A series of manganese(II) complexes [Mn(L)Cl2] 1–5 composed of tripodal tetradentate 4N donor ligands, (L1: tris(pyridin-2-ylmethyl)amine, L2: N,N-bis(pyridin-2-ylmethyl)-2-(pyrrolidin-1-yl)ethan-1-amine, L3: 2-(piperidin-1-yl)-N,N-bis-(pyridin-2-ylmethyl)ethan-1-amine, L4: N,N-bis((6-methylpyridin-2-yl)methyl)-2-(pyrrolidin-1-yl)ethan-1-amine and L5: N,N-bis((6-methylpyridin-2-yl)methyl)-2-(piperidin-1-yl)ethan-1-amine), have been synthesized, characterized and evaluated as functional mimics of phenoxazinone synthase enzyme. The single crystal X-ray structures of the complexes [Mn(L3)Cl2] 3, [Mn(L4)Cl2] 4 and [Mn(L5)Cl2] 5 have been determined. All the complexes adopt a distorted octahedral coordination geometry in which the manganese(II) center is wrapped by an N4Cl2 chromophore. The E1/2 values of the complexes 1–5 and manganese(II)-aminophenol adducts were obtained from differential pulse voltammetry and are in the potential range + 0.368 to +0.440 V and + 0.174 to +0.283 V, respectively. The negative shift in the E1/2 values of the adducts is mainly due to the bidentate coordination of the substrate. All the complexes efficiently catalyze the oxidative dimerization of the model substrate o-aminophenol to phenoxazinone synthase-like activity in dioxygen-saturated methanol at 25 °C with impressive reaction rate (Vmax, 1.25 ± 0.01–16.2 ± 0.03 × 10−7 M s−1) and turnover numbers (kcat, 45 ± 0.36–583.20 ± 1.08 h−1). Complex 4, incorporating pyrrolidinyl and 6-methylpyridine nitrogen donor arms, exhibited the highest catalytic efficiency (kcat/Km, 16.76 ± 0.36 × M−1 h−1) within the series. DFT-optimized [Mn(L)(OAP)] adducts, axial coordination occurs via either the phenolic OH donor (1A–5A, Δd = 0.134–0.175 Å) or the amino –NH donor (1B–5B, Δd = 0.134–0.182 Å). The octahedral mean deviation (Δd) is correlated with the catalytic activity, suggesting that the steric and electronic effects modulate the manganese(II) coordination geometry and influence substrate activation.
The effect of sterically bulky phosphine ligands on the electrocatalytic properties of diiron monothiolate ligand-based models of [FeFe] hydrogenase is outlined. The reaction of the hexacarbonyl precursor complex [Fe2(μ-naphthalene-2-thiolate)2(CO)6] A with tri(p-tolyl)phosphine (P(PhMe-p)3) and tris(4-methoxy-3,5-dimethylphenyl)phosphine (P(3,5-CH3,4-OCH3Ph)3) in refluxing toluene has been studied. Two new diiron monothiolate ligand-based complexes [Fe2(μ-naphthalene-2-thiolate)2(CO)5(P(PhMe-p)3)] 1 and [Fe2(μ-naphthalene-2-thiolate)2(CO)5(P(3,5-CH3,4-OCH3Ph)3)] 2 were obtained in 60–70% yield and characterized by various spectroscopic techniques. Electrocatalytic reduction of protons to dihydrogen by complexes 1 and 2 was examined by cyclic voltammetric measurements in acetonitrile under argon atmosphere with and without acid additions. Complexes 1 and 2 reduced protons with overpotentials of 0.68 (1) and 0.63 V (2) in the presence of AcOH. Moreover, the two catalysts were less stable in the presence of TFA (~ 10–12 mM; colour change observed at higher acid concentrations) in comparison to AcOH (stable up to ~88 mM). ECEC (AcOH) and CECE (TFA) were the plausible mechanisms for electrocatalytic hydrogen production.
Reactions of selected lanthanoids (Ln = La, Pr, Nd and Sm), scandium and sulfur in 1:1:3 M ratios at 750 °C for seven days in glassy silica ampoules yielded single crystals of LnScS3, when appropriate amounts of cesium bromide (CsBr) are present as flux. These LnScS3 representatives crystallize in the orthorhombic space group Pnma with the lattice parameters a = 719.51(5), b = 959.82(6), c = 654.27(4) pm for Ln = La, a = 713.92(5), b = 953.47(6), c = 648.13(4) pm for Ln = Pr, a = 711.67(5), b = 951.30(6), c = 645.81(4) pm for Ln = Nd and a = 706.84(5), b = 948.93(6), c = 642.78(4) pm for Ln = Sm, adopting the centrosymmetric GdFeO3-type structure with Z = 4. Thus, [ScS6]9− octahedra (d(ScS) = 253–259 pm) share common vertices to build up a ∞3{[ScS6/2]3−} framework with the topology of a cubic perovskite. According to its orthorhombic distortion the former cuboctahedral holes adapt to the early Ln3+ cations to provide them an eightfold sulfur coordination (d(Ln–S) = 276–334 pm). The high quality structure refinements from single-crystal X-ray diffraction data leave no doubt that all LnScS3 representatives with Ln = La, Pr, Nd and Sm clearly prefer the centrosymmetric (Pnma) and not the non-centrosymmetric space group (Pna21) as previously suggested elsewhere. Single crystals of Pr3ScS6 occurred as by-product, crystallizing with a = 1386.41(9), b = 1656.08(11), c = 393.46(3) pm orthorhombically in the space group Pnnm with the U3ScS6-type structure. Here, [ScS6]9− octahedra share trans-oriented edges to create ∞1{[ScS4/2S'2/1]5−} chains along [001], which are held together by Pr3+ cations (alongside extra S2− anions) in seven- and eightfold sulfur coordination. Moreover, optical properties, such as the lacking SHG and the Raman spectrum for LaScS3, and the different colors (yellow for LaScS3 versus black for La2S3 and colorless for Sc2S3) are discussed, based on non-bonding S2−···S2− distances.
The reaction of DyBr3 with the Schiff base ligand N-salicylidene-o-aminophenol (saphH2) in the presence of NEt3 under a MeOH/MeCN solvent mixture has afforded the new nonanuclear cluster [Dy9(OH)8(saph)8(MeCN)(MeOH)5(H2O)3]Br3 (1) in good yield. Single-crystal X-ray diffraction studies revealed that 1 comprises a structurally unprecedented {Dy9(μ3-OH)8(μ3-OR)2(μ-OR)10}7+ core assembled through the combined bridging action of eight μ3-OH− ions and the phenoxido groups of eight fully deprotonated saph2− ligands adopting three distinct coordination modes. The metallic skeleton can be described as a central windmill-like {Dy7} unit decorated by two additional DyIII ions or, alternatively, as eight edge-sharing {Dy3(μ3-OH)}8+ triangular subunits. To the best of our knowledge, such a topology has no structural precedence in homometallic 4f-metal cluster chemistry. Direct-current magnetic susceptibility measurements indicate the presence of weak antiferromagnetic interactions and magnetic anisotropy arising from the DyIII ions. Alternating-current magnetic studies reveal frequency-dependent out-of-phase signals under zero applied dc field, indicating slow relaxation of the magnetization, although efficient quantum tunnelling processes prevent the observation of well-defined maxima. The present results further demonstrate the remarkable ability of the saph2− Schiff base ligand to facilitate the self-assembly of high-nuclearity dysprosium clusters with unusual topologies and interesting magnetic properties.
This study investigates the structural origin of high Z′ crystal formation using a pseudopolymorphic cyanoalkyl cobalt complex that exhibits both Z′ = 1 and Z′ = 8 crystal structures. Single-crystal X-ray diffraction and DFT calculations reveal that the Z′ = 1 crystal achieves a periodic structure with higher crystallographic symmetry by adopting a less stable, folded conformation of the cyanobutyl group. In contrast, in the Z′ = 8 crystal, the complex molecules adopt more energetically favorable conformations that cannot be packed efficiently under symmetry constraints, and dense packing is achieved only through the assembly of eight crystallographically independent molecules. Furthermore, two independent lattice water molecules fill the residual voids and provide additional stabilization through intermolecular hydrogen bonding. These results demonstrate that high Z′ structures emerge from the balance between symmetry retention and the combined effects of conformational stability, packing efficiency, and intermolecular interactions, providing a clear structural rationale for the emergence of high Z′ phases in molecular crystals.
In this work, the binding properties of chiral ruthenium(II) complexes Λ-[Ru(bpy)2(bipp)]2+ ((bpy = 2,2′-bipyridine, bipp = 2-benzimidazolyl-pyrazinyl[2,3-f][1,10]phenanthroline; Λ-1) and Δ-[Ru(bpy)2(bipp)]2+ (Δ-1) with double-stranded RNA poly(A) • poly(U) were systematically examined using a variety of experimental methods. UV spectroscopic titration experiments indicated that poly(A) • poly(U) preferentially bound to Δ-1, and suggested that both Δ-1 and Λ-1 interacted with the double-stranded RNA primarily via an intercalative mode. Steady-state fluorescence emission titration studies demonstrated that Δ/Λ-1 could serve as “molecular light switches” for poly(A) • poly(U), and that the presence of the imidazole moiety in the main ligand endowed them with superior “light switch” effects compared with classical Ru(II)-dppz complexes. In addition, the differences in luminescence enhancement upon RNA binding further confirmed the preferential binding of Δ-1 to poly(A) • poly(U). Thermal denaturation studies revealed that Δ-1 exhibited a stronger ability to stabilize and bind to poly(A) • poly(U) than Λ-1. Viscosity and circular dichroism (CD) spectroscopic results not only confirmed that both chiral complexes bound to and stabilized poly(A) • poly(U) primarily via intercalation, but also underscored the importance of chiral matching between small chiral molecules and biomacromolecules. Favorable spatial interactions can lead to tighter binding and even specificity between chiral molecules and their biological targets. The present study is intended to deepen the understanding of the interaction mechanism between chiral ruthenium(II) complexes and double-stranded RNA, and to provide useful reference for the future design of nucleic acid-targeting chiral binders and stabilizers.
In recent years, the COFs from 2,4-diaminotriazinyl (DAT) building block have been synthesized via Schiff base reactions, but all the COFs are amino-linked COFs. This study represents the first successful synthesis of stable luminescent imine-linked COF, NOP-DPT, via solvothermal method with hexa(4-formyl-phenoxy)cyclotriphosphazene (NOP-6-CHO) and 2,4-diamino-6-phenyl-1,3,5-triazine (DPT)). NOP-DPT exhibits excellent thermal properties with a specific surface area of up to 1947 m2 g−1. Its interlaced benzene ring structure, triazine framework, and imine bond (CN) enable fluorescence sensing of picric acid (PA) and uptake iodine. NOP-DPT exhibits a “turn off” fluorescence sensing to PA at a wavelength of 408 nm with a quenching constant (Ksv) of 2.11 × 104 L mol−1 and detection limit (LOD) of 2.01 × 10−7 mol L−1. The quenching mechanism originates from photoinduced electron transfer (PET) and the absorption competition quenching (ACQ) mechanism. NOP-DPT exhibits exceptional iodine capture capability of 3.84 g g−1, attributed to the electron transfer from imine-linked COF to iodine, forming polyiodide anionic complexes. This work proposed a simple synthetic method for the construction of an imine-linked COF platform for the sensitive determination of PA and efficient iodine sequestration.
The increasing release of toxic heavy-metal ions into aquatic habitats bring a major danger to human health and ecosystems, necessitating the development of efficient techniques for their detection and removal. Two-dimensional (2D) transition metal dichalcogenides (TMDs) because of their unique two-dimensional structures with layers, high surface-to-volume ratio, tuneable electronic properties, and abundance of active sites, become promising materials in wastewater treatment. With a focus on electro-chemical and fluorescence-based sensing mechanisms, this review provides a comprehensive summary of recent developments in the application of TMDs and TMD-based materials for the identification and elimination of heavy-metals from wastewater. In relation to material composition, synthesis strategies, the sensing performance including sensitivity, selectivity, detection limits, and response mechanisms is critically examined. Furthermore, an overview of the function of TMDs in eliminating heavy metals with the aid of electrochemistry and adsorption is provided, emphasizing the connections between structure and performance. Future research directions for the useful implementation of TMD-based platforms in environmental monitoring and remediation are suggested, and current issues, such as stability, scalability, and real-sample applicability, are addressed.
