Applied Organometallic Chemistry

AbstractThe term ligand isomerism stands for two or more isomeric coordination complexes having regioisomeric ligands coordinated around the metal center. Single‐cavity discrete coordination cages (SCDCCs) and multi‐cavity discrete coordination cages (MCDCCs) are exotic class of self‐assembled complexes that should be suitable for exploration of ligand isomerism. This work describes rare varieties of double‐cavity tetranuclear, triple‐cavity pentanuclear and quadruple‐cavity hexanuclear MCDCCs to exemplify ligand isomerism. Square planar Pd(II) and pyridine‐based bis‐, tris‐ and tetrakis‐monodentate ligands are employed as the modular building blocks for constructing the cages. The frameworks of all the ten cages studied here (four reported and six new) contain trinuclear Pd3L6 type double‐walled triangular core (or sub‐framework) that is decorated with one, two and three units of Pd2L4 type entity or sub‐framework resulting in tetra, penta and hexanuclear MCDCCs, respectively. Suitable incorporation of isomeric arms as part of the double‐walled trinuclear core by sourcing from the basket of regioisomeric ligands would offer ligand isomerism in the MCDCCs. Our ligand design afforded four members for the tetra or pentanuclear and two for the hexanuclear architectures to demonstrate ligand isomerism in MCDCCs.

AbstractWe report the synergistic use of Pd(OAc)₂ and Ag₂O for the direct C−H arylation of polyfluoroarenes with aryl iodides in DMF as the solvent. This method is straightforward, can be conducted in air, and does not require additional ligands, yielding fluorinated unsymmetrical biaryl products in up to 99 %. Experimental studies and DFT calculations suggest that the formation of [(DMF)2PdII(C6F5)2] in DMF as a coordinating solvent does not inhibit the reaction, as the Pd complex reacts with aryl iodides by oxidative addition upon dissociation of a single DMF ligand to form [(DMF)PdIV(C6F5)2(Ar)(I)] before the desired arylation product is released. This contrasts with our previous report on the nucleophilic coupling between C₆F₅H and aryl‐Bpin, in which the formation of [(DMF)₂PdII(C₆F₅)₂] was found to halt the reaction.

Graphene has emerged as a promising support material for Cu‐Zn catalysts in CO2 hydrogenation to methanol due to its high surface area and potential for functionalization with heteroatoms like nitrogen and oxygen, with nitrogen believed to contribute to the reaction. In this study, we combined machine learning and data analysis with experimental work to investigate this effect. Machine learning (using a decision tree model) identified copper particle size, average pore diameter, reduction time, surface area, and metal loading content as the most impactful features for catalyst design, while nitrogen doping showed negligible influence on methanol space‐time yield. However, experimental results indicated that nitrogen doping on graphene support improved the space‐time yield by up to four times compared to pristine graphene. This improvement is attributed to nitrogen’s role in lowering the catalyst’s reduction temperature, enhancing its quality under identical reduction conditions, though nitrogen itself does not directly affect methanol formation. Moreover, machine learning provided insights into the critical features and optimal conditions for catalyst design, demonstrating significant resource savings in the lab. This work exemplifies the integration of machine learning and experimentation to optimize catalyst synthesis and performance evaluation, providing valuable guidance for future catalyst design.

AbstractUrea‐assisted water electrolysis is a promising and energy‐efficient alternative to electrochemical water splitting due to its low thermodynamic potential of 0.37 V, which is 860 mV less than that needed for water splitting (1.23 V). Ni(OH)2 has proven to be an efficient catalyst for this reaction. However, the non‐spontaneous desorption of CO2 molecules from the catalyst surface leads to active site poisoning, which significantly impacts its long‐term stability. Herein, we have demonstrated that Pd incorporated NiOH2 (Pd/Ni(OH)2) results in a significant decrease in the overpotential by 40 mV at 10 mA cm−2 as compared to Ni(OH)2. The decrease in the Tafel slope and charge transfer resistance of Pd/Ni(OH)2 indicates an improvement in the kinetics of the reaction, resulting in a maximum current density of 380 mA cm−2 at 1.5 V, which is higher than that observed for Ni(OH)2 (180 mA cm−2). XAS analysis was utilized to determine the nature of the metal species in the catalyst. It revealed that while Pd predominantly exists in its metallic state within the bulk of the catalyst, the surface is enriched with the oxide phase. The presence of Pd prevents the strong adsorption of CO2 at the active site in Pd/Ni(OH)2, resulting in a substantial improvement of stability of up to 300 h as compared to Ni(OH)2. DFT calculations were performed to explore the detailed reaction mechanism of urea oxidation on Ni(OH)2 and Pd/Ni(OH)2. These calculations provided further insight into the experimental observations and evaluated the contribution of Pd in enhancing the catalytic efficiency of Ni(OH)2. Additionally, the operando Raman and IR spectroscopy were used to understand the formation of the active sites and the intermediates during urea electrooxidation.

AbstractThe observation of slow relaxation of magnetization in low‐spin square planar cobalt complexes is exceedingly rare, likely due to the synthetic challenges of stabilizing such geometries, along with the complexities introduced by hyperfine interactions and spin‐orbit coupling. Additionally, accurately characterizing the ground‐state electronic configuration of these complexes remains a significant challenge. In this article, we report a unique and rare square planar cobalt complex, [Co(L1⋅−)2] (1), where the coordination sites are occupied by the phenanthroiminoquinone (L1). The molecular structure of complex 1 was determined using single‐crystal X‐ray diffraction studies. A structurally analogous nickel complex, [NiII(L1⋅−)2] (2), was also synthesized and characterized. Detailed DC magnetic susceptibility measurements of 2 reveal strong antiferromagnetic exchange interactions between the radical centers, rendering it diamagnetic. For cobalt complex 1, this strong antiferromagnetic coupling results in a doublet ground state, as corroborated by X‐band EPR measurements (at 5 K) conducted on both polycrystalline and frozen solution samples. To gain deeper insights into the electronic structure of the cobalt ion in 1, a comprehensive suite of experimental and theoretical investigations was conducted, including X‐ray diffraction, DC magnetic studies, X‐band EPR, UV‐Vis‐NIR spectroscopy, and ab initio calculations. These studies collectively indicate that the cobalt ion in 1 exists in a divalent low‐spin state. Furthermore, the observed slow relaxation of magnetization for the doublet state of 1 highlights its potential as an ideal candidate for designing spin‐based molecular qubits.

AbstractIn recent years, there has been a noteworthy expansion in the field of main‐group compounds, attributed to their intrinsic capacity for the activation of small molecules. In this regard, the alkaline earth metal complexes have garnered important attention. Herein, we showed the utilization of a Mg complex Mg‐1 as a catalyst in cyanosilylation reactions involving several aromatic and aliphatic aldehydes, conducted under mild reaction conditions. Although complex Mg‐1 demonstrated its effectiveness in this transformation, complexes Mg‐2 and Mg‐3 yielded lower amounts of cyanosilylated products, highlighting the influence of the ligand spacer in catalytic activity. To further assess this effect, a mononuclear magnesium complex, Mg‐4, was synthesized and the catalytic performance of Mg‐4 in the cyanosilylation of aldehydes was found to be lower than that of Mg‐1. This study establishes that magnesium complexes can independently catalyze the cyanosilylation of aldehydes, with those featuring an oxygen‐bridged spacer exhibiting enhanced catalytic efficiency. Furthermore, employing complex Mg‐1, we explored the cyanosilylation and hydroboration reactions involving N‐heteroarene carboxaldehyde, an area with limited substrate scopes. Experimental and theoretical studies were performed to establish the mechanism which shows that the cyanosilylation reaction initiates with the initial coordination of trimethylsilyl cyanide (TMSCN) with the catalyst, followed by the subsequent attack of aldehydes. Whereas, in the hydroboration reaction, HBpin first reacts with the Mg complex Mg‐1 to form Mg–H, which subsequently reacts with the aldehyde to form a hydroborylated product via a four‐membered transition state.

AbstractSolar‐driven CO2 reduction has gained significant attention as a sustainable approach for CO2 utilization, enabling the selective production of fuels and chemicals. SnS2, a non‐precious metal sulfide semiconductor, has great potential in photocatalytic CO2 reduction due to its unique physicochemical properties. However, low electrical conductivity and susceptibility to aggregation of pure SnS2 lead to a high charge recombination rate and hinder the photocatalytic efficiency. In this study, we report that single/few‐layered MXene induces ordered growth of SnS2 through electrostatic interactions and in situ solvothermal heating. Interconnected SnS2 nano‐array with abundant sulfur vacancies was successfully prepared on MXene surface (Vs‐SnS2/MXene). This unique structure promotes the separation and migration of photogenerated charges and effectively inhibits electron‐hole recombination. Compared with pure SnS2, the average lifetime of photogenerated charges in Vs‐SnS2/MXene increased by 45.6 %. Meanwhile, its CO production rate reached 47.6 μmol⋅g−1⋅h−1, which was 2.6‐fold higher than that of pure SnS2 (18.3 μmol⋅g−1⋅h−1), and showed excellent photocatalytic CO2 reduction performance in gas‐solid‐phase reaction mode. In addition, Vs‐SnS2/MXene also showed excellent stability. The results showcased the transformative potential of integration strategies for designing high‐performance photocatalytic systems.

AbstractHere, two mixed‐ligand mononuclear [Cu(L1)py] (1), [Cu(L2)Him] (2) and one dinuclear copper(II) complex [Cu2(L3)2(DMSO)(MeOH)] (3) were isolated in solid state and characterized through single‐crystal X‐ray diffraction. Herein, we highlight the solution behavior of these complexes in solution medium through HRMS and ESR. Though the complexes maintain their integrity with respect to the ligand coordination, there is solvent or co‐ligand exchange and generation of both [Cu(L)(py/Him)] or [Cu(L)(H2O)] species. G‐quadruplex (G4‐DNA) structures in the human telomeric DNA (hTelo) and promoter regions of oncogenes (c‐MYC) can behave as potential therapeutic targets for the cancer treatment. Hence, the interaction of these complexes with G4‐DNA and also duplex DNA was investigated through spectroscopy and molecular docking studies. The results reveal that the copper complexes show higher affinity for G4‐DNA over duplex DNA, with 3 demonstrating the strongest binding among them. The complexes have also been tested for DNA nuclease activity against pUC19 plasmid DNA. Finally, the complexes showed significant cytotoxicity towards cancerous cell lines, namely HeLa and MCF‐7 in comparison to the noncancerous cell line NIH‐3T3. Annexin V/PI double staining assay demonstrated the apoptotic mode of cell death caused by the complexes. Overall, the results of G4‐DNA interaction and anticancer activity are consistent, suggesting G4‐DNA is the target for their biological activity.

Graphite‐phase carbon nitride is regarded as a highly promising piezoelectric catalyst, yet its interlayer and in‐plane charge transfer capabilities pose significant limitations to its application. Graphite‐phase carbon nitride is regarded as a highly promising piezoelectric catalyst, yet its interlayer and in‐plane charge transfer capabilities pose significant limitations to its application. In this study, Cl, K co‐modulated carbon nitride was synthesized via the molten salt method. The in‐plane introduction of Cl, which exhibits an electron‐withdrawing effect, breaks the symmetry of the carbon nitride crystals and enhances the structural polarity. Meanwhile, the interlayer intercalation of K reduces the localized states of electrons, and expands the π‐conjugated system, serving as a new transfer channel for carriers for facilitating the interlayer transfer of carriers. The piezocatalytic hydrogen production rate from pure water of the optimized CNM‐7.5 is 13.9 times that of the unmodified pristine CN. This work offers valuable foundation for application of piezocatalytic water splitting for hydrogen production, contributing to the advancement of hydrogen energy technology and the realization of a clean and sustainable energy system.

AbstractThe rapid expansion of the global population and technological advancements have heightened the need for efficient energy conversion and electrochemical energy storage. Electrochemical energy systems like batteries and supercapacitors have seen notable developments to meet this demand. However, conventional polymeric membrane separators in these systems face challenges due to limited porosity and poor mechanical and thermal properties, reducing overall electrochemical performance. Researchers have incorporated nanoparticles into the polymer matrix to address these limitations and enhance separator properties. Carbon‐based nanomaterials, in particular, have gained prominence due to their unique features, such as surface‐dependent characteristics, size, porosity, morphology, and electrical conductivity. These properties make carbon‐based nanomaterials advantageous in improving energy storage compared to conventional materials. Advanced carbon‐doped polymeric membrane separators have emerged as a potential solution to the issues faced by conventional separators. Adding carbon nanoparticles, such as graphene‐based materials and carbon nanotubes to the polymeric separators of batteries and supercapacitors has helped researchers solve problems and improve electrochemical performance. This review article provides a state‐of‐the‐art overview of carbon‐doped polymeric membrane separators, their properties, fabrication processes, and performance in lithium batteries, as well as supercapacitors. It emphasizes advantages of these novel separator materials and suggests future research directions in this field.

AbstractThe addition reactions of propylene with singly bonded G13/P‐based (G13=Group 13 element) and B/G15‐based (G15=Group 15 element) molecules, all yielding the >G13–G15< geometrical structure, have been analyzed theoretically using density functional theory (DFT). The current DFT findings indicate that, of all singly bonded G13/P‐based and Al/G15‐based molecules, only Al/P‐Rea can reversibly carry out the [2+2] addition reaction with propylene, both from kinetic and thermodynamic viewpoints. The activation strain model suggests that the deformation energy of the singly bonded >G13–G15< fragment is pivotal in determining the barrier heights that allow for optimal orbital interactions between G13/P‐Rea, Al/G15‐Rea, and propylene. Our theoretical analyses demonstrates that donor–acceptor bonding (singlet–singlet) has a greater impact compared to electron‐sharing bonding (triplet–triplet) in the transition states G13/P‐TS and Al/G15‐TS. Sophisticated analytical frameworks suggest that the forward interaction (lone pair (G15)→p‐π* of C=C in propylene) predominantly affects the addition reactions of singly bonded G13/P‐Rea and Al/G15‐Rea with propylene, whereas the backward interaction (p‐π*(G13) ← p‐π of C=C in propylene) is less influential. Our current DFT calculations, focusing on the structures and relative energetics of stationary points analyzed through the earlier mentioned advanced methods, conform to the Hammond postulate.

AbstractA library of three dinuclear complexes [Yb(hfac)3(L)]2⋅3(CH2Cl2) (1)⋅3(CH2Cl2), [Dy2(hfac)6(L)3]⋅3(CHCl3) (4)⋅3(CHCl3), [Yb(tta)3(L)]2 (6), four dinuclear enantiomers [Ln(facam)3(L)]2⋅CH2Cl2 Ln=Dy ((−)7⋅CH2Cl2, (+)7⋅CH2Cl2) and Yb ((−)8⋅CH2Cl2, (+)8⋅CH2Cl2), two tetranuclear complexes [Ln2(hfac)6(L)]2⋅(CH2Cl2)n (Ln=Yb, n =1 (2)⋅CH2Cl2; Ln=Dy, n=0 (3)) and two pentanuclear complexes [Dy5(hfac)15(L)3]⋅2(C2H4Cl2) (5)⋅2(C2H4Cl2) and [Nd5(hfac)15(L)3]⋅2(CH2Cl2) (10)⋅2(CH2Cl2) (1,1,1,5,5,5‐hexafluoroacetylacetonate (hfac−), 2‐tenoyltrifluoroacetylacetonate (tta−), 3‐(trifluoro‐acetyl‐(+/−)‐camphorate (facam−) and L=[4’‐(4’’’‐pyridyl‐N‐oxide)‐1,2’:6’1’’‐bis‐(pyrazolyl)pyridine] ligand) were isolated and characterized by single crystal X‐ray diffraction. The final molecular architectures could be controlled by playing with the ionic radii of Yb(III), Dy(III) and Nd(III) ions and steric hindrance of the β‐diketonate. Natural circular dichroism (NCD) highlighted no exciton CD couplet for chiral compounds. All the compounds involving Nd(III) in both O9 and N3O6, Dy(III) in O9 and Yb(III) in both O8 and N3O6 coordination sphere present field‐induced SMM while Dy(III) in O8 environment displays SMM behavior in zero applied dc field. The relaxation of the magnetization occurs mainly through a Raman process with contribution of QTM in zero field and Direct process under applied field. The relaxation time of the magnetization increases with the enhancement of the steric hindrance of the ancillary β‐diketonate ligands.

AbstractPhotodynamic therapy has emerged as a potent strategy for treatment of cancer due to its non‐invasiveness, minimal toxicity, high spatial selectivity, and potential for combination therapies. However, self‐aggregation of photosensitizers, tumour hypoxia and low penetration depth of excitation photons remain prominent challenges towards its clinical application. Nanoscale metal‐organic frameworks have emerged as one of the most promising materials due to their tunable composition which allows the adjustment of optical and chemical properties by changing the metal ions or organic linkers. Due to their high porosity, they serve as carriers for photosensitizers and demonstrate high tumour accumulation rates, target specificity, and penetration depth with enhanced permeability and retention effect. This review aims to explore recent developments in nanoscale metal‐organic frameworks focusing on the design strategies to enhance their effectiveness in tumour microenvironment. Specifically, we have examined the approaches to address challenges posed by hypoxic tumour environment and tissue penetration depth of the various light sources. Furthermore, this review provides insights into the targeting strategies that improve the overall efficacy through stimulus‐activated release and sub‐cellular internalization of photosensitizers. Finally, we discussed the on‐going challenges and some future directions for harnessing their full potential as therapeutic agents for effective outcome of photodynamic therapy.

AbstractAzulene, a non‐alternative aromatic hydrocarbon, has attracted significant attention due to its unique electronic properties, and potential applications in organic electronics and optoelectronics. This review highlights recent advances in the synthesis, reactivity, and functional properties of ring‐fused azulene derivatives. The discussion encompasses classical synthetic routes, including the Ziegler–Hafner and Nozoe methods, as well as novel approaches such as transition metal‐catalyzed cyclizations. Key advancements in the construction of benzo[a]azulenes, naphthoazulenes, and other polycyclic azulene frameworks are detailed, emphasizing their regioselective functionalization and enhanced stability. Moreover, the incorporation of azulene moieties into polycyclic aromatic hydrocarbons (PAHs) and heterocyclic systems is explored, highlighting their potential applications in organic light‐emitting diodes (OLEDs), field‐effect transistors (OFETs), and photovoltaic devices. Special attention is given to azulene‐fused helicenes and nanographenes, which demonstrate promising chiroptical properties and extended π‐conjugation. This review aims to provide a comprehensive overview of the synthetic strategies and emerging applications of azulene‐based compounds, contributing to the development of advanced materials for future electronic and photonic technologies.

AbstractPerfluoroalkyl substances (PFAS) represent a broad group of synthetic chemicals that have raised concerns related to their long‐term environmental persistence and potential health risks. Although several efforts have been dedicated to establishing international restrictions on their use, the definition of what qualifies as a PFAS remains a matter of debate among scientists, regulatory agencies, and industry. This article provides a brief overview of the different approaches proposed and adopted to date for identifying and grouping of these pollutants, either based on common structural motifs or on the combination of multiple factors, including functional uses, degradation behavior, physicochemical properties, and toxicity. The diversity and complexity of PFAS substances suggests the need of a multifaceted classification system that can guide regulatory efforts, risk assessment, and environmental monitoring through standardized criteria accepted on an international scale. A pivotal role in establishing a universal definition of PFAS will be played by the International Union of Pure and Applied Chemistry (IUPAC), which is currently supporting a project on the terminology and classification of these chemicals.