A self-assembled metallo-macrocycle two-qubit spin system.

A self-assembled, charge-neutral dicopper(II) metallo-macrocycle with a near degenerate singlet-triplet ground state is a prototype molecular two-qubit system. The weakly-coupled spin centres delivered a long phase memory time of 5.4 μs, and each spin can be selectively switched using an applied potential providing a convenient means to modulate the quantum levels.

Kinetics and Mechanism of PPh/Ni-Catalyzed, Zn-Mediated, Aryl Chloride Homocoupling: Antagonistic Effects of ZnCl/Cl.

The Ni/PPh-catalyzed homocoupling of aryl chlorides in DMF using Zn as the stochiometric reducing agent is one of a general class of Ni-catalyzed processes, where the mechanism has been a matter of long-standing debate. This study re-evaluates prior conclusions and insights. NMR spectroscopy is used to identify [(PPh)Ni(Ar)Cl] as a key intermediate and to explore the indirect roles of using Zn as the reductant.

Electronic and Molecular Structures of a Series of Nickel Bis-1,1-Dithiolates.

A series of homoleptic Ni bis-1,1-dithiolates, [Ni(SCRR')] (R=CN, R'=CN, COEt, CONH, Ph, Ph-4-Cl, Ph-4-OMe, Ph-4-NO, Ph-3-CF, Ph-4-CF, Ph-4-CN; R=NO, R'=H; R=R'=COEt) have been synthesized from the reaction of the alkali metal salt of the ligand and nickel chloride, and isolated as tetraphenylphosphonium or tetrabutylammonium salts. The complexes were characterized by X-ray crystallography, high-resolution mass spectrometry, and infrared (IR), nuclear magnetic resonance (NMR) and electronic absorption spectroscopies. The molecular structures show a rigidly square planar Ni(II) center linking two four-membered chelate rings whose dimensions are constant across the series.

A Mechanistic Investigation of the -Hydroxyphthalimide Catalyzed Benzylic Oxidation Mediated by Sodium Chlorite.

A detailed investigation into the mechanistic course of -hydroxyphthalimide catalyzed oxidation of benzylic centers using sodium chlorite as the stoichiometric oxidant is reported. Through a combination of experimental, spectroscopic, and computational techniques, the transformation is interrogated, providing improved reaction conditions and an enhanced understanding of the mechanism. Performing the transformation in the presence of acetic acid or a pH 4.

Asymmetric by Design: Heteroleptic Coordination Compounds with Redox-Active Dithiolene and 1,2,4,5-Tetrakis(isopropylthio)benzene Ligands.

The 1,2,4,5-tetrakis(alkylthio)benzenes are redox-active organosulfur molecules that support oxidation to a stable radical cation. Their utility as ligands for the assembly of multimetal complexes with tailored functionality/property is unexamined. Here, 1,2,4,5-tetrakis(isopropylthio)benzene (tptbz, ) is shown to bind PdCl at either one end, leaving the other open, or at both ends to form centrosymmetric [ClPd(tptbz)PdCl], .

Fully Reduced and Mixed-Valent Multi-Copper Aggregates Supported by Tetradentate Diamino Bis(thiolate) Ligands.

Tetradentate diamino bis(thiolate) ligands (l-NS(2-)) with saturated linkages between heteroatoms support fully reduced [(Cu(l-NS))Cu] complexes that bear relevance as an entry point toward molecules featuring the CuCu(μ-S) core composition of nitrous oxide reductase (NOR). Tetracopper [(Cu(l-N(S)))Cu] (l-N(SH) = ,-(2-methyl-2-mercaptopropane)-,-dimethylethane-1,2-diamine) does not support clean S atom oxidative addition but undergoes Cl atom transfer from PhICl or PhCCl to afford [(Cu(l-N(S)))(CuCl)], . When introduced to Cu(I) sources, the l-N(SH) ligand (l-N(SH) = ,-(2-mercaptophenyl)-,-dimethylethane-1,2-diamine), made by a newly devised route from ,-(2-fluorophenyl)-,-dimethylethane-1,2-diamine, ultimately yields the mixed-valent pentacopper [(Cu(l-NS))Cu] (), which has 3-fold rotational symmetry () around a Cu axis.

Role of the Meso Substituent in Defining the Reduction of Uranyl Dipyrrin Complexes.

The uranyl complex UOCl() of the redox-active, acyclic dipyrrin-diimine anion [H = 1,9-di--butyl-imine-5-(mesityl)dipyrrin] is reported, and its redox property is explored and compared with that of the previously reported UOCl() [H = 1,9-di--butyl-imine-5-(pentafluorophenyl)dipyrrin] to understand the influence of the meso substituent. Cyclic voltammetry, electron paramagnetic resonance spectroscopy, and density functional theory studies show that the alteration from an electron-withdrawing meso substituent to an electron-donating meso substituent on the dipyrrin ligand significantly modifies the stability of the products formed after reduction. For UOCl(), the formation of a diamond-shaped, oxo-bridged uranyl(V) dimer, [UO()] is seen, whereas in contrast, for UOCl(), only ligand reduction occurs.

Heterotrimetallic Assemblies with 1,2,4,5-Tetrakis(diphenylphosphino)benzene Bridges: Constructs for Controlling the Separation and Spatial Orientation of Redox-Active Metallodithiolene Groups.

Metallodithiolene complexes of the type [(RCS)M(η-tpbz)] [R = CN, Ph, or -anisyl; M = Ni, Pd, or Pt; tpbz = 1,2,4,5-tetrakis(diphenylphosphino)benzene] chelate transition metals ions to form trimetallic arrays [[(RCS)M(tpbz)]M'], where M' is square planar Pt, tetrahedral Cu, Ag, or Au, or octahedral {ReBr(CO)}/{Re(CO)}. Forcing conditions (190 °C reflux in decalin, 72 h) are demanded for the Re compounds. With third-row metals at the nexus, the compounds are stable to air.

A Self-Assembling Flavin for Visible Photooxidation.

A new flavin-based gelator is reported which forms micellar structures at high pH and gels at low pH. This flavin can be used for the photooxidation of thiols under visible light, with the catalytic efficiency being linked to the self-assembled structures present.

Electronic versatility of vanadium in tris-chelates with redox-active ligands.

Spectroscopic and computational examination of the neutral tris-dioxolene complex [V(dbcat)] (dbcat = 3,6-di--butylcatecholate) reveals a Class III mixed-valent ground state. The radical is stabilised by delocalisation across the ligands mediated by the energy matched d orbital manifold of the V(V) centre. This electronic structure is compared to the tris-dithiolene and tris-diimine analogues that possess V(IV) and V(II) ions, respectively.

Exploring the Redox Properties of Bench-Stable Uranyl(VI) Diamido-Dipyrrin Complexes.

The uranyl complexes UO(OAc)() and UOCl() of the redox-active, acyclic diamido-dipyrrin anion are reported and their redox properties explored. Because of the inert nature of the complexes toward hydrolysis and oxidation, synthesis of both the ligands and complexes was conducted under ambient conditions. Voltammetric, electron paramagnetic resonance spectroscopy, and density functional theory studies show that one-electron chemical reduction by the reagent CoCp leads to the formation of a dipyrrin radical for both complexes [CpCo][UO(OAc)()] and [CpCo][UOCl()].

Open-Ended Metallodithiolene Complexes with the 1,2,4,5-Tetrakis(diphenylphosphino)benzene Ligand: Modular Building Elements for the Synthesis of Multimetal Complexes.

Open-ended, singly metalated dithiolene complexes with 1,2,4,5-tetrakis(diphenylphosphino)benzene (tpbz) are prepared either by ligand transfer to [ClM(tpbz)] from (RCS)SnR' (R = CN, R' = Me; R = Me, R' = Bu) or by a direct reaction between tpbz and [M(SCR)] (M = Ni, Pd, Pt; R = Ph, -anisyl) in a 1:1 ratio. The formation of dimetallic [(RCS)M(tpbz)M(SCR)] attends these syntheses in modest amounts, but the open-ended compounds are readily separated by silica chromatography. As affirmed by X-ray crystallographic characterization of numerous members of the set, the [(RCS)M(tpbz)] compounds show dithiolene ligands in their fully reduced ene-1,2-dithiolate form conjoined with divalent Group 10 ions.

Selective aldehyde reductions in neutral water catalysed by encapsulation in a supramolecular cage.

The enhancement of reactivity inside supramolecular coordination cages has many analogies to the mode of action of enzymes, and continues to inspire the design of new catalysts for a range of reactions. However, despite being a near-ubiquitous class of reactions in organic chemistry, enhancement of the reduction of carbonyls to their corresponding alcohols remains very much underexplored in supramolecular coordination cages. Herein, we show that encapsulation of small aromatic aldehydes inside a supramolecular coordination cage allows the reduction of these aldehydes with the mild reducing agent sodium cyanoborohydride to proceed with high selectivity (ketones and esters are not reduced) and in good yields.

Oxo versus Sulfido Coordination at Tungsten: A Spectroscopic and Correlated Ab Initio Electronic Structure Study.

The tungsten ion that resides at the active site of a unique class of enzymes only found in esoteric hyperthermophilic archaea bacteria is known to possess at least one terminal chalcogenide ligand. The identity of this as either an oxo or sulfido (or both) is difficult to ascertain from structural studies; therefore, small-molecule analogues are developed to calibrate and substantiate spectroscopic signatures obtained from native proteins. The electronic structures of Tp*WECl (E = O, S; Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate) have been scrutinized using electronic, electron paramagnetic resonance (EPR), and X-ray absorption spectroscopy to assess the impact of terminal chalcogen on the adjacent chloride ligands.

Electronic structure study of divanadium complexes with rigid covalent coordination: potential molecular qubits with slow spin relaxation.

The electronic structures of homovalent [V(μ-S)(Rdtc)] (R = Et, Bu) and mixed-valent [V(μ-S)(Rdtc)] are reported here. The soft-donor, eight-coordinate ligand shell combined with the fully delocalised ground state provides a highly rigid and covalent environment that will nurture long spin relaxation times in vanadyl-based molecular qubits.

Electrocatalytic hydrogen production by dinuclear cobalt(II) compounds containing redox-active diamidate ligands: a combined experimental and theoretical study.

The chiral dicobalt(ii) complex [CoII2(μ2-L)2] (1) (H2L = N2,N6-di(quinolin-8-yl)pyridine-2,6-dicarboxamide) and its tert-butyl analogue [CoII2(μ2-LBu)2] (2) were synthesized and structurally characterized. Addition of one equivalent of AgSbF6 to the dichloromethane solution of 1 and 2 resulted in the isolation of the mixed-valent dicobalt(iii,ii) species [CoIIICoII(μ2-L)2]SbF6 (3) and [CoIIICoII(μ2-LBu)2]SbF6 (4). Homovalent 1 and 2 exhibited catalytic activity towards proton reduction in the presence of acetic acid (AcOH) as the substrate.

Unexpected Nickel Complex Speciation Unlocks Alternative Pathways for the Reactions of Alkyl Halides with dppf-Nickel(0).

The mechanism of the reactions between dppf-Ni complexes and alkyl halides has been investigated using kinetic and mechanistic experiments and DFT calculations. The active species is [Ni(κ-dppf)(κ-dppf)], which undergoes a halide abstraction reaction with alkyl halides and rapidly captures the alkyl radical that is formed. The rates of the reactions of [Ni(COD)(dppf)] with alkyl halides and the yields of prototypical nickel-catalyzed Kumada cross-coupling reactions of alkyl halides are shown to be significantly improved by the addition of free dppf ligand.

Investigating Complex Magnetic Anisotropy in a Co(II) Molecular Compound: A Charge Density and Correlated Ab Initio Electronic Structure Study.

Understanding magnetic anisotropy and specifically how to tailor it is crucial in the search for high-temperature single-ion magnets. Herein, we investigate the magnetic anisotropy in a six-coordinated cobalt(II) compound that has a complex geometry and distinct triaxial magnetic anisotropy from the perspective of the electronic structure, using electronic spectra, ab initio calculations, and an experimental charge density, of which the latter two provides insight into the d-orbital splitting. The analysis showed that the d-orbital splitting satisfactorily predicted the complex triaxial magnetic anisotropy exhibited by the compound.

Modulating the Magnetic Properties of Copper(II)/Nitroxyl Heterospin Complexes by Suppression of the Jahn-Teller Distortion.

A series of six-coordinate [Cu(L)L][BF] (L = 2,6-bis{1-oxyl-4,4,5,5-tetramethyl-4,5-dihydro-1-imidazol-2-yl}pyridine) complexes are reported. Ferromagnetic coupling between the Cu and L ligand spins is enhanced by an L coligand with distal methyl substituents, which is attributed to a sterically induced suppression of its Jahn-Teller distortion.

Heteroleptic Samarium(III) Chalcogenide Complexes: Opportunities for Giant Exchange Coupling in Bridging σ- and π-Radical Lanthanide Dichalcogenides.

The introduction of (N) radicals into multinuclear lanthanide molecular magnets raised hysteresis temperatures by stimulating strong exchange coupling between spin centers. Radical ligands with larger donor atoms could promote more efficient magnetic coupling between lanthanides to provide superior magnetic properties. Here, we show that heavy chalcogens (S, Se, Te) are primed to fulfill these criteria.

Durable infrared optical coatings based on pulsed DC-sputtering of hydrogenated amorphous carbon (a-C:H).

Optical properties of low-temperature pulsed DC-sputter deposited ($ {\le} {70° {\rm C}}$≤70°C) hydrogenated carbon are presented. Increasing hydrogen incorporation into the sputter deposited carbon significantly decreases infrared optical absorption due to a decrease in deep absorptive states associated with dangling bonds. Hydrogen flow is optimized (hydrogen flow 3 sccm), achieving the best compromise between increased infrared transmittance and hardness for durable coating performance.

Towards a better understanding of the electrosynthesis of 2,5-dicarboxy-2,5-dihydrofurans: structure, mechanism and influence over stereochemistry.

2,5-Dicarboxy-2,5-dihydrofurans are key constituents of a number of natural products and have roles as intermediates in the formation of other such compounds of interest. Typically, these species are synthesized using toxic Pb(IV) salts. Electrochemical syntheses of 2,5-diacetoxy-2,5-dihydrofuran that do not require the use of lead have been reported, but a general lack of experimental detail has prevented these procedures from being more widely adopted.

Comment on "Stabilization of Low-Valent Iron(I) in a High-Valent Vanadium(V) Oxide Cluster".

A recent Communication in this journal reported the stabilization of low-valent iron(I) in a fully oxidized polyoxovanadate. With no ligand-field argument to support such an assignment, a re-evaluation of the data accompanied by detailed computational analysis reveals the redox chemistry is localized to the polyoxovanadate, and when reduced, instigates a spin transition at iron.

Kinetic Control of Interpenetration in Fe-Biphenyl-4,4'-dicarboxylate Metal-Organic Frameworks by Coordination and Oxidation Modulation.

Phase control in the self-assembly of metal-organic frameworks (MOFs) is often a case of trial and error; judicious control over a number of synthetic variables is required to select the desired topology and control features such as interpenetration and defectivity. Herein, we present a comprehensive investigation of self-assembly in the Fe-biphenyl-4,4'-dicarboxylate system, demonstrating that coordination modulation can reliably tune between the kinetic product, noninterpenetrated MIL-88D(Fe), and the thermodynamic product, two-fold interpenetrated MIL-126(Fe). Density functional theory simulations reveal that correlated disorder of the terminal anions on the metal clusters results in hydrogen bonding between adjacent nets in the interpenetrated phase and this is the thermodynamic driving force for its formation.

Enhanced Fe-Centered Redox Flexibility in Fe-Ti Heterobimetallic Complexes.

Previously, we reported the synthesis of Ti[N( o-(NCHP( Pr))CH)] and the Fe-Ti complex, FeTi[N( o-(NCHP( Pr))CH)], abbreviated as TiL (1), and FeTiL (2), respectively. Herein, we describe the synthesis and characterization of the complete redox families of the monometallic Ti and Fe-Ti compounds. Cyclic voltammetry studies on FeTiL reveal both reduction and oxidation processes at -2.