A comprehensive mechanistic study of electrocatalytic CO2 reduction by ruthenium 2,2′:6′,2″-terpyridine (tpy) pyridyl-carbene catalysts reveals the importance of stereochemical control to locate the strongly donating N-heterocyclic carbene ligand trans to the site of CO2 activation. Computational studies were undertaken to predict the most stable isomer for a range of reasonable intermediates in CO2 reduction, suggesting that the ligand trans to the reaction site plays a key role in dictating the energetic profile of the catalytic reaction. A new isomer of [Ru­(tpy)­(Mebim-py)­(NCCH3)]2+ (Mebim-py is 1-methylbenzimidazol-2-ylidene-3-(2′-pyridine)) and both isomers of the catalytic intermediate [Ru­(tpy)­(Mebim-py)­(CO)]2+ were synthesized and characterized. Experimental studies demonstrate that both isomeric precatalysts facilitate electroreduction of CO2 to CO in 95/5 MeCN/H2O with high activity and high selectivity. Cyclic voltammetry, infrared spectroelectrochemistry, and NMR spectroscopy studies provide a detailed mechanistic picture demonstrating an essential isomerization step in which the N-trans catalyst converts in situ to the C-trans variant. Insight into molecular electrocatalyst design principles emerge from this study. First, the use of an asymmetric ligand that places a strongly electron-donating ligand trans to the site of CO2 binding and activation is critical to high activity. Second, stereochemical control to maintain the desired isomer structure during catalysis is critical to performance. Finally, pairing the strongly donating pyridyl-carbene ligand with the redox-active tpy ligand proves to be useful in boosting activity without sacrificing overpotential. These design principles are considered in the context of surface-immobilized electrocatalysis.

This tutorial review gives a synthetic chemistry perspective of magnetic relaxation phenomena through the lens of the reaction-coordinate diagram.

Hybrid metal halides yield highly desirable optoelectronic properties and offer significant opportunity due to their solution processability. This contribution reports a new series of hybrid semiconductors, (C7H7)MX4 (M = Bi 3+ , Sb 3+ ; X = Cl-, Br-, I-), that are composed of edge-sharing MX6 chains separated in space by -stacked tropylium (C7H7 +) cations; the inorganic chains resemble the connectivity of BiI3. The Bi 3+ compounds have blue shifted optical absorptions relative to the Sb 3+ compounds that span the visible and near-IR region. Consistent with observations, DFT calculations reveal that the conduction band is composed of the tropylium cation and valence band primarily the inorganic chain: a charge-transfer semiconductor. The band gaps for both Bi 3+ and Sb 3+ compounds decrease systematically as a function of increasing halide size. These compounds are a rare example of charge transfer semiconductors that also exhibit efficient crystal packing of the organic cations, thus providing an opportunity to study how structural packing affects optoelectronic properties.

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Here we show how a simple change in the geometry of 1D iron–tetraoxolene chains dramatically alters the observed physical properties, including the presence of valence tautomerism, strong magnetic coupling, and electrical conductivity.

Dinitrogen coordination to iron centers underpins industrial and biological fixation in the Haber-Bosch process and by the FeM cofactors in the nitrogenase enzymes. The latter employ local high-spin metal centers; however, iron-dinitrogen coordination chemistry remains dominated by low-valent states, contrasting the enzyme systems. Here, we report a highspin mixed-valent cis-, where [L bis ] À is a bis(βdiketiminate) cyclophane. Field-applied Mössbauer spectra, dc and ac magnetic susceptibility measurements, and computational methods support a delocalized S = 7 / 2 Fe 2 N 2 unit with D = À 5.23 cm À 1 and consequent slow magnetic relaxation.Converting atmospheric dinitrogen into bioavailable forms (e.g., NH 3 ) is essential to life on Earth. However, scission of dinitrogen is a kinetically-limited reaction. [1] The Haber-Bosch process for industrial production of NH 3 employs the iron-based Mittasch catalyst and high temperatures and pressures to achieve reductive cleavage of N 2 . [2] Contrastingly, nitrogenase enzymes in biological systems effect N 2 reduction to NH 3 under ambient conditions utilizing Fe 7 M (M = Mo, V or Fe) cofactors with local high-spin Fe centers. [3] Whereas iron reactive sites in the Mittasch catalyst are predominantly in reduced states, [2] the nitrogenase cofactors are proposed to employ a cluster with minimal, if any, low valent iron character for N 2 conversion to NH 3 . [4][5][6][7]

Hybrid metal halides yield highly desirable optoelectronic properties and offer significant opportunity due to their solution processability. This contribution reports a new series of hybrid semiconductors, (C7H7)MX4 (M = Bi 3+ , Sb 3+ ; X = Cl -, Br -, I -), that are composed of edge-sharing MX6 chains separated in space by -stacked tropylium (C7H7 + ) cations; the inorganic chains resemble the connectivity of BiI3. The Bi 3+ compounds have blue shifted optical absorptions relative to the Sb 3+ compounds that span the visible and near-IR region. Consistent with observations, DFT calculations reveal that the conduction band is composed of the tropylium cation and valence band primarily the inorganic chain: a charge-transfer semiconductor. The band gaps for both Bi 3+ and Sb 3+ compounds decrease systematically as a function of increasing halide size. These compounds are a rare example of charge transfer semiconductors that also exhibit efficient crystal packing of the organic cations, thus providing an opportunity to study how structural packing affects optoelectronic properties. Introduction.Hybrid perovskites and their derivatives have emerged as highly efficient solution processable semiconducting materials, making them attractive for numerous applications such as light-emitting devices, photovoltaics, photodetectors, and radiation detectors. 1-8 These compounds combine many of the desirable properties of traditional inorganic semiconductors such as high carrier mobilities and absorption coefficients with the processability of organic electronics. 6,[9][10] However, many questions remain as to how the inorganic framework can influence or couple to the electronic behavior of the organic components. In the realm of hybrid perovskites, much focus has been on compounds containing small organic cations such as methylammonium or formamidinium. [11][12][13][14][15] Unlike smaller cations, organic cations with delocalized electrons can have electronic states near the valence and conduction band of the inorganic lattice, allowing for charge-transfer from the inorganic to organic subunits.

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