This study revisits the electroabsorption (EA) spectrum of polyacetylene, (CH)(x) thin films, for both the cis- and trans-isomers, as functions of the electric field strength, isomerization degree, and light polarization states. The EA spectrum of cis-(CH)(x) reveals an oscillatory feature that follows the Stark shift-related first derivative of the material's absorption spectrum that contains v(0-1) and v(0-2) sidebands of the excited C=C stretching vibration that agrees well with the Raman scattering (RS) spectrum. In contrast, the EA spectrum of trans-(CH)(x) does not match the first derivative of the material's absorption spectrum, and the phonon sideband frequency does not agree with the RS spectrum. In addition, the EA spectrum of trans-(CH)(x) reveals a band below the first allowed 1B(u) exciton. We interpret this feature as due to the electric field activated even-parity dark (forbidden) exciton, namely mA(g) (m > 2), showing that the "nonluminescent" trans-(CH)(x) is due to the reverse order of the excited states, where a series of dark mA(g) excitons lies below the allowed 1B(u) exciton. This agrees with the unusual phonon sideband in trans-(CH)(x) absorption, since the excited state attenuation caused by the fast internal conversion from 1B(u) to mA(g) influences the apparent frequency that determines the phonon sideband. Consequently, from the EA and RS spectra we estimate the 1B(u) lifetime in trans-(CH)(x) to be similar to 30 fs. Moreover, the integrated EA spectrum of trans-(CH)(x) shows a traditional Huang-Rhys type series with a relaxation parameter, S similar to 0.5. This indicates that the EA spectrum of the trans isomer is also determined by a Stark shift related to the first derivative of the absorption spectrum, but preferentially for the longest chains in the film's chain lengths distribution. This is due to the N-3 response of the nonlinear susceptibility, chi((3)) (similar to EA), dependence on the chain length having N monomers.

Organic‐based magnetic materials have been used for spintronic device applications as electrodes of spin aligned carriers and spin‐pumping substrates. Their advantages over more traditional inorganic magnets include reduced magnetic damping and lower fabrication costs. Vanadium tetracyanoethylene, V[TCNE] x ( x ≈ 2), is an organic‐based ferrimagnet with an above room‐temperature magnetic order temperature ( T c ≈ 400 K). V[TCNE] x has deposition flexibility and can be grown on a variety of substrates via low‐temperature chemical vapor deposition (CVD). A systematic study of V[TCNE] x thin‐film CVD parameters to achieve optimal film quality, reproducibility, and excellent magnetic properties is reported. This is assessed by broadband ferromagnetic resonance (FMR) that shows most narrow linewidth of ≈1.5 Gauss and an extremely low Gilbert damping coefficient. The neat V[TCNE] x films are shown to be efficient spin injectors via spin pumping into an adjacent platinum layer. Also, under an optimized FMR linewidth, the V[TCNE] x films exhibit Fano‐type resonance with a continuum broadband absorption in the microwave range, which can be readily tuned by the microwave frequency.

A mechanistic investigation into the origins of the regio- and chemoselectivities observed in iron/pyridine dialdimine (PDAI)-catalyzed intermolecular [2+2+2] cycloaddition reactions of terminal alkynes and cyanamides to yield substituted 2-amino-pyridines is reported. The combination of experimental and computational studies disclosed herein reveals the role of the hemilabile PDAI ligand as an important factor controlling the resultant product's observed regio- and chemoselectivity.

A critically important process in catalysis is the formation of an active catalyst from the combination of a metal precursor and a ligand, as the efficacy of this reaction governs the amount of active catalyst. This Review is a comprehensive overview of reactions catalyzed by nickel and an added bidentate phosphine, focusing on the steps transforming the combination of precatalyst and ligand into an active catalyst and the potential effects of this transformation on nickel catalysis. Reactions covered include common cross-coupling reactions, such as Suzuki, Heck, Kumada, and Negishi couplings, addition reactions, cycloadditions, C-H functionalizations, polymerizations, hydrogenations, and reductive couplings, among others. Overall, the most widely used nickel precatalyst with free bidentate phosphines is Ni(cod)2, which accounts for ∼50% of the reports surveyed, distantly followed by Ni(acac)2 and Ni(OAc)2, which account for ∼10% each. By compiling the reports of these reactions, we have calculated statistics of the usage and efficacy of each ligand with Ni(cod)2 and other nickel sources. The most common bidentate phosphines are simple, relatively inexpensive ligands, such as DPPE, DCPE, DPPP, and DPPB, along with others with more complex backbones, such as DPPF and Xantphos. The use of expensive chiral phosphines is more scattered, but the most common ligands include BINAP, Me-Duphos, Josiphos, and related analogs.

Spin waves, quantized as magnons, have low energy loss and magnetic damping, which are critical for devices based on spin-wave propagation needed for information processing devices. The organic-based magnet [V(TCNE)x ; TCNE = tetracyanoethylene; x ≈ 2] has shown an extremely low magnetic damping comparable to, for example, yttrium iron garnet (YIG). The excitation, detection, and utilization of coherent and non-coherent spin waves on various modes in V(TCNE)x is demonstrated and show that the angular momentum carried by microwave-excited coherent spin waves in a V(TCNE)x film can be transferred into an adjacent Pt layer via spin pumping and detected using the inverse spin Hall effect. The spin pumping efficiency can be tuned by choosing different excited spin wave modes in the V(TCNE)x film. In addition, it is shown that non-coherent spin waves in a V(TCNE)x film, excited thermally via the spin Seebeck effect, can also be used as spin pumping source that generates an electrical signal in Pt with a sign change in accordance with the magnetization switching of the V(TCNE)x . Combining coherent and non-coherent spin wave detection, the spin pumping efficiency can be thermally controlled, and new insight is gained for the spintronic applications of spin wave modes in organic-based magnets.

A Ni-catalyzed (4 + 2) cycloaddition of alkynes and azetidinones toward piperidinones was used as key reaction in the enantioselective synthesis of naturally occurring indolizidine alkaloids. The reaction benefits from the use of an easily accessible azetidinone as an advanced and divergent intermediate to build the indolizidine core. This methodology has been applied in the total syntheses of (+)-septicine, (+)-ipalbidine, and (+)-seco-antofine to illustrate the applicability of the general approach.

[2+2+2] Cycloadditions of heterocumulenes and nitriles represent an efficient, atom‐economical method of synthesizing heterocycles and, to a lesser extent, carbocycles. Cycloadditions of heterocumulenes including isocyanates, carbodiimides, carbon dioxide, carbon disulfide, ketenes, as well as nitriles are explored. The heterocumulene is typically coupled with an alkyne or diyne, forming 6‐membered heterocycles, although multiple heterocumulenes are sometimes incorporated. The reactions are generally catalyzed by late‐transition‐metal catalysts, albeit nucleophilic catalysts and early‐transition metals are sometimes used. [2+2+2]; cycloaddition; heterocumulene; isocyanate; carbodiimide; carbon dioxide; carbon disulfide; ketene; nitrile; alkyne; diyne; pyridone; pyridine; transition‐metal catalysis

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Electronically variant (dppf)Ni(ketene) complexes were synthesized and characterized to perform kinetic analysis on their decomposition through a decarbonylation/disproportion process to Ni–CO complexes and alkenes. Ligands containing electron-donating groups stabilized such complexes, whereas an electron-withdrawing group was found to destabilize them. Hammett analysis on the decomposition reaction revealed the buildup of negative charges in the rate-determining step, which corroborates past computational models.

The investigation of the stereoelectronic influence of N-aryl substituted NHC ligands on Ni(0) is reported. The structural analysis of a family of [(NHC)Ni(styrene)2] complexes are correlated to known literature parameters (TEP and %VBur). The analysis involved NMR spectroscopic techniques and X-ray crystallography analysis of the isolated [(NHC)Ni(styrene)2] complexes. The synthesis and characterization of this user-friendly and easy accessible Ni(0) precatalysts can be realized in a two-step synthesis starting from deprotonation of the imidazolium salt followed by direct coordination onto nickel in the presence of excess styrene.

A comprehensive study of the reactions of chelating phosphines with Ni(cod)2 to form (phosphine)Ni(cod), (phosphine)2Ni, or mixtures thereof is presented. A series of (phosphine)Ni(cod) complexes were isolated and characterized. The structural differences between the (phosphine)Ni(cod) and (phosphine)2Ni complexes were examined using X-ray crystallography and 1H and 31P NMR spectroscopy. In addition, the effects of ring size, rigidity, and bulk of the phosphine backbone on the formation of either (phosphine)Ni(cod) or (phosphine)2Ni were investigated. These studies show that the Ni–P bond lengths in both the (phosphine)Ni(cod) and (phosphine)2Ni complexes and the size of the ring formed by the chelating phosphine and Ni are crucial in determining whether or not (phosphine)Ni(cod) complexes can be isolated. Other factors such as π-stacking interactions were found to have marginal influence.

Two new Ni(II) complexes, the homoleptic [Ni-(8P(2)(Cy)N(H))(2)](2+) complex (8P(2)(Cy)N(H) = 3,7-cyclohexyl-1-atnino-3,7-diphosphacyclooctane) containing two pendant amines on adjacent ligands, and the heteroleptic [Ni(8P(2)(Cy)N(H))center dot(dppe)(2+) complex (dppe = bis(diphenylphosphino)ethane) containing only a single pendant, amine, have been syrithesited, and theii electrochemical properties are reported. The [Ni(8P(2)(Cy)N(H))(dppe)(2+) complex is capable of heterolytically cleaving hydrogen, allowing for the first observation of an endoprotonated nickel hydride related to the [Ni((P2N2R)-N-R')(2)](2+) family of complexes. The [Ni(88P(2)(Cy)N(H))(dppe)](2+) complex did not exhibit electrocatalytic H-2 oxidation activity; however, [Ni(8P(2)(Cy)N(H))(2)](2+) is an active electrocatalyst for H-2 OXidaiOrl with a maximum turnover:frequency (k(obs)) of 18 s(-1) under 1 atm H-2 at E-cat/2 = -0.71 V versus the ferrocenium/ferrocene (Cp2Fe+/0) couple. In addition to an analysis of the effect of the number of pendant amines. on the rates of electrocatalytic H2 oxidation of compounds related to the [Ni((P2N2R)-N-R')(2)](2+) family, the effect of the secondary pendant amine on intermolecular deprotonation is discussed.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

In addition to 3,5‐disubstituted 2‐aminopyridines the 4,6‐substituted isomers are isolated in trace to significant amounts.

An attractive path to increase energy storage capacities, lower the material costs, and improve operation safety involves the use of multi-valent elements with low reduction potentials. Key benefits of multi-valent systems over mono-valent (i.e. Li, Na) include (1) Increased electrons available per molecule that significantly impacts energy density characteristics. Potential candidates include magnesium (Mg) that can lose two electrons and aluminum three electrons, coupled with increased abundance and decreased production cost makes them viable alternatives for low cost energy storage. In this presentation, a novel [Mg2(μ-Cl)2]2+ cation complex, which is highly active for reversible Mg electrodeposition, was identified for the first time in this work. This complex was found to present in electrolytes formulated in dimethoxyethane (DME) through dehalodimerization of non-nucleophilic MgCl2 by reacting with either Mg salts (such as Mg(TFSI)2, TFSI= bis(trifluoromethane)sulfonylimide) or Lewis acid salts (such as AlEtCl2 or AlCl3).The electrolyte synthesis and understandings developed in this work could be insightful for rational formulation of a family of electrolytes with the general formula [Mg2(μ-Cl)2(DME)4][anion]x, and provide new opportunities for developing cathode materials, and therefore could be significant for practical Mg batteries.

The regioselectivity of the Ni/SIPr-catalyzed cyc addition terminal alkynes and cyanamides was explored. In general, 3,5-disubstituted 2-aminopyridines were formed as the major product.

A novel [Mg2(μ-Cl)2](2+) cation complex, which is highly active for reversible Mg electrodeposition, was identified for the first time in this work. This complex was found to be present in electrolytes formulated in dimethoxyethane (DME) through dehalodimerization of non-nucleophilic MgCl2 by reacting with either Mg salts (such as Mg(TFSI)2, TFSI = bis(trifluoromethane)sulfonylimide) or Lewis acid salts (such as AlEtCl2 or AlCl3). The molecular structure of the cation complex was characterized by single crystal X-ray diffraction, Raman spectroscopy and NMR. The electrolyte synthesis process was studied and rational approaches for formulating highly active electrolytes were proposed. Through control of the anions, electrolytes with an efficiency close to 100%, a wide electrochemical window (up to 3.5 V) and a high ionic conductivity (>6 mS cm(-1)) were obtained. The understanding of electrolyte synthesis in DME developed in this work could bring significant opportunities for the rational formulation of electrolytes of the general formula [Mg2(μ-Cl)2][anion]x for practical Mg batteries.

To convert solar energy into viable fuels, coupling light-harvesting materials to catalysts is a crucial challenge. Now, the combination of an organic supramolecular hydrogel and a non-precious metal catalyst has been demonstrated to be effective for photocatalytic H 2 production.

We report solvent and electrolyte effects on the electrocatalytic oxidation of H2 using Ni(P(Cy)2N(R')2)2 (R = Bn, (t)Bu) complexes. A turnover frequency of 46 s(-1) for Ni(P(Cy)2N(Bn)2)2 was obtained using 0.2 M [(n)Bu4N][BF4] in THF. A turnover frequency of 51 s(-1) was observed for Ni(P(Cy)2N(tBu)2)2 using 0.2 M [(n)Bu4N][B(C6F5)4] in fluorobenzene. These observations, in conjunction with previous studies, indicate nitrile binding inhibits catalysis supported by Ni(P(Cy)2N(Bn)2)2.