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A multifunctional polyoxometalate-ionic liquid (POM-IL)-based hybrid material comprising silicotungstic acid, [BmIm] 4 [SiW 12 O 40 ], has been synthesized and demonstrated its efficiency toward methylene blue removal and as an antibacterial agent. Single-crystal XRD analysis confirms that the material crystallizes in monoclinic symmetry (SG: Pn ), with lattice parameters a = 13.1396(5) Å, b = 16.9655(8) Å, c = 14.3493(7) Å, and Z = 2. The structure comprises a single polyanionic [SiW 12 O 40 ] 4- moiety surrounded by four cationic [BmIm] + units of two different conformations, which supported DFT and Hirshfeld surface analysis. The material shows excellent removal efficiency for methylene blue, with a maximum adsorption capacity of 92.47 mg/g and 83.05% reusability after five cycles. On the contrary, FTIR and ζ-potential analyses confirm that electrostatic interactions are the predominant factors governing the adsorption process. The material also acts as a superior antibacterial agent against the opportunistic pathogens Pseudomonas aeruginosa , Klebsiella pneumoniae , and Escherichia coli with a MIC of 500-700 μg/mL. However, a comparative assessment showed that the material was more effective against P. aeruginosa compared to the other two pathogens. PXRD analysis confirms the phase purity, and FESEM and TEM analyses exhibit block-shaped morphology with particle sizes ∼2-3 μm.

Atom-precise metal nanoclusters, which contain a few tens to hundreds of atoms, have drawn significant interest due to their interesting physicochemical properties. Structural analysis reveals a fundamental architecture characterized by a central core or kernel linked to a staple motif with metal-ligand bonding playing a pivotal role. Ligands not only protect the surface but also exert a significant influence in determining the overall assembly of the larger superstructures. The assemblies of nanoclusters are driven by weak interaction between the ligand molecules; it also depends on the ligand type and functional group present. Here, we report an achiral ligand and Ag(I)···Ag(I) interaction-driven spontaneous resolution of silver-thiolate structure, [Ag 18 (C 6 H 11 S) 12 (CF 3 COO) 6 (DMA) 2 ], where silver atoms and cyclohexanethiolate are connected to form a one-dimensional chain with helicity. Notably, silver atoms adopt different types of coordination modes and geometries. The photoluminescence properties of the one-dimensional (1D) chain structure were investigated, and it was found to exhibit excitation-dependent emission properties attributed to hydrogen-bonding interactions. Experimental and theoretical investigations corroborate the presence of triplet-emitting ligand-to-metal charge-transfer transitions.

NU-1000, being a hydrothermally stable metal-organic framework (MOF), with structural robustness is viable for functionalization with various entities. A postsynthetic modification strategy called solvent-assisted ligand incorporation (SALI) is chosen for functionalizing NU-1000 with thiol moieties using 2-mercaptobenzoic acid. In accordance with soft acid-soft base interactions, the thiol groups on NU-1000, as a scaffold, can immobilize the gold nanoparticles without much aggregation. The catalytically active gold sites on thiolated NU-1000 are utilized for hydrogen evolution reaction (HER). The catalyst delivered an overpotential of 101 mV at a current density of 10 mAcm -2 in 0.5 M H 2 SO 4 . The faster charge transfer kinetics determined from the Tafel slope of 44 mV/dec enhances the HER activity. The sustainable performance of the catalyst for 36 h proves its utility as a potential catalyst to produce neat hydrogen.

The reaction of [( p -cymene)RuCl 2 ] 2 with the triphosphine ligand bis(2-di- tert -butylphosphinophenyl)phosphine ( tBu P H PP) results in an unusual exchange reaction in which a chloride ligand and a phosphorus-bound H atom are exchanged ("H-P/Ru-Cl exchange") to give the (chlorophosphine)ruthenium hydride complex ( tBu P Cl PP)RuHCl [ 1 Cl -HCl ; tBu P Cl PP = bis(2-di- tert -butylphosphinophenyl)chlorophosphine]. Density functional theory calculations indicate that the presumed initial product of metalation, ( tBu P H PP)RuCl 2 ( 1 H -Cl2 ), undergoes an H-P/Ru-Cl exchange via sequential P-to-Ru α-H migration to give the intermediate ( tBu PPP)RuHCl 2 , followed by Ru-to-P α-Cl migration to give the observed product 1 Cl -HCl (crystallographically characterized). Dehydrochlorination of 1 Cl -HCl under a H 2 atmosphere gives ( tBu P Cl PP)RuH 4 ( 1 Cl -H4 ), which then can undergo a second dehydrochlorination and addition of H 2 to give ( tBu P H PP)RuH 4 ( 1 H -H4 ). This reaction may proceed via the reverse of the intramolecular exchange by 1 H -Cl2 , i.e., loss of H 2 from 1 Cl -H4 to give 1 Cl -H2 , which could undergo Cl-P/Ru-H exchange to give ( tBu P H PP)RuHCl ( 1 H -HCl ). Accordingly, the thermodynamics of Cl-P/Ru-H exchange are found to be highly dependent on the nature of the ancillary anionic ligand (H or Cl), which is not directly involved in the exchange. The origin of this thermodynamic dependence can be explained in terms of the high stability of complexes ( R P X PP)RuHCl (X = H, Cl; R = Me, t Bu), in which the hydride is approximately trans to a vacant coordination site and the central phosphine group is approximately trans to the weak-trans-influence chloride ligand. This conclusion has general implications for five-coordinate d 6 complexes, both pincer- and nonpincer-ligated.

The self-assembly of a redox-active ethylenedioxythiophene (EDOT)-terpyridine-based tridentate ligand and cobalt(II) unit with different counteranions has led to a series of new cobalt(II) complexes [Co( L ) 2 ](X) 2 (X = BF 4 ( 1 ), ClO 4 ( 2 ), and BPh 4 ( 3 )) ( L = 4'-(3,4-ethylenedioxythiophene)-2,2':6',2″-terpyridine). The impact of various counteranions on stabilization and spin-state switching of the cobalt(II) center was explored through detailed magneto-structural investigation using variable temperature single-crystal X-ray diffraction, magnetic, spectroscopic, electrochemical, and spectroelectrochemical studies. All three complexes 1 - 3 consisted of an isostructural dicationic distorted octahedral CoN 6 coordination environment offered by the two L ligands in a bis-meridional fashion and BF 4 - , ClO 4 - , and BPh 4 - as a counteranion, respectively. Complex 2 with ClO 4 - counteranion showed a reversible, gradual, and nearly complete spin-state switching between low-spin (LS) ( S = 1/2) and high-spin (HS) ( S = 3/2) states, while an incomplete spin-state switching behavior was observed for complexes 1 (BF 4 - ) and 3 (BPh 4 - ) in the measured temperature range of 350-2 K. The non-covalent cation-anion interactions played a significant role in stabilizing the spin-state in 1 - 3 . Additionally, complexes 1 - 3 also exhibited interesting redox-stimuli-based reversible paramagnetic HS cobalt(II) ( S = 3/2) to diamagnetic LS cobalt(III) ( S = 0) conversion, offering an alternate way to switch the magnetic properties.

Small-sized silver nanoparticles are incorporated into a thiol-functionalized stable Zr-based metal-organic framework (MOF). Thiol functionalization has been carried out using 2-mercapto benzoic acid (2-MBA) as the modulator, which promotes defect formation in the MOF structure. The incorporation of silver nanoparticles aided by the silver-sulfur interactions in this defective MOF gives rise to catalytic activity. Its catalytic efficiency in the highly atom-efficient A 3 coupling reaction has been studied for a variety of substrates with impressive recyclability. The synergistic effect of the electron-rich silver core and electron-deficient surface of the thiol-bonded silver nanoparticle is key for this catalytic reaction.

UiO-66 has been tailored using defect engineering methodology to introduce thiol functionalities into the MOF skeletal structure. The thiolated UiO-66 serves as a scaffold to support the platinum nanoparticles with a size of ∼2 nm through a soft-soft interaction. This Pt@UiO-66-SH, utilized as an HER catalyst, exhibited an overpotential of 57 mV at a current density of 10 mA cm -2 in an acidic medium with a Tafel slope of 75 mV/dec and a high TOF value (389.37 s -1 ). This catalyst showed long-term durability for 30 h, specifying the potential of the material to produce neat hydrogen.

The isolation, characterization, and dioxygen reactivity of monomeric [(TPA)M II (mandelate)] + (M = Fe, 1 ; Co, 3 ) and dimeric [(BPMEN) 2 M II 2 (μ-mandelate) 2 ] 2+ (M = Fe, 2 ; Co, 4 ) (TPA = tris(2-pyridylmethyl)amine and BPMEN = N 1 , N 2 -dimethyl- N 1 , N 2 -bis(pyridin-2-yl-methyl)ethane-1,2-diamine) complexes are reported. The iron(II)- and cobalt(II)-mandelate complexes react with dioxygen to afford benzaldehyde and benzoic acid in a 1:1 ratio. In the reactions, one oxygen atom from dioxygen is incorporated into benzoic acid, but benzaldehyde does not derive any oxygen atom from dioxygen. While no O 2 -derived intermediate is observed with the iron(II)-mandelate complexes, the analogous cobalt(II) complexes react with dioxygen at a low temperature (-80 °C) to generate the corresponding cobalt(III)-superoxo species ( S ), a key intermediate implicated in the initiation of mandelate decarboxylation. At -20 °C, the cobalt(II)-mandelate complexes bind dioxygen reversibly leading to the formation of μ-1,2-peroxo-dicobalt(III)-mandelate species ( P ). The geometric and electronic structures of the O 2 -derived intermediates ( S and P ) have been established by computational studies. The intermediates S and P upon treatment with a protic acid undergo decarboxylation to afford benzaldehyde (50%) with a concomitant formation of the corresponding μ-1,2-peroxo - μ-mandelate-dicobalt(III) ( P1 ) species. The crystal structure of a peroxide species isolated from the cobalt(II)-carboxylate complex [(TPA)Co II (MPA)] + ( 5 ) (MPA = 2-methoxyphenylacetate) supports the composition of P1 . The observations of the dioxygen-derived intermediates from cobalt complexes and their electronic structure analyses not only provide information about the nature of active species involved in the decarboxylation of mandelate but also shed light on the mechanistic pathway of two-electron versus four-electron reduction of dioxygen.

A soft acid-soft base interaction is highly predictable. However, we demonstrate how the crystal packing of the newly synthesized zinc framework [Zn 2 (5-AIA) 2 (DPTTZ)]·DMF (where 5-AIA = 5-aminoisophthalic acid, DPTTZ = N,N' -di(4-pyridyl)thiazolo-[5,4- d ]thiazole, DMF = N,N' -dimethylformamide) directs an unexpected interaction between the soft acid Hg(II) and the hard base oxygen instead of having a soft center like nitrogen and sulfur in the system attributed to a strong solvent interaction and a favorable ionic radius of Hg(II) ion for oxygen chelation. This engenders selective Hg(II) ion sensing through a "turn-off" emission quenching in water (limit of detection = (2.174 ± 0.06) × 10 -9 M) along with natural water resources and in a broad pH range. A quantum-chemical calculation elucidates the turn-off quenching mechanism and favorable Hg(II) interaction with encompassed oxygen atoms inside the framework.

Two mononuclear ruthenium(II) complexes of the types [Ru(trpy)(HL 1 )(OH 2 )] 2+ ( 1 Aq ) and [Ru(trpy)(L 2 -κ-N 2 O)] ( 2 ) [where trpy = 2,2':6',2″-terpyridine, HL 1 = 2-(2-pyridyl)benzimidazole, H 2 L 2 = 2-(pyridin-2-yl)-1 H -benzo[ d ]imidazole-4-carboxylic acid] have been synthesized and thoroughly characterized by analytical and spectroscopic [UV-vis, NMR, high-resolution mass spectrometry, and IR] techniques. Complex 1 Aq has been further characterized by X-ray crystallography. In an acidic aqueous medium (pH 1), complex 2 undergoes carboxylate/water exchange readily to form an aqua-ligated complex, [Ru(trpy)(H 2 L 2 -κ-N 2 )(OH 2 )] 2+ ( 2 Aq ), having a dangling carboxylic group. This exchange phenomenon has been followed by IR, 1 H NMR, and UV-vis spectroscopic techniques. Electrochemical analyses of 1 Aq and 2 Aq (Pourbaix diagram) suggest the generation of a formal Ru V ═O species that can potentially promote the oxidation of water. A comparative study of the water oxidation activity catalyzed by 1 Aq and 2 Aq is reported here to see the effect of a dangling carboxylic group in the catalytic performance. Complex 2 Aq shows an enormously higher rate of reaction than 1 Aq . The pendant carboxylic group in 2 Aq participates in an intramolecular O-O bond formation reaction with the reactive formal Ru V ═O unit to form a percarboxylate intermediate and provides an electron-deficient carbon center where water nucleophilic attack takes place. The isotope labeling experiment using 18 O-labeled water verifies the attack of water at the carbon center of the carboxylic group rather than a direct attack at the oxo of the formal Ru V ═O unit. The present work provides experimental evidence of the uncommon functionality of the carboxylic group, the oxide relay, in molecular water oxidation chemistry.

The structure-property correlation of a series of silver nanoclusters (NCs) is essential to understand the origin of photophysical properties. Here, we report a series of face-centered cubic (fcc)-based silver NCs by varying the halogen atom in the thiolate ligand to investigate the influence of the halide atoms on the electronic structure. These are {Ag 14 (FBT) 12 (PPh 3 ) 8 ·(solvent) x } ( NC-1 ), Ag 14 (CBT) 12 (PPh 3 ) 8 ( NC-2 ), and Ag 14 (BBT) 12 (PPh 3 ) 8 ( NC-3 ), where 4-fluorothiophenol (FBT), 4-chlorothiophenol (CBT), and 4-bromothiophenol (BBT) have been utilized as thiolate ligands, respectively. Interestingly, the optical and electrochemical bandgap values of these NCs nicely correlated with the electronic effect of the halides, which is governed by the intracluster and interclusters π-π interactions. These clusters are emissive at room temperature and the luminescence intensity increases with the lowering of temperature. The short lifetime data suggest that the emission is predominantly originating due to the interband relaxation (d → sp) of the Ag cores. Femtosecond transient absorption (TA) spectra revealed similar types of decay profiles for NC-2 and NC-3 and longer decay time for NC-2 . The relaxation dominates the decay profile to the surface states and most of the excited-state energy dissipates via this process. This supports the molecular-like dynamics of these series of NCs with an fcc core. This overview shed light on an in-depth understanding of ligand's role in luminescence and transient absorption spectra.

Unraveling the total structure of the atom-precise silver cluster-assembled materials (CAMs) is extremely significant to elucidating the structure-property correlation, but it is a very challenging task. Herein, a new silver CAM is synthesized by a facile synthetic pathway with a unique distorted elongated square-bipyramid-based Ag 11 core geometry. The core is protected by two different kinds of the surface protecting ligands (adamantanethiolate and trifluoroacetate) and connected through a bidentate organic linker. The crystallographic data show that this material embraces a one-dimensional periodic structure that orchestrates by various noncovalent interactions to build a thermally stable supramolecular assembly. Further characterization confirms its n-type semiconducting property with an optical band gap of 1.98 eV. The impact of an adamantanethiol-protected silver core on the optical properties of this type of periodic framework is analyzed by the UV-vis absorbance and emission phenomena. Theoretical calculations predicted that the occupied states are majorly contributed by Ag-S. Solvent-dependent photoluminescence studies proved that a polar solvent can significantly perturb the metal thiolate and thiolate-centered frontier molecular orbitals that are involved in the electronic transitions.

Distinct functional materials in their combined form in a well-designed hybrid architecture offer great possibilities for creating a highly active photocatalytic system. Herein, a uniform multipod-shaped ZnO is synthesized through a natural template assisted route and progressively integrated with Ag nanoparticles (NPs) and Bi 2 S 3 to form a three-component (3C) ternary photocatalytic system by a facile, two -step wet chemical approach. Encapsulation of polycrystalline Bi 2 S 3 and assimilation of Ag NPs in between the interface of ZnO and Bi 2 S 3 in the ternary hybrid are confirmed from electron microscopy and X-ray photoelectron spectroscopy, which resulted in improved UV-vis absorption, charge separation efficiency, and photocurrent response evaluated from optical absorption spectroscopy, photoluminescence, and photoelectrochemical cell measurements. This ternary hybrid shows high photoredox activity toward the hydrogen evaluation reaction (HER) (218.7 μmol h -1 g -1 ) and methyl orange (MO) oxidation ( k = 3.21 × 10 -2 min -1 ) compared to their binary and single counterparts. Moreover, on the basis of the estimation of the predominant active species (O 2 •- , • S 2 S 3 S 2 S 3 S 2 S 3 and ZnO along with plasmonic photosensitization to trigger the generation of plasmon-induced hot electrons. Such a cooperative concurrent dual role of Ag NPs in the Z-scheme ternary hybrid system considerably boosts the photoredox performance compared to direct Z-scheme binary hybrids. This work will enlighten and uncover the essential roles of metal NPs along with their cooperative synergy in Z-scheme photocatalytic systems as a prototypical example for substantial solar energy conversion.

Boronic acid groups have a high affinity toward cis -diols, which, when suspended in a metal-organic framework, generate a novel adsorbent for cis -diols. In this work, we followed a metal-ligand-fragment-coassembly (MLFC) approach to develop a series of water-stable barium metal-organic frameworks with uniform distribution of free boronic acid in the scaffold. The 11 B nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopic (XPS) investigations show the enhancement in the inclusion as the feed amount of boronic acid moiety increases. The findings of the adsorption studies elucidated the importance of furanose isomeric form of cis -diols in determining the adsorption efficiency. Galactose is the favorable adsorbate which has the maximum number of molecules in its furanose isomeric form (∼7%). The developed MOFs are promising candidates for the isolation of cis -diols from aqueous solutions.

Cerium(IV)-driven water oxidation catalysis mediated by a mononuclear ruthenium(III) complex, [Ru(L)(pic) 3 ] (H 3 L = 2,2'-iminodibenzoic acid, pic = 4-methylpyridine), has been demonstrated in this work. The mechanistic details of water oxidation have been investigated by the combined use of spectroscopy, electrochemistry, kinetic analysis, and computational studies. It was found that water oxidation proceeds via formal high-valent Ru VII species. The capability of accessing such a high-valent state is derived from the non-innocent behavior of the anionic tridentate ligand frame which helps in accumulation of oxidative equivalents in cooperation with metal center. This metal-ligand cooperation facilitates the multi-electron-transfer reaction such as water oxidation. Kinetic analysis suggests water oxidation at a single site of Ru where O-O bond formation occurs via radical-radical coupling pathway between the oxygen atom of ruthenium-oxo species and the oxygen atom of the hydroxocerium(IV) ion.

The synthesis and characterization of a new pyrazine-based ditopic organoplatinum(II) complex having a bite angle of 180° is reported. The facile and efficient syntheses are described of three discrete neutral Fe(II)/Pt(II) heterobimetallic SCCs with Pt(II) acceptor clips of different binding angles, 0, 120, and 180°. These new SCCs were characterized by multinuclear NMR and mass spectrometry. Electrochemical response of these ferrocene containing self-assembled ensembles was studied using cyclic voltammetry. The diplatinum acceptor organometallic clips significantly quench the fluorescence of highly emitting carbon quantum dots (CD), while the self-assembled macrocycles tend to nullify the quenching effect of the organometallic clips. Interestingly, the inefficient quenching of CD fluorescence by these SCCs was found to be directly related to the angular disposition of the binding sites in the Pt(II) based organometallic clips.

Here we describe, a simple solution and solid-state sensor for the ultrasensitive detection of Hg(II) ions in both standardized and environmental samples through changes of fluorescence intensity of a zinc-based metal-organic framework (MOF). The MOF is highly water stable in a wide pH range from 4 to 11. The lower detection limit of Hg 2+ is 10 -11 M with a very high binding constant of 1.011 × 10 9 M -1 s -1 . It also exhibits a high selectivity toward mercury ion in the presence of other interfering metal ions. The MOF is found to retain its efficiency in detecting mercury ion in spiked environmental water samples.

A new, three-dimensional cadmium based metal-organic framework [Cd 3 (PDA) 1 (tz) 3 Cl(H 2 O) 4 ]·3H 2 O {PDA = 1,4-phenylenediacetate and tz = 1,2,4-triazolate}, 1, has been successfully synthesized using slow diffusion method at room temperature. The structure of compound 1 has been determined using single crystal X-ray diffraction. The triazolate ligands connect three different types of octahedral Cd 2+ ions to form a two-dimensional structure. The chloride ion and PDA ligands connect the two-dimensional layers to form a three-dimensional structure. The phase purity of 1 was confirmed by powder X-ray diffraction, thermogravimetric analysis, and IR spectroscopy. Aqueous dispersion of compound 1 gives intense luminescence emission at 290 nm upon excitation at 225 nm. This emission was used for the luminescence based detection of pesticides, especially azinphos-methyl, chlorpyrifos, and parathion in aqueous medium. The selectivity of pesticide detection remains unaltered even in the presence of surfactant molecules. The mechanisms of luminescence quenching were successfully explained by the combination of absorption of excitation light, resonance energy transfer, and the possibility of electron transfer. Experimental findings are also well supported by the density functional theory calculations. Selectivity of pesticides detection in real samples such as apple and tomato juice has also been observed.

A new three-dimensional europium-based metal-organic framework has been synthesized with the newly designed ligand L (6-[1-(4-carboxyphenyl)-1 H-1,2,3-triazol-4-yl]nicotinic acid). This compound acts as a dual sensor for the phosphate anion and Fe 3+ ion in aqueous media. The mechanistic aspect of this selectivity and sensitivity was explored through several spectroscopic methods and then correlated with the corresponding structure.

Postsynthetic modification is a promising tool for introducing multifunctional properties in metal-organic frameworks (MOFs). The effects of postsynthetic metal addition/exchange in a barium-based MOF have been well examined toward their magnetic and electrical properties. The rattling motion of the extraframework organic cation is responsible for the ferroelectric behavior. The strong magnetic frustration in Tb@1 is found to arise from the nearly triangular arrangement of Tb 3+ ions in its secondary building unit along the chain direction.

A 5-fold-interpenetrated zinc-based coordination polymer can discriminately detect aliphatic amines through a fluorescence "turn-on" method. This compound can sense aliphatic amines in the solid state, solution state, and vapor phase. Theoretical calculations revealed that the ground-state dipole moment of the corresponding amines guides the order of enhancement.

We have isolated two copper-based coordination polymers through solvent diffusion and solvothermal methods using copper salt, furan dicarboxylic acid (FDC), 4,4'-bipyridine (bpy) in MeOH/ethylene glycol, and water solvents. Compound 1 is adopting P2 1 /c space group and adopts a one-dimensional wirelike structure with a free carboxylate anion. Compound 2 crystallizes in chiral space group P6 5 . This is a three-dimensional structure with helical chains. This helicity might be the reason for chiral generation and symmetry breaking. We have converted compound 1 to compound 2 using grinding, followed by a solvothermal method. The circular dichroism data of 2 showed that it is an enantioenriched compound. We have shown that compound 2 is a very good catalyst for chemo- and regioselective enamination reaction and for azide-alkyne Huisgen cycloaddition, respectively.

The design of multinuclear metal complexes requires a match of the ligand-to-metal vectors and the preferred coordination geometries of the metal ions. Only a few ligands are known with a parallel orientation of N→M vectors that brings the metal ions into close proximity. We establish here the adenine derivative 1,N(6)-ethenoadenine (εA) as an ideal bis(monodentate) ligand. Scanning tunneling microscope images of alkylated εA on graphite surface clearly indicate that these ligands bind to Ag(I) ions. The molecular structures of [Ag2(1)2](ClO4)2 and [Ag2(2)2](ClO4)2 (1, 9-ethyl-1,N(6)-ethenoadenine; 2, 9-propyl-1,N(6)-propylenoadenine) confirm that dinuclear complexes with short Ag···Ag distances are formed (3.0256(3) and 2.984(1) Å, respectively). The structural motif can be extended to divalent metal ions, as was shown by determining the molecular structure of [Cu2(1)2(CHO2)2(OH2)2](NO3)2·2H2O with a Cu···Cu distance of 3.162(2) Å. Moreover, when introducing the 1,N(6)-ethenoadenine deoxyribonucleoside into parallel-stranded DNA duplexes, even dinuclear Ag(I)-mediated base pairs are formed, featuring the same transoid orientation of the glycosidic bonds as the model complexes. Hence, 1,N(6)-ethenoadenine and its derivatives are ideally suited as bis(monodentate) ligands with a parallel alignment of the N→M vectors for the construction of supramolecular metal complexes that require two metal ions at close distance.

Efficient uptake of Hg(2+) ions in mercury-resistant bacteria is attributed to the presence of cysteine thiolates in the Mer proteins. In this work, a pyridine-appended pyridine-fused imidazolyl-2-thione scaffold was used as a mimic for the cysteinyl residues for efficient binding of the Hg(2+) ions. In the presence of Hg(2+) ions, an aryl C-H bond of the ligand is activated. The sulfur and nitrogen donors on the other end of the ligand coordinate with a second Hg(2+) ion. This motif in the presence of acetate ions forms a one-dimensional polymeric crystalline network characterized by singal-crystal X-ray diffraction studies. The formation of this polymeric structure leads to efficient removal (∼99%) of Hg(2+) ions from aqueous solutions through an underexplored "kamikaze" approach involving a small-molecule ligand as a sacrificial agent for trapping the ion.

Three chemical reactions of two 2-aminothioethers and 2-aminothiophenol with CpRu(II)Cl(PPh3)2 (Cp(-) = cyclopentadienyl anion), under identical reaction conditions, are reported. While 2-(methylthio)aniline, H2L(1) and an analogous substrate, 2-(phenylthio)aniline yielded dicationic dinuclear complexes [(PPh3)CpRu(II)(L(3/)L(4))Ru(II)Cp(PPh3)]Cl2 (where L(3) = (4E)-4-(4-imino-3-(methylthio)cyclohexa-2,5-dienylidene)-2-(methylthio)cyclohexa-2,5-dienimine ([1a]Cl2) and L(4) = (4E)-4-(4-imino-3-(phenylthio)cyclohexa-2,5-dienylidene)-2-(phenylthio)cyclohexa-2,5-dienimine ([1b]Cl2)), the reaction with 2-aminothiophenol (H2L(2)) produced a mononuclear complex [(PPh3)CpRu(II)(L(2))]Cl (where L(2) = 6-iminocyclohexa-2,4-dienethione) ([2]Cl). All these complexes are obtained in high yields (65%-75%). Formations of the products from the above reactions involve a similar level of oxidation of the respective substrate, although their courses are completely different. A comparison between the above two chemical transformations are scrutinized thoroughly. Characterizations of these complexes were made using a host of physical methods: X-ray crystallography, nuclear magnetic resonance (NMR), cyclic voltammetry, ultraviolet-visible (UV-vis), electron paramagnetic resonance (EPR) spectroscopy, and density functional theory (DFT). The complexes [1a]Cl2 and [1b]Cl2 showed intense metal-to-ligand charge transfer transition in the long wavelength region of the spectrum, at 860 and 895 nm, respectively, and displayed two reversible electron transfer (ET) processes at [1a](2+): -0.28 and -0.52 V; [1b](2+): -0.13 and -0.47 V, along with an irreversible ET process at 0.76 and 0.54 V, respectively. The ET processes at negative potentials are due to successive reductions of the bridging ligand, which are characterized by EPR and UV-vis spectroscopy. The one-electron reduced compound, [1a](+), showed a intraligand charge transfer transition (ILCT) at 1530 nm. The complex [2](+) showed a reversible ET process at -0.36 V and two irreversible ET processes at -1.04 and 1.18 V, respectively. DFT calculations were used to support the spectral and redox properties of the complexes and also to throw light on the difference of redox behavior between thioether and thiophenol substrates.

The work in this report describes the syntheses, electrospray ionization mass spectromtery, structures, and experimental and density functional theoretical (DFT) magnetic properties of four tetrametallic stars of composition [M(II)(Cu(II)L)3](ClO4)2 (1, M = Mn; 2, M = Ni; 3, M = Cu; 4, M = Zn) derived from a single-compartment Schiff base ligand, N,N'-bis(salicylidene)-1,4-butanediamine (H2L), which is the [2 + 1] condensation product of salicylaldehyde and 1,4-diaminobutane. The central metal ion (Mn(II), Ni(II), Cu(II), or Zn(II)) is linked with two μ2-phenoxo bridges of each of the three [Cu(II)L] moieties, and thus the central metal ion is encapsulated in between three [Cu(II)L] units. The title compounds are rare or sole examples of stars having these metal-ion combinations. In the cases of 1, 3, and 4, the four metal ions form a centered isosceles triangle, while the four metal ions in 2 form a centered equilateral triangle. Both the variable-temperature magnetic susceptibility and variable-field magnetization (at 2-10 K) of 1-3 have been measured and simulated contemporaneously. While the Mn(II)Cu(II)3 compound 1 exhibits ferromagnetic interaction with J = 1.02 cm(-1), the Ni(II)Cu(II)3 compound 2 and Cu(II)Cu(II)3 compound 3 exhibit antiferromagnetic interaction with J = -3.53 and -35.5 cm(-1), respectively. Variable-temperature magnetic susceptibility data of the Zn(II)Cu(II)3 compound 4 indicate very weak antiferromagnetic interaction of -1.4 cm(-1), as expected. On the basis of known correlations, the magnetic properties of 1-3 are unusual; it seems that ferromagnetic interaction in 1 and weak/moderate antiferromagnetic interaction in 2 and 3 are possibly related to the distorted coordination environment of the peripheral copper(II) centers (intermediate between square-planar and tetrahedral). DFT calculations have been done to elucidate the magnetic properties. The DFT-computed J values are quantitatively (for 1) or qualitatively (for 2 and 3) matched well with the experimental values. Spin densities and magnetic orbitals (natural bond orbitals) correspond well with the trend of observed/computed magnetic exchange interactions.

Thermal water oxidation by cerium(IV) ammonium nitrate (CAN) was catalyzed by nonheme iron complexes, such as Fe(BQEN)(OTf)2 (1) and Fe(BQCN)(OTf)2 (2) (BQEN = N,N'-dimethyl-N,N'-bis(8-quinolyl)ethane-1,2-diamine, BQCN = N,N'-dimethyl-N,N'-bis(8-quinolyl)cyclohexanediamine, OTf = CF3SO3(-)) in a nonbuffered aqueous solution; turnover numbers of 80 ± 10 and 20 ± 5 were obtained in the O2 evolution reaction by 1 and 2, respectively. The ligand dissociation of the iron complexes was observed under acidic conditions, and the dissociated ligands were oxidized by CAN to yield CO2. We also observed that 1 was converted to an iron(IV)-oxo complex during the water oxidation in competition with the ligand oxidation. In addition, oxygen exchange between the iron(IV)-oxo complex and H2(18)O was found to occur at a much faster rate than the oxygen evolution. These results indicate that the iron complexes act as the true homogeneous catalyst for water oxidation by CAN at low pHs. In contrast, light-driven water oxidation using [Ru(bpy)3](2+) (bpy = 2,2'-bipyridine) as a photosensitizer and S2O8(2-) as a sacrificial electron acceptor was catalyzed by iron hydroxide nanoparticles derived from the iron complexes under basic conditions as the result of the ligand dissociation. In a buffer solution (initial pH 9.0) formation of the iron hydroxide nanoparticles with a size of around 100 nm at the end of the reaction was monitored by dynamic light scattering (DLS) in situ and characterized by X-ray photoelectron spectra (XPS) and transmission electron microscope (TEM) measurements. We thus conclude that the water oxidation by CAN was catalyzed by short-lived homogeneous iron complexes under acidic conditions, whereas iron hydroxide nanoparticles derived from iron complexes act as a heterogeneous catalyst in the light-driven water oxidation reaction under basic conditions.

Chemical model systems possessing the reactivity aspects of both tyrosinase and catechol oxidase are presented. Using two m-xylyl-based ligands providing bidentate alkylamine terminal coordination, 1,3-bis[(N,N-dimethylaminoethyl)aminomethyl]benzene (L(H,H)) and 1,3-bis[(N,N,N'-trimethylaminoethyl)aminomethyl]benzene (L(Me,Me)), four new dicopper(I) complexes, [Cu(I)(2)(L(H,H))(MeCN)(4)][ClO(4)](2) (1), [Cu(I)(2)(L(H,H))(PPh(3))(2)(MeCN)(2)][ClO(4)](2) (2), [Cu(I)(2)(L(Me,Me))(MeCN)(2)][ClO(4)](2) (3), and [Cu(I)(2)(L(Me,Me))(PPh(3))(2)][ClO(4)](2) (4), have been synthesized and characterized. Complex 2 has been structurally characterized. Reaction of the dicopper(I) complex 3(2+) with dioxygen at 183 K generates putative bis(μ-oxo)dicopper(III) intermediate (absorption spectroscopy). Oxygenation of 1 and 3 brings about m-xylyl-ring hydroxylation (monooxygenase-like activity), with a noticeable color change from pale-yellow to dark green. The presence of phenoxo- and hydroxo-bridges in the end products [Cu(II)(2)(L(H,H)-O)(OH)(MeCN)(2)][ClO(4)](2) (5) and [Cu(II)(2)(L(Me,Me)-O)(OH)(OClO(3))][ClO(4)]·MeCN(6) has been authenticated by structural characterization. Oxygenation of 3 afforded not only the green complex 6 isolation but also a blue complex [Cu(II)(2)(L(Me,Me))(OH)(2)][ClO(4)](2) (7). Variable temperature magnetic susceptibility measurements on 5 and 6 establish that the Cu(II) centers are strongly antiferromagnetically coupled [singlet-triplet energy gap (J) = -528 cm(-1) (5) and -505 cm(-1) (6)]. The abilities of phenoxo- and hydroxo-bridged dicopper(II) complexes 5 and 6, the previously reported complex [Cu(II)(2)(L(1)-O)(OH)(OClO(3))(2)]·1.5H(2)O (8) (L(1)-OH = 1,3-bis[(2-dimethylaminoethyl)iminomethyl]phenol), and [Cu(II)(2)(L(2)-O)(OH)(OClO(3))()][ClO(4)]() (9) (L(2)-OH = 1,3-[(2-dimethylaminoethyl)iminomethyl][(N,N,N'-trimethyl)aminoethyl]-4-methylphenol) have been examined to catalyze the oxidation of catechol to quinone (catecholase activity of tyrosinase and catechol oxidase-like activity) by employing the model substrate 3,5-di-tert-butylcatechol. Saturation kinetic studies have been performed on these systems to arrive at the following reactivity order [k(cat)/K(M) (catalytic efficiency) × 10(-3) (M(-1) h(-1))]: 470 (6) > 367 (5) > 128 (9) > 90 (8).

The preparation and characterization of three new macrocyclic ligands with pendant arms based on the [2+2] condensation of isophthalaldehyde and the corresponding triamine substituted at the central N-atom is reported. None of these new macrocyclic ligands undergo any equilibrium reaction, based on imine hydrolysis to generate [1+1] macrocyclic formation or higher oligomeric compounds, such as [3+3], [4+4], etc., at least within the time scale of days. This indicates the stability of the newly generated imine bond. In sharp contrast, the reaction of the [2+2] macrocyclic Schiff bases with Cu(I) generates the corresponding dinuclear Cu(I) complexes [Cu(2)(L(1))](2+), 1(2+); [Cu(2)(L(2))(CH(3)CN)(2)](2+), 2(2+); and [Cu(2)(L(3))(CH(3)CN)(2)](2+), 3(2+), together with their trinuclear Cu(I) homologues [Cu(3)(L(4))](3+), 4(3+); [Cu(3)(L(5))(CH(3)CN)(3)](3+), 5(3+); and [Cu(3)(L(6))(CH(3)CN)(3)](3+), 6(3+), where the [2+2] ligand has undergone an expansion to the corresponding [3+3] Schiff base that is denoted as L(4), L(5), or L(6). The conditions under which the dinuclear and trinuclear complexes are formed were analyzed in terms of solvent dependence and synthetic pathways. The new complexes are characterized in solution by NMR, UV-vis, and MS spectroscopy and in the solid state by X-ray diffraction analysis and IR spectroscopy. For the particular case of the L(2) ligand, MS spectroscopy is also used to monitor the metal assisted transformation where the dinuclear complex 2(2+) is transformed into the trinuclear complex 5(3+). The Cu(I) complexes described here, in general, react slowly (within the time scale of days) with molecular oxygen, except for the ones containing the phenolic ligands 2(2+) and 5(3+) that react a bit faster., (© 2011 American Chemical Society)

Four dinuclear nickel(II) complexes [Ni(II)(2)(L(1))(O(2)CMe)(2)(H(2)O)(2)][PF(6)].MeOH.3H(2)O (1), [Ni(II)(2)(L(1))(O(2)CMe)(2)(NCS)] (2), [Ni(II)(2)(L(2))(O(2)CMe)(2)(MeOH)(H(2)O)][ClO(4)] (3), and [Ni(II)(2)(L(2))(O(2)CMe)(2)(MeOH)(H(2)O)][BPh(4)].3MeOH.H(2)O (4) have been synthesized [HL(1): 2,6-bis[N-methyl-N-(2-pyridylethyl)amino]-4-methylphenol; HL(2): 2,6-bis[3-(pyridin-2-yl)pyrazol-1-ylmethyl]-4-methylphenol]. Complexes 1, 3, and 4 are new while complex 2 was reported previously by Fenton and co-workers (the structure of 2 was presented but no physicochemical properties of this complex were reported; in this work such studies have been completed). X-ray crystallographic analyses of 1 and 4 reveal that each nickel(II) center is six-coordinate, terminally coordinated by two nitrogen donors [(pyridin-2-yl)ethylamine unit in 1 and 3-(pyridin-2-yl)pyrazole moiety in 4], and bridged by an endogenous phenolate ion. Each of the acetate ions in 1 adopts a eta(2)-coordination mode (chelating) whereas in 4 each is coordinated in a mu-eta(1):eta(1) syn-syn bridging mode. In 1 each Ni(II) center has water coordination whereas in 4 one Ni(II) center has a methanol and the other has water coordination. The X-ray structure of 3 could not be determined. The physicochemical properties (electronic spectroscopy and cyclic voltammetry) of the cation of 3 are identical to that of 4. Magnetic susceptibility measurements have revealed the occurrence of ferromagnetic coupling of spins of the nickel(II) centers in 2 [J = +9.80 cm(-1)]. The nickel(II) centers in 1 and 3 are antiferromagnetically coupled, but to different extents [J = -48.4 cm(-1) (1); J = -1.24 cm(-1) (3)]. The magnetic properties are correlated with the nature of bridges between the nickel(II) ions. The two coordinated aqua ligands in 1 and the aqua and methanol ligands in 3 have enabled these dinuclear nickel(II) complexes to function as catalysts in the hydrolysis of 2-hydroxypropyl-p-nitrophenylphosphate (HPNP). Complex 1 is more effective in the conversion of substrate to product (p-nitrophenolate ion) than 3, under identical experimental conditions. Pseudo first-order kinetic treatment has been done for complexes 1 and 3. Temperature-dependent measurements were done to evaluate kinetic/thermodynamic parameters for the hydrolysis/transesterification reaction of HPNP and to propose a mechanistic pathway. The activation parameters are DeltaH(++) = 64 kJ mol(-1), DeltaS(++) = -104 J mol(-1) K(-1) for 1 and DeltaH(++) = 68 kJ mol(-1), DeltaS(++) = -109 J mol(-1) K(-1) for 3. A mechanism consistent with the kinetic data is presented.

Five new zinc phosphites, [C10N4H26][Zn2(HPO3)4].2H2O, 1, [C10N4H26][Zn5(H2O)4(HPO3)6].4H2O, 2, [C10N4H26][Zn4(HPO3)6].2H2O, 3, [C10N4H26][Zn4(HPO3)6].2H2O, 4, and [Zn2(HPO3)2(C10N4H24)], 5, were synthesized employing solvo/hydrothermal reactions in the presence of 1,4-bis (3-aminopropyl) piperazine (APPIP). Single crystal X-ray diffraction studies indicate that all the compounds form a hierarchy of structures. While the structures 1 and 2 are low-dimensional, 3-5 have three-dimensional connectivity. ZnO4 and HPO3 units form a 4-membered ring and are connected through their corners forming a one-dimensional chain structure in 1. 2 has one-dimensional ladders connected by ZnO2(H2O)4 octahedral units forming a layer with 4- and 8-membered apertures. Compounds 3 and 4 have similar molecular formulae and connectivity, which makes them polymorphic in nature. The amine molecules exist in gauche and all-trans form in 3 and 4, respectively. The amine molecule binds with the zinc center in 5 and acts as a pillar between the two zinc phosphite layers. The present study outlines the possible role of synthesis parameters for the isolation of a number of different structures by employing a single amine molecule, APPIP. The observation of polymorphic structures along with the interconvertibilities of one of the phases is important and noteworthy. The 31P chemical shifts observed in NMR studies, consistent with the single crystal data, have been correlated with the valence sum values of the oxygen that are bound with the distinct phosphorus.

Three new amine templated uranium phosphites, [C2N2H10][U2IVF6(HPO3)2], 1, [C4N2H12][U2IVF6(HPO3)2], 2, and [C4N2H12][(UVIO2)2F2(HPO3)2], 3, have been synthesized by hydrothermal methods. All of the compounds are built up from a connectivity between U(O/F)x (x = 7, 8) and HPO3 polyhedral units. The observation of a well-established secondary building unit, SBU-4, in 1 and 2 is noteworthy. In 1, the SBU-4 units are connected to form U-F-U chains, which are linked by U-O-P chains, forming the layered structure. In 2, the SBU-4 units are edge-shared and also interconnected forming the 3D structure. In 3, the connectivity between the building units forms a layer, the topology of which is similar to the mineral, johannite. To the best of our knowledge, this is the first observation of a well-known secondary building unit (SBU-4) in actinide framework compounds. Optical studies on 1 and 2, containing U(4+) species, indicate an intense blue emission through an upconversion process, and the magnetic susceptibility studies show antiferromagnetic behavior.

A series of complexes with [Fe(II)(2)(mu-OH)(2)] cores has been synthesized with N3 and N4 ligands and structurally characterized to serve as models for nonheme diiron(II) sites in enzymes that bind and activate O(2). These complexes react with O(2) in solution via bimolecular rate-limiting steps that differ in rate by 10(3)-fold, depending on ligand denticity and steric hindrance near the diiron center. Low-temperature trapping of a (mu-oxo)(mu-1,2-peroxo)diiron(III) intermediate after O(2) binding requires sufficient steric hindrance around the diiron center and the loss of a proton (presumably that of a hydroxo bridge or a yet unobserved hydroperoxo intermediate). The relative stability of these and other (mu-1,2-peroxo)diiron(III) intermediates suggests that these species may not be on the direct pathway for dioxygen activation.

Comparisons of the spectroscopic properties of a number of Ru(III) complexes of imidazole ligands provide methods of distinguishing between various types of bonding that can occur in proteins and nucleic acids. In particular, EPR and (1)H NMR parameters arising from the paramagnetism of Ru(III) should aid in determining binding sites of Ru(III) drugs in macromolecules. Electrochemical studies on several imidazole complexes of ruthenium suggest that imidazole may serve as a significant pi-acceptor ligand in the presence of anionic ligands. Crystal structures are reported on two active immunosuppressant complexes. cis-[(Im)(2)(NH(3))(4)Ru(III)]Br(3) crystallizes in the triclinic space group P&onemacr; (No. 2) with the cell parameters a = 8.961(2) Å, b = 12.677(3) Å, c = 7.630(2) Å, alpha = 98.03(2) degrees, beta = 100.68(2) degrees, gamma = 81.59(2) degrees, and Z = 2 (R = 0.044). [(1MeIm)(6)Ru(II)]Cl(2).2H(2)O crystallizes in the monoclinic space group P2(1)/n (No. 14) with the cell parameters a = 7.994(2) Å, b = 13.173(4) Å, c = 14.904(2) Å, beta = 97.89(1) degrees, and Z = 2 (R = 0.052). The average Ru(II)-N bond distance is 2.106(8) Å.

Solutions of the Ni(IV) complex of the dianion of 2,6-diacetylpyridine dioxime (chelate II in text) are reduced very slowly by 2-aminoethanethiol at pH 2.3-3.0, but this reaction is catalyzed dramatically and specifically by dissolved copper, with Cu(I) the active reductant. When the [thiol]/[Ni(IV)] ratio exceeds 1.6, each Ni(IV) oxidizes two molecules of thiol, forming Ni(II) and R(2)S(2). At low concentrations of catalyst and reductant, reaction profiles are almost exponential, but at higher concentrations of either, curves become progressively more nearly linear. Reactions are sharply retarded by increases in acidity. Profiles for 14 runs, carried out with [H(+)] = 0.001-0.0040 M, [Ni(IV)] = (0.94-1.2) x 10(-)(5) M, [thiol] = (2.0-32) x 10(-)(4) M, and [Cu(2+)] = (2.5-80) x 10(-)(6)M, are consistent with a reaction sequence (eqs 2-10 in text) in which Cu(I) is generated in competing homolyses of the complexes Cu(II)(SRH) and Cu(II)(SRH)(2). Reduction of Ni(IV) appears then to proceed through a Ni(IV)Cu(I) adduct, which can undergo electron transfer (yielding Ni(III) and Cu(II)), either in a unimolecular fashion or, alternatively, as a result of attack by a second Cu(I) species. The Ni(IV)Cu(I) + Cu(I) process is reflected in approach to second-order dependences on [Cu(II)] and [thiol] (which generate Cu(I)) at high concentrations of these reagents. Reductions of the Ni(III) intermediate are taken to be much more rapid than those of Ni(IV). Kinetic trends in the present system stand in contrast to the more familiar catalytic patterns such as those seen when the same combination of thiol and catalyst is used to reduce superoxo complexes of cobalt(III). With the latter reactions, decay profiles for the oxidant tend to be exponential at high reagent concentrations but approach linearity at low.