Category Archives: European Journal of Inorganic Chemistry

Covalent Organic Frameworks as a Versatile Platform for Iron‐Catalyzed sp3 C−H Activation and Cross‐Coupling via Decarboxylative Oxidation

Posted on 1 March 2024 by

Efficient oxidative cross-coupling of cinnamic acids with toluene using FeCl₃ immobilized on COF pore walls, producing 1,3-arylpropene derivatives. Fine-tuning adjustment of heterogeneous catalytic systems to uncover a significant relationship between pore size and the efficiency of the reaction.

Abstract

This work demonstrates the oxidative cross-coupling of cinnamic acids with toluene using FeCl₃ immobilized on a covalent organic framework (COF) pore wall, resulting in the synthesis of 1,3-arylpropene derivatives. This iron-based heterogeneous catalytic system affords the desired products in moderate yields ranging from 51 % to 65 %. Investigations using COFs with varying pore sizes indicate that larger pores facilitate the reaction, suggesting a spatial requirement for this transformation within the catalyst. The correlation between pore size and reaction efficiency provides insights into developing tailored catalysts to match the spatial requirements of the transformation. This version emphasizes the novelty of the study and the synthesis of 1,3-arylpropene derivatives. It also clarifies that the iron-based heterogeneous catalytic system is responsible for the reaction. Additionally, it provides a more detailed explanation of the findings regarding pore size and spatial requirements.

Enhanced Red Emission of Na5Lu9F32: Eu3+ Single Crystal by Introducing of GdF3

Posted on 29 February 2024 by

A series of Eu³⁺/Gd³⁺ co-doped Na₅Lu₉F₃₂ single crystals are prepared by Bridgman technique method. The emission intensity at 611 nm of Eu³⁺ ion in the single crystal increases obviously as Gd³⁺ doping upon excitation of 394 nm. The intensity of 1.8 mol % Gd³⁺ doped sample is boosted by 3.56 times compared with the un-doped one. The substitution of Gd³⁺ for the Lu³⁺ lattice position causes a variation of the Eu³⁺ ion local environment confirming from the change of red and orange emission intensities and enlargement of the unit cell, which are the reasons for the emission enhancement. The Na₅Lu₉F₃₂: Eu³⁺ single crystal doped with an appropriate concentration of GdF₃ is a type of promising red emission single crystal for related optical devices of detectors and laser.

Abstract

The bulk Na₅Lu₉F₃₂ single crystals with high quality serial Eu³⁺/Gd³⁺ co-doped were grown by an ameliorative Bridgman technique. The measurement of X-ray diffraction (XRD) and analysis of Rietveld refinement were implemented to validate the crystal phase. The Eu³⁺ doped Na₅Lu₉F₃₂ single crystal emits intense red emission at 611 nm excited by 394 nm light. The intensity of 1.8 mol % Gd³⁺ doped sample is boosted by 3.56 times compared with the un-doped one. The doping of Gd³⁺ ions replace competitively Lu³⁺ lattice sites with Eu³⁺ ions. Thus, they cause the lattice distortion and reduction of symmetry, enabling Eu³⁺ ions to overcome their 4f forbidden transitions. The change of Eu³⁺ ion local environment induced by Gd³⁺ ion doping was explored by the Eu³⁺ emission spectra and the variations of ratios between red and orange emission intensities (R/O). The fluorescence lifetime indicates that the introduction of GdF₃ decreases the probability of non-radiative transitions and increases the fluorescence lifetime. These results demonstrated that the Na₅Lu₉F₃₂: Eu³⁺ single crystal doped with an appropriate concentration of GdF₃ is a type of promising red emission single crystal for related optical devices of detector and laser due to its strong red emission, high transparency and high physico-chemical stability.

Beyond the Limits of Perbromo‐Substituted Octahedral Pnictogenaboranes: A Spectroscopic and Computational Study

Posted on 28 February 2024 by nWilli Keller, nJindřich Fanfrlík, nDrahomír Hnykn

Octahedral closo-1,2-Pn ₂B₄Br₄ (Pn=P, As) react with tetrahydrotoluene (THT) to get conjuncto-3,3’-(1,2-P₂B₄Br₃)₂. 4-THT-closo-1,2-P₂B₄Br₃ has also been detected which is isomerized through a pentagonal pyramidal intermediate to the corresponding 3-THT isomer to yield the conjuncto motif. This reaction is due to the presence of σ-holes on Br's. The σ-holes on Pn has enabled ESI-MS to detect various anions.

Abstract

Octahedral closo-1,2-Pn₂B₄Br₄ (Pn=P, As) molecules react with tetrahydrothiophene (THT), regarded as a soft base, much slower than with tetrahydrofuran (THF), considered a hard base. Namely, the reaction begins with only Pn=P at temperatures above 140 °C; 4-Br(CH₂)₄S-closo-1,2-P₂B₄Br₃ has been detected as the first product resulting from the cleavage and insertion of a thiobutylate group into the B−Br bond. Unlike in the reaction with THF, the addition of a second THT moiety has not been observed. Conversely, also starting from 140 °C, conjuncto-3,3’-(1,2-Pn ₂B₄Br₃)₂ has been found as the final product of the reaction, which indicates the presence of 3-Br(CH₂)₄S-closo-1,2-P₂B₄Br₃ as another intermediate during the conversion. A computational examination has revealed that it occurs through a pentagonal pyramidal stationary point as an additional intermediate, the latter of which serves as the crucial structural assembly for the thermal conversion that produces the conjuncto motif. Computations of the energy balance and ¹¹B and ³¹P NMR chemical shifts are in agreement with experimental observations. This reaction is made possible by the presence of σ-holes on the bromine atoms. In addition, the presence of the σ-holes on the pnictogens has enabled ESI-MS to detect various anions appearing during earlier and current syntheses.

Redox Reactivity Control Through Electromerism

Posted on 28 February 2024 by

The potential of electromerism for the tuning of redox reactivity on a large scale is demonstrated in a systematic study on copper complexes with redox-active diguanidine ligands.

Abstract

In this work, we demonstrate that electromerism could be used to regulate the redox reactivity. Electron self-exchange rates k _ex were measured for a series of diamagnetic, monocationic Cu^I complexes with two redox-active diguanidine ligands and the corresponding paramagnetic, dicationic complexes. The electronic structures of the paramagnetic, dicationic complexes differ. Some complexes are exclusively present as Cu^II complexes with reduced, neutral diguanidine ligands. In other complexes, an equilibrium is established between the Cu^II electromer and the Cu^I electromer with the unpaired electron delocalized on the two partially-oxidized ligands. For these complexes, the k _ex values increase with increasing contribution of the Cu^I electromer. One of the dicationic molecules is exclusively present as Cu^I complex with radical ligands in dichloromethane at room temperature, and as Cu^II electromer with neutral ligands at 200 K. Consequently, the electron self-exchange rate k _ex is maximal at room temperature, and strongly decreases with decreasing temperature. The temperature effect is much stronger than for similar complexes that remain in the Cu^II form at all temperatures, demonstrating the use of electromerism to control the redox reactivity on a large scale.

Effect of Ge Incorporation on Lead‐free Cs‐based Triiodide Sn−Ge Co‐alloy Perovskite Thin Films by Spin Coating

Posted on 28 February 2024 by

The effect of Ge incorporation on spin-coated CsSn_1–x Ge _x I₃ (0≤x≤1) thin films was studied. When the incorporation of Ge increases, CsSn_1–x Ge _x I₃ experiences lattice shrinkage, which is accompanied by the adjustment of the crystallographic phase. The morphology and roughness of the film surface undergo changes as the Ge content increases.

Abstract

A new Sn−Ge co-alloy perovskite that does not contain toxic Pb is attracting attention due to its excellent predicted optoelectronic properties. However, most current research only focuses on compositions with Ge content up to 50 %, resulting in a limited overall understanding on this material system. In this study, CsSn_1–x Ge _x I₃ (0≤x≤1) perovskite thin films were fabricated using spin coating method and characterized in terms of crystallographic, morphological and optical characteristics systematically. The results show that the Ge incorporation causes lattice shrinkage and a change in the crystallographic phase from orthorhombic to trigonal. Additionally, the coverage varies much as Ge increases. The Ge incorporation also results in a blueshift of the photoluminescence peak and a decrease in luminescence intensity as compared to the composition with lower Ge content. Moreover, the carrier dynamics measurement shows that the Ge incorporation increases the carrier nonradiative recombination. This work provides important hints for the development of the Sn−Ge alloy-based perovskite solar cell.

Monocopper model of CuB site of pMMO in N4‐environment oxidizes C−H bonds

Posted on 28 February 2024 by

A tetradentate N-ligand binds Cu^II in a geometric and electronic environment that resembles the properties of the Cu_B site of particulate Methane Monooxygenase (pMMO). Its Cu^I counterpart undergoes ligand oxidation during exposure to air, establishing the flexibility of the tetradentate scaffold that allows O₂ activation and subsequent formation of a cupric amidato complex. This reactivity may be relevant for a reevaluation of the active site of pMMO, in which Cu_B has been relegated due to its “saturated” coordination environment.

Abstract

Discrepancies regarding the coordination environment, donor atoms, nuclearity, and oxidation state of the active site of particulate methane monooxygenase (pMMO), a copper-dependent enzyme capable of activating the strong C−H bond of methane, persist despite numerous structural and spectroscopic studies. To address the proposed mono- (Cu^II) or bimetallic (2Cu^I) nature of the so-called Cu_B site, we report the bis(benzimidazole)-based NMe−N,N’-(1-Me-2-CH₂C₇H₄N₂)₂C₆H₄ ligand (N4) and its copper complexes. In the solid state [Cu(N4)(ClO₄)]ClO₄ features tetragonal geometry defined by the chelating ligand and an axial perchlorate; geometric and EPR parameters are very close to those reported for the Cu_B site. Attempts to obtain a dicopper(I) analog resulted in [Cu(N4)][CuCl₂], based on spectroscopic, electrochemical, and ESI-MS data. Although these results support the assignment of Cu_B as a monometallic site, air exposure of [Cu(N4)][CuCl₂] leads to ligand oxidation in the structurally characterized [Cu(N4=O)Cl], raising the possibility of distorted tetragonal Cu(I) centers activating O₂ and oxidizing substrates, in C−H activation chemistry that may take place at Cu_B.

Biocompatible Phosphorescent Ir(III) Complexes for Hypoxia Sensing in PLIM Mode

Posted on 28 February 2024 by

Two new biscyclometalated Ir(III) complexes with diimine ligands were synthesized and utilized to assess the oxygen status of living cells by using time-resolved luminescent microscopy.

Abstract

In this work, two new biscyclometalated Ir(III) complexes with diimine ligands were synthesized. The compounds were characterized by 1D and 2D NMR spectroscopy and HR ESI mass spectrometry. All complexes exhibit efficient phosphorescence with pronounced sensitivity to the presence of oxygen. The photophysical properties of the obtained compounds, including absorption, emission spectra, lifetimes and quantum yields of phosphorescence were measured in various aqueous and model biological media with variations in pH, temperature and at various O₂ concentrations. The complexes exhibit a very good sensory response to the changes in oxygen concentration, resulting in an increase in quantum yields and lifetimes by 2.8–5.5 times upon oxygen removal from aerated aqueous solutions. Biological tests with CHO-K1 cell line have shown that these compounds display low toxicity, rapid internalization into cells and localization predominantly in lysosomes. For the most promising complex the phosphorescence lifetime imaging experiments were conducted, revealing that this sensor markedly changes the phosphorescence lifetime values in cells from 1.8 to 4.1 μs upon transition from normoxia to simulated hypoxia. The obtained results indicate that this type of iridium chromophores can be effectively used for assessing the oxygen status of living objects by using time-resolved luminescent microscopy.

Chemical Structure Elucidation in the Development of Inorganic Drugs: Evidence from Ru‐, Au‐, As‐, and Sb‐based Medicines

Posted on 27 February 2024 by

The importance of molecular structure elucidation in medicinal inorganic chemistry drug development is discussed and illustrated using three vignettes on Ru-, Au-, and As-based drugs. An outlook on Sb-based drugs is provided. The development of three classes of medicinal inorganic compounds is reviewed, highlighting the important role of structure elucidation. The progress of Ru-, Au-, and As-based compounds provide a justification for working to understand the structures of clinically used Sb-containing antiparasitic drugs.

Abstract

Structure elucidation plays a critical role across the landscape of medicinal chemistry, including medicinal inorganic chemistry. Herein, we discuss the importance of structure elucidation in drug development and then provide three vignettes that capture key instances of its relevance in the development of biologically active inorganic compounds. In the first, we describe the exploration of the biological activity of the trinuclear Ru compound called ruthenium red and the realization that this activity derived from a dinuclear impurity. We next explore the development of Au-based antitubercular and antiarthritic drugs, which features a key step whereby ligands were discovered to bind to Au through S atoms. The third exposition traces the development of As-based antiparasitic drugs, a key step of which was the realization that the reaction of arsenic acid and aniline does not produce an anilide of arsenic acid, as originally thought, but rather an amino arsonic acid. These case studies provide the motivation for an outlook in which the development of Sb-based antiparasitic drugs is described. Although antileishmanial pentavalent antimonial drugs remain in widespread use to this day, their chemical structures remain unknown.

Trans‐Dioxidomolybdenum(VI) Porphyrins and their Catalytic Activity Mimicking Oxidative Bromination

Posted on 27 February 2024 by nMannar R. Maurya, nVed Prakash, nMuniappan Sankarn

trans-Dioxidomolybdenum(VI)-meso-tetraphenylporphyrin and trans-dioxidomolybdenum(VI)-meso-tetra(p-chlorophenyl)porphyrin have been synthesised and used as catalyst for the biomimetic haloperoxidases mimicking oxidative bromination of phenol and its derivatives.

Abstract

Synthesis of trans-dioxidomolybdenum(VI)-meso-tetraphenylporphyrin (trans-[Mo^VIO₂(TPP)], 1) and trans-dioxidomolybdenum(VI)-meso-tetra(p-chlorophenyl)porphyrin (trans-[Mo^VIO₂(TCPP)], 2) by reacting the corresponding free-base porphyrins with Mo(CO)₆ in 1,2,4-trichlorobenzene at 190 °C has been reported. These are the second examples in the literature where molybdenum-porphyrins have trans-[Mo^VIO₂] group, identified by single crystal X-ray study. Both complexes have been utilized as functional model of haloperoxidases for the oxidative bromination of various phenol derivatives using KBr, H₂O₂ and HClO₄ as green brominating reagents in aqueous medium. These complexes displayed very high TOF values (up to 16.2 s⁻¹ for catalyst 2) representing excellent catalytic activity. To the best of our knowledge, this is the first report presenting trans-dioxidomolybdenum(VI) based porphyrin as haloperoxidases mimicking oxidative bromination of various phenol derivatives.

Ligand Functionalization of Metal‐Organic Frameworks for Photocatalytic H2O2 Production

Posted on 27 February 2024 by nJianhao Qiu, nJianfeng Yaon

Ligand functionalization of MOFs for photocatalytic H₂O₂ production was systematically discussed. The strategies of ligand functionalization include grafting of functional groups and multiple ligand decoration, which can realize efficient H₂O₂ production by photocatalysis.

Abstract

H₂O₂ production by photocatalysis has received considerable attention, while using MOF-based materials as photocatalysts is still less explored. Ligand functionalization of MOFs is a decoration way at the molecular level, which provides the basis for the further modification of MOFs. In this concept, ligand functionalization of MOFs for photocatalytic H₂O₂ production has been systematically and extensively discussed. The strategies of ligand functionalization include grafting of functional groups (e. g. amino, methoxyl, boron and alkyl) and multiple ligand decoration. Correspondingly, some specific effects are achieved, e. g. improved charge carrier separation, enhanced O₂ adsorption and hydrophobicity, which can realize efficient H₂O₂ production by photocatalysis. Meanwhile, reaction conditions and activities of photocatalytic H₂O₂ production have also been explicitly introduced in these studies. At last, the future perspectives are proposed. This concept sheds fresh light on the great potential of ligand functionalization of MOFs for photocatalytic H₂O₂ production.