Electro-magnetic-field-induced flow and interfacial instabilities in confined stratified liquid layers

The electro-magneto-hydrodynamic (EMHD) flow and instabilities engendered by the Lorenz force arising from interaction between externally applied perpendicular electric and magnetic fields are investigated in layers of two immiscible liquids in a channel. A new finite wave-number EMHD instability mode is uncovered by the Orr–Sommerfeld analysis, in addition to the interfacial and shear modes which also arise in the pressure-driven flows. Thus, EMHD can be controlled for micro-channel transport, heat and mass transfer, mixing, micro-emulsion generation, etc.     

Palladium-mediated reductive Mizoroki-Heck cyclization strategy for the regioselective formation of dibenzoazocinone framework

The synthesis of dibenzoazocine framework through palladium-mediated reductive Mizoroki-Heck cyclization has been described. The procedure is simple, straightforward, and regioselective.     

Ion acoustic solitons in a streaming relativistic plasma with negative ions

We analyze the effect of a nonzero streaming velocity of both positive and negative ions on the formation of solitary waves in a relativistic plasma. The thermodynamic situation is considered to be isothermal. For various values ofu _0/C andn _o/nowe obtain the variations of the amplitude and the width of the solitary wave.     

Preferential mode of cyclization of tetrahydrofuran amino acids containing peptides: some theoretical insights

Theoretical insights have been provided for the observed preference of cyclodimerization over intramolecular cyclization reactions in linear tripeptides containing “2,5‐cis” (2S,5R)‐tetrahydrofuran amino acid as well as in those containing “2,5‐trans” (2S,5S)‐tetrahydrofuran amino acid, using quantum chemical methods. The geometries of species involved as well as the feasibility of cyclization reactions are studied at the B3LYP/6‐31G(d,p) level of theory in gas phase as well as in solvent phase. Thermodynamic data from Hessian calculations favor the intermolecular cyclization. Analysis of optimized geometries reveals the existence of additional stabilizing hydrogen bonding interactions in intermolecularly cyclized products. The existence of these second‐order interactions is substantiated by topological (atoms in molecules (AIM)) and natural bond orbital (NBO) analyses. Such interactions are absent in the intramolecular cyclization products. Further justification for the presence of stabilizing interactions in intermolecularly cyclized products comes from the molecular electrostatic potentials and electron density surfaces. Kinetic control favoring the intermolecularly cyclized products due to additional entropy of activation in the intramolecular case is surmised. Copyright © 2009 John Wiley & Sons, Ltd.     

Rhenium chemistry of azooximes: oxygen atom transfer, azoimine chelation, and imine-oxime contrast

The concerned azooximes (L1OH, 1) are of type p-X-C6H4C(N2Ph)(NOH) (X = H, Me, Cl). The reaction of [Re(MeCN)Cl3(PPh3)2] with [Ag(L1OH)(L1O)] in cold dichloromethane-acetonitrile solvent has furnished the green colored ionized azoimine complex [ReV(O)Cl(PPh3)2(L1)](PF6), 2. In effect L1O- has undergone oxidative addition, the oxygen atom being transferred to the metal site. Upon treatment of [ReV(NPh)Cl3(PPh3)2] with L1OH in solution, the neutral azoimine complex [ReV(NPh)Cl3(L1H)], 3, resulted due to the spontaneous transfer of the oxime oxygen atom to a PPh3 ligand, which is eliminated as OPPh3. In contrast, the oxime of 2-acetylpyridine (L2OH, 4) did not undergo oxygen atom transfer and simply afforded the imine-oxime complex [ReV(NC6H4Y)Cl2(PPh3)(L2O)], 5, upon reacting with [ReV(NC6H4Y)Cl3(PPh3)2] (Y = H, Me, Cl). The spectral and electrochemical properties of 2, 3, and 5 and the structures of three representative compounds are reported. In the cation of 2 (X = H) the two PPh3 ligands lie trans to each other and the equatorial plane is defined by the five-membered azoimine chelate ring and the oxo and chloro ligands. The oxo ligand which forms a model triple bond (Re-O length 1.616(6) A) lies cis to the imine-N atom. In 3 (X = Cl) the ReCl3 fragment has meridional geometry and the imido nitrogen lies trans to the imine nitrogen of the planar azoimine chelate ring. In 5 x H2O (Y = Me), the Cl, oximato-N, and P atoms define an equatorial plane and the pyridine-N lies trans to the imido-N. The water of crystallization is hydrogen bonded to the oximato oxygen atom (O...O, 2.829(5) A). Reaction models in which chelation of the azooxime precedes oxygen atom transfer are proposed on the basis of oxophilicity of trivalent rhenium, Lewis acid activity of pentavalent rhenium, electron withdrawal by the azo group, and observed relative disposition of ligands in products.     

Unusual Stabilization of an Intermediate Spin State of Iron upon the Axial Phenoxide Coordination of a Diiron(III)–Bisporphyrin: Effect of Heme–Heme Interactions

The binding of a series of substituted phenols as axial ligands onto a diiron(III)? bisporphyrin framework have been investigated. Spectroscopic characterization revealed high‐spin states of the iron centers in all of the phenolate complexes, with one exception in the 2,4,6‐trinitrophenolate complex of diiron(III)? bisporphyrin, which only stabilized the pure intermediate‐spin (S=3/2) state of the iron centers. The average Fe? N (porphyrin) and Fe? O (phenol) distances that were observed with the 2,4,6‐trinitrophenolate complex were 1.972(3) Å and 2.000(2) Å, respectively, which are the shortest and longest distances reported so far for any Fe^III? porphyrin with phenoxide coordination. The alternating shift pattern, which shows opposite signs of the chemical shifts for the meta versus ortho/para protons, is attributed to negative and positive spin densities on the phenolate carbon atoms, respectively, and is indicative of π‐spin delocalization onto the bound phenolate. Electrochemical data reveals that the E_1/2 value for the Fe^III/Fe^II couple is positively shifted with increasing acidity of the phenol. However, a plot of the E_1/2 values for the Fe^III/Fe^II couple versus the pK_a values of the phenols shows a linear relationship for all of the complexes, except for the 2,4,6‐trinitrophenolate complex. The large deviation from linearity is probably due to the change of spin for the complex. Although 2,4,6‐trinitrophenol is the weakest axial ligand in the series, its similar binding with the corresponding Fe^III? monoporphyrin only results in stabilization of the high‐spin state. The porphyrin macrocycle in the 2,4,6‐trinitrophenolate complex of diiron(III)? bisporphyrin is the most distorted, whilst the “ruffling” deformation affects the energy levels of the iron d orbitals. The larger size and weaker binding of 2,4,6‐trinitrophenol, along with heme? heme interactions in the diiron(III)? bisporphyrin, are responsible for the larger ring deformations and eventual stabilization of the pure intermediate‐spin states of the iron centers in the complex.     

Oximato bridged RhIII2MII and RhIIIMI species (MII = Mn, Co, Ni; MI = Cu, Ag)

The reaction of [RhCl₂(HPhL)(PhL)] with M^II(ClO₄)₂·6H₂O in presence of alkali has furnished trinuclear [RhCl₂(PhL)₂]₂M(H₂O)₂·H₂O (HPhL is phenylazobenzaldoxime; M = Mn, Co, Ni). A similar reaction with M^I(PPh₃)₂NO₃ yielded binuclear [RhCl₂(PhL)₂]M(PPh₃)₂ (M = Cu, Ag). In these molecules the oximato group acts as a bridge between Rh^III (bonded at N) and M^II or M^I (bonded at O). In structurally characterized [Rh^IIICl₂(PhL)₂]₂Mn(H₂O)₂.H₂O the centrosymmetric distorted octahedral MnO₆ coordination sphere is spanned by four oximato oxygen atoms and two water molecules lying in trans position. In the lattice the neighbouring molecules are held together by H₂O⋯H₂O⋯H₂O hydrogen bonds generating infinite zigzag chains. The manganese atoms lie parallel to the C-axis, the shortest Mn...Mn distance being 7.992 ?. Magnetic exchange interactions if any are small as seen in room temperature magnetic moments. The manganese system displays a strong EPR signal near g = 2.00. In the complex [RhCl₂(PhL)₂]Cu(PPh₃)₂ the copper atom is coordinated to two oximato oxygen atoms and the two phosphorus atoms in a distorted tetrahedral geometry. The softness of the phosphine ligand is believed to sustain the stable coordination of hard oximato oxygen to soft Cu^I. The coordination sphere of the RhIII atom in both the complexes is uniformly trans-RhN₄Cl₂.     

Use of HNO(3) as the source of NO to prepare a nitric oxide complex of ruthenium

Reaction of cis-Ru(bisox)(2)Cl(2), where bisox is 4,4,4',4'-tetramethyl-2,2'-bisoxazoline, with HNO(3) in 1 : 4 molar proportion in boiling water under N(2) atmosphere and subsequent addition of an excess of NaClO(4).H(2)O yields [Ru(bisox)(HL)(NO)](ClO(4))(NO(3)) (1). HL is a hydrolysed form of bisox where one of the oxazoline rings opens up. X-Ray crystallography shows that 1 contains an octahedral RuN(5)O core. HL binds the metal through an imino N, an amide N and an alcoholic O atom. Reaction of cis-Ru(bisox)(2)Cl(2) with an excess of NaNO(2) in water gives cis-Ru(bisox)(2)(NO(2))(2) (2). On acidification by HClO(4) in methanol, is smoothly converted to cis-[Ru(bisox)(2)(NO(2))(NO)](ClO(4))(2) (3) due to equilibrium (1). [formula: see text] (1) The X-ray crystal structures of 2 and 3 have also been determined. NO binds Ru in 1 and 3 linearly. The Ru-NO bond length in 1 is 1.764(13) A and that in 3 is approximately 1.78 A. All the three complexes have been characterised by FTIR, NMR and ESIMS. The NO stretching frequencies in 1 and 3 are 1897 and 1936 cm(-1) respectively. While 3 reverts back to 2 readily in presence of OH(-) [equilibrium (1)], 1 does not react with OH(-). It is concluded that while in the reaction of cis-Ru(bisox)(2)Cl(2) with HNO(3), bisox is hydrolysed following abstraction of NO from HNO(3), generation of the nitrosyl complex 3 via reaction (1) is not accompanied with such hydrolysis.     

Synthesis,structure, optical and magnetic properties of [CrL(X)3], {L = 4′-(2-pyridyl)-2,2′:6′,2″-terpyridine; X = Cl,N3, NCS}

Three complexes of composition [CrL(X)₃], where L = 4′-(2-pyridyl)-2,2′:6′,2″-terpyridine and X = Cl⁻, N₃⁻, NCS⁻ are synthesized. They are characterized by IR, UV–Vis, fluorescence, EPR spectroscopic, and X-ray crystallographic studies. Structural studies reveal that the Cr(III) ion is coordinated by three N atoms of L in a meridional fashion. The three anions occupy the other three coordination sites completing the mer-N₃Cl₃ (1) and mer-N₃N₃ (2 and 3), distorted octahedral geometry. The Cr–N2 has a shorter length than the Cr–N1 and Cr–N3 distances and the order Cr–N(NCS⁻) < Cr–N(N₃⁻) < Cr–Cl is observed. They exhibit some of the d–d transitions in the visible and intra-ligand transitions in the UV regions. The lowest energy d–d transition follows the trend [CrLCl₃] < [CrL(N₃)₃] < [CrL(NCS)₃] consistent with the spectrochemical series. In DMF, they exhibit fluorescence having π → π^∗ character. All the complexes show a rhombic splitting as well as zero-field splitting (zfs) in X-band EPR spectra at 77 K.