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Mixed metal oxyhalides are an exciting class of photocatalysts, capable of the sustainable generation of fuels and remediation of pollutants with solar energy. Bismuth oxyhalides of the types Bi4MO8X (M = Nb and Ta; X = Cl and Br) and Bi2AO4X (A = most lanthanides; X = Cl, Br, and I) have an electronic structure that imparts photostability, as their valence band maxima (VBM) are composed of O 2p orbitals rather than X np orbitals that typify many other bismuth oxyhalides. Here, flux-based synthesis of intergrowth Bi4NbO8Cl–Bi2GdO4Cl is reported, testing the hypothesis that both intergrowth stoichiometry and M identity serve as levers toward tunable optoelectronic properties. X-ray scattering and atomically resolved electron microscopy verify intergrowth formation. Facile manipulation of the Bi4NbO8Cl-to-Bi2GdO4Cl ratio is achieved with the specific ratio influencing both the crystal and electronic structures of the intergrowths. This compositional flexibility and crystal structure engineering can be leveraged for photocatalytic applications, with comparisons to the previously reported Bi4TaO8Cl–Bi2GdO4Cl intergrowth revealing how subtle structural and compositional features can impact photocatalytic materials.

Morpholine motif is an important pharmacophore and, depending on the molecular design, may localize in cellular acidic vesicles. To understand the importance of the presence of pendant morpholine in a metal complex, six bidentate N,O-donor ligands with or without a pendant morpholine unit and their corresponding ruthenium(II) p-cymene complexes (1–6) are synthesized, purified, and structurally characterized by various analytical methods including X-ray diffraction. Complexes 2–4crystallized in the P21/cspace group, whereas 5and 6crystallized in the P1̅ space group. The solution stability studies using 1H NMR support instantaneous hydrolysis of the native complexes to form monoaquated species in a solution of 3:7 (v/v) dimethyl sulfoxide-d6and 20 mM phosphate buffer (pH* 7.4, containing 4 mM NaCl). The monoaquated complexes are stable for at least up to 24 h. The complexes display excellent in vitro antiproliferative activity (IC50ca. 1–14 μM) in various cancer cell lines, viz., MDA-MB-231, MiaPaCa2, and Hep-G2. The presence of the pendant morpholine does not improve the dose efficacy, but rather, with 2-[[(2,6-dimethylphenyl)imino]methyl]phenol (HL1) and its pendant morpholine analogue (HL3) giving complexes 1and 3, respectively, the antiproliferative activity was poorer with 3. MDA-MB-231 cells treated with the complexes show that the acidic vesicles remain acidic, but the population of acidic vesicles increases or decreases with time of exposure, as observed from the dispersed red puncta, depending on the complex used. The presence of the 2,6-disubstituted aniline and the naphthyl group seems to improve the antiproliferative dose. The complex treated MDA-MB-231 cells show that cathepsin D, which is otherwise present in the cytosolic lysosomes, translocates to the nucleus as a result of exposure to the complexes. Irrespective of the presence of a morpholine motif, the complexes do not activate caspase-3 to induce apoptosis and seem to favor the necrotic pathway of cell killing.

Water oxidation is a primary step in natural as well as artificial photosynthesis to convert renewable solar energy into chemical energy/fuels. Electrocatalytic water oxidation to evolve O2, utilizing suitable low-cost catalysts and renewable electricity, is of fundamental importance considering contemporary energy and environmental issues, yet it is kinetically challenging owing to the complex multiproton/electron transfer processes. Herein, we report the first cobalt-based pincer catalyst for catalytic water oxidation at neutral pH with high efficiency under electrochemical conditions. Most importantly, ligand (pseudo)aromaticity is identified to play an important role during electrocatalysis. A significant potential jump (∼300 mV) was achieved toward a lower positive value when the aromatized cobalt complex was transformed into a (pseudo)dearomatized cobalt species. The dearomatized species catalyzes the water oxidation reaction to evolve oxygen at a much lower overpotential (∼340 mV) on the basis of the onset potential (at a current density of 0.5 mA/cm2) of catalysis at pH 10.5, outperforming other Co-based molecular catalysts reported to date. These observations may provide a new strategy for the judicious design of earth-abundant transition-metal-based water oxidation catalysts.

Metal–ligand coordination interactions are usually much stronger than weak intermolecular interactions. Nevertheless, here, we show experimental evidence and theoretical confirmation of a very rare example where metal–ligand bonds dissociate in an irreversible way, helped by a large number of weak intermolecular interactions that surpass the energy of the metal–ligand bond. Thus, we describe the design and synthesis of trinuclear Mn2Fe complex {[Mn(L)(H2O)]2Fe(CN)6},2–starting from a mononuclear Mn(III)-Schiff base complex: [Mn(L)(H2O)Cl] (1) and [Fe(CN)6]4–anions. This reaction implies the dissociation of Mn(III)-Cl coordination bonds and the formation of Mn(III)-NC bonds with the help of several intermolecular interactions. Here, we present the synthesis, crystal structure, and magnetic characterization of the monomeric Mn(III) complex [Mn(L)(H2O)Cl] (1) and of compound (H3O)[Mn(L)(H2O)2]{[Mn(L)(H2O)]2Fe(CN)6}·4H2O (2) (H2L = 2,2′-((1E,1′E)-(ethane-1,2-diylbis(azaneylylidene))bis(methaneylylidene))bis(4-methoxyphenol)). Complex 1is a monomer where the Schiff base ligand (L) is coordinated to the four equatorial positions of the Mn(III) center with a H2O molecule and a Cl–ion at the axial sites and the monomeric units are assembled by π–π and hydrogen-bonding interactions to build supramolecular dimers. The combination of [Fe(CN)6]4–with complex 1leads to the formation of linear Mn-NC-Fe-CN-Mn trimers where two transcyano groups of the [Fe(CN)6]4–anion replace the labile chloride from the coordination sphere of two [Mn(L)(H2O)Cl] complexes, giving rise to the linear anionic {[Mn(L)(H2O)]2Fe(CN)6}2–trimer. This Mn2Fe trimer crystallizes with an oxonium cation and a mononuclear [Mn(L)(H2O)2]+cation, closely related to the precursor neutral complex [Mn(L)(H2O)Cl]. In compound 2, the Mn2Fe trimers are assembled by several hydrogen-bonding and π–π interactions to frame an extended structure similar to that of complex 1. Density functional theoretical (DFT) calculations at the PBE1PBE-D3/def2-TZVP level show that the bond dissociation energy (−29.3 kcal/mol) for the Mn(III)-Cl bond is smaller than the summation of all the weak intermolecular interactions (−30.1 kcal/mol). Variable-temperature magnetic studies imply the existence of weak intermolecular antiferromagnetic couplings in both compounds, which can be can cancelled with a critical field of ca. 2.0 and 2.5 T at 2 K for compounds 1and 2, respectively. The magnetic properties of compound 1have been fit with a simple S= 2 monomer with g= 1.959, a weak zero-field splitting (|D| = 1.23 cm–1), and a very weak intermolecular interaction (zJ= −0.03 cm–1). For compound 2, we have used a model with an S= 2 monomer with ZFS plus an S= 2 antiferromagnetically coupled dimer with g= 2.009, |D| = 1.21 cm–1, and J= −0.42 cm–1. The metamagnetic behavior of both compounds is attributed to the weak intermolecular π–π and hydrogen-bonding interactions.

Plutonium (Pu) exhibits a complex redox behavior in aqueous solutions. This is due to the ability of the element to adapt a wide range of oxidation states typically from +3 to +6 and the tendency for dynamic interconversion between the oxidation states that primarily depend upon acid concentration and presence of coordinating ligands. This work interrogates the Pu redox behavior in aqueous nitric acid via a combination of voltammetry and in situ vis–NIR spectroelectrochemistry under controlled potentials to map the interconversion between the various Pu oxidation states. The NIR-spectroelectrochemistry studies used to complement the visible spectroscopy bring a new and more complete perspective into the plutonium redox transformations. This allows elucidation of the mechanisms of the involved redox reactions facilitating an in-depth understanding of the relative stability of the Pu oxidation states as a function of redox potentials and nitric acid concentrations. It is observed that oxidation of Pu(III) results in generation of Pu(IV) and Pu(VI) (the latter as PuO22+), bypassing the Pu(V) oxidation state. Further, with increasing acid concentrations, the formation of the Pu(VI) species progressively decreases so that the dynamic equilibrium between the Pu(III) and Pu(IV) oxidation states dominates. These findings have significant implications for developing separation processes for used nuclear fuel reprocessing and treatment.

Two Cu(II)-based metal–organic frameworks (MOFs) having paddle-wheel secondary building units (SBUs), namely, 1Meand 1ipr, were synthesized solvothermally using two new bent di-isophthalate ligands incorporating different substituents. The MOFs showed high porosity (BET surface area, 2191 m2/g for 1Meand 1402 m2/g for 1ipr). For 1Me, very high CO2adsorption (98.5 wt % at 195 K, 42.9 wt % at 273 K, 23.3 wt % at 298 K) at 1 bar was found, while for 1ipr,it was significantly less (14.3 wt % at 298 K and 1 bar, 54.4 wt % at 298 K at 50 bar). 1Meexhibited H2uptake of 3.2 wt % at 77 K and 1 bar of pressure, which compares well with other benchmark MOFs. For 1ipr, the H2uptake was found to be 2.54 wt % under similar experimental conditions. The significant adsorption of H2and CO2for 1Mecould be due to the presence of micropores as well as unsaturated metal sites in these MOFs besides the presence of substituents that interact with the gas molecules. The experimental adsorption behavior of the MOFs could be justified by theoretical calculations. Additionally, catalytic conversions of CO2and CS2into useful chemicals like cyclic carbonates, cyclic trithiocarbonates, and cyclic dithiocarbonates could be achieved.

New synthetic routes have been developed to synthesize osmaborane clusters featuring B4and B5rings in the coordination spheres of osmium. Thermolysis of [Os(PPh3)3Cl2], 1in the presence of excess of [BH3·THF] led to the formation of [Os(PPh3)2H2(η4-B4H8)], 2along with [HOs(PPh3)2B5H10], 3. Cluster 2features a planar tetraborane ring coordinated to an osmium center in an η4fashion. Cluster 3can be considered an osmium analogue of hexaborane(10), in which the osmium center is situated at the base of the pentagonal pyramid geometry. In a different synthetic protocol, we have carried out the metathesis reaction of [Cp*OsBr2]2(Cp* = η5-pentamethylcyclopentadienyl), 5with [LiBH4·THF] followed by thermolysis in the presence of [BH3·THF] that generated [Cp*Os(η5-B5H10)], 6. Cluster 6has a planar pentaborane ring that is stabilized in the coordination sphere of osmium, making it a boron analogue of osmocene. Clusters 2and 6are the first examples of structurally characterized planar B4and B5rings, respectively, that are stabilized in the coordination sphere of osmium. All the synthesized molecules were characterized using multinuclear NMR and IR spectroscopy, mass spectrometry, and single crystal X-ray diffraction analyses. Theoretical calculations were carried out to visualize the electronic structures and bonding scenarios in 2and 6.

The synthesis, structural characterization, and reactivity of an iron(III) chloride compound of 6,6′-di(3,5-di-tert-butyl-2-hydroxybenzene)-2,2′-bipyridine (Fe(tbudhbpy)Cl), under electrochemically reducing conditions is reported. In the presence of carbon dioxide (CO2) under anhydrous conditions in N,N-dimethylformamide (DMF), this complex mediates the 2e–reductive disproportionation of two equivalents of CO2to carbon monoxide (CO) and carbonate (CO32–). Upon addition of phenol (PhOH) as a proton source under CO2saturation, catalytic current is observed; product analysis from controlled potential electrolysis experiments shows the majority product is formate (68 ± 4% Faradaic efficiency), with H2as a minor product (30 ± 10% Faradaic efficiency) and minimal CO (1.1 ± 0.3% Faradaic efficiency). On the basis of data obtained from cyclic voltammetry and infrared spectroelectrochemistry (IR-SEC), the release of CO from intermediate Fe carbonyl species is extremely slow and undergoes competitive degradation, limiting the activity and lifetime of this catalyst. Mechanistic studies also indicate the phenolate moieties coordinated to Fe are sensitive to protonation in the reduced state, suggesting the possibility of cooperative pendent proton interactions being involved in CO2reduction.

The synthesis and reactivity of a new trimetallic complex Ti(NP)4Ni2(NP = 2-diphenylphosphinopyrrolide) (3) is reported. Single-crystal X-ray diffraction and X-ray absorption studies point to a unique bonding motif: a d10–d10, Ni0–Ni0bond stabilized by a proximal d0TiIVmetal center. The coordination chemistry of 3with a variety of L (L = isocyanide and alkyne) donors has also been explored. In the case of isocyanide coordination, the Ni–Ni bond is broken, while diphenylacetylene binding results in a symmetric butterfly μ2-κ2-alkyne bridge across the Ni–Ni moiety. Finally, complex 3is capable of the 4-electron cleavage of the N═N double bond in benzo[c]cinnoline, the first example of N═N bond cleavage by Ni. The resulting product, 7, has been characterized structurally and spectroscopically, and the mechanistic implications are discussed in the context of metal–metal cooperativity.

In this work, we report affinity controlled surface modifications of two different metal nanoparticles (MNPs) using a hydrophilic natural ionophore (microbial chelator) aeruginic acid (abbreviated as H2L) that possesses two different types of binding pockets viz. O/O from carboxylic acid group and N/O from a phenol–thiazole moiety. Preferred binding of the former donor set (i.e., O/O) on to the surface of silver nanoparticles (AgNPs) has resulted in a colorimetric nanomaterial HL@AgNPs, which showed naked eye observable easy detection of Hg2+in aqueous HEPES buffer at pH 7.4, even in the presence of other metal ions. On the other hand, excellent affinity of the phenol–thiazole moiety (i.e., N/O) for iron nanosurfaces (FeNPs) develops a fluorogenic nanomaterial HL@FeNPs. Brilliant emission behavior of this nanomaterial enabled it to be useful for highly selective recognition of Al3+under identical experimental conditions. Remarkable fluorescence enhancement (122-folds) of HL@FeNPs upon addition of Al3+remain unchanged even in the presence of other competing metal ions. The nanomaterials HL@AgNPs and HL@FeNPs could even detect the target analytes instantly offering lower detection limits of 2 and 80 nM, respectively. Presence of toxic metal ions as environmental pollutant demands for dual-functional materials capable of performing the task of probing cum removal. Surface functionalizations of the nanomaterials of silver and iron with H2L have also resulted two removal agents that can efficiently and easily extract Hg2+and Al3+ions from contaminated water, respectively. We are not aware of any work that highlights the manifold utilization of a microbial chelator (i.e., natural ionophore) in the facile construction of different metal nanoparticles for environmental applications such as detection cum removal of toxic metal ions from aqueous solutions.

A new ternary compound Cu3ZnSb was synthesized by high temperature solid state synthesis and characterized by single crystal X-ray diffraction and energy dispersive X-ray analysis. The ternary Cu3ZnSb crystallizes in the tetragonal crystal system with the space group P4/nmm(129), and its unit cell contains 10 atoms which are distributed over 4 independent crystallographic positions. The structure is built up with [Cu3Sb] slabs that correspond to the unit cells of Cu2Sb and planar 44nets of Zn atoms. The planar nets of Zn atoms are interspersed between two adjacent [Cu3Sb] slabs. The structure can be viewed as alternating units of Cu2Sb and CsCl type β′-brass (CuZn) structures in the [001]. An unusual atomic ordering of two neighboring transition metals Cu and Zn is observed and is confirmed by first principle calculations. The atomic ordering of Cu and Zn is retained from binary β′-brass structure (CuZn) to ternary Cu3ZnSb. Total energy calculations confirmed the experimental model of Cu/Zn ordering to be the most stable in the structure of Cu3ZnSb. The calculated density of states (DOS) and crystal orbital Hamiltonian population (COHP) explain the stability and bonding characteristics in the structure of Cu3ZnSb. The implication of the persistent Cu/Zn ordering in ternary phases for materials design is emphasized.

α-Ketoglutarate-dependent nonheme halogenases catalyze the halogenation of aliphatic C–H bonds in the biosynthesis pathway of many natural products. An iron(IV)-oxo-halo species has been established as the active oxidant in the halogenation reactions. With an objective to emulate the function of the nonheme halogenases, two iron(II)-α-keto acid complexes, [(phdpa)Fe(BF)Cl] (1) and [(1,4-tpbd)Fe2(BF)2Cl2] (2) (where phdpa = N,N-bis(2-pyridylmethyl)aniline, 1,4-tpbd = N,N,N′,N’-tetrakis(2-pyridylmethyl)benzene-1,4-diamine, and BF = benzoylformate), have been prepared. The iron complexes are capable of carrying out the oxidative halogenation of aliphatic C–H bonds using O2as the terminal oxidant. Although the complexes are not selective toward C–H bond halogenation, they are the only examples of nonheme iron(II)-α-keto acid complexes mimicking the activity of nonheme halogenases. The dinuclear complex (2) exhibits enhanced reactivity toward C–H bond halogenation/hydroxylation.

Understanding fundamental Tc chemistry is important to both the remediation of nuclear waste and the reprocessing of nuclear fuel; however, current knowledge of the electronic structure and spectral signatures of low-valent Tc compounds significantly lags behind the remainder of the d-block elements. In particular, identification and treatment of Tc speciation in legacy nuclear waste is challenging due to the lack of reference data especially for Tc compounds in the less common oxidation states (I–VI). In an effort to establish a spectroscopic library corresponding to the relevant conditions of extremely high ionic strength typical for the legacy nuclear waste, compounds with the general formula of [fac-Tc(CO)3(OH2)3–n(OH)n]1–n(where n= 0–3) were examined by a range of spectroscopic techniques including 99Tc/13C NMR, IR, XPS, and XAS. In the series of monomeric aqua species, stepwise hydrolysis results in the increase of the Tc metal center electron density and corresponding progressive decrease of the Tc–C bond distances, Tc electron binding energies, and carbonyl stretching frequencies in the order [fac-Tc(CO)3(OH2)3]+> [fac-Tc(CO)3(OH2)2(OH)] > [fac-Tc(CO)3(OH2)(OH)2]−. These results correlate with established trends of the 99Tc upfield chemical shift and carbonyl 13C downfield chemical shift. The lone exception is [fac-Tc(CO)3(OH)]4which exhibits a comparatively low electron density at the metal center attributed to the μ3-bridging nature of the –OH ligands causing less σ-donation and no π-donation. This work also reports the first observations of these compounds by XPS and [fac-Tc(CO)3Cl3]2–by XAS. The unique and distinguishable spectral features of the aqua [fac-Tc(CO)3]+complexes lay the foundation for their identification in the complex aqueous matrixes.