Spectroscopic and electrochemical properties of mixed-ligand cyclopalladinized complexes of deprotonated forms of 2-(2-thienyl)pyridine and 2-phenylpyridine with 1,10-phenantroline and its 1,4-diazine derivatives

A comparative study of [Pd(N?C)(N?N)]⁺ complexes {(N?C)^? are deprotonated forms of 2-phenylpyridine and 2-(2-thienyl)pyridine and (N^N) is 1,10-phenantroline, dipyrido[f,h]quinoxaline, dipyrido[a,c]phenazine or 6,7-dicyanodibenzo[f,h]quinoxaline} was carried out by the methods of ¹H NMR, electronic absorption and emission spectroscopy, and cyclic voltammetry. Optical and electrochemical properties of dipyrido-substituted 1,4-diazines are conditioned by the electron transfer involving π* orbitals localized on weakly interacting phenantroline (π*_phen) and diazne (π*_diaz) components.     

Spectroscopic and electrochemical properties of dichlorodiimine complexes of Au(III) and Pt(II) with 1,4-diazine derivatives of o-phenanthroline

A series of dichlorodiimine complexes [M(N N)Cl₂]^z of Au(III) and Pt(II) with 1,4-derivatives of o-phenanthroline [(N N) = o-phenanthroline (phen), dipyrido[f,h]quinoxaline (dpq), dipyrido[a,c]phenazine (dppz), 6,7-dicyanodipyrido[f,h]quinoxaline (dicnq)] were prepared and characterized by ¹H NMR, electronic absorption, and emission spectroscopy and by cyclic voltammetry. In all the complexes, the ³(π-π*)-type transition is the spin-forbidden transition of the lowest energy, responsible for the luminescence. The longest wave bands in the absorption spectra of the Au(III) and Pd(II) complexes were assigned in accordance with the results of the electrochemical studies to the ¹(d*)-and ¹(d*)-type transitions, respectively.     

Crystal structures,theoretical calculations,spectroscopic and electrochemical properties of Cr(III) complexes with dipicolinic acid and 1,10-phenantroline

The crystal structures of compounds Na[Cr(dipic)₂] · 2H₂O (1) and [Cr(dipic)(phen)Cl] · 1/2H₂O (2), dipic = dipicolinate, phen = 1,10-phenantroline, were determined. In both complexes, Cr(III) is in a distorted octahedral environment. In complex (1), the metal is coordinated to two nearly perpendicular dipic anions acting as tridentate ligands through one oxygen of each carboxylate group and the pyridinic nitrogen atom. In complex (2), Cr(III) ion is similarly coordinated to a dipic anion, defining a ligand equatorial plane. The phen molecule bridges the remaining equatorial coordination site and one of the axial positions through its N-atoms. The other axial position is occupied by a chloride ion.     

Cyclometallation of 2-(2-thienyl)pyridine and 2-(3-thienyl)pyridine with palladium(II), rhodium(III) and ruthenium(II)

Summary 2-(2-Thienyl)pyridine [H(2-tp)] and 2-(3-thienyl)pyridine [H(3-tp)] react with lithium tetrachloropalladate(II), hexachlorotetrakis(tri-n-butylphosphine) dirhodium(III), and tetrachlorohexacarbonyldiruthenium(II) to give [PdCl(C-N)]₂-(CN=2-tp and 3-tp), [RhCl₂(C-N)PBu₃]₂ (C-N = 2-tp and 3-tp), and [RuCl(2-tp)(CO)₂]₂, respectively. Some bromo analogues are also prepared. These complexes react with pyridine and tri-n-butylphosphine to give adducts in which 2-tp is chelated through pyridine-N and thiophene-3-C and 3-tp through pyridine-N and thiophene-2-C atoms. The structures of these complexes are similar to those of the corresponding complexes of cyclometallated 2-phenylpyridine.     

Redox properties of bis(1,10-phenanthroline)-(pyridine)ruthenium(II) complexes

The redox properties of a series of [Ru(phen)₂(py)X]ⁿ⁺ cations (X = pyridine, NH₃, Cl, Br, I, CN, SCN, N₃ and NO₂) have been investigated in acctonitrile. Two reversible reduction steps are seen at ? 1.35 and ? 1.6 V vs Ag/AgCl; the invariance of these processes with X-group is indicative of electron addition to molecular orbitals mainly of phenanthroline ligand π^* origin. Irreversible multi-electron reductions follow below ? 2.20 V. The Ru(II)/Ru(III) couple is seen as a reversible wave near + 0.8 V vs the normal hydrogen electrode, from calibration with ferrocene, except in the cases of the NO₂ and SCN complexes, where rapid reactions involving these ligands occur.     

Synthesis of 2-amino-4-(2-thienyl)thiazole and its derivatives

The bromination of substituted methyl 2-R-thienyl ketones with bromine in chloroform yielded bromomethyl 2-thienyl ketones. The latter were converted to quaternary pyridinium salts and 2-amino-4-(2-thienyl)thiazoles.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1369–1371, October, 1971.     

Synthesis and spectral-luminescence properties of carbonyl derivatives of 2-(2-thienyl)-5-aryloxazoles

Electrophilic substitution reactions in the 2-(2-thienyl)-5-aryloxazole series and the spectral-luminescence properties of the compounds obtained were investigatedTranslated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 839–844, June, 1989.     

Spectroscopic studies on chromotropic mixed-ligand copper(II) complexes containing o-hydroxy benzoyl derivatives and dinitrogen bases

Synthesis of chromotropic copper(II) mixed ligand complexes of o-hydroxy benzoyl derivatives (L1) and dinitrogen bases (L2), general formula Cun(L1)(L2)nXn; where n=1 or 2, L1=4,6-diacetyl-resorcinol (H2DACR), o-hydroxy benzaldhyde (HOHBZ) or o-hydroxy acetophenone (HOHAP), L2=N,N,N',N'-tetramethylethylenediamine (Me4en), 1,10-phenanthroline (phen) or bipyridine (bipy) and X=ClO4-, NO3- or Br- have been reported. Spectral, magnetic and molar conductance measurements as well as analytical data of these complexes show either mononuclear structure for OHBZ and OHAP or binuclear structure for DACR complexes. The IR stretching vibration frequencies of Cu-N and Cu-O are linearly correlated with the d-d absorption frequencies. The d-d absorption bands of Me4en-complexes in weak donor solvents suggest square-planar, distorted octahedral and distorted trigonal bipyramid geometries for the perchlorate, nitrate and bromide complexes, respectively. However, an octahedral structure is identified for the complexes in strong donor solvents. Perchlorate complexes show a remarkable color change from violet to green as the donor ability of the axial ligand increases, whereas bromide complexes are mainly affected by the Lewis acidity of the axial ligand. Specific and non-specific interactions of solvent molecules with the complexes are investigated using the unified solvation model. Calculations of the electronic transition probability (f) of the d-d band along with molecular orbital calculations of ligands have been carried out and correlated with the experimental data.     

Emissive metallomesogens based on 2-phenylpyridine complexes of iridium(III)

Preparation of Ir(III) complexes using anisotropic 2,5-di(4-alkoxyphenyl)pyridine ligands leads to emissive, liquid-crystalline complexes containing bound Cl and dimethyl sulfoxide. Using analogous poly(alkoxy) ligands allows the preparation of bis(2-phenylpyridine)iridium(III) acac complexes, which are also mesomorphic. The observation of liquid crystallinity in octahedral complexes of this type is without precedent.     

Study of 2-(o-carboxyphenyliminomethyl)pyridine acid and its ferrous complexes

The synthesis, properties (UV, IR and fluroescence spectra, ionization constants and thermal behavior) and reactions with several metal complexes of 2-(o-carboxyphenliminomethyl)pyridine acid—(CPIMPA) are described. The reaction between Fe(II) and CPIMPA, studied, spectrophotometrically showed the existence of two complexes, with stoicheiometries 2:1 (CPIMPA: iron) (ϵ = 1.06 × 10³ 1 mol⁻¹ cm⁻¹ at 660 nm) and 1:1 (ϵ = 6.45 × 10³ 1 mol⁻¹ cm⁻¹ at 575 nm). The 2:1 solid complex has been isolated, its thermal behavior and IR spectrum are reported. It is shown that CPIMPA acts as a tridentate ligand.     

Spectroscopic and electrochemical properties of iron(II) complexes of polydentate Schiff bases containing pyrazine, pyridine and imidazole groups

We report the synthesis and spectroscopic/electrochemical properties of iron(II) complexes of polydentate Schiff bases generated from 2-acetylpyridine and 1,3-diaminopropane, acetylpyrazine and 1,3-diaminopropane, and from 2-acetylpyridine and L-histidine. The complexes exhibit bis(diimine)-iron(II) chromophores in association with pyrazine, pyridine or imidazole groups displaying contrasting pi-acceptor properties. In spite of their open geometry, their properties are much closer to those of macrocyclic tetraimineiron(II) complexes. An electrochemical/spectroscopic correlation between E degrees (FeIII/II) and the energies of the lowest MLCT band has been observed, reflecting the stabilization of the HOMO levels as a consequence of the increasing backbonding effects in the series of compounds. M?ssbauer data have also confirmed the similarities in their electronic structure, as deduced from the spectroscopic and theoretical data.     

Spectroscopic properties of some mixed ligand copper(II) complexes of N-(2-aminoethyl)-1,2-ethanediamine and ethanediamine and its alkylated derivatives

IR, EPR and electronic spectral studies have been made on a series of complexes with general formula [M(dien)L](BØ₄)₂nH₂O (M = Cu(II), Zn(II), Cd(II), dien = N-(2-aminoethyl)-1,2-ethanediamine, L = ethanediamine (en), Me₄en, Et₂en, Me = methyl, Et = ethyl, BØ₄ = tetraphenylborate, n = 0 or 2] taking copper(II) as a magnetic probe in polycrystalline and solution forms to obtain stereochemical information. A five-coordinate square-based pyramidal (SBP) geometry with CuN₃N′₂ moiety having moderately covalent metal-ligand σ-bonds is found to exist in unalkylated mixed ligand complexes. Among alkylated complexes [Cu/Cd(dien)(Me₄en)](BØ₄)₂ is found to possess two species having tetrahedral and SBP with trigonal bipyramidal distortion geometries unlike the other alkylated complexes which have indicated the presence of one species having SBP coordination geometry with varying degrees of trigonal bipyramidal distortions and metal-ligand σ-bond strengths. EPR studies in dilute dmf and pyridine solutions of copper(II) complexes indicated the presence of solute-solvent interaction.     

Bromination of 4-(2-thienyl)thiazoles and 2-(2-thienyl)quinoline

Depending on the substituent, the bromination of 4-(2-thienyl)thiazoles and 2-(2-thienyl)quinoline takes place in the 5 position of the thiophene or thiazole ring. When an amino group is present in the 2 position of the thiazole ring, bromination takes place in the 5 position of the thiazole ring. When excess brominating agent is present, a second bromine atom enters the 5 position of the free ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 35–38, January, 1982.     

Spectroscopic characterization of chloride and pseudohalide ruthenium(II) complexes with 4-(4-nitrobenzyl)pyridine

Chloride, isocyanate and isothiocyanate hydride carbonyl ruthenium(II) complexes of 4-(4-nitrobenzyl)pyridine were synthesized from the precursor complex [RuHCl(CO)(PPh₃)₃] and characterized by IR, NMR, UV–Vis spectroscopy and X-ray crystallography. The electronic structures of the complexes were investigated by means of DFT calculations, based on their crystal structures. The spin-allowed singlet–singlet electronic transitions of the complexes were calculated by time-dependent DFT, and the UV–Vis spectra are discussed on this basis. The emission properties of the complexes were studied at ambient temperature, and the quantum yields of fluorescence, the lifetimes and nature of the excited states are discussed. The chloride and isothiocyanate complexes are practically nonemissive, with quantum yields under 0.01 %. Interpretation of spectra, supported by TD-DFT calculations, indicates that in this energy region, the transitions have MLCT character with admixture of LLCT (chloride and isothiocyanate complexes). The dominant LLCT character was visible in the case of the most emissive (isocyanate) complex. The low values of the lifetimes and quantum yields for these complexes indicate the influence of the metal center in the emission process.     

N-substituted 2,5-Di(2-thienyl)pyrroles. Synthesis and electrochemical properties

2,5-Dithienylpyrroles containing p-substituted benzene ring at the nitrogen atom were synthesized. The formylation and subsequent crotonic condensation of N-(4-nitrophenyl)-2,5-di (2-thienyl)pyrrole was performed. Electrochemical behavior of the compounds and electrochromic properties of 2,5-di(2-thienyl)-pyrrole containing p-semidine fragment at its nitrogen atom were studied.     

In search of oligo(2-thienyl)-substituted pyridine derivatives: a modular approach to di-, tri- and tetra(2-thienyl)pyridines

Herein, we describe our attempts to systematically prepare a series of oligo(2-thienyl)-substituted pyridine derivatives. The crucial starting material, a β-alkoxy-β-ketoenamide, is easily available on a large scale by the reaction of lithiated methoxyallene with thiophene-2-carbonitrile and thiophene-2-carboxylic acid. This three-component reaction is followed by intramolecular cyclization to yield the suitably functionalized 2,6-di(2-thienyl)-substituted pyridine derivates. The two oxygen atoms allow the programmed activation of positions C-3, C-4, or C-5 of the pyridine ring to perform palladium-catalyzed coupling reactions with thiophene-2-boronic acid or 2-(tributylstannyl)thiophene, and alternatively, reductive removal of groups. With this concept, we were able to prepare five pyridine derivatives with 2-thienyl substituents in the 2,6-, 2,3,6-, 2,4,6-, 2,3,4,6-, and 2,3,5,6-positions. 2,3,4,5,6-Penta(2-thienyl)pyridine was not available with our methods. The UV/Vis and fluorescence spectra of all pyridines were recorded and showed a dependence on the substitution pattern and protonation state. For the protonated 2,3,5,6-tetra(2-thienyl)-substituted pyridine, a Stokes shift of about 180 nm with an emission at 515 nm was observed.     

Homoligand and mixed-ligand complexes of mercury(II) with aspartic acid and iminodiacetic acid and its derivatives

The formation of homoligand mercury(II) complexes with aspartic acid (H₂Asp) and aspartate-chelant mixed-ligand mercury(II) complexes with iminodiacetic acid (H₂Ida, IDA), 2-hydroxyethyliminodiacetic acid (H₂Heida, HEIDA), and nitrilotriacetic acid (H₃Nta, NTA) in an aqueous perchlorate medium was studied by spectrophotometry and pH-potentiometric titration. The following complexes were identified: [Hg(OH)Asp]^?, [HgAsp₂]^2?, [Hg(Asp)Ida]^2?, [Hg(Asp)Heida]^2?, and [Hg(Asp)Nta]^3?. The logarithms of their stability constants are, respectively, 11.74 ± 0.12, 20.18 ± 0.17, 20.11 ± 0.10, 19.82 ± 0.09, 19.48 ± 0.11, and 20.58 ± 0.07 (μ = 0.1 (NaClO₄), t = (20 ± 2)°C). The hydrogen and hydroxyl competition regions were located in the systems, and relationships between the molar yields of complex species and the reactant concentrations were established. The protonation and dissociation constants of aspartic acid were derived from pH-potentiometric titrations. Experimental data were analyzed using mathematical models allowing one to judge the existence of various complex species in the solution and to identify the species that are sufficient to reproduce the observed data.     

Stability constants of complexes formed by some metal ions with 2-(phenyliminomethyl)pyridine and 2-(o-hydroxyphenyliminomethyl)pyridine

The stability constants of some metal complexes of these two reagents have been determined.