functionalization of Mono- and Bimetallic MIL-100(Al,Fe) MOFs by Ethylenediamine: Postfunctionalization, Brønsted Acido-Basicity, and Unusual CO2 Sorption Behavior.

The metal sites of MIL-100(Fe), MIL-100(Fe,Al), and MIL-100(Al) metal-organic frameworks (MOFs) were decorated with ethylenediamine (EN). Interestingly, the Al-containing MOFs presented hierarchized porosity, and their structural integrity was maintained upon functionalization. Solution and solid-state NMR confirmed the grafting efficiency in the case of MIL-100(Al) and the presence of a free amine group. It was shown that MIL-100(Al) can be functionalized by only one EN molecule in each trimeric Al3O cluster unit, whereas the other two aluminum sites are occupied by a hydroxyl and a water molecule. The -NH2 sites of the grafted ethylenediamine can be used for further postfunctionalization through amine chemistry and are responsible for the basicity of the functionalized material as well as increased affinity for CO2. Furthermore, the presence of coordinated water molecules on the Al-MOF is responsible for simultaneous Brønsted acidity. Finally, the Al-containing MOFs show an unusual carbon dioxide sorption mechanism at high pressures that distinguishes those materials from their iron and chromium counterparts and is suspected to be due to the presence of polarized Al-OH bonds.

FDTD Study on Evolution of Trimer Silver@Silica Nanospheres to Dimer for SERS Characteristics.

Light enhancement occurs strongly within the plasmonic clusters by interaction with surface plasmons. Surface-enhanced Raman spectroscopic (SERS) characteristics of a series of silver@silica trimer core–shell (CS) nanosphere (NS) clusters are investigated in this paper. It is significant to understand the electric field (EF) enhancement mechanism behind the SERS technique. The effect of symmetry breaking is studied for the series starting from the highly symmetric trimer cluster and transformed to linear dimer geometry which progresses through the gradual reduction in the vertex NS. The optical activity such as the evolution of LSPR peak is discussed, the formation of hot spots is demonstrated and the strength of the local EF enhancement is calculated and correlated with the plasmon dipolar modes by using plasmon hybridization theory to understand the underlying physical concepts.

Catalytic oxidation of NO to NO2 on pure and doped AunPt3-n (n=0–3) clusters: A DFT perspective

A systematic density functional theory (DFT) calculations are performed on pure as well as doped Au3 trimer clusters to study the catalytic oxidation of NO to NO2 using the M06L functional combined with a def2QZVPP basis set. Adsorption energies and Bader charges of adsorbed NO and O2 on the AunPt3-n clusters have been calculated to observe the stability of the adsorbed species. Results show that the adsorption of both NO and O2 on the bimetallic clusters is stronger on the Pt site than that of Au site. Owing to the high adsorption energy of both the reactants, we further propose a reaction mechanism of NO oxidation over AunPt3-n (n = 0–3) clusters following the Langmuir-Hinshelwood (L-H) mechanism. The rate constants of NO2 production at each step of the reaction mechanism are determined using the Transition State Theory (TST). Energetic span model is also used to determine the efficient catalytic system among the four clusters. This study offers a new insight into the fundamental effect of doping Pt on Au3 and conveys an understanding for the NO oxidation mechanism at the molecular level which in turn will help in building efficient catalysts for large-scale processes.

Theoretical study of the effect of water clusters on the enol content of acetone as a model for understanding the effect of water on enolization reaction

The enolization of simple carbonyl compounds is a key reaction for many chemical and biochemical processes. Numerous theoretical and experimental studies have been done to probe aspects of the mechanism of this reaction. In this work, the effect of small water clusters, (H2O)n, n = 1–9, on the enol content of acetone has been investigated by using density functional theory calculations at the M06 level of theory in the gas and solution phases. The calculations indicated that the formation of hydrogen-bonded assemblies between water clusters and both tautomers of acetone affect the enolization reaction. Among them, the trimeric water cluster has the highest binding energy difference (ΔEb) in the solution phase and greatly shifts the equilibrium in the favor of the enol form. The results also show that under this condition, the enol content of acetone increased with decreasing polarity of the solvent. The practical conclusion of this study is that the enol content of carbonyl compounds can be maximized only by addition of a defined amount of water.

Ultrafast optical melting of trimer superstructure in layered 1T\u2032-TaTe2

Quasi-two-dimensional transition-metal dichalcogenides are a key platform for exploring emergent nanoscale phenomena arising from complex interactions. Access to the underlying degrees-of-freedom on their natural time scales motivates the use of advanced ultrafast probes sensitive to self-organised atomic-scale patterns. Here, we report the ultrafast investigation of TaTe2, which exhibits unique charge and lattice trimer order characterised by a transition upon cooling from stripe-like chains into a (3 × 3) superstructure of trimer clusters. Utilising MeV-scale ultrafast electron diffraction, we capture the photo-induced TaTe2 structural dynamics – exposing a rapid ≈ 1.4 ps melting of its low-temperature ordered state followed by recovery via thermalisation into a hot cluster superstructure. Density-functional calculations indicate that the initial quench is triggered by intra-trimer Ta charge transfer which destabilises the clusters, unlike melting of charge density waves in other TaX2 compounds. Our work paves the way for further exploration and ultimately rapid optical and electronic manipulation of trimer superstructures.

Activation of small molecules by the unsaturated complex Pt(IBut)(PBut3): First structural characterization of a peroxycarbonate complex of platinum

The reaction of Pt(COD)2 with one equivalents of IBut and PBut3 at room temperature yields the unsaturated platinum mixed N-heterocyclic carbene and phosphine complex Pt(IBut)(PBut3), 1. Complex 1 reacts rapidly with O2 and CO to form the dioxygen adduct Pt(IBut)(PBut3)(η2-O2), 2 and Pt3 trimer cluster complex [Pt(IBut)(CO)]3, 3, respectively. Complex 2 further reacts with CO2 at room temperature to give the peroxycarbonate complex Pt(IBut)(PBut3)[η2-OOC(O)O], 4, and the first example characterized by single crystal X-ray diffraction. The reaction of complex 2 with acetone also resulted in the formation of the peroxoacetonate complex Pt(IBut)(PBut3)[η2-OOC(CH3)2O], 5. All the structures for the complexes 1–5 were characterized by X-ray crystallographic studies.

Lifetimes of Be32- and Mg32- Cluster Dianions.

The alkaline earth metal trimer cluster dianions Be32- and Mg32- lie energetically above their respective monoanions and can therefore decay by electron autodetachment. Consequently, these dianions possess only short-lived resonance states, and here we study these states using regularized analytic continuation as well as complex absorbing potentials combined with a wide a variety of quantum chemistry methods including CCSD(T), SACCI, EOM-CCSD, CASPT2, and NEVPT2. For both Be32- and Mg32-, four low-energy resonance states corresponding to different occupation patterns of the two excess electrons in the two lowest p-σ and p-π orbitals are identified: Two states are dominated by doubly occupied configurations and can be characterized as showing σ and π aromatic character. The other two states correspond to the open-shell singlet/triplet pair. All dianion states are found to be highly unstable and to possess short lifetimes: They show resonance positions in the energy range 2.3-4.3 eV above the ground states of their respective monoanions and broad widths between 1 and 1.5 eV translating into femtosecond lifetimes. For both Be32- and Mg32-, the differences between the four states are small, but the triplet states tend to be slightly more stable than the three singlet states. Thus, in the case of the multicharged ion aromatic character of the excess electrons takes second stage while Coulomb repulsion takes front and center. In addition to the two isolated cluster dianions, model stabilization by small water clusters is explored. Our results show a dramatic drop in resonance position and width corresponding to a lifetime increase by 2 orders of magnitude. However, the "solvated" clusters are still resonances, and a more pronounced perturbation by, for example, yet larger water clusters or a ligand environment providing larger bond dipoles will be needed to fully stabilize two excess electrons localized on a small system such as an alkaline metal trimer.

Nitrogen monoxide as dopant for enhanced selectivity of isomeric monoterpenes in drift tube ion mobility spectrometry with 3H ionization

The ion mobility spectra of the isomeric monoterpenes α-pinene, β-pinene, myrcene, and limonene in drift tube ion mobility spectrometry (IMS) with 3H radioactive ionization are highly similar and difficult to distinguish. The aim of this work was to enhance the selectivity of IMS by the addition of nitrogen monoxide (NO) as dopant and to investigate the underlying changes in ion formation responsible for the modified ion signals observed in the ion mobility spectra. Even though 3H-based-IMS systems have been used in hyphenation with gas chromatography (GC) for profiling of volatile organic compounds (VOCs), the investigation of ion formation still remains challenging and was exemplified by the investigated monoterpenes. Nonetheless, the formation of monomeric, dimeric, and trimeric ion clusters could be tentatively confirmed by a mass-to-mobility correlation and the highly similar pattern of ion signals in the monomer region was attributed to isomerization mechanisms potentially occurring after proton transfer reactions. The addition of NO as dopant could finally lead to the formation of additional product ions and increased the selectivity of IMS for the investigated monoterpenes as confirmed by principal component analysis (PCA). The discrimination of monoterpenes in the volatile profile is highly relevant in the quality control of hops and was given as the example for application. The results indicate that additional product ions were obtained by the formation of NO+ adduct ions, next to hydride abstraction, charge transfer, or fragmentation reactions. This approach can potentially leverage selectivity issues in VOC profiling of complex matrices, such as food matrices or raw materials in combination with chemometric pattern recognition techniques.Graphical abstract

Symmetry analysis of trimer-based all-dielectric metasurfaces with toroidal dipole modes

Herein, we discuss the conditions for excitation of symmetry-protected toroidal dipole modes in all-dielectric metasurfaces composed of trimer or twin-trimer clusters of dielectric disks. Such metasurfaces permit enhanced light–matter interaction due to spatially confined light in resonant systems with a high-quality factor. To describe characteristics of toroidal modes existing in the clusters, we use the magnetic dipole moments approximation, group-theoretical methods, group representation theory, symmetry-adapted linear combination method, and circuit theory. To validate the obtained theoretical results, we fulfill both full-wave numerical simulations and microwave experiments. In particular, we have shown that the toroidal dipole mode appears as a quasi-dark state of the trimer. It can be excited in the metasurface by the field of a linearly polarized wave, providing the symmetry of the trimer is properly reduced. In the metasurface, the properties of the toroidal dipole mode are determined primarily by the parameters of a single trimer and are not a consequence of the periodicity of the array. The coupling of the toroidal dipole modes in the twin-trimers can appear in both bonding and anti-bonding fashion resulting in different orders of the net toroidal dipole moment. Due to the unique field configuration of these modes, the proposed metasurfaces can be considered as a platform for efficient light–matter interaction for enhanced absorption, non-linear switching, and sensing.

Manifold dynamic non-covalent interactions for steering molecular assembly and cyclization.

Deciphering rich non-covalent interactions that govern many chemical and biological processes is crucial for the design of drugs and controlling molecular assemblies and their chemical transformations. However, real-space characterization of these weak interactions in complex molecular architectures at the single bond level has been a longstanding challenge. Here, we employed bond-resolved scanning probe microscopy combined with an exhaustive structural search algorithm and quantum chemistry calculations to elucidate multiple non-covalent interactions that control the cohesive molecular clustering of well-designed precursor molecules and their chemical reactions. The presence of two flexible bromo-triphenyl moieties in the precursor leads to the assembly of distinct non-planar dimer and trimer clusters by manifold non-covalent interactions, including hydrogen bonding, halogen bonding, C–H⋯π and lone pair⋯π interactions. The dynamic nature of weak interactions allows for transforming dimers into energetically more favourable trimers as molecular density increases. The formation of trimers also facilitates thermally-triggered intermolecular Ullmann coupling reactions, while the disassembly of dimers favours intramolecular cyclization, as evidenced by bond-resolved imaging of metalorganic intermediates and final products. The richness of manifold non-covalent interactions offers unprecedented opportunities for controlling the assembly of complex molecular architectures and steering on-surface synthesis of quantum nanostructures.

Pressure-Engineered Photoluminescence Tuning in Zero-Dimensional Lead Bromide Trimer Clusters.

Zero-dimensional (0D) hybrid metal halides are promising light emitters. However, it is still challenging to accurately design their structures with targeted photoluminescence properties. Herein, high pressure is used to change the self-trapped exciton (STE) emission of 0D (bmpy)9 [ZnBr4 ]2 [Pb3 Br11 ] (bmpy: 1-butyl-1-methylpyrrolidinium). Under initial compression, the simultaneous contraction and distortion of photoactive [Pb3 Br11 ]5- vary the equilibrium of STE emissions between different excited states, tuning the emission color from yellow green to cyan. Notably, sufficient structural distortion under continuous compression leads to the formation of more and deeper STE states, exhibiting an unprecedented broadband white-light emission. This study reveals the structure-dependent optical properties of 0D hybrid metal halides, providing novel insights into the mechanism of STE emission.

Pressure‐Engineered Photoluminescence Tuning in Zero‐Dimensional Lead Bromide Trimer Clusters

AbstractZero‐dimensional (0D) hybrid metal halides are promising light emitters. However, it is still challenging to accurately design their structures with targeted photoluminescence properties. Herein, high pressure is used to change the self‐trapped exciton (STE) emission of 0D (bmpy)9[ZnBr4]2[Pb3Br11] (bmpy: 1‐butyl‐1‐methylpyrrolidinium). Under initial compression, the simultaneous contraction and distortion of photoactive [Pb3Br11]5− vary the equilibrium of STE emissions between different excited states, tuning the emission color from yellow green to cyan. Notably, sufficient structural distortion under continuous compression leads to the formation of more and deeper STE states, exhibiting an unprecedented broadband white‐light emission. This study reveals the structure‐dependent optical properties of 0D hybrid metal halides, providing novel insights into the mechanism of STE emission.

Ambient Temperature Synthesis and Structural Characterization of Six Transition Metal Acetylenedicarboxylate Coordination Polymers

This work reports the ambient temperature synthesis and structural characterization of six new first row transition metal acetylenedicarboxylate coordination polymers. The Co and two Ni compounds adopt structures in which the octahedral metals are connected into 1D chains via the acetylenedicarboxylate ligand. In contrast the Mn and two Zn compounds adopt 3D metal‐organic frameworks; while the Mn compound is non‐porous the two Zn structures contain dimeric or trimeric clusters connected into frameworks that are potentially porous. These two anionic metal‐organic frameworks are, however, charged balanced by cations siting in their pores which greatly reduces the ability to access their porosity.