A Sharp-Interface Immersed Boundary Method with Improved Mass Conservation and Reduced Spurious Pressure Oscillations

A method for reducing the spurious pressure oscillations observed when simulating moving boundary flow problems with sharp-interface immersed boundary methods (IBMs) is proposed. By first identifying the primary cause of these oscillations to be the violation of the geometric conservation law near the immersed boundary, we adopt a cut-cell based approach to strictly enforce geometric conservation. In order to limit the complexity associated with the cut-cell method, the cut-cell based discretization is limited only to the pressure Poisson and velocity correction equations in the fractional-step method and the small-cell problem tackled by introducing a virtual cell-merging technique. The method is shown to retain all the desirable properties of the original finite-difference based IBM while at the same time, reducing pressure oscillations for moving boundaries by roughly an order of magnitude.     

Probing the Reactivity and Radical Nature of Oxidized Transition Metal-Thiolate Complexes by Mass Spectrometry

Transition metal thiolate complexes such as [PPN]⁺[RuL₃]^- (PPN?=?bis(triphenylphosphoranylidene) ammonium and L?=?diphenylphosphinobenzenethiolate) are known to undergo addition reactions with unsaturated hydrocarbons via the formation of new C-S bonds in solution upon oxidation. The reaction mechanism is proposed to involve metal-stabilized thiyl radical intermediates, a new type of distonic ions such as [RuL₃]⁺ ion in the case of [PPN]⁺[RuL₃]^-. This study presents the reactivity and structure investigation of [RuL₃]⁺ by mass spectrometry (MS) in conjunction with ion/molecule reactions. The addition reactions of [RuL₃]⁺ with alkenes or methyl ketones in the gas phase are indeed observed, in agreement with the proposed mechanism. Such reactivity is also maintained by several fragment ions of [RuL₃]⁺, indicating the preserved thiyl diradical core structure is responsible for the addition reaction. The thiyl radical nature of [RuL₃]⁺ was further verified by the ion/molecule reaction of [RuL₃]⁺ with dimethyl disulfide, in which the characteristic CH₃S? transfer occurs, both at atmospheric pressure and also at low pressure (~mTorr). These results provide, for the first time, clear mass spectrometric evidence of the radical nature of [RuL₃]⁺ (i.e., the distonic ion structure of [RuL₃]⁺), arising from the oxidation of non-innocent thiolate ligands of the complex [PPN]⁺[RuL₃]^-. Similar thiolate complexes, including ReL₃ and NiL₂, were also examined. Although reactions of oxidized ReL₃ or NiL₂ with CH₃SSCH₃ take place at atmospheric pressure, the corresponding reaction did not occur in vacuum. Consistent with these data, the addition of ethylene was not observed either, indicating lower reactivities of [ReL₃]⁺ and [NiL₂]⁺ in comparison to [RuL₃]⁺.      

Dissociation of homonuclear diatomic halogens via multireference coupled cluster calculations

We have computed the potential energy surfaces (PESs) of F₂, Cl₂, Br₂, and I₂ using the size-extensive state specific multireference coupled cluster (SS-MRCC) method. The MR character of the system considered here at large distances and the presence of low-lying intruder states are known to be the major causes of incorrect or inaccurate predictions of the PES. The SS-MRCC theory is tailored to treat degeneracies of varying extent while bypassing the intruder problem. The quality of the computed PES has been gauged by computing spectroscopic constants. The calculated properties show a good agreement with available experimental data and the errors in the calculated molecular properties compare favourably with the most elaborate current-generation calculations of the literature. The accuracy of the computed PES of F₂ is such that it has been proved to calculate the vibrational spectrum of the 22 levels with a minimum and maximum absolute deviation of 2 and 57 cm^?1, respectively, from the experimental values. The highly satisfactory performance of the SS-MRCC method, vis-a-vis the other sophisticated methods, in describing the vibrational levels is noticeable for one of the more difficult systems such as F₂ clearly indicates that the present method is reliable in studying the vibrational energy levels.     

Improved virtual orbital multireference Møller-Plesset study of the ground and excited electronic states of protonated acetylene, C2H3+

The ground state geometries and associated normal mode frequencies of the classical and nonclassical protonated acetylene ion, i.e., the vinyl cation C(2)H(3) (+), are computed using the complete active space self-consistent field and improved virtual orbital (IVO) complete active space configuration interaction methods. In addition, the minimum-energy reaction path for the classical to nonclassical interconversion is determined (as are excitation energies) using the IVO modification of multireference Moller-Plesset (MRMP) perturbation theory. The IVO-MRMP treatment predicts the nonclassical structure to be 4.8 kcalmol more stable than the classical one, which is consistent with other high level theoretical estimates. The proton affinity of acetylene from the IVO-MRMP treatment (154.8 kcalmol) also agrees well with experiment (153.3 kcalmol) and with earlier CASPT2 calculations (154.8 kcalmol). We further report geometries and vibrational frequencies of low lying excited states of C(2)H(3) (+), which have not been observed and/or studied before. Comparisons with previous highly correlated calculations further demonstrate the computational efficiency of the IVO-MRPT methods.     

Strategic Synthesis of Heptacoordinated FeIII Bifunctional Complexes for Efficient Water Electrolysis

In this research, highly efficient heterogeneous bifunctional (BF) electrocatalysts (ECs) have been strategically designed by Fe coordination (C_R) complexes, [Fe₂L₂(H₂O)₂Cl₂] (C1) and [Fe₂L₂(H₂O)₂(SO₄)].2(CH₄O) (C2) where the high seven C_R number synergistically modifies the electronic environment of the Fe centre for facilitation of H₂O electrolysis. The electronic status of Fe and its adjacent atomic sites have been further modified by the replacement of −Cl⁻ in C1 by −SO₄²⁻ in C2 . Interestingly, compared to C1 , the O−S−O bridged C2 reveals superior BF activity with extremely low overpotential (η) at 10 mA cm⁻² (140 mV_OER, 62 mV_HER) and small Tafel slope (120.9 mV dec⁻¹_OER, 45.8 mV dec⁻¹_HER). Additionally, C2 also facilitates a high-performance alkaline H₂O electrolyzer with cell voltage of 1.54 V at 10 mA cm⁻² and exhibits remarkable long-term stability. Thus, exploration of the intrinsic properties of metal–organic framework (MOF)-based ECs opens up a new approach to the rational design of a wide range of molecular catalysts.     

Completing an extension of Tunnell's theorem

We look at a special case of a familiar problem: Given a locally compact group G, a subgroup H and a complex representation π₊ of G how does π₊ decompose on restriction to H. Here G is GL⁺(2,F), where F is a nonarchimedian local field of characteristic not two, K a separable quadratic extension of F, GL⁺(2,F) the subgroup of index 2 in GL(2,F) consisting of those matrices whose determinant is in NK/F(K^∗), π₊ is an irreducible, admissible supercuspidal representation of GL⁺(2,F) and H=K^∗ under an embedding of K^∗ into GL(2,F).     

Theoretical study on the electronic states of formylcarbene (HC.CHO) and triplet ketene (H2CCO) and the ultraviolet absorption spectra attributable to these molecules

The adiabatic energies, vibrational frequencies, and geometries of the ground and excited electronic states of formylcarbene and the triplet electronic states of ketene are calculated employing the state-of-the art ab initio methods. With the help of these calculations, certain ultraviolet (UV) absorption bands observed in the flash photolysis of oxazole and iso-oxazole are assigned to formylcarbene and triplet ketene.     

Reusable amine-based structural motifs for green house gas (CO2) fixation

A series of compounds with an amine based structural motif (ASM) have been synthesized for efficient atmospheric CO(2) fixation. The H-bonded ASM-bicarbonate complexes were formed with an in situ generated HCO(3)(-) ion. The complexes have been characterized by IR, (13)C NMR, and X-ray single-crystal structural analysis. ASM-bicarbonate salts have been converted to pure ASMs in quantitative yield under mild conditions for recycling processes.     

Synthesis and Crystal Structure of [Cu(BDBPH)(ClO<Subscript>4</Subscript>)<Subscript>2</Subscript>] (BDBPH = Butane-2,3-dione bis(2′-pyridylhydrazone)

Abstract  

Butane-2,3-dione bis(2′-pyridylhydrazone) (BDBPH), a Schiff-base condensate, was synthesized by 1:2 mol ratio condensation of butane-2,3-dione with 2-hydrazino pyridine in dehydrated methanol. BDBPH has been characterised by C, H and N microanalyses, FT-IR, ¹H NMR and UV–Vis spectra. Reaction of 1:1 stoichiometric proportion of BDBPH with copper(II)perchlorate hexahydrate in methanol affords a mononuclear copper(II) complex, [Cu(BDBPH)(ClO₄)₂] (1). 1 crystallizes in the monoclinic space group P [`1] \overline{1} with a = 8.4230(2), b = 9.7869(3), c = 12.3508(3) ?, α = 103.784(2), β = 90.900(2), γ = 94.906(2)^°, V = 984.51(5) ?³ and Z = 2. The copper(II) compound is octahedral and one-electron paramagnetic. Bond Valence Sum (BVS) model calculation was also performed to assign the oxidation number of the copper center.     

Dinuclear PdII complexes bearing mixed NHC/Py/PPh3 donor set ligands: Catalytic applications and electrochemical investigations

Bimetallic palladium(II) complexes containing classical NHC donor ligands are becoming increasingly popular owing to their various catalytic applications. However, examples of the aforementioned complexes with mixed NHC/PPh₃ ligands are still rare. Bimetallic palladium(II) complexes possessing these mixed ligands are described starting from a C2-symmetric bis-imidazolium salt containing 4,4′-substituted central biphenyl ring. All the palladium(II) complexes have been tested as precatalysts in α-arylation of oxindole and Suzuki–Miyaura coupling reactions. The complex composed of mixed NHC/PPh₃ donor ligands shows superior catalytic activity compared with the corresponding PEPPSI type complexes when applied in α-arylation of oxindole. The dinuclear complexes display better activity compared with the mononuclear complexes. The preliminary electrochemical measurements show the facile oxidation of Pd^II in the presence of combined NHC/PPh₃ ligands compared with a combination of NHC/Py ligands.