Complex three-dimensional platinum-indium networks in the ternary indides Dy2Pt7In16 and Tb6Pt12In23

Well crystallized samples of Dy₂Pt₇In₁₆ and Tb₆Pt₁₂In₂₃ were synthesized by an indium flux technique. Arc-melted precursor alloys with the starting compositions ∼DyPt₃In₆ and ∼TbPtIn₄ were annealed with a slight excess of indium at 1200 K followed by slow cooling (5 K/h) to 870 K. Both indides were investigated by X-ray diffraction on powders and single crystals: Cmmm, a=1211.1(2), b=1997.8(3), c=439.50(6) pm, wR2=0.0518, 1138 F² values, 45 variable parameters for Dy₂Pt₇In₁₆ and C2/ma=2834.6(4), b=440.05(7), c=1477.1(3) pm, β=112.37(1)°, wR2=0.0753, 2543 F² values, 126 variable parameters for Tb₆Pt₁₂In₂₃. The platinum atoms in the terbium compound have a distorted trigonal prismatic coordination. In Dy₂Pt₇In₁₆, trigonal and square prismatic coordination occur. The shortest interatomic distances are observed for Pt-In followed by In-In contacts. Considering these strong interactions, both structures can be described by complex three-dimensional [Pt₇In₁₆] and [Pt₁₂In₂₃] networks. The networks leave distorted pentagonal channels in Dy₂Pt₇In₁₆, while pentagonal and hexagonal channels occur in Tb₆Pt₁₂In₂₃. The crystal chemistry and chemical bonding of the two indides are briefly discussed.     

Efficient stereoselective alkenylation through a homolytic domino reaction involving a 1,5 sulfur-to-carbon translocation

An effective method for cis-stereoselective attachment of functionalized alkenyl appendages to sp3 carbon is reported. This method is based on a free-radical process, involving a sequence of addition-elimination steps, resulting in alkenyl group transposition from divalent sulfur to a prochiral carbon radical. Absolute stereoselectivity is secured since the new carbon-carbon bond is formed in a ring-closure reaction leading to a bridged bicyclic carbon-centered radical intermediate. The latter undergoes beta-scission of the C-S bond, leaving the alkenyl side chain in its predetermined position while releasing a thiyl radical. This thiyl radical is trapped by tri-n-butylstyryltin, affording a (styrylsulfanyl)methyl side chain and a tri-n-butyltin radical that continues the chain. When 2-(alkenylsulfanyl)methyl-4-bromo(or iodo)pyrrolidines were used as starting materials 2,4-cis-disubstituted 4-alkenyl-2-(styrylsulfanyl)methylpyrrolidines were obtained as products (70-90% yield). Tri-n-butylstyryltin was used rather then the more common n-Bu3SnH as tin radicals sources because the latter led predominantly to bridged bicyclic 3-thia-6-azabicyclo[3.2.1]octanes (up to 77% yield). An additional advantage of using tri-n-butylstyryltin derives from the discovery that the resulting styrylsulfide functionality is an excellent synthetic equivalent to the formyl group. Thus, using a Pummerer-type oxidative desulfurization, 4-cis-alkenyl-proline aldehydes were obtained.     

New rare earth metal-rich indides RE14Ni3In3 (RE=Sc, Y, Gd-Tm, Lu)—synthesis and crystal chemistry

The rare earth-nickel-indides RE₁₄Ni₃In₃ (RE=Sc, Y, Gd-Tm, Lu) were synthesized from the elements by arc-melting and subsequent annealing. The compounds were investigated on the basis of X-ray powder and single crystal data: Lu₁₄Co₂In₃ type, P4₂/nmc, Z=4, a=888.1(1), c=2134.7(4), wR2=0.0653, 1381 F² values, 63 variables for Sc_13.89Ni_3.66In_2.45; a=961.2(1), c=2316.2(5), wR2=0.0633, 1741 F² values, 64 variables for Y_13.84Ni_3.19In_2.97; a=965.3(1), c=2330.5(5), wR2=0.0620, 1765 F² values, 63 variables for Gd₁₄Ni_3.29In_2.71; a=956.8(1), c=2298.4(5), wR2=0.0829, 1707 F² values, 64 variables for Tb_13.82Ni_3.36In_2.82; a=951.7(1), c=2289.0(5), wR2=0.0838, 1794 F² values, 64 variables for Dy_13.60Ni_3.34In_3.06; a=948.53(7), c=2270.6(1), wR2=0.1137, 1191 F² values, 64 variables for Ho_13.35Ni_3.17In_3.48; a=943.5(1), c=2269.1(5), wR2=0.0552, 1646 F² values, 64 variables for Er_13.53Ni_3.14In_3.33; a=938.42(7), c=2250.8(1), wR2=0.1051, 1611 F² values, 64 variables for Tm_13.47Ni_3.28In_3.25; a=937.3(1), c=2249.6(5), wR2=0.0692, 1604 F² values, 64 variables for Tm_13.80Ni_3.49In_2.71; and a=933.4(1), c=2263.0(5), wR2=0.0709, 1603 F² values, 64 variables for Lu_13.94Ni_3.07In_2.99. The RE₁₄Ni₃In₃ indides show significant Ni/In mixing on the 4c In1 site. Except the gadolinium compound, the RE₁₄Ni₃In₃ intermetallics also reveal RE/In mixing on the 4c RE1 site, leading to the refined compositions. Due to the high rare earth metal content, the seven crystallographically independent RE sites have between 9 and 10 nearest RE neighbors. The RE₁₄Ni₃In₃ structures can be described as a complex intergrowth of rare earth-based polyhedra. Both nickel sites have a distorted trigonal-prismatic rare earth coordination. An interesting feature is the In2-In2 dumb-bell at an In2-In2 distance of 304 pm (for Gd₁₄Ni_3.29In_2.71). The crystal chemical peculiarities of the RE₁₄Ni₃In₃ indides are briefly discussed.     

Anisotropic Nucleation,Growth and Ripening under Stirring—A Phenomenological Model

The anisotropic formation of elongated metal-oxide aggregates in water under intensive stirring is analyzed. It is treated in terms of anisotropic ballistically mediated aggregation kinetics in open systems. The basic kinetic equations describing the stages of homogeneous nucleation, independent growth, and ripening of the aggregates are formulated for the open system under the external influence with the stirring intensity as the main parameter governing the process. The most significant elongation of the aggregates is shown to evolve at the ripening stage.     

Univariate Global Optimization with Multiextremal Non-Differentiable Constraints Without Penalty Functions

This paper proposes a new algorithm for solving constrained global optimization problems where both the objective function and constraints are one-dimensional non-differentiable multiextremal Lipschitz functions. Multiextremal constraints can lead to complex feasible regions being collections of isolated points and intervals having positive lengths. The case is considered where the order the constraints are evaluated is fixed by the nature of the problem and a constraint i is defined only over the set where the constraint i−1 is satisfied. The objective function is defined only over the set where all the constraints are satisfied. In contrast to traditional approaches, the new algorithm does not use any additional parameter or variable. All the constraints are not evaluated during every iteration of the algorithm providing a significant acceleration of the search. The new algorithm either finds lower and upper bounds for the global optimum or establishes that the problem is infeasible. Convergence properties and numerical experiments showing a nice performance of the new method in comparison with the penalty approach are given. This research was supported by the following grants: FIRB RBNE01WBBB, FIRB RBAU01JYPN, and RFBR 04-01-00455-a. The author thanks Prof. D. Grimaldi for proposing the application discussed in the paper. An erratum to this article is available at .     

Quantum Dot-Antibody Conjugates for Immunofluorescence Studies of Biomolecules and Subcellular Structures

Journal of Fluorescence - Quantum dots, or nanoscale semiconductors, are one of the most important materials for various research and development purposes. Due to their advantageous...