Spectroscopy study on the photochromism of Schiff bases N,N'-bis(salicylidene)-1,2-diaminoethane and N,N'-bis(salicylidene)-1,6-hexanediamine

The photochromism of Schiff bases N,N'-bis(salicylidene)-1,2-diaminoethane (BSE) and N,N'-bis(salicylidene)-1,6-cyclohexanediamine (BSH) was studied by steady-state and time-dependent fluorescence, UV Vis absorption spectroscopy and theoretical chemistry calculations. The experimental results show that BSH can perform the photochromism easier than BSE, may be due to the molecular topology difference.     

THE EPR SPECTRA OF TETRADENTATE SCHIFF BASE COMPLEXES OF COPPER (II) II. N,N'-bis(salicylidene)ethylenediimine and 7-methyl-N,N'-bis (salicylidene)ethylenediimine

Abstract

The EPR spectra of single crystals of ⁶³Cu(II) doped N, N'-bis(salicylidene)ethylenediimine Ni(II), [Ni(sal)₂en] and 7-methyl-N, N'-bis(salicylidene)ethylenediimine Ni(II), [Ni(7-me sal)₂en] have been studied. The usual doublet spin-Hamiltonian parameters for the complexes have been found to be: Cu(II)[(sal)₂en]; g _z =2.192 ± 0.002; g _x =2.046 ± 0.004; g _y =2.049 ± 0.004; A _z =201.0 × 10^?4 cm^?1; A _x =29.3 × 10^?4 cm^?1; A _y =31.3 × 10^?4 cm^?1; A^N _z =12.6 × 10^?4 cm^?1; A ^N _x =14.5 × 10^?4 cm^?1; A ^N _y =15.7 × 10^?4 cm^?1; A ^H _z =6.3 × 10^?4 cm^?1; A ^H _x =7.3 × 10^?4 cm^?1; A ^H _y =7.9 × 10^?4 cm^?1; Cu(II)[(7-me sal)₂en]; g _z =2.189 ± 0.002; g _x =2.037 ± 0.004; g _y =2.046 ± 0.004; A _z =203.0 × 10^?4 cm^?1; A _x =36.9 × 10^?4 cm^?1; A _y =22.7 × 10^?4 cm^?1; A ^N _z =12.6 × 10^?4 cm^?1; A ^N _x =13.3 × 10^?4 cm^?1; A ^N _y =14.0 × 10^?4 cm^?1. Values of molecular orbital coefficients calculated for these complexes show that their bonding properties are similar to those of other compounds of this type. There is considerable covalency in the metal-ligand [sgrave]-bonds, and significant in-plane pi-bonding is present.     

New templating strategies with salen scaffolds (Salen=N,N'-bis(salicylidene)ethylenediamine dianion)

Templated approaches towards selective organic synthesis is a common feature in nature in which nucleic acid templated synthesis plays a crucial role in various fundamental biological processes. The key feature that allows control over the amazing selectivity found in natural processes is evidently the effective molarity of the reaction partners that is mediated by the macromolecular templation event. An ongoing challenge within many chemical sciences is to exploit similar templating principles and make use of synthetic systems that are designed for specific chemical conversions. Here, we describe the recent developments that involve (metallo)salen scaffolds that are used for diverse templating events (salen=N,N'-bis(salicylidene)ethylenediamine dianion).     

Spectroscopic, thermal and voltammetric studies of crystalline complex trans-N,N'-bis(salicylidene)-1',2'-cyclohexanediamine with Cu(II)

The dimeric complex, [C20H20CuN2O2]2, has been prepared and characterized by thermal analysis, IR spectroscopy and single-crystal X-ray diffraction techniques. The Cu atom in the binuclear complex exists in a distorted square-pyramidal configuration, defined by three O atoms and two N atoms. The crystal structure is stabilized by intermolecular C-H...O hydrogen bonding interaction. The electrochemical property of the complex was investigated in CH2Cl2 by cyclic voltammetry at 100 mV s(-1) scan rate.     

A lead(II)-selective PVC membrane based on a Schiff base complex of N,N'-bis(salicylidene)-2,6-pyridinediamine

PVC membrane electrodes for lead ion based on N,N’-bis(salicylidene)-2,6-pyridinediamine as membrane carrier were prepared. Among their membranes, a membrane electrode (m-3) containing o-NPOE as a plasticizer and 50 mol% additive displays an excellent Nernstian response (29.4 mV/decade) and the limit of detection of −log a (M) = 6.04 to Pb²⁺ in Pb(NO₃)₂ solutions at room temperature. It has a rapid response time within 10 s over the entire concentration range. The proposed electrode revealed good selectivity and response for Pb²⁺ over a wide variety of other metal ions in a pH 5.0 buffer solutions, and good reproducibility of base line in subsequent measurements.     

Highly selective iodide electrode based on the copper(II)-N,N'-bis(salicylidene)-1,2-bis(p-aminophenoxy)ethane tetradentate complex.

In this paper, a new PVC-based liquid-membrane anion-selective electrode based on a copper(II) of N,N'-bis(salicylidene)-1,2-bis(p-aminophenoxy)ethane tetradentate complex (Cu(II)BBAP) is described, which displays a preferential potentiometric response to iodide ion at pH 2.0 and an anti-Hofmeister selectivity sequence: I->SCN->ClO4->NO2->H2PO4->NO3->SO4(2-)>Br->Cl-. The electrode exhibits a near-Nernstian potential linear range of 8.2x10(-7)-1.0x10(-1) M with a detection limit of 5.3x10(-7) M and a slope of -58.8 mV per decade. The A.C. impedance technique and the UV/Vis spectroscopy technique were used to analyze the response mechanism. The electrode could be applied to determine iodide in medicine analysis, and the obtained results were fairly satisfactory.     

Anionic N-heterocyclic carbenes with N,N'-bis(fluoroaryl) and N,N'-bis(perfluoroaryl) substituents

A series of rhodium complexes, [Rh(cod)(NHC-F(x))(OH(2))] (cod = 1,5-cyclooctadiene; NHC = N-heterocyclic carbene), incorporating anionic N-heterocyclic carbenes with 2-tert-butylmalonyl backbones and 2,6-dimethylphenyl (x = 0), 2,6-difluorophenyl (x = 4), 2,4,6-trifluorophenyl (x = 6), and pentafluorophenyl (x = 10) N,N'-substituents, respectively, has been prepared by deprotonation of the corresponding zwitterionic precursors with potassium hexamethyldisilazide, followed by immediate reaction of the resulting potassium salts with [{RhCl(cod)}(2)]. These complexes could be converted to the related carbonyl derivatives [Rh(CO)(2)(NHC-F(x))(OH(2))] by displacement of the COD ligand with CO. IR and NMR spectroscopy demonstrated that the degree of fluorination of the N-aryl substituents has a considerable influence on the σ-donating and π-accepting properties of the carbene ligands and could be effectively used to tune the electronic properties of the metal center. The carbonyl groups on the carbene ligand backbone provided a particularly sensitive probe for the assessment of the metal-to-ligand π donation. The ortho-fluorine substituents on the N-aryl groups in the carbene ligands interacted with the other ligands on rhodium, determining the conformation of the complexes and creating a pocket suitable for the coordination of water to the metal center. Computational studies were used to explain the influence of the fluorinated N-substituents on the electronic properties of the ligand and evaluate the relative contribution of the σ- and π-interactions to the ligand-metal interaction.     

Interaction of bis(ethylene)tin(bis(salicylidene)ethylenediamine) with DNA.

The fluorescence spectral characteristics and interaction of bis(ethylene)tin(bis(salicylidene)ethylenediamine) [Et2Sn(salen)] with DNA are described. The polarity of the solvent has a strong effect on the fluorescence characteristics of Et2Sn(salen). Et2Sn(salen) bound to DNA showed a marked decrease in the fluorescence intensity with a bathochromic shift of the excitation and emission peaks. A hypochromism in the UV absorption spectra was also observed. KI quenching and competitive binding to DNA between Et2Sn(salen) and ethidium bromide (EB) were studied in connection with other experimental observations to show that the interactive model between Et2Sn(salen) and DNA is an intercalative one. The pH and salt effect on the fluorescence properties was also investigated. The intrinsic binding constant was estimated to be 1.071 x 10(5) mol L(-1) in base pairs and the binding site number is 1.98, respectively. A linear relationship between F/F0 and the concentration of calf thymus DNA covers 5.1 x 10(-6) - 2.41 x 10(-4) mol L(-1), which can be utilized for determining traces of calf thymus DNA with a detection limit of 1.1 x 10(-7) mol L(-1) in base pairs.     

Synthesis of metal-(pentadentate-salen) complexes: asymmetric epoxidation with aqueous hydrogen peroxide and asymmetric cyclopropanation (salenH2: N,N'-bis(salicylidene)ethylene-1,2-diamine)

It is known that the rates and stereochemical outcomes of epoxidations and cyclopropanations using a metallosalen (salenH(2): N,N'-bis(salicylidene)ethylene-1,2-diamine) complex as catalyst are affected by a trans effect of the apical ligand of the complex. By taking into consideration this trans effect, we have synthesized optically active pentadentate salen ligands bearing an imidazole or pyridine derivative as the fifth coordinating group, and have prepared the corresponding manganese(III) and cobalt(II) complexes, in which the fifth ligand is expected to intramolecularly coordinate to the metal center and exert a trans effect. Indeed, high enantioselectivity has been achieved in epoxidations using aqueous hydrogen peroxide as the terminal oxidant and in cyclopropanations with these complexes as catalysts. In general, metallosalen-catalyzed reactions have been carried out in the presence of an excess of a donor ligand; however, the present reactions do not need the addition of any extra donor ligand.     

Copper(II) trinuclear complex with trimesic acid salicylidene hydrazone: Synthesis,structure, and magnetic properties

A trinuclear copper(II) complex of trimesic acid salicylidene hydrazone (H₆L) having the composition [Cu₃L · 4Py] · CH₃OH was synthesized and characterized. By X-ray crystallography, the crystals are triclinic: a = 11.7940(4) Å, b = 13.7241(5) Å, c = 15.8993(6) Å, α = 107.4120(10)°, β = 94.2900(10)°, γ = 105.5650(10)°, space group \(P\bar 1\), Z = 2. The number of symmetrically unique reflections having I > 2σ(I) is 7636, R = 0.0465, and R _w = 0.1198. The newly prepared complex contains, in its unit cell, two [Cu₃L · 4Py] molecules which are linked to form a dimer on account of phenoxo bridges (the Cu-O bond length is 2.555 the Cu…Cu distance is 3.348 Separations between them are 9.414, 9.371, and 9.667 of temperature is satisfactorily fitted in terms of a triangular cluster model (?2J = 2.2 cm^?1) with extra intermolecular interactions (zJ′ = 0.4 cm^?1). EPR spectra of solutions at 360–380 K feature a poorly resolved HFS, whose modeling gives a satisfactory result with allowance for the interaction of unpaired electrons with three equivalent copper nuclei (g = 2.098; a _Cu = 25.8 × 10^?4 cm^?1).     

Determination of Aluminium by Potentiometry Using Carbon Paste Ion Selective Electrode Based on N,N'-bis(salicylidene)-1,3-Propanediamine Ligand

Journal of Analytical Chemistry - A new Al3+ carbon paste ion selective electrode based on N,N'-bis(salicylidene)-1,3-propanediamine (SB-Salpr) was prepared for the quantification of trace...