Catalytic efficacy of Schiff-base copper(II) complexes: Synthesis,X-ray structure and olefin oxidation

Three copper(II) Schiff-base complexes, [Cu(L¹)(H₂O)](ClO₄) (1), [Cu(L²)] (2) and [Cu(L³)] (3) have been synthesized and characterized [where HL¹ = 1-(N-ortho-hydroxy-acetophenimine)-2-methyl-pyridine], H₂L² = N,N′-(2-hydroxy-propane-1,3-diyl)-bis-salicylideneimine and H₂L³ = N,N′-(2,2-dimethyl-propane-1,3-diyl)-bis-salicylideneimine]. The structure of complex 1 has been determined by single crystal X-ray diffraction analysis. In complex 1, the copper(II) ion is coordinated to one oxygen atom and two nitrogen atoms of the tridentate Schiff-base ligand, HL¹. The fourth coordination site of the central metal ion is occupied by the oxygen atom from a water molecule. All the complexes exhibit high catalytic activity in the oxidation reactions of a variety of olefins with tert-butyl-hydroperoxide in acetonitrile. The catalytic efficacy of the copper(II) complexes towards olefin oxidation reactions has been studied in different solvent media.     

Binding of inorganic cations by p-sulfonatocalix[4]arene monitored through competitive fluorophore displacement in aqueous solution

A new working principle for detecting inorganic cation binding by water-soluble calix[4]arenes involves the displacement of a fluorescent azoalkane as guest. Fluorescence regeneration is observed for various metal ions, and binding of monovalent cations (alkali and ammonium) to p-sulfonatocalix[4]arene is detected and quantified for the first time.     

The coordination polymers poly[μ‐4,4′‐bipyridyl‐di‐μ‐formato‐copper(II)] and catena‐poly[[[diaqua(1‐benzofuran‐2,3‐dicarboxylato)copper(II)]‐μ‐1,2‐di‐4‐pyridylethane] dihydrate]

The title compounds, [Cu(CHO₂)₂(C₁₀H₈N₂)]_n, (I), and {[Cu(C₁₀H₄O₅)(C₁₂H₁₂N₂)(H₂O)₂]·2H₂O}_n, (II), are composed of one‐dimensional linear coordination polymers involving copper(II) ions and bidentate bipyridyl species. In (I), the polymeric chains are located on twofold rotation axes at (x, x, 0) and are arranged in layered zones centered at z = 0, , ½ and parallel to the ab plane of the tetragonal crystal. Weak coordination of the formate anions of one layer to the copper centers of neighboring layers imparts a three‐dimensional connectivity to this structure. In (II), the polymeric chains propagate parallel to the a axis of the crystal. Noncoordinated water molecules link the chains through O—H...O hydrogen bonding in directions perpendicular to c, imparting to the entire structure three‐dimensional connectivity. The metal ions adopt distorted octahedral and square‐based pyramidal environments in (I) and (II), respectively. This study indicates that, under the given conditions, extended coordination involves Cu^II centers associating with the bipyridyl ligands rather than with the competing benzofurandicarboxylate entities.     

Square‐grid coordination networks of (5,10,15,20‐tetra‐4‐pyridylporphyrinato)zinc(II) in its clathrate with two guest molecules of 1,2‐dichlorobenzene: supramolecular isomerism of the porphyrin self‐assembly

The title compound, (5,10,15,20‐tetra‐4‐pyridylporphyrinato)zinc(II) 1,2‐dichlorobenzene disolvate, [Zn(C₄₀H₂₄N₈)]·2C₆H₄Cl₂, contains a clathrate‐type structure. It is composed of two‐dimensional square‐grid coordination networks of the self‐assembled porphyrin moiety, which are stacked one on top of the other in a parallel manner. The interporphyrin cavities of the overlapping networks combine into channel voids accommodated by the dichlorobenzene solvent. Molecules of the porphyrin complex are located on crystallographic inversion centres. The observed two‐dimensional assembly mode of the porphyrin units represents a supramolecular isomer of the unique three‐dimensional coordination frameworks of the same porphyrin building block observed earlier. The significance of this study lies in the discovery of an additional supramolecular isomer of the rarely observed structures of metalloporphyrins self‐assembled directly into extended coordination polymers without the use of external ligand or metal ion auxiliaries.     

Single end-on azido bridged 1D chain copper(II) complex: Synthesis,X-ray crystal structure and catalytic activity in homogeneous epoxidation of cyclooctene

A new azido derivative of a NNO donor tridentate Schiff-base copper(II) complex, [CuL(μ_1,1-N₃)]_n (1) (HL = 1-(N-ortho-hydroxyacetophenimine)-2-(N-ethyl)aminoethane), containing a single end-on μ_1,1-azido bridged 1D infinite chain has been synthesized and characterized. X-ray single crystal structure analysis reveals that the complex [CuL(μ_1,1-N₃)]_n (1) is a 1D chain in which neighboring Cu(II) chromophores are related by glide planes and linked by single azido bridges in the EO mode. No measurable magnetic interaction was evidenced in the complex [CuL(μ_1,1-N₃)]_n (1) through variable temperature magnetic susceptibility measurements (10–300 K). The complex was used as an active catalyst for the epoxidation of cyclooctene using tert-butyl-hydroperoxide as an oxidant. The catalytic activity of the complex has been compared in a series of solvents. The results show that in acetonitrile medium, the epoxide was produced in high yield with high selectivity.     

Controlled construction of metal-organic frameworks: hydrothermal synthesis, X-ray structure, and heterogeneous catalytic study

The role of pH in the formation of metal-organic frameworks (MOFs) has been studied for a series of magnesium-based carboxylate framework systems. Our investigations have revealed the formation of five different zero-dimensional (0D) to three-dimensional (3D) ordered frameworks from the same reaction mixture, merely by varying the pH of the medium. The compounds were synthesized by the hydrothermal method and characterized by single-crystal X-ray diffraction. Increase of the pH of the medium led to abstraction of the imine hydrogen from the ligand and a concomitant increase in the OH(-) ion concentration in the solution, facilitating the construction of higher dimensional framework compounds. A stepwise increase in pH resulted in a stepwise increase in the dimensionality of the network, ultimately leading to the formation of a 3D porous solid. A gas adsorption study of the 3D framework compound confirmed its microporosity with a BET surface area of approximately 450?m(2) g(-1). Notably, the 3D framework compound catalyzes aldol condensation reactions of various aromatic aldehydes with acetone under heterogeneous conditions.     

Cucurbituril Encapsulation of Fluorescent Dyes

The potential of cucurbiturils, water-soluble macrocyclic host molecules composed of glycoluril units, for tuning the properties of fluorescent dyes and advancing new applications is illustrated. Cucurbit[7]uril (CB7), which presents a particularly attractive derivative due to its intermediary size and high water solubility, has been shown to display a variety of advantageous effects on fluorescent dyes, which include increased fluorescence intensity and brightness, enhanced photostability, protection towards fluorescence quenchers, solubilization, and deaggregation. Particularly noteworthy is the prolongation of the fluorescence lifetimes of different dyes, which can be traced back to the low polarizability of the host cavity. In addition, the host serves as cation receptor, which causes a considerable shift of protonation equilibria and assists the protonation of fluorescent dyes. The latter effect can be exploited in the design of protolytic fluorophore displacement assays. The perspective of cucurbiturils as stabilizers for laser dyes, enhancement agents in time-resolved fluorescence (TRF) assays, contrast agents for fluorescence lifetime imaging (FLIM), and dyes for fluorescent collectors for solar cells is mentioned. Original experimental results for the effect of CB7 on the fluorescence properties of three dyes (Macrolex Yellow 10 GN, Dapoxyl, and 4-(dimethylamino)benzonitrile) are presented.     

End-on double azido bridged copper (II) complex with (N, N, O) schiff base: synthesis, structure and magnetic study

A rare asymmetric end-on double-bridged copper (II) azido complex with ∠Cu-N(azide)-Cu=89.1°, has been synthesized and characterized structurally and magnetically. The Cu-N(azide)-Cu angle is unusually low in the complex reported here in comparison to the same in other similar complexes. The magnetic study reveals that the interaction between metal centers in this complex is antiferromagnetic in nature. Though a ferromagnetic interaction between the metal centers is expected in the complex the coupling has actually been found to be antiferromagnetic, instead.