Search

To study the effect of diamagnetic ions on magnetic interactions, utilizing a compartmental ligand (Z)-2-(hydroxymethyl)-4-methyl-6-((quinolin-8-ylimino)methyl)phenol (LH2), two different series of ZnII–LnIII complexes, namely the trinuclear series of [DyZn2(L)2(μ2-OAc)2(CH3OH)2]·NO3·MeOH (1), [TbZn2(L)2(μ2-OAc)2(CH3OH)2]·NO3·5MeOH·H2O (2), and [GdZn2(L)2(μ2-OAc)2(CH3OH)2]·NO3·MeOH·CHCl3 (3) and the tetranuclear series of [Dy2Zn2(LH)4(NO3)4(μ2OAc)]·NO3·MeOH·H2O (4), [Tb2Zn2(LH)4(NO3)4(μ2-OAc)]·NO3·MeOH·2H2O (5), and [Gd2Zn2(LH)4(NO3)4(μ2-OAc)]·NO3·MeOH·2H2O (6), were synthesized. Trinuclear ZnII–LnIII complexes 1–3 consist of one LnIII ion sandwiched between two peripheral ZnII ions forming a bent type ZnII–DyIII–ZnII array with an angle of 110.64°. Tetranuclear ZnII–LnIII complexes 4–6 are basically a combination of two dinuclear moieties of [LnZn(LH)2(NO3)2]+ connected by one bidentate bridging acetate ion in μ2-OAc coordination mode. The detailed magnetic analysis reveals that complexes 1 and 4 are single molecule magnets having energy barriers of 34.98 K and 46.71 K with relaxation times (τ0) of 5.05 × 10−4 s and 5.24 × 10−4 s, respectively. Ab initio calculations were employed to analyze the magnetic anisotropy and magnetic exchange interaction between the ZnII and LnIII centers with the aim of gaining better insights into the magnetic dynamics of complexes 1–6. [ABSTRACT FROM AUTHOR]

In this paper, we report the synthesis and characterization of a mononuclear zinc complex (1) containing a redox-active bis(4-antipyrinyl) derivative of the 3-cyanoformazanate ligand. Complex 1 was readily obtained by refluxing zinc acetate with 3-cyano-1,5-(4-antipyrinyl)formazan (LH) in a methanolic solution. Single-crystal X-ray diffraction analysis of complex 1 shows that the formazanate ligands bind to the zinc center in a five-member chelate "open" form via the 1- and 4-positions of the 1,2,4,5-tetraazapentadienyl formazanate backbone leading to the formation of the mononuclear bis(formazanate) zinc complex exhibiting a distorted octahedral geometry. We also report the study of resistive-switching random access memory application of this solution-processable bis(formazanate) Zn(II) complex to facilitate the practical implementation of transition metal complex-based molecular memory devices. The complex demonstrated high conductance switching with a large ON–OFF ratio, good stability, and a long retention time. A trap-controlled space charge limited current mechanism is proposed for the observed resistive switching behavior of the device, wherein the role played by the [ZnIIL2] complex that comprises the extended redox-active conjugated ligand backbone is revealed by corroborating electrochemical studies, spectrochemical experiments, and DFT calculations. In addition to providing significant insights into the molecular design of transition metal complexes for memory applications, this study also presents the utilization of ZnIIL2 towards the realization of non-volatile resistive random access memory (RRAM) devices with inorganic/organic hybrid active layers that are highly cost-effective and sustainable. These devices exhibited multilevel switching and low current operation, both of which are desirable for advanced memory applications. [ABSTRACT FROM AUTHOR]

Closed-shell phenalenyl (PLY) systems are increasingly becoming more attractive as building blocks for developing promising catalysts and electroactive cathode materials, as they have tremendous potential to accept electrons and participate in redox reactions. Herein, we report a PLY-based dinuclear [Fe III2 (hmbh-PLY)3] complex, 1, and its utility as a cathode material in a H2O2 fuel cell. Complex 1 was synthesized from a new Schiff base ligand, (E)-9-(2-(2-hydroxy-3-methoxybenzylidene)hydrazineyl)-1H-phenalen-1-one, hmbh-PLYH2, designed using a PLY precursor, Hz-PLY. The newly derived ligand and complex 1 were characterized by various analytical techniques, including single-crystal X-ray diffraction (SCXRD). The cyclic voltammetry (CV) study revealed that complex 1 undergoes five electron reductions under an applied electric potential. When the electroactive complex 1 was employed as a cathode in a membrane-less one-compartment H2O2 fuel cell, with Ni foam as the corresponding anode, the designed fuel cell exhibited an exceptionally high peak power density (PPD) of 2.41 mW cm−2, in comparison with those of all the previously reported Fe-based molecular complexes. DFT studies were performed to gain reasonable insights into the two-electron catalytic reduction (pathway I) of H2O2 by the Fe-center of complex 1 and to explore the geometries, energetics of the electrocatalyst, reactive intermediates and transition states. [ABSTRACT FROM AUTHOR]

Herein, we present the synthesis of two new dicobaloxime complexes, [{ClCo(dmgH)2(4-PyCOO)}2Zn(DMF)2] (1) and [{ClCo(dmgH)2(4-PyCOO)}2Cd(H2O)3(DMF)].4H2O (2) bridged by isonicotinate-Zn(II) and Cd(II) moieties. These complexes were synthesized upon reaction of a monomeric chlorocobaloxime [ClCo(dmgH)2(4-PyCOOH)] with Zn(NO3)2·6H2O and Cd(OAc)2·2H2O in a methanol/DMF solvent mixture. Both complexes are fully characterized by UV-Visible, FT-IR, and NMR (1H and 13C{1H}) spectral studies. The solid-state structures are also determined by single-crystal X-ray crystallography. In complex 1, Zn (II) metal ions reside within a four coordinated distorted tetrahedral geometry (ZnO4) formed by two oxygen atoms of isonicotinate connected to cobaloxime units and two oxygen atoms of DMF molecules. In complex 2, the Cd(II) metal ion exhibited distorted octahedral geometry (CdO6), with two oxygen atoms of isonicotinate that connect to cobaloxime units, one DMF, and three water molecules. The Co(III) metal center of cobaloxime units in both complexes 1 and 2 displayed distorted octahedral geometry with two dmgH units in the equatorial plane whereas chloride ion (Cl−) and the nitrogen atom of isonicotinate occupy the axial coordination sites. The redox behaviour of both complexes was studied by cyclic voltammetry at variable scan rates in deoxygenated DMF/H2O (95 : 5) solution using 0.1 M TBAPF6 as the supporting electrolyte and a glassy carbon (GC) electrode as the working electrode. Both complexes exhibited similar redox properties and two redox couples CoIII/II and CoII/CoI are observed in the reductive scan. Furthermore, complexes are investigated as electrocatalysts for proton reduction in the presence of acetic acid (AcOH) and complex 1 exhibited impressive electrocatalytic activity compared to complex 2 and monomer. The stability study indicated the retention of molecular structural integrity during HER electrocatalytic experiments. [ABSTRACT FROM AUTHOR]

A series of halogenated podands (P1–P8) have been synthesized from 1,3,5-tris(bromomethyl)mesitylene and halogen-substituted phenols to study the structure-directing roles of C–H hydrogen bonds and halogen bonds in the formation of self-assembled supramolecular frameworks. The ethereal podands are suitable for the study of C–H hydrogen bonds in the crystalline state due to the presence of three different types of C–H donors, such as methyl, methylene, and aromatic –CH groups, and three different types of acceptors such as ethereal oxygen, halogens, and aromatic rings. Single crystal X-ray structures of three halophenyl-functionalized podands (P2, P3 and P4) and a cyanophenyl-functionalized podand (P9) were determined at room temperature (298 K), and detailed Hirshfeld surface analysis of the crystal structures was performed to quantify the close contact contributions (in %) from different types of non-covalent interactions involved in the self-assembly of podands. The crystal structures of the halophenyl-functionalized podands (P2, P3, and P4) showed self-assembly primarily via intermolecular C–H⋯O, C–H⋯π, and halogen bonding interactions. Hirshfeld surface analysis of the crystal structures revealed significantly higher contributions from H⋯C and H⋯X (X = halogen) close contacts in comparison to H⋯O and X⋯C close contacts in 2D-fingerprint plots. The self-assembly of the cyanophenyl-functionalized podand (P9) was largely governed by intermolecular C–H⋯O and C–H⋯N interactions. The podand crystals showed relatively high thermal stability in thermogravimetry analysis (250–290 °C), which can be attributed to the hydrogen and halogen bond assisted formation of 3D supramolecular frameworks. 19F-NMR spectra of tetraethylammonium fluoride in the presence of an equivalent amount of tris(2-halophenoxymethyl)mesitylene podand (P5 or P6) showed a downfield shift of the fluoride signal (Δδ 3.2 ppm) indicating C–X⋯F− halogen bonding in solution. Further, 19F-NMR spectra of hydrogen bifluoride (HF2−) in the presence of P5 or P6 showed a large upfield shift of ≈21–22 ppm suggesting C–X⋯F−⋯H–F halogen bonding in solution. [ABSTRACT FROM AUTHOR]

We report the isolation of five new discrete diorganotin di-/mono-carboxylate structures achieved by employing an intramolecular coordination approach. Two diorganotin dicarboxylates, complexes 1 and 2, were obtained from reactions of R2SnCl2 (R = 2-phenylazophenyl) with pyridine-2,6-dicarboxylic acid and pyrazole-3,5-dicarboxylic acid, respectively, in the presence of a base. However, the reactions of R2SnCl2 with 3,4,5-trimethoxybenzoic acid in different stoichiometric ratios in the presence of a base produced two diorganotin monocarboxylates, complexes 3 and 4. An equimolar reaction of R2SnO with 2-(1,8-naphthalimido)ethanoic acid afforded a dinuclear diorganotin carboxylate [R2Sn(μ-OH){C14H8NO4}]2 (5). All the complexes (1–5) are structurally characterized using single-crystal X-ray diffraction analysis. The molecular structures of complexes (1–5) revealed the retention of both N → Sn intramolecular coordinations. Each tin (Sn) center in complexes (1–5) is present in a high coordination number of seven with distorted pentagonal bipyramidal geometry. Time-dependent density functional theory (TDDFT) calculations revealed that ligand-to-ligand transitions dominate electronic transitions in these complexes. The Hirshfeld surfaces and 2D fingerprint plots were analyzed for all the complexes to understand the intermolecular interactions involved in crystal packing. [ABSTRACT FROM AUTHOR]

A modified "click" reaction between 2-azidopyridine and di(prop-2-yn-1-yl)phthalate [dpp] (2) produces a novel bis(1,2,3-triazolyl-pyridine) ligand on an ortho-phthalic acid platform [bptmp] (3). The [bptmp] ligand is prepared to produce transition metal complexes through selective N-3 coordination of the inverse triazolyl-pyridine ligand. An equimolar reaction between [bptmp] (3) and PdCl2(CH3CN)2 in acetonitrile leads to the isolation of a light-yellow solid (4). Several spectroscopic and spectrometry data established that the formed complex has a molecular formula of PdCl2[bptmp] (4). Molecular structure determination using a single crystal X-ray diffraction study further established the formation of a 1 : 1 metal–ligand complex, where PdCl2 bridges the two side-arms of the phthalic acid platform. As per the design of [bptmp], in complex (4), the chelating bidentate triazolyl-pyridine units are not coordinated, whereas the N-3 nitrogen of the inverse triazolyl-pyridine selectively coordinated to Pd(II). Furthermore, complex (4) is proved to be a highly effective catalyst for the Suzuki–Miyaura coupling reaction in a water/ethanol solvent combination with very modest catalyst loading. The high reactivity of complex 4 in the catalytic Suzuki–Miyaura coupling reaction is attributed to the electronic and steric properties of the [bptmp] ligand. [ABSTRACT FROM AUTHOR]