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Synthesis, characterization, electronic structure, and redox reactions of a mononuclear {FeNO}7complex with a very high N–O stretching frequency in solution are presented. Nitrosylation of [(LKP)Fe(DMF)]2+(1) (LKP= tris((1-methyl-4,5-diphenyl-1H-imidazol-2-yl)methyl)amine) produced a five-coordinate {FeNO}7complex, [(LKP)Fe(NO)]2+(2). While complex 2could accommodate an additional water molecule to generate a six-coordinate {FeNO}7complex, [(LKP)Fe(NO)(H2O)]2+(3), the coordinated H2O in 3dissociates to generate 2in solution. The molecular structure of 2features a nearly linear Fe–N–O unit with an Fe–N distance of 1.744(4) Å, N–O distance of 1.162(5) Å, and

Hexavalent chromium exposure via inhalation, ingestion, or both has been proven to adversely affect internal organs, induce toxic effects, cause allergies, and contribute to the development of cancer. It requires a substantial and challenging effort to detect several heavy metal ions conveniently, sensitively, and reliably by using materials that are easy to synthesize and have a high yield. The impact of light on the electrocatalytic oxidation/reduction process proves an environmentally friendly methodology with numerous applications in pollution control. The extensive use of photoactive materials in photoelectrochemical (PEC) sensors necessitates the development of stable and highly effective photoactive materials. Hence, the solvothermal synthesis of the organic–inorganic hybrid nanocomposite β-Bi2O3–Bi2WO6/H2TPP with varying weight percentages of meso-tetraphenylporphyrin (H2TPP) resulted in a selective electrode for electrocatalytic and photoelectrocatalytic reduction of Cr6+on fluorine-doped tin oxide (FTO) by an adsorption–reduction mechanism. H2TPP increases the active site density and provides an effective surface area for efficient adsorption by providing both pyridinic- and pyrrolic-N atoms to β-Bi2O3–Bi2WO6/H2TPP. H2TPP could effectively adsorb Cr6+in the β-Bi2O3–Bi2WO6/H2TPP composite system through electrostatic interaction, and the adsorbed Cr6+ions were reduced to trivalent chromium Cr3+, resulting in promising Cr6+sensing. The projected density of states and Bader charge calculations result in the electrostatic attraction among the N-2p orbital of H2TPP and the 3d and 4s orbitals of the Cr atom, resulting in the adsorption of the hexavalent Cr atom onto the active center of H2TPP. Moreover, the addition of H2TPP results in the development of a mesoporous surface that offers strong electrical conductivity, a substantial surface area, improved charge–mass transport, intimate contact between the electrolyte and catalyst, an extended fluorescence lifetime, and increased stability. The role of pH values was thoroughly investigated. All electrochemical and photoelectrochemical studies were carried out on 5 wt % H2TPP-ornated β-Bi2O3–Bi2WO6. Nanocomposite β-Bi2O3–Bi2WO6/5 wt % H2TPP demonstrated reliable cyclic stability, reproducibility, good sensitivity (8.005 μA mM cm–2), and a low limit of detection (LOD) (8.0 nM) toward photoelectrocatalytic reduction of Cr6+. The interference study in the presence of a few inorganic entities exhibited excellent selectivity. This tale amplification approach for developing a β-Bi2O3–Bi2WO6/5 wt % H2TPP nanocomposite system suggests a deeper understanding of the application of photoelectrocatalytic reduction of Cr6+in environmental remediation with real samples under light irradiation.

A luminescent nanoprobe (NP), MnO2-modified Er3+/Yb3+-codoped Ag2MoO4upconversion nanoparticles (UCNPs; cod-AMO-3/MnO2), was constructed for rapid, sensitive, and selective “turn-on” detection of trace As3+. Herein, two kinds of luminescent NPs were developed based on luminescence resonance energy transfer (LRET) between cod-AMO-3 as the energy donor and MnO2as the energy acceptor. By using MnO2as the matrix in cod-AMO-3/MnO2fluorometric assay, the upconversion luminescence (UCL) intensity (IUCL) of the cod-AMO-3 probe was quenched significantly through LRET, illustrating MnO2as an efficient quencher for UCL. With the addition of As3+, a stable bidentate binuclear (BB) corner-sharing bridged complex (As5+-MnO2) was probably formed, which alters the surface of the upconversion NP, leading to gradual separation between UCNPs and MnO2and subsequent recovery of IUCL. Interestingly, it possessed superior sensitivity, reaction kinetics, and also high selectivity toward As3+in aqueous solution. Our optimized cod-AMO-3/MnO2nanocomposite (NComp) demonstrated a linear range of 0–150 ppb and an ultrasensitive detection limit of 0.028 ppb for As3+, which is extremely below the regulatory level, signifying the promising practical usage of this system. To the best of our knowledge, such a surface-modified Ln3+-codoped Ag-based nanosensor being applied for As3+detection probably has not been reported yet, and it is rather unexplored. In a nutshell, the ability to monitor the As3+concentration may enable the rational design of a convenient platform for a diverse range of environmental monitoring applications.

A selective electrode for oxygen reduction reaction (ORR) and electrocatalytic reduction of 4-nitrophenol (p-NP) was fabricated on a glassy carbon electrode using organic–inorganic Bi2MoO6/H2TPP nanocomposites with different weight percentages of tetraphenylporphyrin, synthesized by the solvothermal process. Materials thus synthesized were characterized through UV–Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) analysis. The electrocatalytic performance of the modified electrode toward ORR in the 0.1 M KOH solution, the onset potential Eonset(0.942 V), E1/2(0.704 V) vs RHE, Jd(−5.545 mA cm–2), and n= 4 physicochemical parameters were well appreciable. It exhibits good catalytic activity toward ORR through a four-electron pathway with excellent stability and high active site density, and thus, the in situ Porphy-decorated metal oxide system facilitates the electron transport process. High selectivity and efficacy for the oxygen reduction reaction (ORR) are a significant measure for several energy-converting applications. The decorated electrode, glassy carbon electrode (GCE)/Bi2MoO6/3 wt % Porphy, serves as an electrochemical sensor that exhibited good sensitivity (0.4683 μAμM–1cm–2), good reproducibility, a low detection limit (0.0940 μM), and long-term stability in the aqueous phase without any appreciable effect in the presence of some common organic and inorganic interferences for the detection of p-NP in a linear concentration range of 0.5–350 μM. Therefore, the material performs as an effective electrode for both the ORR and the electrocatalytic reduction of p-NP with real matrix samples at room conditions.

The present work is part of our ongoing quest for developing functional inorganic complexes using unorthodox pyridyl–pyrazolyl-based ligands. Accordingly, we report herein the synthesis, characterization, and luminescence and magnetic properties of four 3d–4f mixed-metal complexes with a general core of Ln2Zn6(Ln = Dy, Gd, Tb, and Eu). In stark contrast to the popular wisdom of using a compartmental ligand with separate islands of hardand softcoordinating sites for selective coordination, we have vindicated our approach of using a ligand with overcrowded N-coordinating sites that show equal efficiency with both 4f and 3d metals toward multinuclear cage-cluster formation. The encouraging red and green photolumiscent features of noncytotoxic Eu2Zn6and Tb2Zn6complexes along with their existence in nanoscale dimension have been exploited with live-cell confocal microscopy imaging of human breast adenocarcinoma (MCF7) cells. The magnetic features of the Dy2Zn6complex confirm the single-molecule-magnet behavior with befitting frequency- and temperature-dependent out-of-phase signals along with an Ueffvalue of ∼5 K and a relaxation time of 8.52 × 10–6s. The Gd2Zn6complex, on the other hand, shows cryogenic magnetic refrigeration with an entropy change of 11.25 J kg–1K–1at a magnetic field of 7 T and at 2 K. Another important aspect of this work reflects the excellent agreement between the experimental results and theoretical calculations. The theoretical studies carried out using the broken-symmetry density functional theory, ORCAsuite of programs, and MOLCAScalculations using the complete-active-space self-consistent-field method show an excellent synergism with the experimentally measured magnetic and spectroscopic data.

A quaternary compound, Na15Cu3Ga6S18, the first member in the A–Cu–Ga–S (A = alkali metal) series, has been synthesized from a solid-state metathesis reaction between Na6Ga2S6and CuCl as well as from a combination of Na2S, Ga, Cu, and S. The compound crystallizes in a monoclinic crystal system, space group C2/c, and represents a unique open-framework structure with channels filled with eight crystallographically distinct Na ions. The anionic framework is built up of infinite chains of corner-shared GaS4tetrahedra fused together by an edge-shared dimer of CuS4tetrahedra forming one-dimensional ribbons of (Cu2Ga6S18)16–, which are cross-linked by linearly coordinated S–Cu–S linkages resulting in a three-dimensional network with tunnels filled with Na atoms. Optical band gap measurements show that the compound has a direct band gap of 3.00 eV that is in good agreement with the theoretical band gap derived from density functional theory calculations. Band structure calculations further indicate that the states near the Fermi level are dominated by tetrahedral Cu+(d) and S(p) states resulting from the antibonding interactions, while s–d hybridization is prevalent in linear Cu+coordination. Ionic conductivity measurements show that the compound has a room-temperature Na ion conductivity of 2.72 × 10–5mS/cm with an activation energy of 0.68 eV, which corroborates well the nudged elastic band calculations.

In this study, we report the synthesis and characterization of [Fe(T1Et4iPrIP)(2-OH-AP)(OTf)](OTf) (2), [Fe(T1Et4iPrIP)(2-O-AP)](OTf) (3), and [Fe(T1Et4iPrIP)(DMF)3](OTf)3(4) (T1Et4iPrIP = tris(1-ethyl-4-isopropyl-imidazolyl)phosphine; 2-OH-AP = 2-hydroxyacetophenone, and 2-O-AP–= monodeprotonated 2-hydroxyacetophenone). Both 2and 3serve as model complexes for the enzyme–substrate adduct for the nonheme enzyme 2,4′-dihydroacetophenone (DHAP) dioxygenase or DAD, while 4serves as a model for the ferric form of DAD. Complexes 2–4have been characterized by X-ray crystallography which reveals T1Et4iPrIP to bind iron in a tridentate fashion. Complex 2additionally contains a bidentate 2-OH-AP ligand and a monodentate triflate ligand yielding distorted octahedral geometry, while 3possesses a bidentate 2-O-AP–ligand and exhibits distorted trigonal bipyramidal geometry (τ = 0.56). Complex 4displays distorted octahedral geometry with 3 DMF ligands completing the ligand set. The UV–vis spectrum of 2matches more closely to the DAD-substrate spectrum than 3, and therefore, it is believed that the substrate for DAD is bound in the protonated form. TD-DFT studies indicate that visible absorption bands for 2and 3are due to MLCT bands. Complexes 2and 3are capable of oxidizing the coordinated substrate mimics in a stoichiometric and catalytic fashion in the presence of O2. Complex 4does not convert 2-OH-AP to products under the same catalytic conditions; however, it becomes anaerobically reduced in the presence of 2 equiv 2-OH-AP to 2.

A novel metal–organic framework (MOF), [Zn2(tdca)2(bppd)2]·2DMF, has been synthesized solvothermally using the ligand thiophene-2,5-dicarboxylic acid (H2tdca), coligand N,N′-bis(4-pyridylmethylene)-1,4-benzenediamine (bppd), and Zn(NO3)2. Single crystal X-ray crystallography reveals that the titled MOF is a three-dimensional pillared-layered MOF. A layer is constituted by a Zn(tdca) unit, and the layers are stabilized by the long hydrocarbon coligand, bppd, which acts as a pillar. A rectangular pore size of 11.42 × 8.12 Å2is found in the framework. The porous framework is found to be an excellent fluorescence sensor for the detection of toxic Cd2+ion. The sensor shows high selectivity and sensitivity and a quick response toward Cd2+. The synthesized MOF is able to not only detect cadmium ions but also adsorb iodine in the gas phase. The MOF can adsorb ∼66% iodine, verified by thiosulfate-iodine titration and TG analysis. Adsorbed iodine can also be removed easily in acetonitrile as well as in n-hexane, which shows that iodine can be reversibly loaded as well as unloaded into the framework.

A series of quaternary sulfides of the composition Na3MGaS4(M= Mn (1), Fe (2), and Co (3)) have been synthesized in sealed quartz ampules. In these compounds, divalent transition metal and Ga occupy the same crystallographic site in the Ga–S network, forming a supertetrahedral, T2 (adamantane) unit, through the corner-sharing of four M/GaS4tetrahedra. The corner sulfur atoms of the T2 clusters are further connected to similar T2 units to form an open continuous three-dimensional (3D) anionic framework of composition {[Ga2M2S8]n}6–. The framework resembles a zinc blende structure type if each T2 cluster is considered as a single tetrahedron and two such frameworks are intertwined to generate channels wherein reside the extra-framework Na+ions. Placement of transition metals (Mn or Fe or Co) in the corner of a perfect supertetrahedron, adamantane building unit, generates an ideal lattice for geometrical magnetic frustration, which, on dilution with nonmagnetic metal (Ga), creates an ideal case for random frustration. Preliminary magnetic measurements indicate high negative values of the Weiss constant (−200 to −400 K) and the absence of any magnetic ordering, reinforcing the presence of magnetic frustration in all of these compounds.

The physico- and electrochemical behaviors of a series of [WZn3(H2O)2(ZnW9O34)2]12–(Zn–WZn3) and its first-row transition-metal-substituted analogues [WZn(TM)2(H2O)2(ZnW9O34)2]12–(Zn–WZn(TM)2; TM = MnII, CoII, FeIII, NiIIand CuII) are reported. Various spectroscopic studies, including Fourier transform infrared (FTIR) spectroscopy, UV–visible spectroscopy, electrospray ionization (ESI)–mass spectrometry, and Raman spectroscopy, show similar spectral patterns in all sandwich polyoxometalates (POMs) because of their isostructural geometry and constancy of the overall negative charge (−12). However, the electronic properties highly depend on the transition metals at the “sandwich core” and correlate well with the density functional theory (DFT) study. Further, depending on the substituted TM atoms, there is a decrease in the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) band-gap energy in these transition-metal-substituted POM (TMSP) complexes wrt Zn–WZn3, as confirmed by diffuse reflectance spectroscopy and DFT study. Cyclic voltammetry reveals that the electrochemistry of these sandwich POMs (Zn–WZn3and TMSPs) is highly dependent on the pH of the solution. Moreover, the dioxygen binding/activation studies of these polyoxometalates show that Zn–WZn3and Zn–WZnFe2have better efficiency toward dioxygen binding, as confirmed by FTIR spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA), which is also reflected in their catalytic activity toward imine synthesis.