Oxo- and oxoperoxo-molybdenum(VI) complexes with aryl hydroxamates: synthesis, structure, and catalytic uses in highly efficient, selective, and ecologically benign peroxidic epoxidation of olefins

A solution obtained by dissolving MoO3 in H2O2 reacts separately with secondary hydroxamic acids (viz., N-benzoyl N-phenyl hydroxamic acid (BPHAH), N-benzoyl N-ortho-, -meta-, -para-tolyl hydroxamic acids, (BOTHAH, BMTHAH, and BPTHAH, respectively), and N-cinnamoyl N-phenyl hydroxamic acid (CPHAH) affording [MoO(O2)(BPHA)2] (1), [MoO(O2)(BOTHA)2] (2), [MoO(O2)(BMTHA)2] (3), [MoO(O2)(BPTHA)2] (4), and [Mo(O)2(CPHA)2](5), respectively. The O and O2 are situated cis to each other in 2-4, but in each case, they are disordered and distributed over four sites. This disorder does not exist in the 6-coordinate cis dioxo complex 5, to which crude MoO(O2)(CPHA)2 (5') was converted during recrystallization. An aqueous molybdate solution readily reacts with all those hydroxamic acids producing [Mo(O)2(hydroxamate)2] (6). While 2, 3, and 4 possess a very distorted pentagonal bipyramidal structure, 5 has a distorted octahedral geometry. In the solid state, as well as in solution, 5 exists as two apparently enantiomerically related molecules differing in the orientation of the pendant phenyl rings. To emphasize that the formation and structural uniqueness of 5 compared to 1-4 is caused by the influence of the cinnamoyl residue, one compound of the 6 series, namely, [Mo(O)2(BPHA)2] (6A), was structurally characterized to prove directly that the special stereochemical properties of 5 rely on the special electronic structure of CPHA- ligand. Complexes 1-5, as well as 6, show high potential and selectivity as catalysts in the epoxidation of olefins at room temperature in the presence of NaHCO3 as a promoter and H2O2 as a terminal oxidant. A comparative epoxidation study has been performed to determine the relative efficiency of the catalysts. To make the epoxidation method cost effective, a study to optimize the use of H2O2 has also been performed. To obtain evidence in favor of our suggested mechanism to this homogeneous olefin --> epoxide conversion, it was necessary to synthesize a peroxo-rich compound, namely, [MoO(O2)2BMTHA]- (7), but the attempted synthesis culminated in the isolation of [MoO(O2)2(C6H5COO)]- (8), obviously, via the hydrolysis of coordinated BMTHA.     

Crystal structure of manganese-rich variety of eudialyte from Suchina Hill,India, and manganese ordering in eudialyte-group minerals

The crystal structure of eudialyte of hydrothermal genesis from Sushina Hill, India, where it was found associated with potassium feldspathoid, albite, aegirine, and nepheline, has been solved by X-ray diffraction analysis. One specific feature of the chemical composition of this mineral is a low content of CaO (7–8.5 wt %) and an elevated manganese content (9–10.5 wt % MnO). When compared with eudialytes of magmatic genesis, this eudialyte is enriched in Nb, Sr, Y, and rare earth elements (REEs). It is described within the sp. gr. R3m, with the unit-cell parameters a = 14.2483(3) Å and b = 30.294(1) Å; R = 4.7%. The idealized formula (Z = 3) is (Na,□,Sr)₁₅(Ca,Mn)₆Mn₃(Si,Nb)₂Zr₃[Si₂₄O₇₂](OH,Cl,H₂O)_5.5. It is established that Mn atoms occupy three sites: two subsites in five-vertex polyhedra M2a and M2b, spaced by a distance of 0.87 Å and characterized by occupancies of 0.51 and 0.49, respectively, and the M1 site in the octahedron of six-membered ring, jointly with Ca and REE. With allowance for the established features of chemical composition and structure, the mineral under study can be considered as a strontium-rich variety of kentbrooksite.     

Influence of steric factors on exciplex energy and magnetic field effect

With the advent of spin chemistry, magnetic field effect (MFE) on exciplex luminescence has emerged as an important domain of research. MFE is a diffusion controlled phenomenon and hence is solvent dielectric (epsilon) dependent. It maximizes at a particular epsilon (epsilon(max)) for a specific exciplex system. Various attempts have been made to explain the variation of this epsilon(max) from one exciplex to another. In our present work we have succeeded for the first time to enmark the energy of exciplex (E(ex)) as the prime factor in determining the epsilon(max). We have indicated a definite inverse correlation (1:1) between epsilon(max) and E(ex). We have also tried to correlate some parameters that are important in exciplex formation, e.g. Charton's steric constant (nu(c)), repulsive energy (R(e)) and E(ex).     

Post-assembly Functionalization of Organoplatinum(II) Metallacycles via Copper-free Click Chemistry

We describe the use of a strain-promoted copper-free click reaction in the post-self-assembly functionalization of organoplatinum(II) metallacycles. The coordination-driven self-assembly of a 120° cyclooctyne-tethered dipyridyl donor with 60° and 120° di-Pt(II) acceptors forms molecular rhomboids and hexagons bearing cyclooctynes. These species undergo post-self-assembly [3+2] Huisgen cycloaddition with a variety of azides to give functionalized ensembles under mild conditions.     

Application of INAA for phyto-accumulation study of selenium by chickpea plant

The phyto-accumulation efficacy of selenium (Se) from soil by chickpea plant is reported. Chickpea plants were grown in soil having different concentrations (1–4 mg kg^?1) of Se. Samples of soil and different parts of chickpea plants in Se rich soil were analyzed for determination of Se concentrations by instrumental neutron activation analysis (INAA). Samples were irradiated in self-serve facility of CIRUS reactor, BARC, Mumbai at a neutron flux of the order of 10¹³ cm^?2 s^?1. The gamma activity at 264.7 keV of ⁷⁵Se (119.8 d) was measured using a 45% relative efficiency HPGe detector coupled to MCA. Dependence of Se distribution in soil and plants on its spiking concentration was evaluated in this work. The Se concentrations determined in plant parts grown in control soil and in soil spiked with Se (4 mg kg^?1) are in the range of 0.6–0.8 and 65–68 mg kg^?1 respectively.     

Fluid flow and heat transfer characteristics for a square prism (blockage ratio = 0.1) placed inside a wind tunnel

Experimental investigations in fluid flow and heat transfer have been carried out to study the effect of wall proximity due to flow separation around a square prism at Reynolds number 2.6 × 10⁴, blockage ratio 0.1, different height-ratios and various angles of attack. The static pressure distribution has been measured on all faces of the square prism. The results have been presented in the form of pressure coefficient, drag coefficient for various height-ratios. The pressure distribution shows positive values on the front face whereas on the rear face negative values of the pressure coefficient have been observed. The positive pressure coefficient for different height-ratios does not vary too much but the negative values of pressure coefficient are higher for all points on the surface as the bluff body approaches towards the upper wall of the wind tunnel. The drag coefficient decreases with the increase in angle of attack as the height-ratio decreases. The maximum value of drag coefficient has been observed at an angle of attack nearly 50° for the square prism at all height-ratios. The heat transfer experiments have been carried out under constant heat flux condition. Heat transfer coefficient are determined from the measured wall temperature and ambient temperature and presented in the form of Nusselt number. Both local and average Nusselt numbers have been presented for various height-ratios. The variation of local Nusselt number has been shown with non-dimensional distance for different angles of attack. The variation of average Nusselt number has also been shown with different angles of attack. The local as well as average Nusselt number decreases as the height-ratio decreases for all non-dimensional distance and angle of attack, respectively, for the square prism. The average Nusselt number for the square prism varies with the angle of attack. But there is no definite angle of attack at which the value of average Nusselt number is either maximum or minimum.     

Two (Z)‐N‐aryl‐3‐benzylideneisoindolin‐1‐ones

Two isoindolin‐1‐one derivatives, (Z)‐3‐benzyl­idene‐N‐phenyl­isoindolin‐1‐one, C₂₁H₁₅NO, (II), and (Z)‐3‐benzyl­idene‐N‐(4‐methoxy­phenyl)­isoindolin‐1‐one, C₂₂H₁₇NO₂, (III), were synthesized by the palladium‐catalysed heteroannulation. The mol­ecules of both compounds have a Z configuration. The interplanar angles between the five‐ and six‐membered rings of the isoindolinone moiety in (II) and (III) are 1.66 (11) and 2.26 (7)°, respectively. The phenyl rings at the N‐position in (II) and (III) are twisted out of the C₄N ring plane by 62.77 (11) and 67.10 (7)°, respectively. The substitutions at the N and C‐3 positions of the isoindolinone system have little influence on the molecular dimensions of the resulting compounds.