Synthesis and spectral properties of 3,3′-bis(dipyrrolylmethene)

Bis(2,4,7,8,9-pentamethyldipyrrolylmethene-3-yl)(4′-methoxyphenyl)methane dihydrobromide was synthesized and its spectral properties were studied. It was found that the basicity of the ligand 3,3′-bis-(dipyrrolylmethene) decreases upon insertion of the methoxyphenyl group in the 3,3′-spacer.     

Complexation between decamethyl-3,3′-bis(dipyrrolylmethene) and zinc(II), copper(II), and cobalt(II) acetates

Decamethyl-3,3′-bis(dipyrrolylmethene) dihydrobromide H₂L · 2HBr (H₂L is bis(3,4,7,8,9-pentamethylpyrrol-3-yl)methane), which is the simplest representative of a novel class of oligo(dipyrrolylmethenes) belonging to chromophore chelating nonmacrocyclic ligands, were examined by ¹H NMR, IR, and electronic absorption spectroscopy. Complexation reactions of H₂L · 2HBr with M(AcO)₂ (M = Zn(II), Cu(II), and Co(II)) in DMF at 298.15 K were monitored by electronic absorption spectroscopy and studied by the molar ratio method. The thermodynamic constants K ⁰ of these reactions were estimated. The d metal ions coordinate H₂L to give the binuclear homoleptic complexes [M₂L₂]. The reactions proceed through the intermediate binuclear heteroleptic complex [M₂L(AcO)₂] detected by spectroscopic methods. The thermodynamic stabilities of [M₂L₂] and [M₂L(AcO)₂] increase when moving from Cu(II) to Zn(II) and Co(II). The probability of formation and stability of [M₂L₂] containing 3,3′-bis(dipyrrolylmethene) are substantially higher than those of analogous complexes with the 2,2′-isomer (decamethyl-2,2′-biladienea, c). The low K ⁰ values for the complexation between H₂L and Cu(AcO)₂ are due to slow oxidation of the biladiene ligand into a bilatriene with participation of Cu²⁺ ions.     

Kinetics of the dissociation of zinc(II) complexes with 3,3′-bis(dipyrrolylmethenes) in acetic acid-benzene binary solvent

A comparative study of the dissociation of zinc(II) helicates with a series of 3,3??-bis(dipyrrolylmethenes) (H₂L) of [Zn₂L₂] composition in acetic acid-benzene binary proton donor solvent in the temperature range from 298.15 to 318.15 K is performed by means of electronic spectroscopy. Quantitative kinetic characteristics are determined and a stoichiometric mechanism of reaction is suggested. It is established that the protolytic dissociation of [Zn₂L₂] helicates proceeds according to a third-order kinetic equation of reaction. The effect of alkyl substituents in the pyrrol rings and nature of central 3,3??-spacer on lability of helicates is analyzed.     

meso-spacer influence on properties of zinc(II) complexes with 2,3′- and 3,3′-bis(dipyrrolylmethenes)

The study and comparative analysis of spectral-luminescent characteristics (absorption and fluorescence spectra), of quantum yield, and fluorescence life time in solutions, of lability in proton-donor media, solid phase thermal stability in air oxygen and argon was carried out for binuclear zinc(II) helicates with decamethyl-substituted 2,3′- and 3,3′-bis(dipyrrolylmethenes). The influence of molecular structure features of the ligands on the physicochemical properties of helicates was discussed.     

Kinetic stability of complexes of some d-metals with 3,3′-bis(dipyrrolylmethene) in the binary proton-donor solvent acetic acid-benzene

The kinetics of dissociation of Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) binuclear homoleptic double-stranded helicates with bis(2,4,7,8,9-pentametyldipyrrolylmethen-3-yl)methane (H₂L) of the [M₂L₂] composition in the binary proton-donor solvent acetic acid-benzene was studied. Protolytic dissociation of the helicates [M₂L₂] proceeds in accordance with the third order kinetic equation. Effect of the complexing metal nature is manifested in increased kinetic inertness in the following series of the helicates: [Cd₂L₂] < [Hg₂L₂] < [Cu₂L₂] < [Ni₂L₂] < [Zn₂L₂] < [Co₂L₂]. By the lability in similar environmental conditions the helicates [M₂L₂] are comparable to the metal complexes of distorted porphyrins and are much more inert than dipyrrolylmethenate mononuclear complexes.     

Coordination reactions of 3,3′-bis(dipyrrolylmethene) with Co(II), Cu(II), and Zn(II) acetylacetonates, valinates, and dipyrrolylmethenates

Using spectrophotometry we found that ligand exchange in the systems of H₂L-[MX₂]-DMF, where M denotes Co²⁺, Cu²⁺, and Zn²⁺; X means Acac^?, Val^?, dpm^?; Hdpm^? is hexamethyldipyrrolylmethene, H₂L is bis(2,4,7,8,9-pentamethyldipyrrolylmethene-3-yl)methane, proceeds through successive stages of formation of hetero- and homoleptic binuclear complexes. Conventional sensitivity of the spectrophotometric determination of Co²⁺, Cu²⁺, and Zn²⁺ reaches 10^?9 M.     

New fluorescent chemosensor for Zn2+ ions on the basis of 3,3′-bis(dipyrrolylmethene)

Luminescence study of the reaction of 3,3′-methanediylbis(2,4,7,8,9-pentamethyldipyrrolylmethene) (H₂L) with a number of metal salts showed that this compound is an efficient fluorescent chemosensor for Zn²⁺ ions in organic solvents. The selectivity and sensitivity of H2L were estimated in various solvents in the presence of other metal cations (Na⁺, Mg²⁺, Co²⁺, Ni²⁺, Cu²⁺, Cd²⁺, Hg²⁺, Pb²⁺).     

Synthesis and spectral properties of the nickel(II) and mercury(II) helicates with 3,3′-bis(dipyrrolylmethenes)

The influence of the nature of the complexing metal on the optical properties of coordination compounds of bis(dipyrrolilmethenes) was studied.     

Synthesis and spectral properties of new 3,3’-bis(dipyrrolylmethene) with acetylene spacer

Bis(2,4,7,9-tetramethyl-8-ethyldipyrrolylmethen-3-yl)acetylene dihydrobromide (H₂L·2HBr), new bis(dipyrrolylmethene), in whose molecule dipyrrolylmethene domains were connected through 3,3′-carbon atoms of internal pyrrole nuclei by acetylene spacer, were synthesized by original procedure. The compound was characterized by element analysis, IR, ¹H NMR, and electronic spectroscopy. The comparative analysis of spectral properties shows the reduction of the basicity of H₂L ligand in comparison with the structural analogs, which contain internal methylene spacer. The quantum-chemical simulation showed that the rigid acetylene spacer gives linear structure to the H₂L molecule in contrast to the spiral-shaped geometry of structural analogs with -CH₂- spacer.     

Comparative analysis of physicochemical properties of dinuclear zinc(II) helicates with 2,2′-, 2,3′-, and 3,3′-bis(dipyrromethenes)

The effect of the attachment position of a methylene spacer in 2,2′-, 2,3′-, and 3,3′-bis(dipyrromethene) N₄-ligands (H₂L) on physicochemical properties of their dinuclear homoleptic helicates [Zn₂L₂], such as specific features of their molecular structure, luminescence spectral characteristics, lability in acid solutions, and thermal stability in an argon atmosphere, has been examined. It has been shown that the substitution of the biladiene-type helicand by its 2,3- and especially 3,3′-analogues leads to a considerable enhancement of the chromophoric properties, an increase (up to 30-fold) of the fluorescence quantum yield, and an increase in the stability of corresponding dinuclear helicates [Zn₂L₂].     

Characteristic features of formation, synthesis, and properties of binuclear zinc(II) helicates with alkyl-substituted 3,3′-bis(dipyrrolylmethenes)

On the basis of spectrophotometric studies, it was demonstrated that complexation of hydrobromides of seven alkylated 3,3′-bis(dipyrrolylmethenes) (H₂L · 2HBr) with zinc(II) acetate dihydrate in DMF (298.15 K) includes successive steps of formation of binuclear helicates of two types: [Zn₂(AcO)₂L] (heteroleptic single-helix complex) and [Zn₂L₂] (homoleptic double-helix complex). An increase in the degree of alkylation of the pyrrole rings of the ligands from 4 to 10 methyl groups induces an increase of overall complexation constants from 7.60 to 13.73. The synthesis of helicates [Zn₂L₂] was described. The products were studied by elemental analysis and IR, ¹H NMR, U/Vis, and fluorescence spectroscopy. The effect of the helicand structure and the solvent nature on the chromophore and fluorescence properties of [Zn₂L₂] was discussed. The kinetic stability of zinc(II) with decamethyl-substituted 3,3′-bis(dipyrrolylmethene) in HCl-DMF medium was estimated.     

Crystal structure of a trinuclear complex of zinc(II) with 2,6-Di-tert-butyl-p-quinone 1′-phthalazinylhydrazone

2,6-Di-tert-butyl-p-quinone 1′-phthalazynylhydrazone (HL) is synthesized; the total energies and geometry of the possible hydrazone tautomeric forms are calculated by quantum chemical methods. The hydrazone phthalazone tautomer is shown to be the most stable, which is well consistent with the ¹H NMR spectroscopic data for hydrazone. An X-ray crystallographic analysis is performed of the hydrazone-based Zn(II) trinuclear complex, in which zinc atoms are linked by the diazine bridge of the phthalazine cycle and two pivalate bridges. The geometric properties of the monodeprotonated hydrazone residue in the complex are similar to the calculated data for the phthalazone hydrazone tautomeric form.     

A novel dicyanamide-bridged zinc(II) complex incorporating the 4,4′-azopyridine ligand

A novel complex {[Zn(azpy)₂(dca)(H₂O)₂]·ClO₄·azpy·2H₂O}_n (1) has been synthesized and structurally and spectroscopically characterized, where azpy is the 4,4′-azopyridine and dca the dicyanamide. The crystal structure analysis of 1 shows that in 1 the dca ligands act as μ _1,5-bridges linking the zinc(II) ions into 1D covalent bonding chains. The zinc(II) ion lies in a distorted octahedral environment completed by two nitrogen atoms from two terminal azpy groups, two nitrogen atoms from two dca bridges, and two water molecules. The most striking feature of 1 is that the 1D covalent bonding chains are linked through O–H·N hydrogen bonds and π–π stacking interactions into a 3D supramolecular structure.     

Complexes of N-aroyl-N′-thiobenzohydrazide with cobalt(II), nickel(II) and zinc(II)

Summary New potential tetradentate ligands, N-benzoyl-N-thiobenzohydrazide (H₂BTBH) and N-salicyl-N-thiobenzohydrazide (H₂SBTH) have been prepared and characterized. Their complexes with Co^II, Ni^II and Zn^II have been prepared and characterized on the basis of elemental analyses, magnetic susceptibility measurements, and u.v.-vis., i.r. and ¹H-n.m.r. spectral studies. The bonding and stereochemistries of the complexes are discussed. H₂BTBH, H₂SBTH and the complexes have been screened towards a number of bacteria.     

Investigation of complexes of zinc(II) and cadmium(II)DI-n-butyldithiocarbamates with 2,2′-bipyridyl

A new mixed-ligand complex, Cd(S₂CN(C₄H₉)_{2 2})₂(2,2′-Bipy), was synthesized. A polycrystal X-ray diffraction analysis was performed (DRON-3M and DRON-UM1 diffractometers, CuK_α radiation, Ni filter) and the crystal structure was determined [Enraf-Nonius CAD-4 automatic diffractometer, MoK_α radiation, 2440 nonzero independent reflections, 153 refined structural parameters, R is 0.11 for I>2σ(I)]. Crystal data for C₂₈H₄₄CdN₄S₄ : a = 28.716(4), b = 6.848(6), c = 17.188(2) Å, space group Pcca, V-3380.2(7) ų, Z = 4, M = 679.42, dcaU.= 1.335 g/cm3. The structure consists of monomeric molecules in which the cadmium atom has a distorted octahedral environment. The polycrystal diffraction analysis revealed that the complex is isostructural with the defined complex Zn(S₂CN(C₄Hg)₂)₂(2,2′-Bipy). A crystal-chemical search on metal dialkyldithiocarbamates in the Cambridge Structural Database was accomplished and isostructural pairs of Zn and Cd metal complexes were found.     

Electrochemical and spectral properties of the polymer form of Cu(II) complex with N,N′-bis(salicylidene)-1,3-propylenediamine

A conductive polymer based on the Cu(II) complex with N,N′-bis(salicylidene)-1,3-propylenediamine was obtained electrochemically. The optimal mode of the synthesis of the polymer under potentiostatic conditions was found. We determined the charge diffusion coefficient and activation barrier and elucidated the nature of the limiting step of the charge transfer in the polymer bulk in the electrolyte medium. The azomethine base, Cu(II) complex, and its polymer form in the oxidized and reduced states were characterized by X-ray photoelectron spectroscopy and electron absorption spectroscopy.     

Determination of manganese(VII) as 3,3′-Dianisole-4,4′-bis(3,5-diphenyltetrazolium chloride) complex and its application

A simple, rapid, selective and sensitive spectrophotometric method is described for the determination of trace amounts of manganese using Blue tetrazolium chloride as a chromogenic reagent. The method is based on the formation of ion-associate complex between manganese(VII) and the cation of ditetrazolium salt, having an absorption maximum at 255 nm. Beer’s law is obeyed in the range of 0.1–1.6 μg mL^?1. The molar absorptivity and Sandell’s sensitivity were found to be 4.97 × 10⁴ L mol^?1 cm^?1 and 1.11 × 10^?3 μg cm^?2, respectively. Limit of deterction is 6.86 ng mL^?1 Mn(VII) and limit of quantitation is 22.8 ng mL^?1 Mn(VII). Optimum reaction conditions were evaluated. The effect of interfering ions on the determination is described. The extraction, distribution and association constants, and the recovery factor have been calculated.     

Synthesis of 4,4′-bis(dichloroamino)- and 4,4′-bis(chloroamino)-3,3′-azofurazans,the first representatives of dichloroamino- and chloroaminofurazans

First representatives of dichloroamino- and chloroaminofurazans, viz., 4,4′-bis(dichloroamino)- and 4,4′-bis(chloroamino)-3,3′-azofurazans, were synthesized by the chlorination of 4,4′-diamino-3,3′-azofurazan with sodium hypochlorite in the CH₂Cl₂—H₂O mixture.     

Synthesis and spectral analysis of alkyl-substituted 3,3′-bis(dipyrrolylmethenes)

Four new alkyl-substituted 3,3′-bis(dipyrrolylmethene) dihydrobromides containing from 4 to 10 alkyl substituents were synthesized. In a highly alkylated ligand of these substances one of the hydrogen atoms of the 3,3′-methylene spacer was substituted with a phenyl group. The compounds obtained were studied by IR, ¹H NMR, electron absorption, and fluorescent spectroscopy. The increased alkylation degree of pyrroles and the introduction of an aryl substituent in the 3,3′-spacer causes a significant high-frequency shift of the N-H stretching vibrations in the IR spectra, an upfield shift of the NH-proton signals in 1H NMR spectra, a decrease in the auxochromic effects of protons on the aromatic system of chromophore in the composition of salts. The red shift of maximum of the strong band in electron absorption spectra and the emission spectra of compounds in DMF, DMSO, C₅H₅N, C₆H₆, and CHCl₃ was established. The salts obtained are stable in benzene and chloroform, while in electron-donor solvents the irreversible processes of solvolytic dissociation of salts to free organic base and HBr take place.