Bis{μ-1,3-bis­[(2-methyl-1H-benzimid­azol-1-yl)meth­yl]benzene-κ2 N 3:N 3′}bis­(diiodidocadmium)

In the title compound, [Cd2I4(C24H22N4)2], the 1,3-bis­[(2-methyl-1H-benzimidazol-1-yl)meth­yl]benzene ligand bridges two CdI2 units, forming a centrosymmetric dinuclear complex. The CdII atom adopts a distorted tetra­hedral coordination geometry. In the crystal, complex mol­ecules are linked into columns parallel to [101] by π–π stacking inter­actions, with centroid–centroid distances of 3.558 (2) Å

Synchrotron Mössbauer spectroscopic study of ferropericlase at high pressures and temperatures

The electronic spin state of Fe^(2+) in ferropericlase, (Mg_(0.75)Fe_(0.25))O, transitions from a high-spin (spin unpaired) to low-spin (spin paired) state within the Earth’s mid-lower mantle region. To better understand the local electronic environment of high-spin Fe^(2+) ions in ferropericlase near the transition, we obtained synchrotron Mössbauer spectra (SMS) of (Mg_(0.75),Fe_(0.25))O in externally heated and laser-heated diamond anvil cells at relevant high pressures and temperatures. Results show that the quadrupole splitting (QS) of the dominant high-spin Fe^(2+) site decreases with increasing temperature at static high pressure. The QS values at constant pressure are fitted to a temperature-dependent Boltzmann distribution model, which permits estimation of the crystal-field splitting energy (Δ_3) between the d_(xy_ and d_(xz) or d_(zy) orbitals of the t_(2g) states in a distorted octahedral Fe^(2+) site. The derived Δ_3 increases from approximately 36 meV at 1 GPa to 95 meV at 40 GPa, revealing that both high pressure and high temperature have significant effects on the 3d electronic shells of Fe^(2+) in ferropericlase. The SMS spectra collected from the laser-heated diamond cells within the time window of 146 ns also indicate that QS significantly decreases at very high temperatures. A larger splitting of the energy levels at high temperatures and pressures should broaden the spin crossover in ferropericlase because the degeneracy of energy levels is partially lifted. Our results provide information on the hyperfine parameters and crystal-field splitting energy of high-spin Fe^(2+) in ferropericlase at high pressures and temperatures, relevant to the electronic structure of iron in oxides in the deep lower mantle

Suppression of the magnetic order in CeFeAsO: non-equivalence of hydrostatic and chemical pressure

We present a detailed investigation of the electronic properties of CeFeAsO under chemical (As by P substitution) and hydrostatic pressure by means of in-house and synchrotron M\"ossbauer spectroscopy. The Fe magnetism is suppressed due to both pressures and no magnetic order was observed above a P-substitution level of 40% or 5.2 GPa hydrostatic pressure. We compared both pressures and found that the isovalent As by P substitution change the crystallographic and electronic properties differently than hydrostatic pressure.Comment: supplement is included in the pdf fil

Petrogenesis of granitoids in the eastern section of the Central Qilian Block: Evidence from geochemistry and zircon U-Pb geochronology

The Caledonian-age Qilian Orogenic Belt at the northern margin of the Greater Tibetan Plateau comprises abundant granitoids that record the histories of the orogenesis. We report here our study of these granitoids from two localities. The Qingchengshan (QCS) pluton, which is situated in the eastern section of the Central Qilian Block, is dated at ~430–420 Ma. It has high-K calc-alkaline composition with high SiO2 (> 70 wt%), enrichment in large ion lithophile elements (LILEs), depletion in high field strength elements (HFSEs), and varying degrees of negative Sr and Eu anomalies. The granitoids in the Tongwei (TW) area, 150 km east of the QCS, are complex, the majority of which are dated at ~440 Ma, but there also exist younger, ~230 Ma intrusions genetically associated with the Qinling Orogeny. The Paleozoic TW intrusions also have high SiO2, fractionated REE (rare earth element) patterns, but a negligible Eu anomaly. The whole rock Sr-Nd-Hf isotopic compositions suggest that all these Paleozoic granitoids are consistent with melting-induced mixing of a two-component source, which is best interpreted as the combination of last fragments of subducted/subducting ocean crust with terrigenous sediments. The mantle isotopic signature of these granitoids (87Sr/86Sri: 0.7038 to 0.7100, εNd(t): −4.8 to −1.3, εHf(t): −0.7 to +4.0) reflects significant (~70 %) contribution of the ocean crust derived in no distant past from the mantle at ocean ridges with an inherited mantle isotopic signature. Partial melting of such ocean crust plus terrigenous sediments in response to the ocean closing and continental collision (between the Qilian and Alashan Blocks) under amphibolite facies conditions is responsible for the magmatism. Varying extents of fractional crystallization (±plagioclase, ±amphibole, ±garnet, ±zircon) of the parental magmas produced the observed QCS and TW granitoids. We note that sample HTC12–01 in the TW area shows an A-type or highly fractionated granite signature characterized by elevated abundances and a flat pattern of REEs, weak Nb-Ta anomaly, conspicuous negative Sr and Eu anomalies (Sr/Sr* = 0.09, Eu/Eu* = 0.22), and thus the high 87Sr/86Sr ratio (0.7851), and moderate εNd(t) (−4.9) and εHf(t) (−2.0), pointing to the significant mantle contribution. Compared with the Paleozoic granitoids, the ~230 Ma granitoids in the TW area represented by sample JPC12–02 have higher initial 87Sr/86Sr (0.7073) and lower εNd(t) (−6.2) and εHf(t) (−4.5) values, offering an ideal opportunity for future studies on tectonic effects of juxtaposition of younger orogenesis on an older orogen

DCAF26, an Adaptor Protein of Cul4-Based E3, Is Essential for DNA Methylation in Neurospora crassa

DNA methylation is involved in gene silencing and genome stability in organisms from fungi to mammals. Genetic studies in Neurospora crassa previously showed that the CUL4-DDB1 E3 ubiquitin ligase regulates DNA methylation via histone H3K9 trimethylation. However, the substrate-specific adaptors of this ligase that are involved in the process were not known. Here, we show that, among the 16 DDB1- and Cul4-associated factors (DCAFs) encoded in the N. crassa genome, three interacted strongly with CUL4-DDB1 complexes. DNA methylation analyses of dcaf knockout mutants revealed that dcaf26 was required for all of the DNA methylation that we observed. In addition, histone H3K9 trimethylation was also eliminated in dcaf26KO mutants. Based on the finding that DCAF26 associates with DDB1 and the histone methyltransferase DIM-5, we propose that DCAF26 protein is the major adaptor subunit of the Cul4-DDB1-DCAF26 complex, which recruits DIM-5 to DNA regions to initiate H3K9 trimethylation and DNA methylation in N. crassa

Redox electrolyte-enhanced carbon-based supercapacitors: recent advances and future perspectives

With the continuous advancement in the dual-carbon strategy, the upswell in the demand for renewable energy sources has motivated extensive research on the development of novel energy storage technologies. As a new type of energy storage device, carbon-based redox-enhanced supercapacitors (RE-SCs) are designed by employing soluble redox electrolytes into the existing devices, exploiting the merits of the diffusion-controlled faradaic process of the redox electrolyte at the surface of carbon electrodes, thus leading to improved energy density without the cost of power density. During the past years, great progress has been made in the design of novel redox electrolytes and the configuration of new devices. However, the development of these systems is plagued by severe self-discharge. Herein, a comprehensive picture of the fundamentals, together with a discussion and outline of the challenges and future perspectives of RE-SCs, are provided. We highlight the impacts of redox electrolytes on capacitance, energy density, and power output. Notably, the self-discharge behavior owing to the introduction of redox electrolyte and its mechanism are also discussed, followed by a summary of the strategies from materials to system optimization. Furthermore, possible directions for future research are discussed

Authentication of Freshness for OutsourcedMulti-Version Key-Value Stores

Data outsourcing offers cost-effective computing power to manage massive data streams and reliable access to data. For example, data owners can forward their data to clouds, and the clouds provide data mirroring, backup, and online access services to end users. However, outsourcing data to untrusted clouds requires data authentication and query integrity to remain in the control of the data owners and users. In this paper, we address this problem specifically for multiversion key-value data that is subject to continuous updates under the constraints of data integrity, data authenticity, and “freshness” (i.e., ensuring that the value returned for a key is the latest version).We detail this problem and propose INCBMTREE, a novel construct delivering freshness and authenticity. Compared to existing work, we provide a solution that offers (i) lightweight signing and verification on massive data update streams for data owners and users (e.g., allowing for small memory footprint and CPU usage on mobile user devices), (ii) integrity of both real-time and historic data, and (iii) support for both real-time and periodic data publication. Extensive benchmark evaluations demonstrate that INCBMTREE achieves more throughput (in an order of magnitude) for data stream authentication than existing work. For data owners and end users that have limited computing power, INCBM-TREE can be a practical solution to authenticate the freshness of outsourced data while reaping the benefits of broadly available cloud services

Exploring the Limits of Dative Boratrane Bonding: Iron as a Strong Lewis Base in Low-Valent Non-Heme Iron-Nitrosyl Complexes

We previously reported the synthesis and preliminary characterization of a unique series of low-spin (ls) {FeNO}⁸⁻¹⁰ complexes supported by an ambiphilic trisphosphineborane ligand, [Fe(TPB)(NO)]^(+/0/−). Herein, we use advanced spectroscopic techniques and density functional theory (DFT) calculations to extract detailed information as to how the bonding changes across the redox series. We find that, in spite of the highly reduced nature of these complexes, they feature an NO+ ligand throughout with strong Fe−NO π-backbonding and essentially closed-shell electronic structures of their FeNO units. This is enabled by an Fe−B interaction that is present throughout the series. In particular, the most reduced [Fe(TPB)(NO)]− complex, an example of a ls-{FeNO}¹⁰ species, features a true reverse dative Fe → B bond where the Fe center acts as a strong Lewis-base. Hence, this complex is in fact electronically similar to the ls-{FeNO}⁸ system, with two additional electrons “stored” on site in an Fe−B single bond. The outlier in this series is the ls-{FeNO}⁹ complex, due to spin polarization (quantified by pulse EPR spectroscopy), which weakens the Fe−NO bond. These data are further contextualized by comparison with a related N₂ complex, [Fe(TPB)(N₂)]⁻, which is a key intermediate in Fe(TPB)-catalyzed N₂ fixation. Our present study finds that the Fe → B interaction is key for storing the electrons needed to achieve a highly reduced state in these systems, and highlights the pitfalls associated with using geometric parameters to try to evaluate reverse dative interactions, a finding with broader implications to the study of transition metal complexes with boratrane and related ligands

Exploring the Limits of Dative Boratrane Bonding: Iron as a Strong Lewis Base in Low-Valent Non-Heme Iron-Nitrosyl Complexes

We previously reported the synthesis and preliminary characterization of a unique series of low-spin (ls) {FeNO}⁸⁻¹⁰ complexes supported by an ambiphilic trisphosphineborane ligand, [Fe(TPB)(NO)]^(+/0/−). Herein, we use advanced spectroscopic techniques and density functional theory (DFT) calculations to extract detailed information as to how the bonding changes across the redox series. We find that, in spite of the highly reduced nature of these complexes, they feature an NO+ ligand throughout with strong Fe−NO π-backbonding and essentially closed-shell electronic structures of their FeNO units. This is enabled by an Fe−B interaction that is present throughout the series. In particular, the most reduced [Fe(TPB)(NO)]− complex, an example of a ls-{FeNO}¹⁰ species, features a true reverse dative Fe → B bond where the Fe center acts as a strong Lewis-base. Hence, this complex is in fact electronically similar to the ls-{FeNO}⁸ system, with two additional electrons “stored” on site in an Fe−B single bond. The outlier in this series is the ls-{FeNO}⁹ complex, due to spin polarization (quantified by pulse EPR spectroscopy), which weakens the Fe−NO bond. These data are further contextualized by comparison with a related N₂ complex, [Fe(TPB)(N₂)]⁻, which is a key intermediate in Fe(TPB)-catalyzed N₂ fixation. Our present study finds that the Fe → B interaction is key for storing the electrons needed to achieve a highly reduced state in these systems, and highlights the pitfalls associated with using geometric parameters to try to evaluate reverse dative interactions, a finding with broader implications to the study of transition metal complexes with boratrane and related ligands

Electronic Structures of an [Fe(NNR_2)]^(+/0/–) Redox Series: Ligand Noninnocence and Implications for Catalytic Nitrogen Fixation

The intermediacy of metal–NNH_2 complexes has been implicated in the catalytic cycles of several examples of transition-metal-mediated nitrogen (N_2) fixation. In this context, we have shown that triphosphine-supported Fe(N_2) complexes can be reduced and protonated at the distal N atom to yield Fe(NNH_2) complexes over an array of charge and oxidation states. Upon exposure to further H^+/e^– equivalents, these species either continue down a distal-type Chatt pathway to yield a terminal iron(IV) nitride or instead follow a distal-to-alternating pathway resulting in N–H bond formation at the proximal N atom. To understand the origin of this divergent selectivity, herein we synthesize and elucidate the electronic structures of a redox series of Fe(NNMe_2) complexes, which serve as spectroscopic models for their reactive protonated congeners. Using a combination of spectroscopies, in concert with density functional theory and correlated ab initio calculations, we evidence one-electron redox noninnocence of the “NNMe_2” moiety. Specifically, although two closed-shell configurations of the “NNR_2” ligand have been commonly considered in the literature—isodiazene and hydrazido(2−)—we provide evidence suggesting that, in their reduced forms, the present iron complexes are best viewed in terms of an open-shell [NNR_2]^•–ligand coupled antiferromagnetically to the Fe center. This one-electron redox noninnocence resembles that of the classically noninnocent ligand NO and may have mechanistic implications for selectivity in N_2 fixation activity