Tetrameric Clusters Research Articles

Syntheses, crystal structure, Hirshfeld Surface Analyzes of cocrystals and salt of a flexible imidazole tethered naphthalenediimide with some organic acids.

One salt and three cocrystals of 2,7-bis(3-(1H-imidazol-1-yl)propyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (L) have been synthesized and reported. 3-Nitro benzoic acid (3NBA) forms salt with L and 4-Nitro benzoic acid (4NBA), 4-Hydroxy benzoic acid (4HBA) and 4-Amino benzoic acid (4ABA) forms cocrystals with L. L forms 1:1 salt with 3-NBA and 1:1 cocrystal with 4-NBA, 4-HBA and 4-ABA respectively. All the complexes were formed in a warm solvent condition. The solid-state structures were determined by single crystal X-ray diffraction method. Salt 1, exhibit zig zag tetrameric water cluster in the solid-state structure. Various types of supramolecular interactions such as OH…O, CH…O, π…π, and CH…π were observed in the x-ray structures and all these interactions guide the formation of 3D supramolecular architecture in the solid-state of all the complexes. Besides these, the 2D-fingerprint (2D-FP) and Hirshfeld surface analysis (HSA) computations were served to prove the 2D-network packed crystal lattice interactions.

Polarization-independent tetramer metastructure with multi-Fano resonances governed by quasi-bound states in the continuum.

We propose what we believe to be a novel metastructure consisting of silicon nanoblock tetramer clusters and investigated theoretically and experimentally how to enhance surface sensing capabilities with polarization-independent properties through bound states in the continuum (BICs). By introducing square defects, three quasi-BIC modes are excited at the wavelengths of 1013.29 nm, 1109.57 nm, and 1310.73 nm with a modulation depth up to 100% and a Q-factor of 16618, while achieving a sensitivity of 256 nm/RIU and a figure of merit of 2519.7 RIU-1. Utilizing the finite-difference method in the time domain (FDTD), we have analyzed the electromagnetic near-field distributions, polarization properties, and robustness corresponding to resonance dips at different wavelengths. Our results reveal that the distinct electromagnetic near-field distributions excited by the quasi-BIC modes are characterized by the strong field confinement within the silica nanoblock tetramer clusters. The modes are primarily governed by magnetic quadrupole (MQ) resonance and toroidal dipole (TD) moment. Additionally, the polarization-independent properties of the metastructure are demonstrated to ensure that they can effectively respond to the incident light regardless of its polarization state, while the robustness is investigated to show the stability and reliability by shifting square defects. Moreover, the transmission spectra of the metastructure is experimentally verified by immersing the sample into CaCl2 solutions in different concentrations. This work plays a pivotal role in creating further novel and high-performance optical metastructures while demonstrating the potential applications of quasi-BIC modes in precision sensing in the future.

Structural Insight into a Sixteen Cyanine Dye Construct via Exciton-Exciton Annihilation.

Molecular (dye) aggregates play a prominent role in light harvesting and are of interest in quantum information science; however, there are limited reports that programmably assemble many (>4) dye aggregates featuring strong coupling and exciton delocalization. Using oligonucleotides with four Cy5s covalently linked in series along the phosphate backbone, we bring 4, 8, and 16 Cy5s in close proximity by assembling four-armed junctions. We elucidate their structure via gel electrophoresis and steady-state and transient optical spectroscopy. We find that Cy5 has a strong propensity to form tetramer clusters, where the exciton is delocalized over all 4 Cy5s, that the exciton is not delocalized beyond tetramer clusters in the 8 and 16 Cy5 constructs, and that the 16 Cy5 construct may consist of pairs of tetramer clusters that are isolated from one another. Many-dye aggregates such as these may serve useful as antennae for their intense light absorption and spatially directed energy transfer.

Calculated Aqueous Reduction Potentials of Neutral and Anionic Halogen Diatomic Molecules.

The free energy of hydration, aqueous, and gas phase electron affinity and aqueous reduction potentials of F2, Cl2, Br2, I2, ClF, BrF, IF, BrCl, ICl, IBr, and their corresponding anions were calculated using an electronic structure approach previously developed for these properties for X• and XO•, where X is a halogen which yielded excellent results. The gas phase electron affinities were calculated at the Feller-Peterson-Dixon level based on complete basis set extrapolation of CCSD(T) results with additional corrections. The agreement with the available experimental data is excellent, and the calculations provide a complete set of reliable electron affinities for these diatomic halogens. The hybrid solvation approach uses single point implicit solvation calculations on gas phase optimized clusters with explicit solvent molecules. The gas phase energy calculations were performed using MP2 and CCSD(T)-F12b for tetramer clusters (four explicit waters) and MP2 for octamer clusters (eight explicit waters). The final redox potentials were obtained at the MP2/aug-cc-pVTZ (aT) with a self-consistent reaction field (SMD) level using the octamer clusters. The aqueous reduction potentials of the neutral diatomic halogens are predicted within 0.06 V of the experiment for diatomic neutrals. The same agreement of 0.06 V is predicted for the redox potential resulting from dissociation electron attachment of the diatomic halogen anions. The current work extends reduction potentials for multiple redox couples for which no experimental data is available, for example, those containing iodine and the interhalogen anions. F2•- is predicted to dissociate for its lowest energy structure in both the tetramer and octamer clusters to form solvated F-, HF, and OH•.

Interpenetrated In(III)-MOF with Multiple Recognition Sites for Single-Step Ethylene Purification.

An interpenetrated indium(III) metal-organic framework (MOF), NTUniv-73, with a rarely reported tetrameric indium cluster is developed for streamlining ethylene purification from C2 gases. At 298 K, the adsorption capacities exhibited a complete reversal sequence of C2H6 > C2H2 > C2H4. Grand canonical Monte Carlo simulation indicated that the corners in a octahedral cage facilitated the C2H2/C2H4 separation, while the pocket-like aperture situated between adjacent octahedral cages allows for full contact of C2H6. Breakthrough experiments illustrated that NTUniv-73 could yield pure C2H4 in a single step with a productivity of 0.42 mmol g-1.

Tetrameric self-assembling of water-lean solvents enables carbamate anhydride-based CO2 capture chemistry

Carbon capture, utilization and storage is a key yet cost-intensive technology for the fight against climate change. Single-component water-lean solvents have emerged as promising materials for post-combustion CO2 capture, but little is known regarding their mechanism of action. Here we present a combined experimental and modelling study of single-component water-lean solvents, and we find that CO2 capture is accompanied by the self-assembly of reverse-micelle-like tetrameric clusters in solution. This spontaneous aggregation leads to stepwise cooperative capture phenomena with highly contrasting mechanistic and thermodynamic features. The emergence of well-defined supramolecular architectures displaying a hydrogen-bonded internal core, reminiscent of enzymatic active sites, enables the formation of CO2-containing molecular species such as carbamic acid, carbamic anhydride and alkoxy carbamic anhydrides. This system extends the scope of adducts and mechanisms observed during carbon capture. It opens the way to materials with a higher CO2 storage capacity and provides a means for carbamates to potentially act as initiators for future oligomerization or polymerization of CO2.

Ultrafast spin dynamics in magnetic trimer and tetramer clusters: a step towards prototypic spin-SHIFT registers

Ultrafast magnetic dynamics is a necessary ingredient for magnetic recording and ultrafast information processing. The shift functionality, although not mandatory for Boolean logic, is always implemented in CMOS CPUs and therefore must be also present in magnetic logic. In this respect, using ab initio calculations we show ultrafast spin dynamics in molecular clusters such as Co3 +CO and Ni4. In this work, we establish that clusters with magnetic atoms can provide a theoretical toolbox for efficient spin charge dynamics whose operation time can range up to a few picoseconds. The prime underlying mechanism for all spin manipulation scenarios in the above mentioned clusters are laser-induced Λ processes where the laser parameters are fully optimized using a genetic algorithm. In general, a structural asymmetry enforces substantial spin localization on the active centers of both magnetic clusters. Keeping in mind the shift functionality, we theoretically suggest a series of spin-transfer scenarios between the Co and Ni atoms in each of these two clusters independently to construct a 3-bit and a 4-bit cyclic spin-SHIFT register, respectively. The maximum operational time for both logic devices is 2 ps, which is much faster than the response time of conventional spintronic devices. Additionally, for a better understanding of the transfer cycles, their feasibility and reversibility are also investigated through the analysis of the optical spectra of the related states. Our results provide important theoretical guidance for ultrafast spin manipulation in molecular structures as well as their potential spin functionality, and thus step closer to the realization of future spin-based logic devices and quantum computation. This effectively motivates the investigation and precise establishment of the shift functionality in magnetic trimers and tetramers.

Structures and stability of I2 and ICl complexes with pyridine: Ab initio and DFT study.

Theoretical investigation of thermodynamic stability and bonding features of possible isomers of the molecular and ionic complexes of pyridine with molecular iodine and iodine monochloride IX (X = I,Cl) is presented. M06-2X DFT functional is found to provide bond distances and dissociation energies which are close to those obtained at high-level ab initio CCSD(T)/aug-cc-pvtz//CCSD/aug-cc-pvtz benchmark computations for the most stable isomers, formed via donation of a lone pair of nitrogen atom of pyridine to the iodine atom. These isomers are by 23-33 kJ mol-1 (in case of I2) and by 39-56 kJ mol-1 (in case of ICl) more stable than other molecular complexes. T-shaped π-σ* bonded isomers turn out to be energetically comparable with van der Waals bound compounds. Among the ionic isomers, structures featuring [IPy2]+ cation with I3 - or ICl2 - counterions are more stable. Oligomerization favors ionic isomers starting from the tetrameric clusters of the composition (IX)4Py4.

Cross-coupling of CO and an isocyanide mediated by a tetrameric magnesium hydride cluster.

Sequential addition of CNXyl (Xyl = 2,6-dimethylphenyl) and CO to a tetrametallic magnesium hydride cluster results in stepwise reduction and cross-coupling of these substrates. Cross-coupling results in the formation of an ethene amidolate ligand [OC1(H1)[double bond, length as m-dash]C2(H2)NAr]2- a previously unknown entity which contains a 1,2-difunctionalised carbon chain reminiscent of those found in aminoalcohols and amino acids. To the best of our knowledge, this is the first example of such reactivity with metal hydride precursors. DFT calculations support a mechanism that parallels that established for coupling of CO to form ethenediolate ligands, with the key carbon-carbon bond step occurring by nucleophilic attack of a putative azamethylene intermediate on CO. The cluster plays a key role in templating the synthesis, providing kinetic control over each of the steps. The ethene amidolate ligand can be transferred to other metals (Al) and semi-metals (B) through onwards metathesis reactions.

Selective recognition and reversible encapsulation of tetrameric alcohol clusters via hydrogen bonds using a perfluorinated dinuclear nickel(ii) complex

A perfluorinated Ni(ii) complex encapsulates MeOH, forming unique tetrameric clusters stabilized by hydrogen bonding in the crystal to achieve remarkable uptake of MeOH over EtOH and water, demonstrating potential for separation and sensing.

Prediction of Aqueous Reduction Potentials of X•, ChH•, and XO• Radicals with X = Halogen and Ch = Chalcogen.

The aqueous electron affinity and aqueous reduction potentials for F•, Cl•, Br•, I•, OH•, SH•, SeH•, TeH•, ClO•, BrO•, and IO• were calculated using electronic structure methods for explicit cluster models coupled with a self-consistent reaction field (SMD) to treat the aqueous solvent. Calculations were conducted using MP2 and correlated molecular orbital theory up to the CCSD(T)-F12b level for water tetramer clusters and MP2 for octamer cluster. Inclusion of explicit waters was found to be important for accurately predicting the redox potentials in a number of cases. The calculated reduction potentials for X• and ChH• were predicted to within ∼0.1 V of the reported literature values. Fluorine is anomalous due to abstraction of a hydrogen from one of the surrounding water molecules to form a hydroxyl radical and hydrogen fluoride, so its redox potential was calculated using only an implicit model. Larger deviations from experiment were predicted for ClO• and BrO•. These deviations are due to the free energy of solvation of the anion being too negative, as found in the pKa calculations, and that for the neutral being too positive with the current approach.

Supramolecular promotion of chemosensing effect in a new amino-acid-derivative macrocyclic ligand toward Fe(III) and Pb(II) by Zn(II) polymerization

A fluorescent synthetic amino acid appended with an N2O2-donor macrocyclic ligand L was prepared and characterized by single-crystal X-ray diffraction (SCXRD), elemental analysis, IR, 1H and 13C NMR, fluorescence (FL), and UV–vis spectroscopy. L exhibited an FL emission quenching in the presence of Fe(III) ion and showed a limit of detection (LOD) of 5.98 × 10−6 M while the periodic addition of EDTA to the Fe(III)/L solution in DMF reversibly enhanced the FL emission. Based on the bridging role of a water tetramer cluster (WTC) in the crystal structure of L for supporting the formation of the self-assembly of L, an aggregation-caused mechanism was proposed for the observed concentration-based quenching phenomena, confirmed by FL, and 1H NMR spectroscopy. Moreover, we synthesized a new one-dimensional Zn(II) coordination polymer (CP) [Zn(LH)(H2O)(NO3)(DMSO)]n (1) consisting of paddle-wheel Zn2(COO)4 subunits and four bridged L linkers, characterized by SCXRD method. 1 was assumed to be formed by replacing the WTC in the crystal structure of L. A parallel FL behavior for L and 1 was determined, attributable to a ligand-based electronic transition. 1 was found as a more sensitive chemosensor for Fe(III) than L, based on an improved LOD of 9.74 × 10−8 M for Fe(III). Meanwhile, the promotional effect of Zn(II) in CP of 1 has overcome the chemosensing incapability of L towards Pb(II), maybe due to the ease of trans-metalation of Pb(II) with Zn(II) in 1 instead of the direct coordination with L.

Electronic Structure of Small Isolated and Supported Manganese Oxide Clusters.

In the present work, possible molecular models of the isolated manganese oxides and supported Mn3Ox/Al2O3 structures were built based on small clusters of passivated MnOx. The support was represented as a simplified model of the alumina tetramer cluster based on small fragments of AlOxHy. Combinations of MnOxHy and AlOxHy clusters were made to form both the isolated and supported manganese oxides clusters. The electronic structure of these systems was characterized by ab initio methods (DFT and CASPT2). It was observed that the vertical excitation energy of the isolated and supported Mn3OxHy clusters is significantly lower than that of the alumina cluster model, while both the isolated and supported Mn3OxHy wave function characters are qualitatively similar with respect to the ground state and electronic transition processes, suggesting that the alumina cluster behaves as an inert support, since there is little contribution of this component in the description of the low-lying electronic states. The present study also reports for the first time the spectroscopic parameters of several clusters containing the manganese transition metal atom.

Symmetric carbon tetramers forming spin qubits in hexagonal boron nitride

Point defect quantum bits in semiconductors have the potential to revolutionize sensing at atomic scales. Currently, vacancy-related defects are at the forefront of high spatial resolution and low-dimensional sensing. On the other hand, it is expected that impurity-related defect structures may give rise to new features that could further advance quantum sensing in low dimensions. Here, we study the symmetric carbon tetramer clusters in hexagonal boron nitride and propose them as spin qubits for sensing. We utilize periodic-DFT and quantum chemistry approaches to reliably and accurately predict the electronic, optical, and spin properties of the studied defect. We show that the nitrogen-centered symmetric carbon tetramer gives rise to spin state-dependent optical signals with strain-sensitive intersystem crossing rates. Furthermore, the weak hyperfine coupling of the defect to their spin environments results in a reduced electron spin resonance linewidth that can enhance sensitivity.

One-Dimensional Selenidostannates Based on an Infrequent Tetrameric Cluster [Sn4Se12] Exhibiting Electro-Catalytic Properties.

The discovery of low-cost and efficient electro-catalytic materials for hydrogen evolution reaction (HER) is very desirable in hydrogen energy technology. Here, a new type of one-dimensional (1-D) organic hybrid selenidostannate [Ni(en)3]n[Sn2Se5]n (SnSe-1, en = ethylenediamine) with an in situ [Ni(en)3]2+ complex was achieved by the solvothermal reaction of Sn, Se, and NiCl2·6H2O in a mixed solvent of en and triethanolamine at 160 °C for 10 days. The crystal structure of SnSe-1 contains a unique 1-D [Sn2Se52-]n chain built up from the sharing-edge connection of a hitherto-unknown tetrameric [Sn4Se12] cluster, which is separated by discrete [Ni(en)3]2+ complexes. SnSe-1 is first combined with Ni nanoparticles supported on conductive porous Ni foam (NF) to constitute a Ni/SnSe-1/NF electrode as the HER electro-catalyst, displaying superior electro-catalytic activity in near-neutral conditions.

Multi‐Band Polarization‐Independent Quasi‐Bound States in the Continuum Based on Tetramer‐Based Metasurfaces and Their Potential Application in Terahertz Microfluidic Biosensing

AbstractQuasi‐bound state in the continuum (quasi‐BIC) has drawn increasing attention in terahertz biosensing and filtering owing to an extremely narrow linewidth and ultra‐high quality factor. However, it is usually polarization‐sensitive due to broken structure or incidence symmetry and mainly holds for polarization‐dependent single or dual bands, which sets a limitation on practical applications. Here, this article proposes and experimentally demonstrates terahertz multi‐band polarization‐independent quasi‐BICs in tetramer‐based metasurfaces by using the laser etching method. Employing a tetramer cluster with C4v symmetry as the structural unit, which consists of four L‐type copper particles on a flexible and optically‐transparent substrate, the metasurfaces can support dual‐band or tri‐band polarization‐independent quasi‐BICs after performing collective perturbation, specific displacement, or both to the constituent particles. Furthermore, the metasurfaces are integrated with microfluidic channels to explore their potential application in terahertz biosensing. Experimental results indicate that when the concentration of bovine serum albumin solutions is below 4 mg mL−1, both resonance modes of the dual‐band terahertz microfluidic biosensor exhibit a sensitivity of ≈12 GHz mg−1 mL each, and the detection limits reach 0.17 mg mL−1. This work provides a general and simple strategy to construct metasurfaces supporting multi‐band polarization‐independent quasi‐BICs, which have promising applications in biosensing, filtering, and lasing.

Dual resonance based on quasi-bound states in continuum in the all-dielectric terahertz metasurface and its application in sensing

In recent years, the concept of bound states in continuum (BIC) in metasurfaces has become a topic of interest. BIC involves the physical mechanics of wave optics, metamaterial sensors and other high-quality factor (Q-factor) applications. In this paper, the basic concept of BIC is introduced, followed by a brief description of the progression of the research regarding the application of BIC in terahertz (THz) metasurfaces. Subsequently, an all-dielectric metasurface consisting of tetramer clusters with dual terahertz resonances is proposed. The materials used for the substrate and the tetramer cluster are quartz and silicon, respectively. Quasi-BIC works by varying the cylinder radius on the metasurface structure. The transmission spectra are analyzed under different structural and material parameters with control variables. When the metasurface is applied as a refractive-index sensor, the Q-factor is 2303.77 and the figure of merit (FOM) is 7022.90, which are calculated using the asymmetric parameter k = 0.8 μm. Additionally, when the incident wave is x- or y-polarized, resonance peaks with the same frequencies can be obtained, and the overall trend of the transmission spectrum remains the same.

Pt : Ge Ratio as a Lever of Activity and Selectivity Control of Supported PtGe Clusters in Thermal Dehydrogenation**

AbstractEthylene is a key molecule in the chemical industry and it can be obtained through the catalytic dehydrogenation of ethane. Pt‐based catalysts show high performance toward alkane dehydrogenation, but suffer from coke formation and sintering that deactivate the catalyst. Ge was recently discovered to be a promising alloying element that suppresses deactivation of Pt while preserving its catalytic activity toward alkane dehydrogenation. This work explores the effect of the Ge content in supported PtGe cluster alloys, on the activity toward ethane dehydrogenation, selectivity against deeper dehydrogenation and coking, and sintering resistance. The model proposed herein is a tetrameric Pt cluster supported on magnesia, with varying amounts of added Ge. The phase diagram for these clusters was computed using global optimization at the density functional theory level, and under the paradigm of a statistical ensemble of many states populated by clusters at catalytic temperatures. The phase diagram shows that various Ge contents should be synthetically accessible, with Pt4Ge/MgO and Pt4Ge4/MgO being the most likely phases. The subsequent adsorption and mechanistic studies show that the clusters with the 1 : 4 Ge to Pt ratio (Pt4Ge/MgO) feature the largest resistance to sintering and best selectivity in the ethane dehydrogenation toward ethylene. Clusters without Ge are too active and easily coke, whereas clusters with higher Ge content start losing the catalytic activity toward ethane dehydrogenation. Thus, Ge concentration is a lever of control of Pt cluster stability and selectivity, and of cluster catalyst design. The effect of the Ge concentration on the cluster properties is explained on the basis of the electronic structure.

Design of a Hierarchical Assembly at a Solid-Liquid Interface Using an Asymmetric Protein Needle.

Design and control of processes for a hierarchical assembly of proteins remain challenging because it requires consideration of design principles with atomic-level accuracy. Previous studies have adopted symmetry-based strategies to minimize the complexity of protein-protein interactions and this has placed constraints on the structures of the resulting protein assemblies. In the present work, we used an anisotropic-shaped protein needle, gene product 5 (gp5) from bacteriophage T4 with a C-terminal hexahistidine-tag (His-tag) (gp5_CHis), to construct a hierarchical assembly with two distinct protein-protein interaction sites. High-speed atomic force microscopy (HS-AFM) measurements reveal that it forms unique tetrameric clusters through its N-terminal head on a mica surface. The clusters further self-assemble into a monolayer through the C-terminal His-tag. The HS-AFM images and displacement analyses show that the monolayer is a network-like structure rather than a crystalline lattice. Our results expand the toolbox for constructing hierarchical protein assemblies based on structural anisotropy.

Impact of the Si/Al ratio on the ethanol/water coadsorption on MFI zeolites revealed using original quantitative IR approaches.

Advanced IR vibrational spectroscopic techniques, e.g., using a coupled gravimetric-IR surface analyzer (AGIR) and a high-throughput in situ IR cell (Carroucell), have been used for the quantitative studies of the adsorption and coadsorption of ethanol and water on MFI zeolites with different Si/Al ratios. The AGIR coupling is a powerful tool for the accurate determination of the molar adsorption coefficients during coadsorption experiments since their evaluation is based on the measurement of the exact amount of adsorbed species. The use of the Carroucell set up allows characterizing all the samples simultaneously, strictly in the same gaseous and temperature environment. The molar absorption coefficients of pure adsorbed ethanol and water are determined: their values are constant whatever the Si/Al ratio of the MFI zeolites. Moreover, these coefficients are found to be identical in the case of the water-ethanol coadsorption experiments. Their use allows obtaining the exact quantity of each adsorbate specie in the binary system. At low partial pressures, the unary water adsorption experiments suggest that the amount of adsorbed water results mainly from the preferential adsorption on Brønsted acid sites in tetrameric clusters. In contrast, the adsorption of EtOH occurs on both silanol groups and Brønsted acid sites (BASs). The effect of the Si/Al ratio is only observed at relatively low partial pressures. The effect of the Si/Al ratio on the ethanol adsorption capacity is also investigated. This study directs the choice of an appropriate zeolite once it is used in membranes for drying ethanol.