Cyclic Cluster Research Articles

Triple crossed 3 C26 cyclic cumulene catenane

Cumulenes are valuable precursors to an entire series of more complex organic derivatives. Cyclic cumulenes present a special case, since they possess an increased potential to possess a high order of symmetry. The stability of the cumulene molecule can be brought forth through the construction of crossed clusters. In this case, molecular modeling tools were employed in order to provide insights into the construction and stability of 3 C26 triple crossed C26 cyclic cumulene cluster. The study revealed that is a very little change in the total energy per atom (or per electron) of triple crossed 3 C26 when compared with C26 (0.00002 Hartree/e, which is less than 0.01 ‰). Other important parameters, such as the HOMO-LUMO gap and the angles between the planes of the molecular rings, suggest its kinship with fullerenes and the regular tetrahedron. Furthermore, in order to proof the suitability of the approach and of its results a symmetry constrained optimization study was conducted using Z-matrix internal coordinates with Gaussian software. At DFT BLYP 6-311 G* theory level a symmetry constrained optimization of the 3 C26 cluster converged, which suggests the possibility of obtaining this cluster by synthetic means.

Ba4@Sn56]36- as a Main-Group Second-Order Superatom. Interpenetrated Dodecahedrons as a Three-Dimensional Cluster-of-Clusters Structure.

Superatomic clusters are relevant species to further understanding of bonding and structural properties of atomically precise molecular nanoparticles. Here, we explore the characteristics of ligand-free [Ba4@Sn56]36- Zintl-ion, as a three-dimensional aggregate of clusters featuring four fused Ba@Sn19 building units as an extension of the understanding in linear and cyclic superatomic cluster arrays. We provide a rational picture of the electronic shell in [Ba4@Sn56]36- as a cluster-of-clusters motif through the recently introduced second-order superatom approach, as a three-dimensional aggregation of superatomic clusters where their shells are able to interact. The electronic structure features both tangential and radial shells from the four building Ba@Sn19 units, leading to a set of 1S'21P'61D'101F'14 and higher angular momentum shells and a second set of 2S'22P'62D'102F'142G'8 second-order shells. Thus, the current approach serves to encourage the rationalization of molecular materials conceived from cluster building blocks toward a rational guide for synthetic efforts.

A molecular mechanics implementation of the cyclic cluster model

Abstract The implementation of the cyclic cluster model (CCM) for molecular mechanics is presented in the framework of the computational chemistry program deMon2k. Because the CCM is particularly well-suited for the description of periodic systems with defects, it can be used for periodic QM/MM approaches where the non-periodic QM part is treated as a defect in a periodic MM surrounding. To this end, we present here the explicit formulae for the evaluation of the Ewald sum and its first- and second-order derivatives as implemented in deMon2k. The outlined implementation was tested in molecular dynamics (MD) simulations and periodic structure optimization calculations. MD simulations of an argon system were carried out using the Nosé-Hoover chain (NHC) thermostat and the Martyna-Tobias-Klein (MTK) barostat to control the temperature and pressure of the system, respectively. For the validation of CCM structure optimization a set of molecular crystals were optimized using the Ewald method for the evaluation of the electrostatic interactions. Two optimization procedures for the determination of the atomic positions and CCM cell parameters were tested. Our results show that the simultaneous optimization of the atomic positions and cell parameters is most efficient.

A nested spin structure and single molecule magnet behaviour in an Fe8Dy12 heterometallic cyclic coordination cluster.

The 20-nuclearity compound [Fe8Dy12(tea)8(teaH)12(NO3)12]·8MeCN (where teaH3 = triethanolamine) was synthesised and characterised through single crystal X-ray diffraction and magnetic measurements. The shape of the magnetic hysteresis in the microSQUID measurements was rationalised using the MAGELLAN program.

Gas-phase electronic spectra of HC2n+1H+ (n = 2-6) chains.

Highly unsaturated carbon chains are generated in combustion processes and electrical discharges, and are confirmed constituents of the interstellar medium. In hydrogen-rich environments smaller carbon clusters tend to exist as linear chains, capped on each end by hydrogen atoms. Although the HC2nH+ polyacetylene chains have been extensively characterized spectroscopically, the corresponding odd HC2n+1H+ chains have received far less attention. Here we use two-colour resonance enhanced photodissociation spectroscopy to measure electronic spectra for HC2n+1H+ (n = 2-6) chains contained in a cryogenically cooled quadrupole ion trap. The HC2n+1H+ chains are formed either top-down by ionizing and fragmenting pyrene molecules using pulsed 266 nm radiation, or bottom-up by reacting cyclic carbon cluster cations with acetylene. Ion mobility measurements confirm that the HC2n+1H+ species are linear, consistent with predictions from electronic structure calculations. The HC2n+1H+ electronic spectra exhibit three band systems in the visible/near infrared spectral range, which each shifts progressively to longer wavelength by ≈90 nm with the addition of each additional CC subunit. The strongest visible HC11H+ band has a wavelength (λ = 545.1 nm) and width (1.5 nm) that match the strong λ 5450 diffuse interstellar band (DIB). However, other weaker HC11H+ bands do not correspond to catalogued DIBs, casting doubt on the role of HC11H+ as a carrier for the λ 5450 DIB. There are no identifiable correspondences between catalogued DIBs and bands for the other HC2n+1H+ chains, allowing upper limits to be established for their column densities in diffuse interstellar clouds.

Is triple crossed C28 cyclic polyyne cluster a stable conformation?

Polyynes sometimes referred to as oligoynes or carbinoids, and their resonance cumulene form are valuable precursors to a whole series of more complex organic derivatives. Motivated by a series of studies that explore the stabilization of polyynes, in different ways, the possibility of their stabilization through the formation of crossed cycles is explored in this article. It is easy to notice that the cyclic conformations represent a special case, in that they possess an increased symmetry. The stability of the polyene molecule can be enhanced by building cross-clusters. In this article, the molecular modeling tools were employed in order to provide insights about the construction and stability of 3C28 triple crossed C28 cyclic polyyne cluster. It has been shown that C28 and 3C28 triple crossed C28 are very similar energetically. HOMO–LUMO gap suggests a metallic conductivity. The angles between the planes of the molecular rings shows almost an axial alignment of the rings. A symmetry-constrained optimization was conducted using Z-matrix internal coordinates and Gaussian software, and it revealed that the geometrical conformation of C28 polyyne as triple crossed cluster is a stable conformation, since in all investigated scenarios the convergence is assured and it is to nearly optimum local points.

A Thiol-Michael Approach Towards Versatile Functionalized Cyclic Titanium-Oxo Clusters.

In expanding our research activities of superlattice engineering, designing new giant molecules is the necessary first step. One attempt is to use inorganic transition metal clusters as building blocks. Efficient functionalization of chemically precise transition metal clusters, however, remains a great challenge to material scientists. Herein, we report an efficient thiol-Michael addition approach for the modifications of cyclic titanium-oxo cluster (CTOC). Several advantages, including high efficiency, mild reaction condition, capability of complete addition, high atom economy, as well as high functional group tolerance were demonstrated. This approach can afford high yields of fully functionalized CTOCs, which provides a powerful platform for achieving versatile functionalization of precise transition metal clusters and further applications.

The intermolecular interactions of methanol diluted in protic and aprotic solvent probed by polarized Raman spectroscopy and HNMR

Polarized Raman spectra of the VV component (R∥) and the VH component (R⊥), 2D-COS synchronous and asynchronous spectra, and HNMR of CH3OH/CH3CN and CH3OH/H2O binary mixture were collected at different volume fractions. The intermolecular interactions of methanol diluted in protic (H2O) and aprotic solvent (CH3CN) were compared and discussed. The experiments showed that the frequency difference ΔνAIS = ν⊥-ν∥ of C-O stretching was −4 for pure methanol and 0 at very dilute concentrations. During the dilution process, the ν∥ of C-O stretching downshifted by approximately 17 cm−1 for CH3OH/H2O binary mixture, while down shifted 5 cm−1 for the CH3OH/CH3CN mixture and 12 cm−1 for the CH3OH/CHCl3 mixture. The dilution process was identified as a cyclic cluster depolymerization process. The difference in amplitude of frequency downshift could be explained by the different properties of the hydrogen bond. Different H-bond cyclic clusters were proposed for different volume fractions of the CH3OH/H2O mixture. Additionally, the chemical shift movement of δOH with concentration also supports the cluster depolymerization process, which is consistent with the results of polarization Raman spectroscopy. The establishment of the coupling-induced spectral splitting theory will play an important role in determining the aggregation behavior of biomolecules and the structure of supramolecular self-assembly.

Assessment of the safety and metabolism characteristics of Streptococcus thermophilus DMST-H2 based on complete genome and phenotype analysis

A genome-based systematic analysis combined with phenotypic experiments was conducted to evaluate the safety properties and metabolic characteristics of Streptococcus thermophilus DMST-H2, isolated from Chinese traditional homemade yogurt in Inner Mongolia. Comparative genomic analysis showed that DMST-H2 had a closer genetic relationship with S. thermophilus KLDS.3.1003 based on the sequence similarities of the 1193 core-genes. No genes related to antibiotic resistance and virulence factor as well as no complete biogenic amine biosynthesis gene clusters were identified in DMST-H2 genome. DMST-H2 was sensitive to various antibiotics and had no hemolytic activity and no biogenic amine production capacity, confirming that DMST-H2 is safe and non-toxic. In addition, multiple genes for carbohydrate metabolism were predicted, including various carbohydrate-active enzymes and sugar transporters that could be involved in the transport of multiple carbon sources. Two exopolysaccharide (EPS) gene clusters (eps-1 and rgp-2) were also detected, indicating that DMST-H2 has the potential to synthesize heteropolysaccharides. Gene functional features revealed a cyclic antimicrobial peptide related gene cluster in DMST-H2, which displayed high identities with the streptide biosynthesis gene cluster as previously reported. Our comprehensive analysis of the whole genome and corresponding phenotypes of S. thermophilus DMST-H2 provides important theoretical basis for its application in food products.

Cadmium-containing windmill-like heteropolyoxoniobate macrocycle with high yield for catalyzing Knoevenagel condensation.

A rare cadmium-containing windmill-like heteropolyoxoniobate macrocycle has been successfully synthesized with stable 1-D cyclic cluster aggregates. The compound exhibited promising basic catalytic ability for Knoevenagel condensation with a high yield under mild reaction conditions and high cycling stability. The theoretical calculation showed that the promising basic catalytic ability is due to the dense and stronger basic sites of the surface terminal O atoms.

Crystal structure of Rb6[B12O18(OH)6]·2H2O.

The solvothermal reaction of H3BO3, sodium tert-butoxide, Rb2CO3 and pyridine led to a new alkaline metal borate hexa-rubidium hexa-hydroxy-dodeca-borate dihydrate, Rb6[B12O18(OH)6]·2H2O. Its structure contains a large cyclic dodeca-oxoboron cluster, [B12O18(OH)6]6-, formed by six {B3O3} rings. In the crystal, O-H⋯O hydrogen bonds between the components lead to the formation of a three-dimensional supra-molecular framework.

Quantum computational advantage attested by nonlocal games with the cyclic cluster state

We propose a set of Bell-type nonlocal games that can be used to prove an unconditional quantum advantage in an objective and hardware-agnostic manner. In these games, the circuit depth needed to prepare a cyclic cluster state and measure a subset of its Pauli stabilizers on a quantum computer is compared to that of classical Boolean circuits with the same, nearest-neighboring gate connectivity. Using a circuit-based trapped-ion quantum computer, we prepare and measure a six-qubit cyclic cluster state with an overall fidelity of 60.6% and 66.4%, before and after correcting for measurement-readout errors, respectively. Our experimental results indicate that while this fidelity readily passes conventional (or depth-0) Bell bounds for local hidden-variable models, it is on the cusp of demonstrating a higher probability of success than what is possible by depth-1 classical circuits. Our games offer a practical and scalable set of quantitative benchmarks for quantum computers in the pre-fault-tolerant regime as the number of qubits available increases.

Mechanical-robust and recyclable polyimide substrates coordinated with cyclic Ti-oxo cluster for flexible organic solar cells

With the rapid development of flexible optoelectronic devices, recyclability is highly desirable for alleviating resource waste and environmental pollution, but remains challenging. Here, a fully closed-loop recyclable crosslinked polyimide (RCPI) was fabricated via carboxyl ligand exchange between the CPI with pendent carboxyl groups and the cyclic Ti-oxo cluster (CTOC) with labile carboxyl ligands, which could be reconverted into reprocessable CPI and CTOC solution by pivalic acid. The RCPI-based embedded AgNWs@RCPI electrode shows comparable high conductivity, transparency and low roughness with ITO (indium tin oxide)/glass electrode, and meanwhile outstanding mechanical robustness. The related flexible organic solar cells (FOSCs) provided a high efficiency of 14.78% and maintained ~97% of the initial efficiency after 5000 bending cycles at a small bending radius of 1 mm. Moreover, the recyclability of the RCPI still retains after being manufactured into the FOSCs. This work provides a promising strategy for recyclable flexible optoelectronic devices.

Crystal structure of [Rh2(μ-OAc)2(μ-HNOCCF3)2(theophylline)2]·6H2O. Metal bonding to theophylline at the unexpected N(9) site due to the crystal packing effect and a review on intra-molecular interligand interactions affecting metal bonding properties of theophylline

• Crystal structure of a dinuclear Rh 2+ complex of theophylline was determined. • The Rh‒Rh core is occupied at either axial-side by theophylline ligands through N9. • Metal bonding not to expected N7 but to N9 is due to the crystal packing effect. • A discrete, cyclic hexameric water cluster intercalates between theophylline rings. • Metal binding sites of theophylline are reviewed in terms of interligand interaction. Reaction of theophylline with [Rh 2 (μ-OAc) 2 (μ-HNOCCF 3 ) 2 ] gave [Rh 2 (μ-OAc) 2 (μ-HNOCCF 3 ) 2 (theophylline) 2 ]·6H 2 O ( 1 ), whose crystal structure was determined by single-crystal X-ray diffraction. The dirhodium core, where the two different acetato and acetamidato ligands bridging the Rh‒Rh bond are in a trans configuration, is occupied at either axial-side by two theophylline ligands through N(9) with the formation of two kinds of intra-molecular interligand C−H (theophylline)···O hydrogen bonds, one being a bifurcated hydrogen bond between the C(3)-methyl hydrogen as a donor and the acetato and amidato oxygens as acceptors and the other between the C(8) hydrogen and the acetato oxygen. In the crystal lattice, a discrete, hydrogen-bonding, cyclic hexameric water cluster with the flattened chair conformation is sandwiched between theophylline bases, providing the first water hexagon that intercalates between aromatic rings. The participation of the acetamidato NH group in the formation of a hydrogen bond with a water molecule belonging to the water hexagon that governs the crystal packing makes it impossible for the acetamidato ligand to form an intra-molecular hydrogen bond with O(6), causing the failure of the metal bonding to theophylline through N(7). A critical review on metal bonding properties of theophylline observed in so far reported crystal structures is given, emphasizing the significance of intra-molecular interligand interactions (H-bonding, electrostatic repulsion, and steric constraint) as a factor that could affect metal binding sites/modes of theophylline.

A Cyclic Titanium-Oxo Cluster with a Tetrathiafulvalene Connector as a Precursor for Highly Efficient Adsorbent of Cationic Dyes.

Titanium-oxo clusters (TOCs) have been studied for applications in catalysis, energy storage and transfer, light emission, and so on; however, use of TOCs for the selective adsorption of dyes has not yet been reported. Herein, a TOC compound formulated as [Ti6O3(OiPr)14(TTFTC)]4 (1, TTFTC = tetrathiafulvalene-tetracarboxylate) was successfully prepared and crystallographically characterized. Compound 1 has a cyclic structure assembled by four Ti6 clusters and four rodlike TTFTC connectors. Red compound 1 self-condenses to form a black polymeric organic-inorganic hybrid material (denoted as B-1), which was characterized by various techniques. B-1 is an amorphous TiO material that is formed by the irregular condensation of 1 by the removal of alkoxyl groups. B-1 exhibits high dye adsorption efficiency toward cationic dyes with a qe value of 651.3 mg/g at 298 K for methylene blue (MB). Moreover, B-1 can be used to selectively remove MB not only from mixed cationic-anionic dye solutions but also from some mixed cationic dyes, which is related to their structures. Kinetic, isotherm, and thermodynamic studies demonstrated that the pseudo-second-order kinetic model and Freundlich model show a good fit to the experimental data. The adsorption process involves an exothermic and entropy decreasing process. In addition, dye-adsorbed B-1 can be further used as a photocurrent-responsive material. The work opens up a new field for the application of TOCs in the selective adsorption and removal of dyes.

Assembly of Interlocked Superstructures with a Titanium Oxide Molecular Ring in Water.

[2]Catenane, [2]rotaxane, and [2]pseudorotaxane based on a cyclic titanium oxide cluster, [Ti8O8(SO4)16]16- (Ti8), and cyclic/linear alkylammonium cations are reported. Their syntheses, structures, spectroscopy, and stability in water were studied. These molecules were synthesized from and remained intact upon redissolution in acidic water. Hence, the cluster Ti8 is a promising metal oxide ring that can be used as an inorganic analogue of crown ether to assemble inorganic-organic hybrid mechanical interlocked supramolecular assemblies in water.

Two Isostructural Titanium Metal-Organic Frameworks for Light Hydrocarbon Separation.

Presented here is the light hydrocarbon separation of titanium metal-organic frameworks (Ti-MOFs). Compared with the cyclic Ti-oxo cluster (Ti8O8(CO2)16, Ti8Ph), porous structures of FIR-125 and FIR-126 (FIR = Fujian Institute Research) can effectively improve the adsorption amounts of light hydrocarbons. The introduction of different functional groups and Ti-oxo clusters with small window sizes enables them to exhibit the highly selective separation of C2 and C3 hydrocarbons versus methane in an ambient atmosphere. The results show that Ti-MOFs are potential porous adsorbents for the separation of light hydrocarbons.

Crystal structures of 9-[bis-(benzyl-sulfan-yl)meth-yl]anthracene and of cyclo-dodeca-kis-(μ2-phenyl-methane-thiol-ato-κ2 S:S)hexa-palladium(6 Pd-Pd)-anthracene-9,10-dione (1/1).

The first title compound, C29H24S2, L1, represents an example of an anthracene-based functionalized di-thio-ether, which may be useful as a potential chelating or terminal ligand for coordination chemistry. This di-thio-acetal L1 crystallizes in the monoclinic space group P21/c. The phenyl rings of the benzyl groups and that of the anthracene unit form dihedral angles of 49.21 (4) and 58.79 (5)° and the crystal structure displays short C-H⋯π contacts. Surprisingly, when attempting to coordinate L1 to [PdCl2(PhCN)2], instead of the targeted chelate complex [PdCl2(κ2-L1)], a cleavage reaction leads to the formation of the centrosymmetric hexa-nuclear cyclic cluster of composition [Pd6(μ2-SCH2Ph)12] Pd6, or [Pd6(C7H7S)12]·C14H8O2. This tiara-shaped hexa-mer crystallizing in the triclinic space group P consists of six approximately square planar Pd(II)S4 centers, which are inter-connected through twelve μ2-bridging benzyl thiol-ate groups. The Pd⋯Pd contacts range from 3.0892 (2) to 3.1609 (2) Å and can be considered as weakly bonding. The unit cell of Pd6 contains also a co-crystallized anthracene-9,10-dione mol-ecule.

An Organic-Inorganic Hybrid Electrolyte as a Cathode Interlayer for Efficient Organic Solar Cells.

An organic-inorganic hybrid electrolyte based on a cyclic Ti-oxo cluster as the inorganic core and naphthalene-based organic ammonium bromide salts as the electrolyte was developed with easy synthesis and low cost. The new hybrid electrolyte exhibits excellent solubility in methanol, aligned work function, good conductivity, and amorphous state in thin film, enabling its successful application as a cathode interlayer in organic solar cells with a high power conversion efficiency of 17.19 %. This work demonstrates that the hybrid electrolytes are a new kind of semiconductor, exhibiting promising applications in organic electronics.

Hydrogen bonding and percolation in propan-2-ol – Water liquid mixtures: X-ray diffraction experiments and computer simulations

Synchrotron X-ray diffraction measurements have been conducted on aqueous mixtures of propan-2-ol (a.k.a. isopropanol, or 2-propanol), for alcohol contents between 10 and 90 mol%, from room temperature down to 230 K. Molecular dynamics simulations, by using an all-atom parametrization of the propan-2-ol molecule and the well-known TIP4P/2005 water model, were able to provide semi-quantitative descriptions of the measured total structure factors. Various quantities related to hydrogen bonding, like hydrogen bond numbers, size distribution of cyclic entities and cluster size distributions, have been determined from the particle co-ordinates obtained from the simulations. The percolation threshold at room temperature could be estimated to be between isopropanol concentrations of 62 and 74 mol%, whereas at very low temperature, calculations yielded a value above 90 mol%.