A remarkably bent diiron(III)-μ-hydroxo bisporphyrin: unusual stabilization of two spin states of iron in a single molecular framework

A novel diiron(III) bisporphyrin bridged by a hydroxo group between two cofacial Fe centers is reported. X-ray structural characterization revealed the remarkably bent μ-hydroxobis[Fe(III) porphyrin] with the smallest known Fe-O(H)-Fe angle [142.5(2)°] reported to date in an iron porphyrin. The close approach of the two rings in the molecule results in an unequal core deformation, and as a result, the geometrical parameters (such as the Fe-N(p), Fe-O and Fe···Ct(p) distances) are all different for the two Fe(III) centers, leading for the first time to a natural way of stabilizing two different spins of iron in a single molecular framework with complete retention of their own spectroscopic identities in both the solid state and solution. The strong antiferromagnetic coupling between the two Fe(III) centers in the μ-oxo dimer (-J = 126.6 cm(-1)) is attenuated to only 4.5 cm(-1) simply by protonation to give the μ-hydroxo complex.     

Alkaline Earth Metals Activate N2 and CO in Cubic Complexes Just Like Transition Metals: A Conceptual Density Functional Theory and Energy Decomposition Analysis Study

Following the recent discovery of stable octa-coordinated alkaline earth metals with N₂ and CO, the role of group II metals in the catalytic reduction of these ligands by means of density functional theory (DFT) calculations and conceptual DFT-based reactivity indices is investigated. Cubic group IV and octahedral group VI transition metal complexes as well as the free ligands are computed for reference. The outer and most accessible atoms of N₂ and CO become much more nucleophilic and electrophilic in all complexes, relevant for N₂ fixation, as probed by the Fukui function and local softness. Within one row of the periodic table, the alkaline earth complexes often show the strongest activation. On the contrary, the electrostatic character is found to be virtually unaffected by complexation. Trends in the soft frontier orbital and hard electrostatic character are in agreement with calculated proton affinities and energy decomposition analyses of the protonated structures, demonstrating the dominance of the soft (HOMO–LUMO) orbital interactions.     

Comment on “Realization of Lewis Basic Sodium Anion in the NaBH3− Cluster”

We challenge the interpretation of the chemical bond in NaBH₃⁻ proposed by Liu et al. We argue that NaBH₃⁻ has an electron-sharing Na−BH₃⁻ covalent bond rather than a dative bond Na⁻→BH₃.     

Embedding a Planar Hypercoordinate Carbon Atom into a [4n+2] π-System

Through delicate tuning of the electronic structure, we report herein a rational design of seventeen new putative global minimum energy structures containing a planar tetra- or pentacoordinate carbon atom embedded in an aromatic hydrocarbon. These structures are the result of replacing three consecutive hydrogen atoms of an aromatic hydrocarbon by less electronegative groups, forming a multicenter σ-bond with the planar hypercoordinate carbon atom and participating in the π-electron delocalization. This strategy that maximizes both mechanical and electronic effects through aromatic architectures can be extended to several molecular combinations to achieve new and diverse compounds containing planar hypercoordinate carbon centers.     

Breaking of longitudinal Akhiezer-Polovin waves

The breaking of longitudinal Akhiezer-Polovin (AP) waves is demonstrated using a one-dimensional simulation based on the Dawson sheet model. It is found that the AP longitudinal waves break through the process of phase mixing at an amplitude well below the breaking amplitude for AP waves, when subjected to arbitrarily small longitudinal perturbations. Results from the simulation show a good agreement with the Dawson phase mixing formula modified to include relativistic mass variation effects. This result may be of direct relevance to the laser- or particle-beam plasma wakefield experiments.     

Sharp signature of a dx2-y2 quantum critical point in the Hall coefficient of cuprate superconductors

We study the behavior of the Hall coefficient, R(H), in a system exhibiting dx(2)(-y(2)) density-wave order in a regime in which the carrier concentration, x, is tuned to approach a quantum critical point at which the order is destroyed. At the mean-field level, we find that n(Hall)=1/R(H) evinces a sharp signature of the transition. There is a kink in n(Hall) at the critical value of the carrier concentration, x(c); as the critical point is approached from the ordered side, the slope of n(Hall) diverges. Hall transport experiments in the cuprates, at high magnetic fields sufficient to destroy superconductivity, should reveal this effect.     

Direct sulfonation of methane to methanesulfonic acid with SO2 using Ca salts as promoters

Direct liquid-phase sulfonation of methane to methanesulfonic acid (MSA) with SO2 has been achieved in triflic acid using K2S2O8 as the oxidant and a small amount of a Ca salt as the promoter. The effects of reaction conditions on the conversion of SO2 to MSA were examined. Included were the influence of solvent acidity, reaction duration, reaction temperature, amount of K2S2O8, and composition and amount of promoters.