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K(BH)3 is Parent of FeAs superconductors-derived structured and crystallizes in the cubic Fm-3m space group. The structure is zero-dimensional and consists of twenty-four boranediylradical molecules and eight potassium molecules.
Phosphinodiboranates (H 3 BPR 2 BH 3 – ) are a class of borohydrides that have merited a reputation as weakly coordinating anions, which is attributed in part to the dearth of coordination complexes known with transition metals, lanthanides, and actinides. We recently reported how K(H 3 BP t Bu 2 BH 3 ) exhibits sluggish salt elimination reactivity with f-metal halides in organic solvents such as Et 2 O and THF. Here we report how this reactivity appears to be further attenuated in solution when the t Bu groups attached to phosphorus are exchanged for R = Ph or H, and we describe how mechanochemistry was used to overcome limited solution reactivity with K(H 3 BPPh 2 BH 3 ). Grinding three equivalents of K(H 3 BPPh 2 BH 3 ) with UI 3 (THF) 4 or LnI 3 (Ln = Ce, Pr, Nd) allowed homoleptic complexes with the empirical formulas U(H 3 BPPh 2 BH 3 ) 3 (1), Ce(H 3 BPPh 2 BH 3 ) 3 (2), Pr(H 3 BPPh 2 BH 3 ) 3 (3), and Nd(H 3 BPPh 2 BH 3 ) 3 (4) to be prepared and subsequently crystallized in good yields (50–80%). Single-crystal XRD studies revealed that all four complexes exist as dimers or coordination polymers in the solid-state, whereas 1 H and 11 B NMR spectra showed that they exist as a mixture of monomers and dimers in solution. Treating 4 with THF breaks up the dimer to yield the monomeric complex Nd(H 3 BPPh 2 BH 3 ) 3 (THF) 3 (4-THF). XRD studies revealed that 4-THF has one chelating and two dangling H 3 BPPh 2 BH 3 – ligands bound to the metal to accommodate binding of THF. In contrast to the results with K(H 3 BPPh 2 BH 3 ), attempting the same mechanochemical reactions with Na(H 3 BPH 2 BH 3 ) containing the simplest phosphinodiboranate were unsuccessful; only the partial metathesis product U(H 3 BPH 2 BH 3 )I 2 (THF) 3 (5) was isolated in poor yields. Here, despite these limitations, our results offer new examples showing how mechanochemistry can be used to rapidly synthesize molecular coordination complexes that are otherwise difficult to prepare using more traditional solution methods.
Metal borohydride complexes have long been the subject of intense fundamental interest because of their unconventional metal–ligand bonding that occurs via three-center, two-electron M–H–B bonds. This type of bonding implies significant delocalization of electron density over all three atoms, but the degree of orbital mixing between the metal and boron has been difficult to assess by direct experimental means. Herein, we demonstrate how ligand K-edge X-ray absorption spectroscopy (XAS) conducted at the B K-edge yields evidence of significant covalent M–H–B bonding with Zr and Hf. To accommodate the B K-edge XAS studies, which were conducted under ultra-high vacuum (<10 −8 torr), we prepared a series of new [Zr(RBH 3 ) 4 ] and [Hf(RBH 3 ) 4 ] complexes with substituents that attenuate volatility (R = benzyl, phenyl, mesityl, 2,4,6-triisopropylphenyl, and anthryl). 1 H and 11 B NMR spectroscopy, IR spectroscopy, and single-crystal X-ray diffraction (XRD) studies revealed metal and ligand dependent differences in the BH 3 chemical shifts that correlate to changes in M−B distances and select B–H vibrational stretching modes. The B K-edge XAS spectra of the Zr and Hf complexes yielded a pre-edge feature that was assigned as B 1s → M–H–B π* based on comparison to time-dependent density functional theory (TDDFT) calculations. The pre-edge transitions appear due to covalent mixing between boron and the metal, thereby demonstrating how B K-edge XAS can provide direct evidence of covalent three-center, two electron M–H–B bonding in borohydride complexes using boron as a spectroscopic reporter.
Herein we report an electronic structure investigation of neutral and oxidized Ru complexes containing a redox noninnocent N 2 S 2 ligand derived from o-phenylenediamide (L1). UV–vis spectroelectrochemistry (SEC) studies were conducted on the square pyramidal complex [Ru I I(L1)(PPh 3 )] (1) and the six-coordinate complexes [Ru I I(μ-BH 3 )(L1)(PPh 3 )] (2) – which has BH 3 bound in a metal–ligand cooperative (MLC) fashion across Ru and L1 – and [Ru II (L1)(PPh 3 )(MeCN)] (3). The SEC results yielded spectra assigned to singly and doubly oxidized 1 and 3, revealing electronic structure changes as a function of oxidation state and in response to the presence and absence of bound MeCN. By contrast, the SEC results of 2 showed that it rapidly loses MLC-bound BH 3 upon oxidation. The SEC results for 1 and 3 were compared to single-crystal XRD data and UV–vis, EPR, and P K-edge, S K-edge, and Ru L 3 -edge X-ray absorption spectroscopy (XAS) data collected on isolated samples of chemically oxidized 3. The data revealed that the first two oxidations are primarily localized on the ligand, which was supported by DFT and TDDFT calculations. DFT calculations for the doubly oxidized species revealed a singlet ground state with a singlet–triplet gap of 8.9 kcal/mol. CASPT2 calculations corroborated the DFT calculations and further revealed that the singlet ground state is multiconfigurational with 21% radical character. Collectively, the results establish redox formalisms and the underlying electronic structure of Ru complexes containing a noninnocent tetradentate ligand in different oxidation states.
σ-Hydrocarbyl complexes of the form [M(η 5 -PC 4 Me 4 ) 2 (μ-η 1 :η 6 -CH 2 Ph) 2 K(η 6 -arene)] (M = La, Ce, Pr, U, Np, Pu; arene = benzene or toluene) were synthesised in one-pot reactions from [MI 3 (THF) 4 ], or [U(BH 4 ) 3 (toluene)] (M = U). All complexes were examined by multinuclear ( 1 H, 13 C{ 1 H}, 31 P{ 1 H}) NMR and UV-vis-NIR spectroscopy, as well as single-crystal X-ray diffraction from which molecular metal–phosphorus bonds for Np and Pu, and a σ-hydrocarbyl metal–carbon bond for Pu, have been structurally authenticated.
Here, the crystal structures of CaB – Hn compounds with n = 1 – 12 in a pressure range of 50–300 GPa were studied using the genetic algorithm method and first-principles density-function theory calculations. Stable structures with stoichiometry of CaB H 6 and CaB H 7 were predicted in different pressure range. BH 4 , BH 5 , and BH 6 units were found to be the main motifs in these compounds. Moreover, metastable Imm2 CaB H 7 is dynamically stable above 180 GPa, with the formation of tetrahedral BH 4 unit surrounded by Ca atom and H 3 unit. Electron-phonon coupling (EPC) calculations reveal that the superconducting properties are closely related to the strong hydrogen-boron bonding of the BH 4 unit in Imm2, and T c can reach ~200 K at 200 GPa. As the major units, BH 4 , BH 5 , and BH 6 units exist in the Imm2, P 2 , and P2 1 /m phases of CaB H 7 at 300 GPa, respectively; the corresponding EPC parameter λ decreases with the increase of hydrogen content in CaB H 7 .
We present observational constraints on large-scale white noise (LSWN) in the cosmic density field, a phenomenon predicted to arise from non-linear mode coupling during cosmological evolution. Building on the theoretical framework of Paper I, where we demonstrated that non-linearities inevitably redistribute power from small to large scales through mode mixing, we confront these predictions with current cosmological data. We modify the CLASS Boltzmann code to incorporate a white noise component $k_\mathrm{BH}/k$ in the primordial power spectrum and perform parameter estimation using current cosmological data. The non-detection of excess power on the largest observable scales places stringent upper bounds: $k_\mathrm{BH} \leq 1.80 \times 10^{-13}~\mathrm{Mpc}^{-1}$ at 99% confidence. These constraints imply the primordial power spectrum must deviate from perfect scale invariance on small scales, either through a cutoff at $k_{\mathrm{cut}} \lesssim 3~\mathrm{pc}^{-1}$ or through running of the spectral index with $α_s \lesssim -0.015$. Our results demonstrate that LSWN provides a powerful probe of the primordial spectrum at scales orders of magnitude smaller than directly observable, offering unique constraints on early-universe physics.
Abstract In this research, anisotropic NdFeB + SmFeN hybrid and NdFeB bonded magnets are additively printed in a polyphenylene sulfide (PPS) polymer binder. Printed NdFeB + SmFeN PPS bonded magnets displayed excellent magnetic properties ( B r [remanence] = 6.9 kG [0.69 T], H cj [coercivity] = 8.3 kOe [660 kA/m], and BH max [energy product] = 9.9 MGOe [79 kJ/m 3 ]) with superior corrosion resistance and thermal stability. The anisotropic NdFeB bonded magnet shows a high coercivity of 14.6 kOe (1162 kA/m) with a BH max of 8.7 MGOe (69 kJ/m 3 ). The coercivity and remanence temperature coefficients for NdFeB + SmFeN hybrid bonded magnets are −0.10%/K and −0.46%/K, and for NdFeB bonded magnets are −0.14%/K and −0.53%/K in the range of 300–400 K, indicating that the hybrid bonded magnets are thermally stable. The average flux aging loss for hybrid magnets was also determined to be very stable over 2000 h at 448 K (175°C) in air with 2.04% compared to that of NdFeB magnets with 3.62%.
Abstract A dinuclear hafnium complex containing the parent imido ligand [(PN)(PNC)Hf=NH{μ 2 ‐K}] 2 ( 2 ) (PN − =(N‐(2‐P i Pr 2 ‐4‐methylphenyl)‐2,4,6‐Me 3 C 6 H 2 ; PNC 2− =(N‐(2‐P i Pr 2 ‐4‐methylphenyl)‐2,4,6‐CH 2 Me 2 C 6 H 2 ), was prepared by reduction of the bisazide trans‐[(PN) 2 Hf(N 3 ) 2 ] ( 1 ) with two equiv of KC 8 . Encapsulation of K + in 2 with crown‐ether or cryptand affords the first discrete salt [K(encap)][(PN)(PNC)Hf≡NH] (encap=18‐crown‐6(THF) 2 , 3 ; 2,2,2‐Kryptofix, 4 ), featuring a terminal parent imide and possessing some of the shortest Hf−N bond lengths known to date. DFT calculations revealed formation of 2 to proceed via an extremely basic monomeric nitrido, [(PN) 2 Hf≡N] − ( A ), having a computed p K BH+ of ∼57 followed by heterolytic splitting of an inert 1,2‐CH bond of a benzylic methyl group across the Hf≡N triple bond in A . An electronic structure analysis reveals A to possess a covalent Hf≡N triple bond and of super‐basic character. We also showcase reactivity of the Hf≡NH bond with various electrophiles.
In this study, a series of iridium hydride complexes featuring dihydrogen bonding are presented and shown to undergo rapid H + /H - exchange (1240 s -1 at 25 °C). We demonstrate that the H + /H - exchange rate can be modified by post-synthetic modification at a remote site using BH 3 , Zn(C 6 F 5 ) 2 , and [Me 3 O][BF 4 ]. This route provides a complementary strategy to traditional methods that rely on pre-metalation modifications to a metal's primary sphere.
Actinide complexes containing the simplest borohydrides (BH 4 ) 1- and (MeBH 3 ) 1- can exhibit remarkably highly volatility, which creates unique hazards and handling challenges, especially when making measurements on solid samples under vacuum. Here we describe efforts to prepare new actinide borohydride complexes with attenuated volatility by adding bulkier benzyl (Bn) and cyclohexyl (Cy) substituents to boron. Reactions of ThCl 4 , UI 3 (thf) 4 , and NdI 3 with the mixed alkali metal salt Li/K(BnBH 3 )(thf) n yielded Th(BnBH 3 ) 4 (thf) 2 , U(BnBH 3 ) 4 (thf) 2 , and K[Nd(BnBH 3 ) 4 ], respectively. Notable amongst these, the reaction with UI 3 (thf) 4 proceeds via oxidation of U(III) to U(IV) despite the presence of reducing borohydride ligands. Similarly, reactions of the same metal halides with four equivalents of Li(CyBH 3 )(Et 2 O) n yielded Th(CyBH 3 ) 4 , U(CyBH 3 ) 4 (thf) 2 , and [Li(Et 2 O) 3 ][Nd(CyBH 3 ) 4 ]. Single crystal X-ray diffraction studies of the M(BnBH 3 ) 4 (thf) 2 complexes with M = Th and U confirmed their formulations. Furthermore, the complexes have approximate D 2d point group symmetry and adopt bicapped hexagonal antiprismatic coordination geometries with axial thf ligands and κ 3 -BnBH 3 ligands bound in the equatorial plane. K[Nd(BnBH 3 ) 4 ] and [Li(Et 2 O) 3 ][Nd(CyBH 3 ) 4 ], which were prepared for comparison to U(III) complexes that were unsuccessfully targeted, were also structurally characterized to reveal complex anions with tetrahedral arrangements of trihydroborate ligands bound to Nd(III). Crystals obtained for Th(CyBH 3 ) 4 and U(CyBH 3 ) 4 (thf) 2 were not suitable for XRD studies, but 1 H and 11 B NMR spectra were consistent with their formulations. Collectively, these complexes represent rare examples of structurally characterized f-element trihydroborate complexes with carbon substituents other than methyl.
New detections of supermassive black hole (BH) candidates are used to update the observed correlation between BH mass M and the luminosity L(sub bulge) of the bulge component of the host galaxy. Our main purpose is to test whether the correlation is real or just the upper envelope of a distribution that extends to smaller Solar Mass. We also illustrate the following conclusions: 1 -- BH mass correlates much better with bulge luminosity than with the total luminosity of the galaxy. 2 -- BH mass correlates with the luminosity of the high-density central component in disk galaxies independent of whether that component is a classical bulge (essentially a mini-elliptical) or a pseudobulge (believed to form via inward transport of disk material). This conclusion is based on only three pseudobulges, so it needs to be checked. 3 -- The BH mass correlates with the velocity dispersion of the bulge component outside the region influenced by the BH. That is, it correlates with the depth of the potential well in which it lives. Our conclusions are consistent with the hypothesis that (pseudo)bulge formation and BH feeding are closely connected. To first order, present data do not show any dependence of M\bullet on the details of whether BH feeding happens rapidly during a collapse or slowly via secular evolution of the disk.
Quantum computation has the potential to revolutionize quantum chemistry through major speedups in computation times and an exponential reduction in computational resources. Here, we combine the symmetry-adapted Jordan–Wigner encoding based on the full Boolean symmetry group $\mathbb{Z}$$^{k}_{2}$ with our new implementation of the Xia–Bian–Kais (XBK) method for improving the efficiency of electronic structure theory calculations on quantum annealers, particularly by reducing the number of qubits needed to achieve the same accuracy. By providing a more extensive symmetry-adapted encoding (SAE) than previous work, we are able to simulate molecules larger than those previously reported that have been studied using methods developed for quantum annealers and without using an active space. We calculated the potential energy surfaces of H 2 , LiH, He 2 , H 2 O, O 2 , N 2 , Li 2 , F 2 , CO, BH 3 , NH 3 , and CH 4 , with the largest molecule in the STO-6G basis set requiring 16 qubits with our SAE, and compared them with full configuration interaction results. The application of SAE to the XBK method provides an exponential reduction in the size of the Hilbert space and scales well with the size of the problem. It does not introduce significant additional errors for even or large values of a key variational parameter that determines the number of ancilla qubits used in the XBK method’s Hamiltonian embedding, or for certain molecules such as He 2 and H 2 O. Here, we provide an explanation for this behavior and a recommendation on the usage of our method. In addition, we briefly discuss the potential of extracting electronic excited states from our method.
Following the discovery of high-temperature superconductivity in the La–H system, we studied the formation of new chemical compounds in the barium-hydrogen system at pressures from 75 to 173 GPa. Using in situ generation of hydrogen from NH 3 BH 3 , we synthesized previously unknown superhydride BaH 12 with a pseudocubic (fcc) Ba sublattice in four independent experiments. Density functional theory calculations indicate close agreement between the theoretical and experimental equations of state. In addition, we identified previously known P6/mmm-BaH 2 and possibly BaH 10 and BaH 6 as impurities in the samples. Ab initio calculations show that newly discovered semimetallic BaH 12 contains H 2 and H 3 – molecular units and detached H 12 chains which are formed as a result of a Peierls-type distortion of the cubic cage structure. Barium dodecahydride is a unique molecular hydride with metallic conductivity that demonstrates the superconducting transition around 20 K at 140 GPa.
Abstract In the last decade, there have been several discoveries of active galactic nuclei (AGN) in dwarf galaxies including an AGN in an ultracompact dwarf galaxy with a black hole mass >10 6 M ⊙ . However, finding a supermassive black hole (SMBH) in a dwarf low surface brightness (LSB) galaxy is rare. We report the discovery of a Seyfert type 2 class AGN that is associated with a nuclear SMBH of mass ∼6.5 × 10 6 M ⊙ in a dwarf LSB galaxy (μ 0,r > 23.8 mag arcsec −2 ) that we denote by MJ0818+2257. The galaxy was previously thought to be an outlying emission blob around the large spiral galaxy LEDA 1678924. In our current analysis, which includes the detection of the optical counterpart of MJ0818+2257, we study its ionized gas kinematics and find that the dynamical mass within the ionized gas disk is ∼5.3 × 10 9 M ⊙ . This is comparable to its stellar mass, which is ∼3 × 10 9 M ⊙ , and suggests that MJ0818+2257 is moderately dark matter dominated within the stellar disk. The SMBH-mass-to-galaxy-stellar-mass ratio isM BH /M(*) > 0.022, which is high compared to disk galaxies. Our detection of an SMBH in a bulgeless LSB dwarf galaxy raises questions about the growth of SMBHs in low-luminosity galaxies and suggests the possibility of detecting heavy seed black holes from early epochs in LSB dwarf galaxies in the low-redshift Universe.
Abstract Black hole (Bh) X-ray binaries cycle through different spectral states of accretion over the course of months to years. Although persistent changes in the Bh mass accretion rate are generally recognized as the most important component of state transitions, it is becoming increasingly evident that magnetic fields play a similarly important role. In this article, we present the first radiative two-temperature general relativistic magnetohydrodynamics simulations in which an accretion disk transitions from a quiescent state at an accretion rate of M ̇ ∼ 10 − 10 M ̇ Edd to a hard-intermediate state at an accretion rate of M ̇ ∼ 10 − 2 M ̇ Edd . This huge parameter space in mass accretion rate is bridged by artificially rescaling the gas density scale of the simulations. We present two jetted BH models with varying degrees of magnetic flux saturation. We demonstrate that in “standard and normal evolution” models, which are unsaturated with magnetic flux, the hot torus collapses into a thin and cold accretion disk when M ̇ ≳ 5 × 10 − 3 M ̇ Edd . On the other hand, in “magnetically arrested disk” models, which are fully saturated with vertical magnetic flux, the plasma remains mostly hot with substructures that condense into cold clumps of gas when M ̇ ≳ 1 × 10 − 2 M ̇ Edd . This suggests that the spectral signatures observed during state transitions are closely tied to the level of magnetic flux saturation.
We observed the X-ray nova A0620-00 with the Hubble Space Telescope (HST) Faint object Spectrograph 16 yr after its 1975 outburst. We present a single spectrum (1250-4750 A), which is approximately an average over a full 7.8 hr orbital cycle of the source. The continuum can be fitted approximately by a blackbody model with T = 9000 K and a small projected source area, which is approximately 1 % of the expected area of the accretion disk. AS0620-00 is faint in the far-UV band; its luminosity is comparable to the luminosity of the quiescent dwarf-nova accretion disk (i.e., excluding the white dwarf). By analogy with dwarf novae, the optical luminosity of the disk (M(sub nu) approximately = 7) and the orbital period of A0620-00 imply that the rate of mass transfer onto the outer disk in M(sub d) approximately 10(exp -10) solar mass/yr. We also observed A0620-00 with the ROSAT PSPC X-ray detector for 3 x 10(exp 4) s and detected a faint source (5 sigma) at the location of the X-ray nova. For an assumed blackbody spectrum the source temperature and luminosity are approximately 0.16 keV and 6 x 10(exp 30) ergs/s, respectively (d = 1 kpc). This luminosity implies that the rate of mass transfer into the black hole is extraordinarily small: M(sub BH) less than 5 x 10(exp -15) solar mass/yr. The much larger mass transfer rate onto the outer disk, and the UV/X-ray faintness of the inner disk confirm key predictions of the disk instability model for the nova outburst of A0620-00 published by Huang and Wheeler and by Mineshige and Wheeler.
The modern scenario of evolution of massive binary systems predicts the existence of a subclass of binary radio pulsars (PSRs) with black holes (BHs). Their Galactic number was evaluated as approximately 1 per 1000 single pulsars (Lipunov et al. 1994b). Distinctive properties of such binaries would be (1) mass of the unseen companion M(sub c) greater than 3-4 solar mass and (2) absence of eclipses of the pulsar radiation with no distinctive variance of the dispersion measure along the pulsar orbit. The pulsars themselves must be similar to standard isolated ones. The recently discovered binary 1 s pulsar PSR B0042-73 = PSR J0045-7319 in the Small Magellanic Cloud (SMC) with a massive companion in a highly elongated (eccentricity e =0.8) 51 day orbit (Kaspi et al. 1994) may be the first such pulsar with a BH. The paradoxical fact that the first pulsar discovered in the SMC proved to be in a binary system can be naturally understood if its companion actually is a 10-30 solar mass black hole. We illustrate this fact by the numerical calculation of evolution of radio pulsars after a star formation burst.