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131.
Wittick LM Murray KS Moubaraki B Batten SR Spiccia L Berry KJ 《Dalton transactions (Cambridge, England : 2003)》2004,(7):1003-1011
A family of tetranuclear mixed-valent Mn(II)(2)/Mn(III)(2) complexes of type [Mn(4)(LH(2))(2)(LH)(2)(H(2)O)(x)(RCO(2))(2)](Y)2.nS has been synthesised and structurally characterised, where LH(3) = triethanolamine (N(CH(2)CH(2)OH)(3)), (R=CH(3), x=2, Y = CH(3)CO(2)-, n=2, S = H(2)O; 1), (R=C(6)H(5), x=0, Y=C(6)H(5)CO(2)-, n=1, S = CH(3)CN; 2), (R=C(2)H(5), x=0, Y=ClO(4)(-), n=0; 3). A common structural core was deduced from X-ray crystallography and consists of a rhomboidal (planar-diamond) array with two 7-coordinate Mn(II) "wingtip (w)" centres and two 6-coordinate Mn(III) "body (b)" centres. The Mn(III) ions are bridged to the Mn(II) ions by mu3-oxygen atoms from a deprotonated alcohol "arm" of each tridentate LH(2-) ligand and by mu2-oxygen atoms from each tetradentate LH(2)(-) ligand. The four nitrogen atoms from LH(2-) and LH(2)(-) groups, together with bridging and terminal carboxylates oxygens complete the outer coordination sites around the Mn atoms. A feature of these clusters is that they are linked together in the crystal lattice by hydrogen-bonding interactions involving a non-coordinated hydroxyl arm on each LH(2-) group. Detailed DC and AC magnetic susceptibility measurements and magnetisation isotherms have been made on the three complexes and show that intra-cluster ferromagnetic coupling is occurring between the S = 2 Mn(III) and S = 5/2 Mn(II) ions to yield S = 9 ground states. The g, J(bb) and J(wb) parameters have been deduced. Inter-cluster antiferromagnetic coupling was noted in and this influences the magnetisation versus field behaviour and the temperature and magnitude of the out-of-phase AC chi"M maxima in comparison to those observed for and. An Arrhenius plot of the reciprocal temperature of the maxima in chi"M obtained at different frequencies (10 to 1500 Hz), in the range 1.75 K to 4 K, against the natural logarithm of the magnetization relaxation rate (1/tau) yielded values of the activation energies and pre-exponential factors for two of these new tetranuclear single-molecule magnets (SMMs), and. The activation energies were compared with the potential energy barrier height, U, for magnetisation direction reversal (U = DS(2)) using the axial zero-field splitting parameter, D, deduced from the DC M/H isotherm analysis for these S = 9 species. The very small separation of S = 9 and 8 levels for these clusters highlights the limitations in the determination of D values from M/H data at low temperatures. 相似文献
132.
Infrared chemliuminescence techniques are applied to the study of vibrationally excited surface reaction products. The method is demonstrated by the detection of infrared emission from highly excited CO2 product molecules in the reaction of CO with O on a platinum surface. 相似文献
133.
Tunable laser I★(2P) quantum-yield measurements are presented for CH2I2 in the wavelength range 248–340 nm. The results suggest that a curve-crossing mechanism is operative in the dissociation. 相似文献
134.
C. H. Collins C. A. Bertran A. L. Pires Valente Priscila de A. Leone A. L. M. Murta K. E. Collins 《Chromatographia》1988,26(1):168-170
Summary Separation of perhalogenated compounds resulting from thermolysis, photolysis or radiolysis of mixtures of halogens in carbon tetrachloride was carried out by programmed temperature gas chromatography. Plots of relative retentions (to CBr4) vs the number of bromine atoms present for known compounds of the general formula CxBryClz (x=1 and 2; y+z=4 or 6) gave three linear correlations (all with r>0.99). These correlations permitted projections of the identities of reaction products for which no standards were available. These projections were later confirmed by CG-MS. *** DIRECT SUPPORT *** A0732166 00010 相似文献
135.
Luigi Pietro Battaglia Anna Bonamartini Corradi Sandra Ianelli 《Journal of chemical crystallography》1993,23(5):411-415
The crystal and molecular structure of the [N(2-ammoniumethyl)piperazinium]tetra-chloromonobromocuprate(II) monohydrate is reported. The crystals are monoclinic, space groupP21/c,Z=4, witha=9.560(2),b=9.240(3),c=18.270(7)Å,=99.20(2)°. The structure consists of discrete N(2-ammoniumethyl)piperazinium cations, uncoordinated water molecules and [CuCl4Br]3– anions, in which four coplanar chlorine atoms occupy the square-basal plane and one bromine atom the axial position, giving the copper(II) ion a moderately elongated square-pyramidal geometry. The structure was refined to a finalR index of 0.0765. 相似文献
136.
L. Menabue M. Saladini L. P. Battaglia A. Bonamartini Corradi G. Marcotrigiano P. Morini 《Journal of chemical crystallography》1987,17(3):313-321
Binary complexes of formula [M(II)(acgly)2(H2O)4] (M(II)=Co(II), Ni(II), acgly=N-acetylglycinate ion) were synthesized, and for the Co(II) complex the crystal and molecular structure was determined. The crystals are monoclinic, space groupP21/c,a=4.838(1),b=10.785(2),c=14.340(6) Å,=96.96(2)°,Z=2. The structure was solved by the heavy-atom method and refined through full-matrix least-squares calculations toR=0.0394 for 1069 observed reflections. The coordination around the cobalt atom is slightly elongated octahedral arising from one carboxylate oxygen of each of the two centrosymmetrically related monodentateN-acetylglycinate anions and four water molecules. 相似文献
137.
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139.
Laser deep engraving is one of the most promising technologies to be used in wood carver operations. In this method, a laser beam is used to ablate a solid wood bulk, following predetermined patterns. The sculpture is obtained by repeating this process on each successive thin layer. Obviously, in order to achieve larger material removal rates, the process needs a controllable variation of the depth to carve a 3D (three dimensional) profiles.The degree of precision of the shape, the removal rate and the surface quality during the engraving process strictly depend on the materials properties, the laser source characteristics and the process parameters.The aim of this work is to investigate the influence of the process parameters on the material removal rates by engraving panels made of different types of wood using a Q-switched diode-pumped Nd:YAG green laser working with a wavelength λ=532 nm. The examined parameters were: the mean power that depends on the pulse frequency, the beam speed and the number of laser scansions, also called repetitions. The working parameters and the engraved depth were related and an energy-based model was proposed in order to predict the latter.Experimental results showed that the Q-switched diode-pumped frequency-doubled Nd:YAG green laser can be successfully used to machine different types of wood, obtaining decorative drawing and 3D engraved geometries without burning. However, an accurate selection of the wood types and the process parameters is necessary in order to obtain deep engraving without carbonization and a homogeneous carving. 相似文献
140.