A Simple Synthesis of 2′,5′-Disubstituted-Spiro [Dihydroacridine 9(10H), 4′-Thiazolines] by the Reaction of Corresponding 3-(Acridin-9-Yl)-Thioureas with Methyl Bromoacetate and Bromoacetonitrile

A convenient method has been devised for the preparation of the spirodihydro-acridinethiazolines 5a-j by the treatment of thioureas 3a-e with methyl bromoacetate and bromoacetonitrile via non-isolable isothioureas 4a-j and their subsequent cyclization with methanolic sodium methoxide.     

Ni(bipy)2Ni(CN)4, a new type of one‐dimensional square tetra­cyano complex

The one‐dimensional structure of catena‐poly­[[bis(2,2′‐bi­pyri­dyl‐1κ²N,N′)‐μ‐cyano‐1:2κ²N:C‐di­cyano‐2κ²C‐di­nickel(II)]‐μ‐cyano‐C:N], [Ni₂(CN)₄(C₁₀H₈N₂)₂]_n, consists of infinite zigzag chains running parallel to the c axis. The chains are composed of paramagnetic [Ni(bipy)₂]²⁺ cations (bricks; nickel on a twofold axis) linked by diamagnetic [Ni(CN)₄]^2? anions (mortar; nickel on an inversion center) via bridging cyano groups. The bridging cyano groups occupy cis positions in the cation and trans positions in the anion, giving rise to a new previously unknown CT‐type chain (i.e. cis–trans‐type) among square tetra­cyano complexes. The coordination polyhedron of the paramagnetic Ni atom (twofold symmetry) is a slightly deformed octahedron with the two Ni—N(bipy) bonds in cis positions being somewhat longer [2.112 (3) Å] than the remaining four Ni—N bonds with a mean value of 2.065 (6) Å. The bond distances and angles in the anion have typical values.     

Total synthesis of (-)- and ent-(+)-vindoline and related alkaloids

A concise 11-step total synthesis of (-)- and ent-(+)-vindoline (3) is detailed based on a unique tandem intramolecular [4 + 2]/[3 + 2] cycloaddition cascade of a 1,3,4-oxadiazole inspired by the natural product structure, in which three rings and four C-C bonds are formed central to the characteristic pentacyclic ring system setting all six stereocenters and introducing essentially all the functionality found in the natural product in a single step. As key elements of the scope and stereochemical features of the reaction were defined, a series of related natural products of increasing complexity were prepared by total synthesis including both enantiomers of minovine (4), 4-desacetoxy-6,7-dihydrovindorosine (5), 4-desacetoxyvindorosine (6), and vindorosine (7) as well as N-methylaspidospermidine (11). Subsequent extensions of the approach provided both enantiomers of 6,7-dihydrovindoline (8), 4-desacetoxyvindoline (9), and 4-desacetoxy-6,7-dihydrovindoline (10).     

Novel example of a chain structure formed by 1,4-dioxane and cobalt(II) links. Chain [Co3(mu-OOCCF3)4(mu-H2O)2(OOCCF3)2(H2O)2(C4H8O2)].2C4H8O2

The trimer [Co3(mu-OOCCF3)4(mu-H2O)2(OOCCF3)2(H2O)2(C4H8O2)].2C4H8O2. (1) is composed of three tetragonally distorted Co(II) centers bridged by four trifluoroacetates and two bridging water molecules. 1,4-Dioxane is coordinated at a distance of 2.120(3) A from the terminal cobalt Co2; the remaining oxygen of this 1,4-dioxane links the terminal cobalt to a neighbor trimer, forming a one-dimensional chain. The crystal structure displays a network of hydrogen bonds between four noncoordinated 1,4-dioxane molecules and the coordinated terminal water molecules. The magnetic properties of 1 were analyzed with the use of the Hamiltonian including isotropic exchange interactions between real spins of a high-spin Co(II), spin-orbit coupling and a low-symmetry crystal field acting within the (4)T(1g) ground manifold of each cobalt ion. A weak antiferromagnetic exchange interaction between cobalt ions in 1 was found. The results of the magnetic model are in good agreement with the experimental observations.     

A novel two-dimensional Ni(II) fumarato complex: Solvothermal synthesis, crystal structure and magnetic properties

Dark green single crystals of [Ni(fum)(phen)] (fum = fumarato, phen = 1,10-phenanthroline) (1) have been prepared under solvothermal conditions. Its crystal structure exhibits two dimensional (2D) character. The formed layers are built of dimers of crystallographically non-equivalent Ni(II) atoms linked by bridging fumarato ligands; one is of the μ₄-bridge type with both carboxylato groups coordinated in syn-anti fashion while in the second one both carboxylate groups form a chelate-like coordination. Both Ni(II) atoms are hexa-coordinated in the cis-NiO₄N₂ form; two coordination positions are occupied by a N-bonded chelate phen molecule and four positions by oxygen atoms from the fum ligands. The layers are interconnected by π–π interactions operating between aromatic rings of the phen ligands. The analysis of the experimental thermodynamic data supports the structural assumptions and showed that magnetic subsystem of 1 can be approximated by an array of antiferromagnetic S = 1 dimers with easy-axis uniaxial magnetic anisotropy D comparable to intradimer exchange coupling J, D/J ≈ 1 and D/k_B = −6 K. The specific heat data clearly indicate the absence of a phase transition to the ordered state at least at temperatures down to 2 K.     

Near-field scanning optical microscopy local luminescence studies of rhodamine dye

This article presents results of near-field scanning optical microscope measurement of local luminescence of rhodamine 3B intercalated in montmorillonite samples. We focus on how local topography affects both the excitation and luminescence signals and resulting optical artifacts. The Finite Difference in Time Domain method (FDTD) is used to model the electromagnetic field distribution of the full tip-sample geometry including far-field radiation. Even complex problems like localized luminescence can be simulated computationally using FDTD and these simulations can be used to separate the luminescence signal from topographic artifacts.