Synthesis,X-ray crystal structure and magnetic study of the 1D {[Cu(N,N-diethyl-1,2-ethanediamine)(μ1,5-dca)(dca)]}n complex

A new complex, {[CuL(μ_1,5-dca)(dca)]}_n (1), has been synthesized from the reaction of Cu(NO₃)₂ · 3H₂O, N,N-diethyl-1,2-ethanediamine (L) and sodium dicyanamide (Nadca) in aqueous medium. Single crystal X-ray analysis reveals that the complex has a 1D infinite zigzag chain structure in which copper(II) ions are bridged by single dicyanamide ligands in an end-to-end fashion. The chains propagate parallel to the crystallographic b-axis and they are stacked one upon another along the c-axis. The coordination environment of the copper(II) centers are distorted square-pyramidal. Of the four coordination sites of the basal plane of the square-pyramid, two are occupied by the nitrogen atoms of the diamine and the remaining two sites are occupied by the terminal nitrogen atoms of the bridging dca groups. One terminal nitrogen atom of a monodentate dca group occupies the apical position of the coordinated polyhedra. [CuL(dca)] units are then connected to each other through a μ_1,5-dca bridge to form 1D chains. The variable temperature magnetic susceptibility measurements evidenced weakly antiferromagnetic interactions (J = −0.35 cm⁻¹) in {[CuL(μ_1,5-dca)(dca)]}_n (1).     

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.     

Synthesis,X-ray Crystal Structure and Magnetic Study of a μ<Subscript>1,5</Subscript>-dca Bridged Dimeric Copper(II) Complex

Abstract  

The reaction of aqueous solution of copper(II) nitrate trihydrate with methanolic solution of the ligand HL and sodium dicyanamide in aqueous medium results in the formation of a dimeric dicyanamide complex of Cu(II), [Cu₂(L)₂(μ_1,5-dca)₂]·0.5 H₂O (1) [where L = 1-(N-salicylideneamine)-2-(N-ethyl)-aminoethane]. The single crystal X-ray structure reveals that the asymmetric unit of complex 1 consists of two dinuclear units. The complex crystallizes in the monoclinic space group P2₁ with cell parameters, a = 9.8828(19) ?, b = 19.018(4) ?, c = 14.851(3) ?, (°) = 92.979(6) and Z = 4. χ_M T, stays in the 0.94–0.91 cm³ mol⁻¹ K range between 300 and 2 K, which is slightly higher than the spin-only value (χ_M T = 0.75 cm³ mol⁻¹ K) for two uncoupled copper(II) (S = ?) ions assuming g = 2.0, thus indicating that the complex 1 behaves like a simple paramagnet.     

A cyano-bridged bimetallic ferrimagnet: Synthesis,X-ray structure and magnetic study

Mixing of trans-[Mn(cyclam)Cl₂]Cl (cyclam = 1,4,8,11-tetraazacyclotetradecane) and potassium hexacyanochromate (K₃[Cr(CN)₆]) aqueous solutions instantaneously yields a 1D infinite chain complex {[Mn(cyclam)(μ-CN)₂Cr(CN)₄]·H₂O}_n (1). The crystal structure of 1, crystallizing in the monoclinic system with space group P2₁/n has been solved from X-ray powder diffraction data following direct space approach and refined by the Rietveld method. The structure analysis of 1 reveals alternating [Cr(CN)₆]³⁻ and [Mn(cyclam)]³⁺ ions generating one-dimensional polymeric (–Cr–CN–Mn–NC–)_n chain propagating along the [0 0 1] direction. The coordination environment of both the metal ions, Mn(III) and Cr(III), is octahedral. While a notable distortion in the coordination environment around Mn(III) centers was observed in complex 1, Cr(III) centers have suffered no such distortion. A ferrimagnetic interaction between the heterobimetallic centers was evidenced through variable temperature magnetic susceptibility measurements. The AC susceptibility measurement reveals that the compound 1 undergoes spontaneous ferrimagnetic ordering. Ferrimagnetic ordering has been rarely observed among the cyano-bridged compounds in the previous studies.     

Diastereomeric discrimination in the lifetimes of Norrish Type II triplet 1,4-biradicals and stereocontrolled partitioning of their reactivity (Yang cyclization versus Type II fragmentation)

The stereochemistry at C2 and C3 carbons controls the partitioning of triplet 1,4-biradicals of ketones 2 among various pathways. Differences in the major reaction pathways, for example, cyclization (syn) and fragmentation (anti), adopted by the diastereomeric 1,4-radicals of ketones 2 have permitted unprecedented diastereomeric discrimination in their lifetimes to be observed by nanosecond laser flash photolysis. From quantum yield measurements and transient lifetime data, the absolute rate constants for cyclization and fragmentation of a pair of diastereomeric triplet 1,4-biradicals have been determined for the first time.     

Porous magnesium carboxylate framework: synthesis, X-ray crystal structure, gas adsorption property and heterogeneous catalytic aldol condensation reaction

A new three-dimensional alkaline-earth metal-organic framework (MOF) compound, [Mg(Pdc)(H(2)O)](n) (1) (H(2)Pdc = pyridine-2,5-dicarboxylic acid), has been synthesized and structurally characterized by single crystal X-ray diffraction analysis. Compound 1 features a 3D porous framework afforded by the Mg(2)-diad centers through formation of interconnected chair like structural motifs. A nitrogen adsorption study confirms the microporosity of compound 1 with a BET surface area of 211 ± 12 m(2) g(-1). Upon dehydration, the BET surface area of 1 is enhanced to a value of 463 ± 36 m(2) g(-1) due to removal of coordinated water molecule. After rehydration, the compound reverts to its original form as evidenced by powder X-ray diffraction and IR spectroscopic analysis and N(2) sorption measurement. Compound 1 retains its pore structure with a variable BET surface area in several cycles of dehydration and rehydration processes indicating robustness of the framework in [Mg(Pdc)(H(2)O)](n) (1). Compound 1 catalyzes the aldol condensation reactions of various aromatic aldehydes with acetone and cyclohexanone in heterogeneous conditions. Notably, the catalytic activity of the compound is enhanced upon dehydration. The catalyst can be recycled and reused several times without significant loss of activity.     

Syntheses, structures, and magnetic properties of diphenoxo-bridged M(II)Ln(III) complexes derived from N,N'-ethylenebis(3-ethoxysalicylaldiimine) (M = Cu or Ni; Ln = Ce-Yb): observation of surprisingly strong exchange interactions

A series of heterodinuclear Cu(II)Ln(III) and Ni(II)Ln(III) complexes, [M(II)L(1)Ln(III)(NO(3))(3)] (M = Cu or Ni; Ln = Ce-Yb), with the hexadentate Schiff base compartmental ligand N,N'-ethylenebis(3-ethoxysalicylaldiimine) (H(2)L(1)) have been synthesized and characterized. The X-ray crystal structure determinations of 13 of these compounds reveal that they are all isostructural. All of these complexes crystallize with the same orthorhombic P2(1)2(1)2(1) space group with closely similar unit cell parameters. Typically, the structure consists of a diphenoxo-bridged 3d-4f dinuclear core, self-assembled to two dimensions due to the intermolecular nitrate...copper(II) or nitrate...nickel(II) semicoordination and weak C-H...O hydrogen bonds. Despite that, the metal centers of the neighboring units are well separated (the ranges of the shortest intermolecular contacts (A) are (M...M) 7.46-7.60, (Ln...Ln) 8.56-8.69, and (M...Ln) 6.12-6.20). Variable-temperature (5-300 K) magnetic susceptibility measurements of all the complexes have been made. The nature of exchange interactions in the Cu(II)Ln(III) systems has been inferred from the Deltachi(M)T versus T plots, where Deltachi(M)T is the difference between the values of chi(M)T for a Cu(II)Ln(III) system and its corresponding Ni(II)Ln(III) analogue. Ferromagnetic interactions seem to be exhibited by the Cu(II)Gd(III), Cu(II)Tb(III), Cu(II)Dy(III), Cu(II)Ho(III), Cu(II)Tm(III), and Cu(II)Yb(III) complexes, while, for the Cu(II)Er(III) complex, no definite conclusion could be reached. On the other hand, among the lower members of the series, the complexes of Ce(III), Nd(III), and Sm(III) exhibit antiferromagnetic interactions, while the Cu(II)Pr(III) and Cu(II)Eu(III) analogues behave as spin-uncorrelated systems. The observations made here vindicate the proposition of Kahn (Inorg. Chem. 1997, 36, 930). The Deltachi(M)T versus T plots also suggest that, for most of the Cu(II)Ln(III) complexes, the exchange interactions are fairly strong, which probably could be related to the small dihedral angle (ca. 4 degrees) between the CuO(2) and LnO(2) planes.     

Syntheses, structures, absorption and emission properties of a tetraiminodiphenol macrocyclic ligand and its dinuclear Zn(II) and Pb(II) complexes

Synthesis of a Robson type macrocyclic ligand [H₄L](ClO₄)₂ (1) obtained on condensation of 2,6-diformyl-4-methylphenol and 2,2′-dimethyl-1,3-diaminopropane, template synthesis of a dinuclear lead(II) complex [Pb^II₂L(NO₃)₂] (2), synthesis of a dinuclear zinc(II) complex [Zn^II₂L(NO₃)(H₂O)](ClO₄) (3) through metal substitution reaction and synthesis of another dinuclear zinc(II) complex [Zn^II₂L(H₂O)₂](ClO₄)₂·(H₂O)₂ (4) obtained directly from 1 are described in the present study. Crystal structure determinations of 1 and 3 have been carried out. Both the compounds 1 and 3 crystallize in the orthorhombic system with the space groups Fdd2 and P2₁2₁2, respectively. Spectrophotometric and spectrofluorometric titrations of 1 with triethylamine as well as with zinc(II) acetate are also reported.