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Potent Inhibition of Thioredoxin Reductase by the Rh Derivatives of Anticancer M(arene/Cp*)(NHC)Cl[subscript 2] Complexes
Abstract not provided
Ambient-Temperature Hydrogen Storage via Vanadium(II)-Dihydrogen Complexation in a Metal-Organic Framework
In this report, the widespread implementation of H 2 as a fuel is currently hindered by the high pressures or cryogenic temperatures required to achieve reasonable storage densities. In contrast, the realization of materials that strongly and reversibly adsorb hydrogen at ambient temperatures and moderate pressures could transform the transportation sector and expand adoption of fuel cells in other applications. To date, however, no adsorbent has been identified that exhibits a binding enthalpy within the optimal range of -15 to -25 kJ/mol for ambient-temperature hydrogen storage. Here, we report the hydrogen adsorption properties of the metal-organic framework (MOF) V 2 Cl 2.8 (btdd) (H 2 btdd, bis(1 H -1,2,3-triazolo[4,5- b ],[4',5'- i ])dibenzo[1,4]dioxin), which features exposed vanadium(II) sites capable of backbonding with weak π acids. Significantly, gas adsorption data reveal that this material binds H 2 with an enthalpy of -21 kJ/mol. This binding energy enables usable hydrogen capacities that exceed that of compressed storage under the same operating conditions. The Kubas-type vanadium(II)-dihydrogen complexation is characterized by a combination of techniques. From powder neutron diffraction data, a V-D 2 (centroid) distance of 1.966(8) Å is obtained, the shortest yet reported for a MOF. Using in situ infrared spectroscopy, the H-H stretch was identified, and it displays a red shift of 242 cm -1 . Electronic structure calculations show that a main contribution to bonding stems from the interaction between the vanadium d π and H 2 σ* orbital. Ultimately, the pursuit of MOFs containing high densities of weakly π-basic metal sites may enable storage capacities under ambient conditions that far surpass those accessible with compressed gas storage.
Photocatalytic dechlorination of unactivated chlorocarbons including PVC using organolanthanide complexes
Simple lanthanide cyclopentadienyl (Cp) complexes can photochemically cleave the sp 3 carbon–chlorine bond of unactivated chlorinated hydrocarbons including polyvinyl chloride (PVC). Further, the excited state lifetimes of these simple complexes are among the longest observed for cerium complexes (175 ns for [(Cp Me4 ) 2 Ce(μ-Cl)] 2 ) and the light absorption by the Cp ligand is efficient, so photocatalytic reactivity is enhanced for cerium and now also made possible for neighboring, normally photoinactive, lanthanide congeners.
Engineered π⋯π interactions favour supramolecular dimers X@[FeL 3 ] 2 (X = Cl, Br, I): solid state and solution structure
The engineered supramolecular recognition of coordination complexes achieved by ligand design is shown in the solid state and in solution via X-ray diffraction and paramagnetic H-NMR spectroscopy.
Apatite, Ca[subscript 10](PO[subscript 4])[subscript 6](OH,F,Cl)[subscript 2]: Structural Variations
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Coupled Cluster Study of the Heats of Formation of UF 6 and the Uranium Oxyhalides, UO 2 X 2 (X = F, Cl, Br, I, and At)
The atomization enthalpies of the U(VI) species UF6 and the uranium oxyhalides UO 2 X 2 (X=F, Cl, Br, I, At) were calculated using a composite relativistic Feller-Peterson-Dixon (FPD) approach based on scalar relativistic DKH3-CCSD(T) with extrapolations to the CBS limit. The inherent multideterminantal nature of the U atom was mitigated by utilizing the singly charged atomic cation in all calculations with correction back to the neutral asymptote via the accurate ionization energy of the U atom. The effects of SO coupling were recovered using full 4-component CCSD(T) with contributions due to the Gaunt Hamiltonian calculated using Dirac-Hartree-Fock. The final atomization enthalpy for UF 6 (752.2 kcal/mol) was within 2.5 kcal/mol of the experimental value, but unfortunately the latter carries a ±2.4 kcal/mol uncertainty that is predominantly due to the experimental uncertainty in the formation enthalpy of U atom. The analogous value for UO 2 F 2 (607.6 kcal/mol) was in nearly exact agreement with experiment, but the latter has a stated experimental uncertainty of ±4.3 kcal/mol. The FPD atomization enthalpy for UO 2 Cl 2 (540.4 kcal/mol) was within the experimental error limits of ±5.5 kcal/mol. FPD atomization energies for the non-U-containing molecules (used for reaction enthalpies) H 2 O and HX (X=F, Cl, Br, I, At) were within at most 0.3 kcal/mol of their experimental values where available. The FPD atomization enthalpies, together with FPD reaction enthalpies for two different reactions, were used to determine heats of formation for all species of this work with estimated uncertainties of ±4 kcal/mol. The calculated heat of formation for UF 6 (-511.0 kcal/mol) is within 2.5 kcal/mol of the accurately-known (±0.45 kcal/mol) experimental value.
Synthesis and spectroscopic characterization of actinyl(VI) tetrahalide coordination compounds containing 2, 2'-bipyridine
A series of three new actinide tetrahalide coordination compounds containing 2,2'-bipyridinium (H 2 bpy) have been synthesized by room temperature evaporation and characterized via single crystal X-ray diffraction, Raman spectroscopy, and infrared spectroscopy. The solid-state compounds (Np1, U1, and U2) contain the AnO 2 2+ cation coordinated to four halide (chloride or bromide) atoms to form the anionic tetrahalide molecular unit [AnO 2 X 4 ] 2– (X = Cl, Br) and are charge balanced by the 2,2'-bipyridinium cations that engage in electrostatic interactions with the actinyl complex. Np1 (N 2 C 10 H 10 )[NpO 2 Cl 4 ] contains 2,2'-bipyridine in the cis conformation where both the nitrogen atoms are directed towards the [NpO 2 Cl 4 ] 2– monomer. Within U1 (N 2 C 10 H 9 )[UO 2 Cl 4 ], the 2,2'-bipyridine is in a trans conformation, and found in the same orientation in the isomorphous structure U2 (N 2 C 10 H 9 )[UO 2 Br 4 ]. The compounds were further characterized by vibrational spectroscopy with specific interest in the actinyl cation. Raman spectroscopy provided information on the actinyl symmetric stretch (ν 1 ) whereas IR spectroscopy is used to determine the location of the asymmetric stretch (ν 3 ). Here, spectral similarities are observed between the two isomorphous structures, but slight variations across the series of structures are found to be associated with bipyridine bands in the various conformations. Additional analysis of these vibrational features in U1 and U2 provided information on the actinyl force constants, allowing insight into the relative uranyl bond strength that was compared to similar tetrahalide compounds.
Synthesis and molecular structure of perhalogenated rhenium-oxo corroles
Abstract As part of our efforts to develop rhenium-oxo corroles as photosensitizers for oxygen sensing and photodynamic therapy, we investigated the potential β -perhalogenation of five ReO meso -tris( para -X-phenyl)corroles, Re[T p XPC](O) (X = CF 3 , H, F, CH 3 , and OCH 3 ), with elemental chlorine and bromine. With Cl 2 , β -octachlorinated products Re[Cl 8 T p XPC](O) were rapidly obtained for X = CF 3 , H, and CH 3 , but X = OCH 3 resulted in overchlorination on the meso -aryl groups. Full β -octabromination proved slower relative to Cu and Ir corroles, but the desired Re[Br 8 T p XPC](O) products were finally obtained for X = H and F after a week at room temperature. For X = CH 3 and OCH 3 , these conditions led to undecabrominated products Re[Br 11 T p XPC](O). Compared to the β -unsubstituted starting materials, the β -octahalogenated products were found to exhibit sharp 1 H NMR signals at room temperature, indicating that the aryl groups are locked in place by the β -halogens, and substantially redshifted Soret and Q bands. Single-crystal X-ray structures of Re[Cl 8 T p CF 3 PC](O), Re[Cl 8 T p CH 3 PC](O), and Re[Br 8 T p FPC](O) revealed mild saddling for one Cl 8 structure and the Br 8 structure. These structural variations, however, appear too insignificant to explain the slowness of the β -octabromination protocols, which seems best attributed to the deactivating influence of the high-valent Re center.
A compact approach to higher-resolution resonant inelastic x-ray scattering detection using photoelectrons
The detection of inelastically scattered soft x-rays with high energy resolution usually requires large grating spectrometers. Recently, photoelectron spectrometry for analysis of x-rays (PAX) has been rediscovered for modern spectroscopy experiments at synchrotron light sources. By converting scattered photons to electrons and using an electron energy analyser, the energy resolution for resonant inelastic x-ray scattering (RIXS) becomes decoupled from the x-ray spot size and instrument length. In this work, we develop PAX towards high energy resolution using a modern photoemission spectroscopy setup studying Ba 2 Cu 3 O 4 Cl 2 at the Cu L 3 -edge. We measure a momentum transfer range of 24% of the first Brillouin zone simultaneously. Our results hint at the observation of a magnon excitation below 100 meV energy transfer and show intensity variations related to the dispersion of dd-excitations. With dedicated setups, PAX can complement the best and largest RIXS instruments, while at the same time opening new opportunities to acquire RIXS at a range of momentum transfers simultaneously and combine it with angle-resolved photoemission spectroscopy in a single instrument.
Direct visualization and control of antiferromagnetic domains and spin reorientation in a parent cuprate
Here, we report magnetic optical second-harmonic generation (SHG) polarimetry and imaging on Sr 2 Cu 3 O 4 Cl 2 , which allows direct visualization of the mesoscopic antiferromagnetic (AFM) structure of a parent cuprate. Temperature- and magnetic-field-dependent SHG reveals large domains with 90° relative orientations that are stabilized by a combination of uniaxial magnetic anisotropy and the Earth's magnetic field. Below a temperature T R ~ 97 K, we observe an unusual 90° spin reorientation transition, possibly driven by competing magnetic anisotropies of the two copper sublattices, which swaps the AFM domain states while preserving the domain structure. This allows deterministic switching of the AFM states by thermal or laser heating. Near T R , the domain walls become exceptionally responsive to an applied magnetic field, with the Earth's field sufficient to completely expel them from the crystal. Our findings unlock opportunities to study the mesoscopic AFM behavior of parent cuprates and explore their potential for AFM technologies.
Dynamic magnetic phase transition induced by parametric magnon pumping
Uncovering pathways to optically drive magnetic order-disorder transitions on ultrashort timescales can lead to the realization of novel out-of-equilibrium quantum phenomena. A long-sought pathway is to directly excite a highly nonthermal energy-momentum distribution of magnons, bypassing both charge and lattice degrees of freedom. However, this remains elusive owing to the weak coupling and large momentum mismatch between photons and magnons. Here we demonstrate strong parametric excitation of magnons across the entire Brillouin zone of the antiferromagnetic insulator Sr 2 Cu 3 O 4 Cl 2 by periodically modulating the superexchange interaction with the electric field of light. The excitation efficiency is greatly enhanced by tuning to the van Hove singularity in the magnon spectrum, sufficient to transiently collapse the antiferromagnetic state using a pulsed laser field of 10 9 V/m. The order parameter recovery timescale increases by over 1000 times as a function of excitation density, reflecting a crossover from high- to low-energy magnon dominated decay dynamics. This electric-field induced parametric magnon pumping mechanism is applicable to a broad range of magnetic insulators and opens up the possibility of dynamically engineering magnon distributions by design.
Flash Communication: Properties and Applications of a Pentavalent Bromoantimony Lewis Acid
While normally reluctant toward oxidation, SbBr 3 can be oxidized with 3,4,5,6-tetrachloro-1,2-benzoquinone (o-chloranil) in the presence of a Lewis base like the bromide anion or triphenylphosphine oxide (PPh 3 O) to form the tetrachlorocatecholate (cat Cl ) derivatives [SbBr 4 (cat Cl )] − ([2-Br] − ) and SbBr 3 (cat Cl )•OPPh 3 (2•OPPh 3 ), respectively. Structural, spectroscopic, and computational data indicate that the SbBr 3 (cat Cl ) fragment is similarly, if slightly less, Lewis acidic than the previously reported SbCl 3 (cat Cl ) fragment. The SbBr 3 /o-chloranil system, as well as its previously reported counterpart SbCl 3 /o-chloranil, were tested as Lewis acid catalysts for C−O bond metathesis and polycarbonate depolymerization. These results identified SbX 3 /o-chloranil pairs (X = Cl, Br) as simple main-group platforms for C−O bond cleavage chemistry.
A Dicationic fac -Re(bpy)(CO) 3 Cl for CO 2 Electroreduction at a Reduced Overpotential
Here, a dicationic Re bipyridine-type complex, fac-Re(6,6'-(2-((trimethylammonio)-methyl)phenyl)-2,2'-bipyridine)(CO) 3 Cl hexafluorophosphate (1 2+ ), has been synthesized and its electrochemical behavior under Ar and CO 2 has been investigated. The presence of pendent tetra-alkylammonium cations induces an anodic shift in the electrocatalytic potential for CO 2 reduction relative to structurally similar model complexes. The electrochemical mechanisms in anhydrous CH 3 CN and in the presence of weak acids (water or trifluoroethanol) have been analyzed using cyclic voltammetry assisted by infrared spectroelectrochemistry and theoretical calculations. The dication enables catalysis at a diminished potential through coulombic stabilization of the doubly reduced pentacoordinate species, its CO 2 adduct, the hydroxide anion, and the conjugate base formed during acid-assisted C-OH bond cleavage of the metallocarboxylic acid to the metallocarbonyl and H 2 O. The major reduction product is CO, but in the presence of trifluoroethanol, formate is also produced with 14% Faradaic efficiency.
Purely Cubic Spin Splittings with Persistent Spin Textures
Purely cubic spin splittings in the band structure of bulk insulators have not been extensively investigated yet despite the fact that they may pave the way for novel spin-orbitronic applications and can also result in a variety of promising spin phenomena. By symmetry analysis and first-principles simulations, we report symmetry-enforced purely cubic spin splittings (SEPCSS) that can even lead to persistent spin textures. In particular, these SEPCSS can be thought to be complementary to the cubic Rashba and cubic Dresselhaus types of spin splittings. Strikingly, the presently discovered SEPCSS are expected to exist in the large family of materials crystallizing in the $\bar{6}m2$ and $\bar{6}$ point groups, including the Ge 3 Pb 5 O 11 , Pb 7 Br 2 F 12 , and Pb 7 Cl 2 F 12 compounds.
Lithium and sodium superionic conductors
Presented are new, earth-abundant lithium superionic conductors, Li 3 Y(PS 4 ) 2 and Li 5 PS 4 Cl 2 , that emerged from a comprehensive screening of the Li—P—S and Li-M-P—S chemical spaces. Both candidates are derived from the relatively unexplored quaternary silver thiophosphates. One key enabler of this discovery is the development of a first-of-its-kind high-throughput first principles screening approach that can exclude candidates unlikely to satisfy the stringent Li+ conductivity requirements using a minimum of computational resources. Both candidates are predicted to be synthesizable, and are electronically insulating. Systems and methods according to present principles enable new, all-solid-state rechargeable lithium-ion batteries.
Anion–Cation–Anion Ion Triplet Characterization by Computation and Photoelectron Spectroscopy
Ion triplets of the chloride salts of two commonly used weakly coordinating cations are reported (i.e., Cl – ·NMe 4 + Cl – (1 – ) and Cl – ·PPh 4 + Cl – (2 – )). Negative ion photoelectron spectra at 20 K afford vertical and adiabatic detachment energies of 5.18 and 5.00 eV (1 – ) and 5.03 and 4.70 eV (2 – ), respectively. These results are well reproduced by coupled cluster calculations with single, double, and perturbative triple excitations (CCSD(T)) whereas M06-2X is systematically too small by ~0.3 eV (i.e., 7 kcal mol –1 ). The structures of both 1 – and 2 – have five or six C–H···Cl – interactions that stabilize these cluster anions by 32 (1 – ) and 27 (2 – ) kcal mol –1 as given by their chloride dissociation enthalpies. In conclusion, these values drop to 7.4 and 3.8 kcal mol –1 in dichloromethane based up conductor-like polarizable continuum model calculations and suggest that X – ·M + X – ion triplets with a weakly coordinating cation maybe the reactive form of salts under some conditions.