Role of ancillary ligands in -nitrosothiol and NO generation from nitrite-thiol interactions at mononuclear zinc(ii) sites.

Generation of -nitrosothiol (RSNO) and nitric oxide (NO) mediated by zinc(ii) coordination motifs is of prime importance for understanding the role of zinc(ii)-based cofactors in redox-signalling pathways. This study uniquely employs a set of mononuclear [LZn] cores (where L = MePzPz/MePzPy/MePzQu) for introducing subtle alterations of the primary coordination sphere and investigates the role of ligand tuning in the transformation of NO in the presence of thiols. Single crystal X-ray diffraction (SCXRD) analyses on [LZn-X](X) (where X = perchlorate/triflate) illustrate consistent changes in the bond distances, thereby showing variations of the metal-ligand interactions depending on the nature of the heterocyclic donor arms (pyrazole/pyridine/quinoline).

Tuning the Reactivity of Copper(II)-Nitrite Core Towards Nitric Oxide Generation.

Insights into the molecular mechanism and factors affecting nitrite-to-NO transformation at transition metal sites are essential for developing sustainable technologies relevant to NO-based therapeutics, waste water treatment, and agriculture. A set of copper(II)-nitrite complexes 1-4 have been isolated employing tridentate pincer-type ligands (L, L, L, L) featuring systematically varied donors. Although the X-ray crystal structures of the copper(II)-nitrite cores in 1-4 are comparable, electrochemical studies on complexes 1-4 reveal that redox properties of these complexes differ due to the changes in the σ-donor abilities of the phenolate/N-heterocycle based donor sites.

Isolation of a chloride-capped cerium polyoxo nanocluster built from 52 metal ions.

Four cerium compounds - (HPy)[CeCl]·2(HPyCl) (Ce1-1), (HPy)[CeCl] (Ce1-2), (HPy)[CeO(OH)Cl(HO)]·HO (Ce38), and (HPy)[CeO(OH)Cl(HO)]·HO (Ce52) - were crystallized from acidic aqueous solutions using pyridinium (HPy) counterions. The latter consists of two unique cerium oxide nanoclusters that are built from 52 metal ions and represents the largest chloride capped {CeO} and/or {MO} (M = Ce, Th, U, Np, Pu) nanocluster that adopts the fluorite-type structure of MO that has been reported.

Organometallic Chirality Sensing via "Click"-Like η-Arene Coordination with an Achiral Cp*Ru(II) Piano Stool Complex.

Piano stool complexes have been studied over many years and found widespread applications in organic synthesis, catalysis, materials and drug development. We now report the first examples of quantitative chiroptical molecular recognition of chiral compounds through click-like η-arene coordination with readily available half sandwich complexes. This conceptually new approach to chirality sensing is based on irreversible acetonitrile displacement of [Cp*Ru(CHCN)]PF by an aromatic target molecule, a process that is fast and complete within a few minutes at room temperature.

Organocatalytic Asymmetric Conjugate Addition of Fluorooxindoles to Quinone Methides.

Fluorooxindoles undergo asymmetric Michael addition to -quinone methides under phase-transfer conditions with 10 mol% of a readily available cinchona alkaloid ammonium catalyst. This reaction affords sterically encumbered, multifunctional fluorinated organic compounds displaying two adjacent chirality centers with high yields, 's and 's.

General alkyl fluoride functionalization via short-lived carbocation-organozincate ion pairs.

Fluorinated organic compounds are frequently used across the chemical and life sciences. Although a large, structurally diverse pool of alkyl fluorides is nowadays available, synthetic applications trail behind the widely accepted utility of other halides. We envisioned that C(sp)-C(sp) cross-coupling reactions of alkyl fluorides with fluorophilic organozinc compounds should be possible through a heterolytic mechanism that involves short-lived ion pairs and uses the stability of the Zn-F bond as the thermodynamic driving force.

Alkaline earth metal-assisted dinitrogen activation at nickel.

Rare examples of trinuclear [Ni-N-M-N-Ni] core (M = Ca, Mg) with linear bridged dinitrogen ligands are reported in this work. The reduction of [PrNN]Ni(μ-Br)Li(thf) (1) (PrNN = 2,4-bis-(2,6-diisopropylphenylimido)pentyl) with elemental Mg or Ca in THF under an atmosphere of dinitrogen yields the complex {PrNNNi(μ-N)}M (thf) (M = Mg, complex 2 and M = Ca, complex 3). The bridging end-on (μ-N)M(thf) moiety connects the two [PrNNNi] nickelate fragments.

Synthesis and Characterization of Cerium-Oxo Clusters Capped by Acetylacetonate.

Cerium-oxo clusters have applications in fields ranging from catalysis to electronics and also hold the potential to inform on aspects of actinide chemistry. Toward this end, a cerium-acetylacetonate (acac) monomeric molecule, Ce(acac) (), and two acac-decorated cerium-oxo clusters, [CeO(acac)(CHO)(CHOH)]·10.5MeOH () and [CeO(OH)(acac)(CHCOO)]·6(CHCN) (), were prepared and structurally characterized.

Thiol and HS-Mediated NO Generation from Nitrate at Copper(II).

Reduction of nitrate is an essential, yet challenging chemical task required to manage this relatively inert oxoanion in the environment and biology. We show that thiols, ubiquitous reductants in biology, convert nitrate to nitric oxide at a Cu(II) center under mild conditions. The β-diketiminato complex [ClNN]Cu(κ-ONO) engages in O-atom transfer with various thiols (RSH) to form the corresponding copper(II) nitrite [Cu](κ-ON) and sulfenic acid (RSOH).

Electrocatalytic Ammonia Oxidation by a Low-Coordinate Copper Complex.

Molecular catalysts for ammonia oxidation to dinitrogen represent enabling components to utilize ammonia as a fuel and/or source of hydrogen. Ammonia oxidation requires not only the breaking of multiple strong N-H bonds but also controlled N-N bond formation. We report a novel β-diketiminato copper complex [PrNN]Cu-NH ([Cu]-NH ()) as a robust electrocatalyst for NH oxidation in acetonitrile under homogeneous conditions.

Lanthanide Luminescence and Thermochromic Emission from Soft-Atom Donor Dichalcogenoimidodiphosphinate Ligands.

The luminescence properties of two divalent europium complexes of the type Eu[N(SPPh)](THF) () and Eu[N(SePPh)](THF) () were investigated. The first complex, Eu[N(SPPh)](THF) (), was found to be isomorphous with the reported structure of complex and exhibited room temperature luminescence with thermochromic emission upon cooling. We found the complex Eu[N(SePPh)](THF) () was also thermochromic but the emission intensity was sensitive to temperature.

Lewis acid-assisted reduction of nitrite to nitric and nitrous oxides via the elusive nitrite radical dianion.

Reduction of nitrite anions (NO) to nitric oxide (NO), nitrous oxide (NO) and ultimately dinitrogen (N) takes place in a variety of environments, including in the soil as part of the biogeochemical nitrogen cycle and in acidified nuclear waste. Nitrite reduction typically takes place within the coordination sphere of a redox-active transition metal. Here we show that Lewis acid coordination can substantially modify the reduction potential of this polyoxoanion to allow for its reduction under non-aqueous conditions (-0.

NO Coupling at Copper to -Hyponitrite: NO Formation via Protonation and H-Atom Transfer.

Copper nitrite reductases (CuNIRs) convert NO to NO as well as NO to NO under high NO flux at a mononuclear type 2 Cu center. While model complexes illustrate N-N coupling from NO that results in symmetric -hyponitrite [Cu]-ONNO-[Cu] complexes, we report NO assembly at a single Cu site in the presence of an external reductant Cp*M (M = Co, Fe) to give the first copper -hyponitrites [Cp*M]{[Cu](κ-ON)[Cu]}. Importantly, the κ-N-bound [Cu] fragment may be easily removed by the addition of mild Lewis bases such as CNAr or pyridine to form the spectroscopically similar anion {[Cu](κ-ON)}.

NO Generation from the Cross-Talks between Ene-diol Antioxidants and Nitrite at Metal Sites.

The one-electron reduction of nitrite (NO) to nitric oxide (NO) and ene-diol oxidation are two important biochemical transformations. Employing mononuclear cobalt-nitrite complexes with Co and Co oxidation states, [()Co(nitrite)](ClO) () and [()Co(nitrite)](ClO) (), this report illustrates NO release coupled to stepwise oxidation of ene-diol antioxidants such as l-ascorbic acid (AH) and catechol. Analysis of the AH end-product reveals that the reaction with complex affords dehydroascorbic acid.

Copper(ii) ketimides in sp C-H amination.

Commercially available benzophenone imine (HN[double bond, length as m-dash]CPh) reacts with β-diketiminato copper(ii) -butoxide complexes [Cu]-O Bu to form isolable copper(ii) ketimides [Cu]-N[double bond, length as m-dash]CPh. Structural characterization of the three coordinate copper(ii) ketimide [MeNN]Cu-N[double bond, length as m-dash]CPh reveals a short Cu-N distance (1.700(2) Å) with a nearly linear Cu-N-C linkage (178.

Harnessing Bismuth Coordination Chemistry to Achieve Bright, Long-Lived Organic Phosphorescence.

A new bismuth(III)-organic compound, Hphen[Bi(HPDC)(PDC)(NO)]·4HO (; PDC = 2,6-pyridinedicarboxylate and phen = 1,10-phenanthroline), was synthesized, and the structure was determined by single-crystal X-ray diffraction. The compound was found to display bright-blue-green phosphorescence in the solid state under UV irradiation, with a luminescent lifetime of 1.776 ms at room temperature.

Uncovering Redox Non-innocent Hydrogen-Bonding in Cu(I)-Diazene Complexes.

The life-sustaining reduction of N to NH is thermoneutral yet kinetically challenged by high-energy intermediates such as NH. Exploring intramolecular H-bonding as a potential strategy to stabilize diazene intermediates, we employ a series of [TpCu](μ-NH) complexes that exhibit H-bonding between pendant aromatic N-heterocycles (Het) such as pyridine and a bridging -NH ligand at copper(I) centers. X-ray crystallography and IR spectroscopy clearly reveal H-bonding in [TpCu](μ-NH) while low-temperature H NMR studies coupled with DFT analysis reveals a dynamic equilibrium between two closely related, symmetric H-bonded structural motifs.

Mechanism of O-Atom Transfer from Nitrite: Nitric Oxide Release at Copper(II).

Nitric oxide (NO) is a key signaling molecule in health and disease. While nitrite acts as a reservoir of NO activity, mechanisms for NO release require further understanding. A series of electronically varied β-diketiminatocopper(II) nitrite complexes [Cu](κ-ON) react with a range of electronically tuned triarylphosphines PAr that release NO with the formation of O═PAr.

Thionitrite and Perthionitrite in NO Signaling at Zinc.

NO and H S serve as signaling molecules in biology with intertwined reactivity. HSNO and HSSNO with their conjugate bases SNO and SSNO form in the reaction of H S with NO as well as S-nitrosothiols (RSNO) and nitrite (NO ) that serve as NO reservoirs. While HSNO and HSSNO are elusive, their conjugate bases form isolable zinc complexes TpZn(SNO) and TpZn(SSNO) supported by tris(pyrazolyl)borate ligands.

Structure-Property Relationships in Photoluminescent Bismuth Halide Organic Hybrid Materials.

Seven novel bismuth(III)-halide phases, BiCl(terpy)·0.5(HO) (), BiCl(terpy)(-TC)() (TC = 2-thiophene monocarboxylate), BiCl(terpy)(-TC) (), BiBr(terpy)(-TC) (), BiCl(terpy)(-TC) (), [BiCl(terpy)(-TC)][Bi(terpy)(-TC)]·0.55(TCA) (), [BiBr(terpy)(MeOH)] (), and [BiBr(terpy)(-TC)][BiBr(terpy)(-TC)] (), were prepared under mild synthetic conditions from methanolic/aqueous solutions containing BiX (X = Cl, Br) and 2,2':6',2″-terpyridine (terpy) and/or 2-thiophene monocarboxylic acid (TCA).

Impact of Noncovalent Interactions on the Structural Chemistry of Thorium(IV)-Aquo-Chloro Complexes.

Five novel tetravalent thorium (Th) compounds that consist of Th(HO)Cl structural units were isolated from acidic aqueous solutions using a series of nitrogen-containing heterocyclic hydrogen (H) bond donors. Taken together with three previously reported phases, the compounds provide a series of monomeric Th complexes wherein the effects of noncovalent interactions (and H-bond donor identity) on Th structural chemistry can be examined. Seven distinct structural units of the general formulas [Th(HO)Cl] ( = 2, 4) and [Th(HO)Cl] ( = 5-7) are described.

Three-Coordinate Copper(II) Alkynyl Complex in C-C Bond Formation: The Sesquicentennial of the Glaser Coupling.

Copper(II) alkynyl species are proposed as key intermediates in numerous Cu-catalyzed C-C coupling reactions. Supported by a β-diketiminate ligand, the three-coordinate copper(II) alkynyl [Cu]-C≡CAr (Ar = 2,6-ClCH) forms upon reaction of the alkyne H-C≡CAr with the copper(II) -butoxide complex [Cu]-OBu. In solution, this [Cu]-C≡CAr species cleanly transforms to the Glaser coupling product ArC≡C-C≡CAr and [Cu](solvent).

Synthesis and photoluminescence of three bismuth(III)-organic compounds bearing heterocyclic N-donor ligands.

Three bismuth(iii)-organic compounds, [Bi4Cl8(PDC)2(phen)4]·2MeCN (1), [BiCl3(phen)2] (2), and [Bi2Cl6(terpy)2] (3), were prepared from solvothermal reactions of bismuth chloride, 2,6-pyridinedicarboxylic acid (H2PDC), and 1,10-phenanthroline (phen) or 2,2';6',2''-terpyridine (terpy). The structures were determined through single crystal X-ray diffraction and the compounds were further characterized via powder X-ray diffraction, Raman and infrared spectroscopy, and thermogravimetric analysis. The photoluminescence properties of the solid-state materials were assessed using steady state and time-dependent techniques to obtain excitation and emission profiles as well as lifetimes.

Excitation-Dependent Photoluminescence Color Tuning in Lanthanide-Organic Hybrid Materials.

A series of lanthanide organic hybrid materials was synthesized via hydrothermal methods and structurally characterized using single-crystal X-ray diffraction. Four phases were obtained from reactions of La, Eu, and Tb ions with 1,10-phenanthroline (phen) and 2-thiophenecarboxylate (TC): [La(phen)(-TC)(μ-TC)(η-TC)(HO)] (), [Eu(phen)(-TC)(μ-TC)(η-TC)]·2(HO) (), and [Tb(phen)(-TC)(μ-TC)]·2(HO) (). Although each of the structures consists of homometallic ligand bridged dimers, the four distinct phases arise from subtle differences in ligand binding modes and supramolecular interactions.