Oxide Ligands Research Articles

Short-chained oligo(ethylene oxide)-functionalized gold nanoparticles: realization of significant protein resistance.

Protein corona formed on nanomaterial surfaces play an important role in the bioavailability and cellular uptake of nanomaterials. Modification of surfaces with oligoethylene glycols (OEG) are a common way to improve the resistivity of nanomaterials to protein adsorption. Short-chain ethylene oxide (EO) oligomers have been shown to improve the protein resistance of planar Au surfaces. We describe the application of these EO oligomers for improved protein resistance of 30nm spherical gold nanoparticles (AuNPs). Functionalized AuNPs were characterized using UV-Vis spectroscopy, dynamic light scattering (DLS), and zeta potential measurements. Capillary electrophoresis (CE) was used for separation and quantitation of AuNPs and AuNP-protein mixtures. Specifically, nonequilibrium capillary electrophoresis of equilibrium mixtures (NECEEM) was employed for the determination of equilibrium and rate constants for binding between citrate-stabilized AuNPs and two model proteins, lysozyme and fibrinogen. Semi-quantitative CE analysis was carried out for mixtures of EO-functionalized AuNPs and proteins, and results demonstrated a 2.5-fold to 10-fold increase in protein binding resistance to lysozyme depending on the AuNP surface functionalization and a 15-fold increase in protein binding resistance to fibrinogen for both EO oligomers examined in this study. Graphical abstract Using capillary electrophoresis, the addition of short-chained oligo(ethylene oxide) ligands to gold nanoparticles was shown to improve protein binding resistance up to 15-fold.

Synthesis and Photophysical Properties of Eu(III) Complexes with Phosphine Oxide Ligands including Metal Ions

Abstract Lanthanide (Ln3+) complexes composed of luminescent Eu3+ complex and joint metal blocks (Al3+, Zn2+ and Pd2+ complexes) are reported. The Eu3+ complexes [Eu(hfa)3(dppy)2PdCl2]n (Eu-Pd), [Eu(hfa)3(dppy)2ZnCl2]n (Eu-Zn) and [Eu(hfa)3(dppy)4AlCl3]n (Eu-Al) (hfa: hexafluoroacetylacetonato, dppy: 4-pyridyldiphenylphosphine oxide) were synthesized by the complexation of [Eu(hfa)3(H2O)2] with [MCln(dppy)m] (M = Pd2+, Zn2+ and Al3+). These predicted structures were estimated using single-crystal X-ray structural analyses and DFT calculations. Photophysical properties of these complexes were evaluated based on the emission lifetimes and emission quantum yields. The emission quantum yields are dependent on the moiety of the joint metal blocks. Eu-Al complex shows the largest emission quantum yield (Φff = 72%). In contrast, the emission quantum yield of Eu-Pd is found to be 1.3%. The structures and photophysical properties of Eu3+ complexes linked with joint metal blocks are demonstrated.

Reactions of Germylenes and Stannylenes with Halo(hydrocarbyl)- and Chloro(amino)phosphines: Oxidative Addition versus Ligand Transfer.

Oxidative addition (OA) is an important elementary step in chemistry, but it has been studied mainly in the context of transition-metal-catalyzed reactions and mainly with carbon-X substrates (X = halogen, H). Reports of main-group metal compounds undergoing OA are rare by comparison, and those involving phosphorus-halogen substrates are rarer still. Acyclic and cyclic diazagermylenes and -stannylenes react with chloro(hydrocarbyl)phosphines with the intermediacy of oxidative addition products. Stannylenes react faster than germylenes, and these reactions are first-order in both reactants and slowed by steric bulk. Kinetic data and the structures of intermediates and products had suggested an adduct/insertion mechanism for these reactions. To gain further insight into these transformations, the work presented herein was extended to chloro(hydrocarbyl)phosphines with varying organic substituents. These studies confirmed prior conclusions concerning the rate-diminishing effect of steric bulk, and the rate dependence on leaving groups also seems to suggest adduct/insertion or SN2 mechanisms. Importantly, these new data now also point to associative decomposition pathways. In the course of the investigation, it was discovered that aliphatic chloro(amino)phosphines react differently with the carbene analogues, giving oxidative addition products for germylenes but metathesis reactions for stannylenes.

Redox-Active Bis(phenolate) N-Heterocyclic Carbene [OCO] Pincer Ligands Support Cobalt Electron Transfer Series Spanning Four Oxidation States.

A new family of low-coordinate Co complexes supported by three redox-noninnocent tridentate [OCO] pincer-type bis(phenolate) N-heterocyclic carbene (NHC) ligands are described. Combined experimental and computational data suggest that the charge-neutral four-coordinate complexes are best formulated as Co(II) centers bound to closed-shell [OCO]2- dianions, of the general formula [(OCO)CoIIL] (where L is a solvent-derived MeCN or THF). Cyclic voltammograms of the [(OCO)CoIIL] complexes reveal three oxidations accessible at potentials below 1.2 V vs Fc+/Fc, corresponding to generation of formally Co(V) species, but the true physical/spectroscopic oxidation states are much lower. Chemical oxidations afford the mono- and dications of the imidazoline NHC-derived complex, which were examined by computational and magnetic and spectroscopic methods, including single-crystal X-ray diffraction. The metal and ligand oxidation states of the monocationic complex are ambiguous; data are consistent with formulation as either [(SOCO)CoIII(THF)2]+ containing a closed-shell [SOCO]2- diphenolate ligand bound to a S = 1 Co(III) center, or [(SOCO•)CoII(THF)2]+ with a low-spin Co(II) ion ferromagnetically coupled to monoanionic [SOCO•]- containing a single unpaired electron distributed across the [OCO] framework. The dication is best described as [(SOCO0)CoII(THF)3]2+, with a single unpaired electron localized on the d7 Co(II) center and a doubly oxidized, charge-neutral, closed-shell SOCO0 ligand. The combined data provide for the first time unequivocal and structural evidence for [OCO] ligand redox activity. Notably, varying the degree of unsaturation in the NHC backbone shifts the ligand-based oxidation potentials by up to 400 mV. The possible chemical origins of this unexpected shift, along with the potential utility of the [OCO] pincer ligands for base-metal-mediated organometallic coupling catalysis, are discussed.

Synthesis, characterization, and reactivity of copper complexes supported by the TPMEN ligand framework

Two new Cu(II) complexes supported by nitrogen-rich ligands have been synthesized and characterized by absorption spectroscopy, magnetic moment, and cyclic voltammetry. Complex 1 is supported by the ligand TPMEN (N,N,N′-tris(2-pyridylmethyl)-N′-methylethylenediamine) with two amine and three pyridyl nitrogen donors; while 2 is supported by the ligand TQMEN (N,N,N′-tris(2-quinolylmethyl)-N′-methylethylenediamine) where quinoline groups replace the pyridyl groups. Replacing the pyridyl moiety with quinoline has a marked effect on the Cu(II/I) reduction couple. The complexes are capable of reducing superoxide (O2−) to hydrogen peroxide (H2O2) in the presence of a proton donor. The reaction between potassium superoxide (KO2) and the Cu-complexes was monitored via absorption spectroscopy, and further probed with electrospray ionization mass spectrometry (ESI-MS). Both 1 and 2 depicted evidence of ligand oxidation in mass-spectrometry.

Controlled Synthesis of CuInS2/ZnS Nanocubes and Their Sensitive Photoluminescence Response toward Hydrogen Peroxide.

We synthesized uniform CuInS2/ZnS nanocubes by adjusting reaction parameters at the ZnS growth stage. Higher temperature and zinc concentration were shown to drive resultant crystals to have cubic morphology, which could be ascribed to the facet-dependent ligand dynamics on the crystal surface and concomitantly preferred directions of crystal growth. It was found that these nanocubes exhibit sensitive responses, as of photoluminescence quenching, toward hydrogen peroxide, compared to pyramid-shaped nanocrystals. The origin of quenching was further analyzed to be the oxidation of thiolate ligands that leaves the quenching center on the surface. It was noted that the quenched photoluminescence could be fully recovered by introducing additional ligand molecules into the system. Being adopted in the shape-controlled crystal growth, the ligand-to-crystal interaction was shown to still govern the interfacial reaction, the oxidation by hydrogen peroxide, of faceted crystals in our system. It turns out that the reactivity at the crystal surface depends on the exposed facets, especially induced by shape control, and the weak ligand-binding nature of the nanocube renders it vulnerable to the surface reaction.

Shape Controlled Synthesis of Au/Ag/Pd Nanoalloys and Their Oxidation-Induced Self-Assembly into Electrocatalytically Active Aerogel Monoliths

The synthesis of size and shape controlled Au/Ag/Pd alloy nanoparticles (NPs) and their self-supported assembly into monolithic aerogels for electro-oxidation of ethanol is reported. Two distinct morphologies of ultrasmall (3–5 nm) Au/Ag/Pd alloy NPs were produced via stepwise galvanic replacement of thiol-coated Ag NPs. The resultant nanoalloys were self-assembled into large, free-standing, aerogel superstructures that exhibit direct NP connectivity, high surface area (269 ± 18.1–76 ± 6.4 m2/g) and mesoporosity (2–50 nm), and high electrocatalytic activity via controlled oxidation of the surfactant ligands. The gelation kinetics have been tuned by varying the oxidant/surfactant molar ratio that governs the acidity of sol–gel reaction and consequently the extent of Ag dealloying with in situ generated HNO3. As-synthesized Au/Ag/Pd aerogels exhibit polymeric or colloidal gel morphology that can be manipulated by varying the shape and composition of precursor NPs. The electrocatalytic activity of ternary al...

C-F bond activation of trifluoroethanol and trifluoroacetic acid catalysed by the dimolybdate anion, [Mo2O6(F)]- †.

Two gas-phase catalytic cycles involving C-F bond activation of trifluoroethanol and trifluoroacetic acid were detected by multistage mass spectrometry experiments. A binuclear dimolybdate centre [Mo2O6(F)]- acts as the catalyst in each cycle. The first cycle, entered via the reaction of [Mo2O6(OH)]- with trifluoroethanol and elimination of water to form [Mo2O6(OCH2CF3)]-, proceeds via four steps: (1) oxidation of the alkoxo ligand and its elimination as aldehyde; (2) reaction of [Mo2O5(OH)]- with trifluoroethanol and elimination of water to form [Mo2O5(OCH2CF3)]; (3) decomposition of the alkoxo ligand via loss of 1,1 difluoroethene; and (4) reaction of [Mo2O6(F)]- with a second equivalent of trifluoroethanol to regenerate Mo2O6(OCH2CF3)]-. Steps (2) and (3) do not occur at room temperature and require collisional activation to proceed. The second cycle is entered via the reaction of [Mo2O6(OH)]- with trifluoroacetic acid and elimination of water to form [Mo2O6(O2CCF3)]- and involves two steps only: (1) fluoride transfer to a molybdenum centre to form [Mo2O6(F)]-; (2) reaction of [Mo2O6(F)]- with trifluoroacetic acid and loss of water to regenerate [Mo2O6(O2CCF3)]-. Comparisons are made with the chemistry of [Mo2O6(OH)]- reacting with acetic acid.

Progesterone (P4) attenuates oxidative stress induced and FAS ligand mediated apoptosis of human granulosa/luteal (hGL) cells by different mechanisms

hGL cells undergo apoptosis in response to extrinsic oxidative stressors (e.g. hydrogen peroxide; H2O2) or ligand activation of intrinsic death receptors (e.g. Fas). P4 inhibits apoptosis of hGL cells but its mechanism is not clearly defined. The present study was designed to assess P4’s ability to inhibit H2O2 or Fas induced apoptosis.

Enhanced Luminescence of Asymmetrical Seven‐Coordinate EuIII Complexes Including LMCT Perturbation

Luminescent mononuclear seven‐coordinate EuIII complexes, with monocapped‐octahedral (point group: C3v), monocapped‐trigonal‐prismatic (C2v), and pentagonal‐bipyramidal (D5h) coordination structures, are reported. The complexes each consist of a EuIII ion, three tetramethylheptanedionates, and a phosphine oxide derivative. Controlling steric hindrance by means of introducing methyl groups into the phosphine oxide ligands resulted in the formation of three types of coordination polyhedral structures. The coordination geometrical structures of the EuIII complexes were evaluated by single‐crystal X‐ray diffraction analysis and shape‐factor calculations. The radiative rate constant of the EuIII complex with a monocapped‐octahedral structure was larger than those with monocapped‐trigonal‐prismatic and pentagonal‐bipyramidal structures. Characteristic photophysical properties of the seven‐coordinate EuIII complexes are discussed with TD‐DFT calculations and Arrhenius analysis of the ligand‐to‐metal charge transfer.

Bisphosphine‐Ligated Nickel Pre‐catalysts in C(sp2)–N Cross‐Couplings of Aryl Chlorides: A Comparison of Nickel(I) and Nickel(II)

AbstractThe influence of ancillary ligand and nickel oxidation state in the nickel‐catalyzed C(sp2)–N cross‐coupling of aryl chlorides is examined by use of experimental and DFT methods for the first time, focusing on (L)NiCl and (L)Ni(o‐tolyl)Cl pre‐catalysts (PAd‐DalPhos, L1; dppf, L2). Whereas Ni(II) pre‐catalysts generally out‐performed Ni(I) species in our study, the viability and in some cases superiority of Ni(I) pre‐catalysts in challenging aminations is established. Computational analyses support the viability of Ni(0)/Ni(II) cycles featuring rate‐limiting C–N reductive elimination, as well as parallel Ni(I)/Ni(III) mechanisms involving rate‐limiting C–Cl oxidative addition.magnified image

Functionalization of Cadmium Selenide Quantum Dots with Poly(ethylene glycol): Ligand Exchange, Surface Coverage, and Dispersion Stability.

Semiconductor quantum dots synthesized using rapid mixing of precursors by injection into a hot solution of solvents and surfactants have surface ligands that sterically stabilize the dispersions in nonpolar solvents. Often, these ligands are exchanged to disperse the quantum dots in polar solvents, but quantitative studies of quantum dot surfaces before and after ligand exchange are scarce. We studied exchanging trioctylphosphine (TOP) and trioctylphosphine oxide (TOPO) ligands on as-synthesized CdSe quantum dots dispersed in hexane with a 2000 g/mol thiolated poly(ethylene glycol) (PEG) polymer. Using infrared spectroscopy we quantify the absolute surface concentration of TOP/TOPO and PEG ligands per unit area before and after ligand exchange. While 50-85% of the TOP/TOPO ligands are removed upon ligand exchange, only a few are replaced with PEG. Surprisingly, the remaining TOP/TOPO ligands outnumber the PEG ligands, but these few PEG ligands are sufficient to disperse the quantum dots in polar solvents such as chloroform, tetrahydrofuran, and water. Moreover, as-synthesized quantum dots once easily dispersed in hexane are no longer dispersible in nonpolar solvents after ligand exchange. A subtle coverage-dependent balance between attractive PEG-solvent interactions and repulsive TOP/TOPO-solvent interactions determines the dispersion stability.

Ytterbium and Europium Complexes of Redox-Active Ligands: Searching for Redox Isomerism.

The reaction of (dpp-Bian)EuII(dme)2 (3) (dpp-Bian is dianion of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene; dme is 1,2-dimethoxyethane) with 2,2'-bipyridine (bipy) in toluene proceeds with replacement of the coordinated solvent molecules with neutral bipy ligands and affords europium(II) complex (dpp-Bian)EuII(bipy)2 (9). In contrast the reaction of related ytterbium complex (dpp-Bian)YbII(dme)2 (4) with bipy in dme proceeds with the electron transfer from the metal to bipy and results in (dpp-Bian)YbIII(bipy)(bipy-̇) (10) - ytterbium(III) derivative containing both neutral and radical-anionic bipy ligands. Noteworthy, in both cases dianionic dpp-Bian ligands retain its reduction state. The ligand-centered redox-process occurs when complex 3 reacts with N,N'-bis[2,4,6-trimethylphenyl]-1,4-diaza-1,3-butadiene (mes-dad). The reaction product (dpp-Bian)EuII(mes-dad)(dme) (11) consists of two different redox-active ligands both in the radical-anionic state. The reduction of 3,6-di-tert-butyl-4-(3,6-di-tert-butyl-2-ethoxyphenoxy)-2-ethoxycyclohexa-2,5-dienone (the dimer of 2-ethoxy-3,6-di-tert-butylphenoxy radical) with (dpp-Bian)EuII(dme)2 (3) caused oxidation of the dpp-Bian ligand to radical-anion to afford (dpp-Bian)(ArO)EuII(dme) (ArO = OC6H2-3,6-tBu2-2-OEt) (12). The molecular structures of complexes 9-12 have been established by the single crystal X-ray analysis. The magnetic behavior of newly prepared compounds has been investigated by the SQUID technique in the range 2-310 K. The isotropic exchange model has been adopted to describe quantitatively the magnetic properties of the exchange-coupled europium(II) complexes (11 and 12). The best-fit isotropic exchange parameters are in good agreement with their density functional theory-computed counterparts.

Metal-Ion Induced In Situ Ligand Oxidation for Self-Assembled Clusters: from Bis(5-(2-pyridine-2-yl)-1,2,4-triazole-3-yl)methane to Alcohol or Ketone.

Hydrothermal reactions of metal nitrates and ligand bis(5-(pyridine-2-yl)-1,2,4-triazol-3-yl)methane (H2 L1 ) gave three cluster compounds, {Cr2 }, {Zn12 } and {Fe8 }. Notably, methylene group of H2 L1 was in situ oxidized either to hydroxymethylated (L2 -O)3- in the metallo-ring {Zn12 } or to a rigid carbonylated (L3 =O)2- in the screw-type {Fe8 }. In light of comparative experimental results, NO3- was deduced to be of a catalytic role in the ligand oxidation. Metal ion could be regarded as an "induced" tool for clusters generation in self-assembly process.

Vibrational Characterization of Microsolvated Electrocatalytic Water Oxidation Intermediate: [Ru(tpy)(bpy)(OH)]2+(H2O)0–4

The infrared predissociation spectra of the mass-selected electrocatalytic water oxidation intermediate [Ru(tpy)(bpy)(OH)]2+(H2O)0-4 are reported. The [Ru(tpy)(bpy)(OH)]2+ species is generated by passing a solution of [Ru(tpy)(bpy)(H2O)](ClO4)2 through an electrochemical flow cell held at 1.2 V and is immediately introduced into the gas phase via electrospray ionization (ESI). The microsolvated clusters are formed by reconstructing the water network in a cryogenic ion trap. Details of the hydrogen bonding network in these clusters are revealed by the infrared predissociation spectra in the OH stretch region. This improved method for capturing microsolvated clusters yielded colder complexes with much better resolved IR features than previous studies. The analysis of these spectra, supported by electronic structure calculations and compared to previous results on [Ru(tpy)(bpy)(H2O)]2+(H2O)0-4 clusters, reveals the nature of the Ru-OH bond and the effect of hydrogen bonding on facilitating the subsequent oxidation to [Ru(tpy)(bpy)(O)]2+ in the proposed catalytic cycle. Particularly, the hydrogen bonding interaction in [Ru(tpy)(bpy)(OH)]2+(H2O)1 is much weaker than that in the corresponding [Ru(tpy)(bpy)(H2O)]2+(H2O)1 and thus is less effective at activating the hydroxyl ligand for further oxidation via proton coupled electron transfer (PCET). Furthermore, the results here reveal that the Ru-OH bond, though formally described as an Ru3+/OH- interaction, has more covalent bond character than ionic bond character.

Role of Crystal Structure and Chalcogenide Redox Properties on the Oxidative Assembly of Cadmium Chalcogenide Nanocrystals.

Oxidative assembly of metal chalcogenide nanocrystals (NCs) enables the formation of 2-D (dense) and 3-D porous structures without the presence of intervening ligands between particles that can moderate transport properties. This route has been demonstrated to be successful for a range of single-component structures including CdQ, PbQ, and ZnQ (Q = S, Se, Te). En route to the controllable assembly of multicomponent nanostructures, the roles of Q redox properties (2Q2- → Q22- + 2e) responsible for particle cross-linking and the native structure (cubic zinc blende vs hexagonal wurtzite) in the kinetics of assembly in single-component CdQ NCs are evaluated using time-resolved dynamic light scattering (TR-DLS). For wurtzite CdQ, the rates follow the ease of oxidation, with telluride as the fastest, followed by selenide and sulfide. However, when comparing CdS wurtzite (w) and zinc blende (zb), the cubic NCs exhibit surprisingly slow kinetics. NMR studies reveal the zb structure to have lower ligand coverage (by a factor of 4) relative to that of w, and the formation of free disulfide (the product of ligand oxidation) is slow. This is attributed to differences in the surface energies of w and zb facets, with w having polar (0001) facets of high energy compared to the neutral facets of the zb structure. The zb-CdS NCs prepared by low-temperature synthesis methods are likely to suffer from surface defects that may moderate reactivity. EPR studies suggest that zb-CdS has paramagnetic sulfur vacancies not present in w-CdS. These data suggest that structure plays an unexpectedly large role in the kinetics of CdQ NC oxidative assembly, providing a useful lever to moderate activities in multicomponent assemblies.

Hydrated and anhydrous cobalt (II) barbiturates: Crystal structures, spectroscopic and thermal properties

Three new complexes of barbituric acid (H2BA), a discrete molecular complex [Co(H2O)4(HBA)2] (1), a barbiturate-bridged 1D Co(II) coordination polymer [Co(H2O)2(μ2-HBA)2] (2) and a 3D Co(II) coordination polymer [Co(μ3-HBA)2] (3) were synthesized and structurally characterized by X-ray powder diffraction. In 1–3, the HBA− ions are coordinated to Co(II) only through O atoms with cobalt ions in an octahedral environment. In 1, Co(II) is coordinated to four terminal water molecules and two HBA− ions. In compound 2, Co(II) is bonded to two terminal water molecules and two μ2-HBA− ions forming polymer chains. In the 3D-polymeric form 3, a bridging μ3-HBA ligand is connected through three oxygen atoms of the carbonyl groups with three Co(II) ions. All three structures are stabilized by intermolecular hydrogen bonds and π–π stacking interactions between HBA− ions. The IR spectroscopic data supports the results of the X-ray diffraction analysis. The thermal decomposition of the compounds comprises the dehydration steps and the organic ligand oxidation to form cobalt oxides.

Blue-to-Green Emitting Neutral Ir(III) Complexes Bearing Pentafluorosulfanyl Groups: A Combined Experimental and Theoretical Study.

A structure–property relationship study of neutral heteroleptic (1 and 2, [Ir(C∧N)2(L∧X)]) and homoleptic (3 and 4, fac-[Ir(C∧N)3]) Ir(III) complexes (where L∧X = anionic 2,2,6,6-tetramethylheptane-3,5-dionato-κO3,κO6 (thd) and C∧N = a cyclometalating ligand bearing a pentafluorosulfanyl (−SF5) electron-withdrawing group (EWG) at the C4 (HL1) and C3 (HL2) positions of the phenyl moiety) is presented. These complexes have been fully structurally characterized, including by single-crystal X-ray diffraction, and their electrochemical and optical properties have also been extensively studied. While complexes 1 ([Ir(L1)2(thd)]), 3 (Ir(L1)3), and 4 (Ir(L2)3) exhibit irreversible first reduction waves based on the pentafluorosulfanyl substituent in the range of −1.71 to −1.88 V (vs SCE), complex 2 ([Ir(L2)2(thd)]) exhibits a quasi-reversible pyridineC∧N-based first reduction wave that is anodically shifted at −1.38 V. The metal + C∧N ligand oxidation waves are all quasi-reversible in the range of 1.08–1.54 V (vs SCE). The optical gap, determined from the lowest energy absorption maxima, decreases from 4 to 2 to 3 to 1, and this trend is consistent with the Hammett behavior (σm/σp with respect to the metal–carbon bond) of the −SF5 EWG. In degassed acetonitrile, for complexes 2–4, introduction of the −SF5 group produced a blue-shifted emission (λem 484–506 nm) in comparison to reference complexes [Ir(ppy)2(acac)] (R1, where acac = acetylacetonato) (λem 528 nm in MeCN), [Ir(CF3-ppy) (acac)] (R3, where CF3-ppyH = 2-(4-(trifluoromethyl)phenyl)pyridine) (λem 522 nm in DCM), and [Ir(CF3-ppy)3] (R8) (λem 507 nm in MeCN). The emission of complex 1, in contrast, was modestly red shifted (λem 534 nm). Complexes 2 and 4, where the −SF5 EWG is substituted para to the Ir–CC∧N bond, are efficient phosphorescent emitters, with high photoluminescence quantum yields (ΦPL = 58–79% in degassed MeCN solution) and microsecond emission lifetimes (τε = 1.35–3.02 μs). Theoretical and experimental observations point toward excited states that are principally ligand centered (3LC) in nature, but with a minor metal-to-ligand charge-transfer (3MLCT) transition component, as a function of the regiochemistry of the pentafluorosulfanyl group. The 3LC character is predominant over the mixed 3CT character for complexes 1, 2, and 4, while in complex 3, there is exclusive 3LC character as demonstrated by unrestricted density functional theory (DFT) calculations. The short emission lifetimes and reasonable ΦPL values in doped thin film (5 wt % in PMMA), particularly for 4, suggest that these neutral complexes would be attractive candidate emitters in organic light-emitting diodes.

Coordination effects in hydrated manganese(II) 1,3-diethyl-2-thiobarbiturates and their thermal stability

Three new complexes of 1,3-diethyl-thiobarbituric acid (HDetba), barbiturate-bridged 2D Mn(II) polymer [Mn(H2O)2(Detba)2] (1), trinuclear [Mn3(H2O)10(Detba)6] (2) and discrete molecular [Mn(H2O)4(Detba)2]·H2O (3) are synthesized and structurally characterized by the X-ray single crystal technique. In 1–3, the Detba− ions are coordinated to Mn(II) only through O atoms with manganese ions in the octahedral environment. In 1, the Mn(II) ion is coordinated by four μ2 bridge Detba− ions and two terminal H2O molecules. In 2, the Mn1 ion is coordinated by three terminal H2O molecules, two terminal and one μ2 bridge Detba− ion, and Mn2 is connected with two μ2-Detba− ions and four H2O molecules. In 3, the Mn(II) ion is coordinated by two terminal Detba− ions and four terminal H2O molecules. There are intermolecular hydrogen bonds O–H⋯O, O–H⋯S in the structures of 1–3 which form the 3D networks. Structure 2 is stabilized by the π–π interaction. The compounds thermal decomposition comprises dehydration steps and the organic ligand oxidation.

Prediction of Extremely Strong Antiferromagnetic Superexchange in Silver(II) Fluorides: Challenging the Oxocuprates(II)

AbstractStrong magnetic coupling between the spins of unpaired electrons is an essential ingredient of many fascinating physical phenomena. Here we report calculations using the hybrid HSE06 functional of magnetic superexchange constants, J, for a series of low‐dimensional CuII and AgII binary and ternary systems with fluoride and oxide ligands. The calculations correctly reproduce the sign and size of the magnetic superexchange constants for prototypical antiferromagnetic (AFM) 1D (J1D) and 2D (J2D) systems, while overestimating the absolute values of J by about 11 %. We find that [AgF][BF4], a quasi‐1D system with linear infinite [AgIIF+] chains, is predicted to exhibit an unprecedented strong AFM superexchange via one atom (F), with J1D about −300 meV. Compression of [AgF][BF4] to 10 GPa should lead to a further increase in AFM interactions with J1D reaching −360 meV at 10 GPa.