Organotin(IV) derivatives of mercaptosuccinic and thiodiacetic acids

Di- and tri-organotin(IV) complexes of general formula R₂SnAH, (R₃Sn)₂AH, R₂SnB, (R₃Sn)₂B (A=dianion of mercaptosuccinic acid; B=dianion of thiodiacetic acid; R=Me, Et, nPr, nBu, nOct in R₂Sn and nBu in R₃Sn) have been synthesized and characterized by elemental analysis, IR and ¹H and ¹³C NMR spectroscopy. These data support the preferential binding of sulphur over carboxylate by tin(IV) in R₂SnAH and (R₃Sn)₂AH. R₂SnAH complexes are assigned pentacoordinated bridged polymeric trigonal bipyramidal geometry whereas (R₃Sn)₂AH complexes are monomeric with trigonal bipyramidal geometry at tin arising from a bidentate carboxylate group at one tin atom and from weak bonding via Sn←O?C at the other tin atom. In R₂SnB and (R₃Sn)₂B, tin(IV) binds to two carboxylate groups in a unidentate and a bidentate manner respectively, resulting in tetracoordinated and pentacoordinated structures. Potential uses of these compounds are discussed.     

Mössbauer studies of solid state photolysis of barium and strontium tris(oxalato) ferrates (III)

Solid state photolysis of strontium and barium tris(oxalato) ferrate(III) was done under a medium pressure lamp and investigated with Mössbauer spectroscopy. The product [Fe^II(C₂O₄) (H₂O)₂]^2? formed during photolysis is found to be quite stable and does not convert to ferric state on long standing in air.     

Pyrimidine analogues. Reaction of 1,3-dimethyl-6-hydroxylaminopyrimidine-2,4-dione with nitrophenyl isothiocyanates

Reaction between 6-hydroxylaminouracil and nitrophenylisothiocyanates gave new purines which could be of biological interest.     

Controlling coherent and incoherent plasma emissions: the role of electron plasma waves

We present results of our two-pulse time resolved measurements of second harmonic and hard X-ray generation in the interaction of an intense (10¹⁶ Wcm^-2, 100 fs, 800 nm) laser with a preplasma generated on a solid surface. The time-resolved study as a function of both plasma scale length and laser polarization brings out interesting features of electron plasma wave dynamics. The harmonic and X-ray emission show contrary behavior and we interpret the results in terms of Resonance Absorption and Wave-Breaking mechanisms. Simple optimization of the scale length of the preplasma and the polarization parameters of the main pulse results in significant enhancements, up to a factor of 100 for X-rays and 10 for the second harmonic respectively. These results can help us understand the governing mechanisms for higher harmonic generation and for fast particle generation, aiding the development of more efficient sources. PACS 52.35.Fp; 42.65.Ky; 52.38.Ph     

Structure of 1,2,3,4,9,9a-hexahydro-6,9a-diphenyl-1H-pyrimido[2,1-c][1,4]thiazine

The title compound C₁₈H₂₀N₂S is monoclinic, witha=10.256(2),b=7.470(4),c=21.377(4) Å,=101.52(2)°,z=4 and space groupP2₁/n. The structure was solved by direct methods, and refined by weighted full-matrix least squares. The refinement, based on 1373 reflections withI2.5 (I), converged to a finalR of 0.062 (R _w=0.060). The conformation of the thiazine ring is a distorted half chair, and that of the pyrimidine ring is a distorted chair. All nonhydrogen intermolecular distances are greater than 3.5 Å.     

Diorganotin(IV) derivatives of N-phthaloyl amino acids

Twentyfour complexes of the general formulae (R₂SnL₂ and R₂(L)SnOSn(L)R₂ (L = N-phthaloyl derivative of l-leucine, dl-alanine and l-phenylalanine; R = CH₃, C₅H₅, n-C₄H₉) and n-C₈H₁₇) have been prepared by reacting ligand and dialkyltin(IV) oxide in 2/1 and 1/1 (ligand/metal) molar ratio. These complexes have been characterised by elemental analysis and structures assigned with the help of infrared, ¹H NMR and ¹¹⁹Sn Mössbauer spectroscopy. These data support six-coordinated distorted octahedral structures with two alkyl groups in trans positions.     

Dichlorosilylene: Rate constant for reaction with carbon monoxide and nitrous oxide

The absolute rate constanss for the gas-phase reactions of 1,1-dichlorosilylene with carbon monoxide and nitrous oxide have been determined using the flash photolysts-kinetic absorpiton spectroscopy technique. The bimolecular rate constant values at 25° C are: $$\begin{gathered} k\left( {Cl_2 Si + CO} \right) = \left( {6.3 \pm 0.7} \right) \times 10^8 M^{ - 1} s^{ - 1} \hfill \\ k\left( {Cl_2 Si + N_2 O} \right) = \left( {5.7 \pm 0.3} \right) \times 10^8 M^{ - 1} s^{ - 1} \hfill \\ \end{gathered} $$      

Energy and intensity distributions of 279 keV multiply scattered photons in bronze — an inverse response matrix approach

An inverse response matrix converts the observed pulse-height distribution of a NaI(Tl) scintillation detector to a true photon spectrum. This also results in extraction of intensity and energy distributions of multiply scattered events originating from interactions of 279 keV photons with thick targets of bronze. The observed pulse-height distributions are a composite of singly and multiply scattered events in addition to bremmstrahlung originating from slowing down of Compton and photo-electrons in thick targets. To evaluate the contribution of multiply scattered events, the spectrum of singly scattered events contributing to inelastic Compton peak is reconstructed analytically. The optimum thickness (saturation depth), at which the number of multiply scattered events saturate, has been evaluated in different energy bin meshes chosen for scintillation detector response unfolding. Monte Carlo calculations based upon the package developed by Bauer and Pattison (Compton scattering experiments at the HMI (1981), HMI-B 364, pp. 1–106) supports the present experimental results.      

Study of aluminium-modified Ge2Sb2Te5 thin films for the applicability as phase-change storage device material

Electrical and optical studies have been carried out on aluminium-modified Ge₂Sb₂Te₅ thin films to check its applicability as an active material in optical and electrical memory storage devices. Five polycrystalline bulk samples were prepared with compositions: Al_x(Ge₂Sb₂Te₅)_1?x; x = 0, 0.08, 0.14, 0.21, 0.25. Amorphous thin films were deposited from the polycrystalline bulk by thermal evaporation. Temperature-dependent resistance shows the increase in crystallization temperature of Ge–Sb–Te films on aluminium addition. Activation energy for conduction, conductivity, optical band gap, coefficient of refraction and extinction coefficient are studied with respect to Al content in both amorphous and crystalline phases of Ge–Sb–Te alloy films.     

MR imaging of cervical spine motion with HASTE

The HASTE (half-Fourier acquisition single-shot turbo spin-echo) technique delivers images with T2-weighting in about half a second and could be ideal for fast dynamic studies when T2-weighting is needed. We evaluated cardiac-triggered HASTE to study cervical spine flexion/extension. The cervical spines of ten asymptomatic volunteers were studied during flexion/extension motion on a 1.5 Tesla imager using a cardiac triggered version of the HASTE technique. Midline sagittal images were acquired every 2 to 3 s during neck flexion and extension. Image quality was compared to traditional T2-weighted Turbo spin-echo. The study duration per flexion/ extension was typically less than 20 seconds and well tolerated. The cardiac-gated T2-weighted HASTE images compared favorably to the traditional T2-weighted TSE images in quality and overall anatomic detail. Range of motion averaged: flexion 30 degrees (range 8 degrees -48 degrees) and extension 23 degrees (range 0 degrees -57 degrees ). Greatest motion occurred in the lower cervical spine (C4-C7). At the intervertebral discs the canal diameter, anterior and posterior CSF spaces were widest in neutral position and decreased with flexion and extension. Therefore, Cardiac-gated T2 HASTE sequences provide diagnostic and time-efficient dynamic MR images of cervical spine motion.