Unraveling the Photophysical Characteristics, Aromaticity, and Stability of π–Extended Acene‐Quinodimethyl Thioamides†

Posted on 19 September 2023 by

Local pro-aromaticity in acene thioamides chromophores is conducive to triplet photochemistry. However, additional aromatic sextet(s) on the π-core of these chromophores would affect their photostability and photochemistry.

Abstract

Poly-aromatic systems that contain quinodimethyl (QDM) units are appealing for several photonic and spintronic applications owing to the unique electronic structure, aromaticity, and spin state(s) of the QDM ring. Herein, we report the synthesis and characterization of novel QDM-based chromophores 1–3, which exhibit unique photo-excited behavior and aromaticity. Extending the aromatic core with a biphenyl/phenanthryl- and a pyrrolo-fragment led to reducing the optoelectronic bandgap and modulating the photophysics QDM 1–3. Yet, QDM 2 and 3 suffer from “aromaticity imbalance” and become relatively unstable compared to the parent compound QDM 1. Further assessment of local aromaticity using computational tools revealed that the pseudo-quinoidal ring B is the main driving force allowing to easily populate the excited triplet state of these chromophores. The present study provides complementary guidelines for designing novel non-classical poly-aromatic systems.

Bromine Adsorption and Thermal Stability on Rh(111): A Combined XPS, LEED and DFT Study

Posted on 19 September 2023 by

The adsorption and thermal stability of bromine on Rh(111) is investigated by synchrotron radiation-based XPS, LEED and DFT. Depending on the coverage, four different superstructures are observed. At low coverages, bromine occupies fcc hollow sites while, at higher coverages, a compression of the overlayer leads to bridge-bound bromine atoms. Br/Rh(111) shows a high thermal stability, which implies strong covalent bonding.

Abstract

This study addresses a fundamental question in surface science: the adsorption of halogens on metal surfaces. Using synchrotron radiation-based high-resolution X-ray photoelectron spectroscopy (XPS), temperature-programmed XPS, low-energy electron diffraction (LEED) and density functional theory (DFT) calculations, we investigated the adsorption and thermal stability of bromine on Rh(111) in detail. The adsorption of elemental bromine on Rh(111) at 170 K was followed in situ by XPS in the Br 3d region, revealing two individual, coverage-dependent species, which we assign to fcc hollow- and bridge-bound atomic bromine. In addition, we find a significant shift in binding energy upon increasing coverage due to adsorbate-adsorbate interactions. Subsequent heating shows a high thermal stability of bromine on Rh(111) up to above 1000 K, indicating strong covalent bonding. To complement the XPS data, LEED was used to study the long-range order of bromine on Rh(111): we observe a (√3×√3)R30° structure for low coverages (≤0.33 ML) and a star-shaped compression structure for higher coverages (0.33–0.43 ML). Combining LEED and DFT calculations, we were able to visualize bromine adsorption on Rh(111) in real space for varying coverages.

Organic Fluorine Compounds and Their Uses as Molecular MR‐Based Temperature Sensors

Posted on 19 September 2023 by

Fluorinated organic molecules can be used as thermosensors for MR-based temperature determination. Thirteen fluorinated organic substrates were investigated with regard to the temperature sensitivity of their ¹⁹F MR signal(s) in aqueous solution. Such molecules can be used as thermosensors for MR-based temperature determination, for example, in medical applications such as hyper- or hypothermia.

Abstract

The interest in fluorinated substances has increased significantly in recent decades due to their diverse properties and possible uses. An important analytical method in this context is NMR spectroscopy, which provides information on the structure as well as on intermolecular interactions or generally on changes in the environment of the nucleus under consideration. A physical quantity that is of great importance in most studies is temperature. However, this is not always easy, e. g. in shielded systems or within an organism. However, the application potential in chemical reactors or in medical diagnosis and therapy is very high and for this reason 13 fluorinated organic compound were chosen for a first ¹⁹F NMR signal temperature sensitivity examination for determination of local temperatures in solution. Polyfluorinated molecules with separate ¹⁹F MR signals are particularly suitable for temperature determination. Those can be serve as internal error-correcting thermometers without the need of a reference substance. Under these conditions, a ¹⁹F MR signal shift of up to 0.03 ppm/K was detectable. Fluorine position and chemical environment were very important for the temperature sensitivity.

A Calcination‐Free Sol‐Gel Method to Prepare TiO2‐Based Hybrid Semiconductors for Enhanced Visible Light‐Driven Hydrogen Production

Posted on 19 September 2023 by nKang Yang, nDan Wei, nChunman Jia, nJianwei Lin

The extensive π system in the naphthalene structure and the carboxylic acid group of 1,4-naphthalene dicarboxylic acid (NA) render it an exceptional organic semiconductor for doping TiO₂ using a calcination-free sol-gel method. The resulting catalyst exhibited a significantly improved hydrogen production rate by photolyzing water molecules under visible light, outperforming the efficiency of the calcined material. Read more about the story behind the cover in the Cover Profile and about the research itself (DOI: 10.1002/cplu.202300172).

Abstract

Invited for this month's cover are the collaborating groups of Dr. Jianwei Li at the University of Turku and Prof. Chunman Jia, Kang Yang and Dan Wei at Hainan University. The cover image compares the structure of calcined (left) and non-calcined (right) rutile TiO₂ doped with a molecule NA. The calcination process enlarges the pores in TiO₂, reducing its surface area and hydrogen production efficiency under visible light. The “sad face” symbolizes the damaged pore structure. Conversely, doping TiO₂ with NA without high-temperature calcination forms a covalent bond, resulting in smaller pores, larger surface area, and improved hydrogen production efficiency. The “smiley face” represents the structurally intact TiO₂ hybrid material. More information can be found in the Research Article by Jianwei Li, Chunman Jia, and co-workers.

Synthesis and Characterization of Homoleptic Zintl Anions [(Pn7)M(Pn7)]4− (M/Pn=Pb/As, Zn/Bi)

Posted on 19 September 2023 by nFuxing Pan, nRodica Ababei, nWerner Massa, nStefanie Dehnenn

Variations of the coordination of nortricyclane-type 7-atom polypnictides to metal ions were achieved upon reactions of either K₃As₇ with PbI₂ in ethane-1,2-diamine and subsequent layering with toluene or by reacting an extraction solution of ‘K₅Ga₂Bi₄’ in pyridine with [ZnPh₂] prior to layering with toluene. The two procedures were specific for the respective elemental combinations, and they afforded the second compound exhibiting the rare Bi₇ ³⁻ ion in the coordination sphere of transition metal ions.

Abstract

The formation and follow-up chemistry of P₇ ³⁻ has been intensely studied in the recent decades. In contrast, corresponding investigations of its heavier polycyclic polypnictide congeners Pn₇ ³⁻ (Pn=As, Sb, Bi), especially Bi₇ ³⁻, have been done to a much lesser extent. In our report, we add to these rare studies, by reporting new coordination compounds with As₇ ³⁻ and Bi₇ ³⁻, respectively. Addition of PbI₂ to a solution of K₃As₇ in ethane-1,2-diamine (en) afforded the heterometallic cluster anion [(As₇)Pb(As₇)]⁴⁻ (with an 8 % co-crystallization of [PbAs₁₅]³⁻ on the same site), in compound [K_3.92(crypt-222)₄][(As₇)Pb(As₇)]_0.92[PbAs₁₅]_0.08 ⋅ 3en (1). A similar reaction of [ZnPh₂] with a pyridine (py) solution of the ternary solid ‘K₅Ga₂Bi₄’, which was previously shown to release Ga and polybismuthide units in situ under certain reaction conditions, resulted in the formation of [K(crypt-222)]₄[(Bi₇)Zn(Bi₇)] ⋅ 2.5py (2), comprising the related heterometallic anion [(Bi₇)Zn(Bi₇)]⁴⁻. The former represents the first Pb−As binary Zintl anions obtained via solution chemistry, and the latter adds one more piece to the remarkably rare coordination compounds reported for Bi₇ ³⁻.

Insight into the Structure of MOF‐Containing Hybrid Polymeric Microspheres

Posted on 19 September 2023 by nMarta Goliszek, nMaria Kochaniec, nB. Beata Podkościelnan

Polymer science has exploited MOFs for various purposes, which is due to the fact that these structures are ideal platforms for identifying design features for advanced functional materials. The mechanism of polymerization using MOFs is still largely unexplored and the detailed characterization of both materials is essential to understand the important interactions between the components.

Abstract

Polymer science exploited metal organic frameworks (MOFs) for various purposes, which is due to the fact that these materials are ideal platforms for identifying design features for advanced functional materials. The mechanism of polymerization using MOFs, is still largely unexplored and the detailed characterization of both materials in essential to understand the important interactions between the components. In this work modern advanced research methods were used to investigate the properties of MOF-containing hybrid polymeric microspheres. Hydrothermal conversion of CFA-derived iron particles was used to obtain MOF nanostructures, which were then introduced to the structure of hybrid polymer microspheres based on ethylene glycol dimethylacrylate (EGDMA) and triethoxyvinylsilane (TEVS). Chemical structures were confirmed by ATR-FTIR method. To provide information about the elemental composition of the tested materials and for the determination of chemical bonds present in the tested samples XPS method was applied. Morphology was studied using SEM microscopy, whereas porosity was investigated using ASAP technique. Swellability coefficients were determined using typical organic solvents and distilled water. Moreover, the ecological aspect concerning the use of fly ashes deserves to be emphasized.

The Reaction of Muonium with Hydrogen Peroxide in Aqueous Solution

Posted on 19 September 2023 by nPaul W. Percival, nJean‐Claude Brodovitchn

Experimental data on muonium kinetics in water greatly expands the set of experimental data on kinetic isotope effects in the reactions of H atoms with H₂O₂ and its conjugate base HOO⁻.

Abstract

Rate constants for the reactions of muonium (Mu) (the ultralight isotope of the hydrogen atom) with H₂O₂ in H₂O and D₂O₂ in D₂O have been determined at various temperatures and pH (pD) values. The data are consistent with the three reactions: , , and the equivalent for the deuterated entities. A significant positive H/D isotope effect was found for the undissociated peroxide, while for the anions the effect was negligible or slightly in the opposite direction. In addition, for concentrated solutions of peroxide a study of the muon spin polarization as a function of applied transverse magnetic field yielded results consistent with the rate constants determined from the direct decay measurements, and indicated that the reaction products are diamagnetic, most likely MuH and MuOH, i. e., no muoniated radical products are formed. These results are potentially relevant for management of the radiolysis products in nuclear industry.

Exposing the Oxygen‐Centered Radical Character of the Tetraoxido Ruthenium(VIII) Cation [RuO4]+

Posted on 19 September 2023 by

Production of gas-phase [RuO₄]⁺ via oxidation of ruthenium cations by ozone allows for the direct probing of its oxygen-centered radical character by X-ray absorption spectroscopy. Combining experiment and quantum-chemical calculations, the authors show that the oxygen-centered singly occupied molecular orbital (SOMO) is signalized by a low-energy peak at the oxygen K edge, and is quenched upon hydrogenation in closed-shell [RuO₄H]⁺.

Abstract

The tetraoxido ruthenium(VIII) radical cation, [RuO₄]⁺, should be a strong oxidizing agent, but has been difficult to produce and investigate so far. In our X-ray absorption spectroscopy study, in combination with quantum-chemical calculations, we show that [RuO₄]⁺, produced via oxidation of ruthenium cations by ozone in the gas phase, forms the oxygen-centered radical ground state. The oxygen-centered radical character of [RuO₄]⁺ is identified by the chemical shift at the ruthenium M₃ edge, indicative of ruthenium(VIII), and by the presence of a characteristic low-energy transition at the oxygen K edge, involving an oxygen-centered singly-occupied molecular orbital, which is suppressed when the oxygen-centered radical is quenched by hydrogenation of [RuO₄]⁺ to the closed-shell [RuO₄H]⁺ ion. Hydrogen-atom abstraction from methane is calculated to be only slightly less exothermic for [RuO₄]⁺ than for [OsO₄]⁺.

Nine‐coordinated Eu3+ Dipicolinate Compounds: Different Crystal Structures and Luminescence Properties as a Function of pH

Posted on 19 September 2023 by nSabina Svava Mortensen, nThomas Just Sørensenn

In this comparative study, two different nine-coordinated Eu³⁺ compounds with [DPA]²⁻ were crystallised. [Eu(DPA)(HDPA)(H₂O)₂] ⋅ 4H₂O and Na₃[Eu(DPA)₃] ⋅ 14H₂O were found to form in all samples, and the ratio between them can be controlled by pH. Despite the presence of both compounds in all samples, this was not evident from luminescence and PXRD data, althhough the data did not show the single crystal data properties.

Abstract

Two compounds, Na₃[Eu(DPA)₃] ⋅ 14H₂O and [Eu(DPA)(HDPA)(H₂O)₂] ⋅ 4H₂O, were created and the structure determined using single crystal X-ray diffraction. The single crystal luminescence properties were compared and related to the Eu³⁺ coordination geometry. The formation of single crystals from solutions of Eu(CF₃SO₃)₃ and H₂DPA was found change with the pH value of the H₂DPA solution. Mixtures of Na₃[Eu(DPA)₃] ⋅ 14H₂O and [Eu(DPA)(HDPA)(H₂O)₂] ⋅ 4H₂O were observed with a pH ratio between the two structures. While visual inspection showed that all samples contained both Na₃[Eu(DPA)₃] ⋅ 14H₂O and [Eu(DPA)(HDPA)(H₂O)₂] ⋅ 4H₂O, the PXRD and luminescence data did not immediately reveal that the samples were pure. Having discovered that the samples were indeed mixtures, quantification was attempted by Rietveld refinement of the PXRD data, and the luminescence spectra were compared to those from single crystals. As the data was not found to reveal that the samples were mixtures, even though we knew that this was the case, we must urge caution when inferring structure-property relationships from powder samples. In this case we were able to isolate monophasic systems and do a comparative study, but this requires that the samples are identified as mixtures.

5‐Nitrofuryl‐Containing Thiosemicarbazone Gold(I) Compounds: Synthesis, Stability Studies, and Anticancer Activity

Posted on 19 September 2023 by

The synthesis of four gold(I) [AuClL] compounds containing chloro and biologically active protonated thiosemicarbazones based on 5-nitrofuryl (L=HSTC) is reported. The cytotoxicity of the gold compounds and thiosemicarbazone ligands was evaluated against selected cancer cell lines and compared to that of Auranofin. Read more about the story behind the cover in the Cover Profile and about the research itself (DOI: 10.1002/cplu.202300115).

Abstract

Invited for this month's cover are the collaborating groups of Esteban Rodríguez-Arce from the University of Chile and María Contel from The City University of New York Brooklyn College. The cover picture shows “Supergold“ a very powerful gender neutral warrior with superpowers who fights against cancer! The warrior's golden armor and sword represent the pharmacological power of the gold atom. Engraved on the shield, the gold-thiosemicarbazone molecules are the warrior's coat of arms. Supergold selectively destroys different cancer cells. More information can be found in the Research Article by Esteban Rodríguez-Arce, María Contel, and co-workers.