Structures and solvatochromic phosphorescence of dicationic terpyridyl-platinum(II) complexes with foldable oligo(ortho-phenyleneethynylene) bridging ligands

A series of binuclear organoplatinum(II) complexes, [(tBu3tpy)Pt--(C[triple chemical bond]C--1,2-C6H4)n--C[triple chemical bond]C--Pt(tBu3tpy)][ClO4]2 (1-7, n=1, 2, 3, 4, 5, 6, 8; tBu3tpy=4,4',4'-tri-tert-butyl-2,2':6',2'-terpyridine) with foldable oligo(ortho-phenyleneethynylene) linkers were prepared and characterized by spectroscopic methods and/or X-ray crystallographic analyses. In the crystal structures of 32.5 CH3OH, 5CH3CN, and 64 CH3CN, each of the bridging ortho-phenyleneethynylene ligands has a partially folded conformation. In aerated water/acetonitrile mixtures with water percentages larger than 40 %, the emission of complexes 3-7 are red-shifted and enhanced when compared to those recorded in acetonitrile. The red-shift in emission energy and enhanced emission intensity can be attributed to the inter- and/or intramolecular interactions induced by the addition of water to solutions of the platinum(II) complexes in acetonitrile. Data from dynamic light scattering and transmission electron microscopy studies revealed that these binuclear platinum(II) complexes aggregated into nanosized particles in acetonitrile/water mixtures. Hydrophobic folding of the ortho-phenyleneethynylene linkers in acetonitrile/water mixtures is postulated.     

Structures of Ni(II), Pd(II) and Cu(II) complexes with 1,2-<Emphasis Type="Italic">bis</Emphasis>(5,5,5-trifluoro-4-oxopent-2-en-2-amino)benzene

A new fluorine-containing tetradentate ligand 1,2-bis(5,5,5-trifluoro-4-oxopent-2-en-2-amino)benzene and its complexes with Ni(II), Pd(II) and Cu(II) are characterized by single crystal X-ray diffraction. It is found that the enaminoketone fragments of the ligand are identical in bond lengths and angles; they are almost planar, and make the angles of 51.3° to the plane of the benzene ring. The structures of Ni(II), Pd(II), and Cu(II) complexes are similar and have a saddle-shape configuration. The metal ions have square planar coordination and are located almost in the center of the N₂O₂ square. The average M-N bond lengths are longer than M-O ones by 0.014 Å and 0.034 Å for the Ni(II) and Cu(II) complexes respectively, while in the Pd(II) complex, M-O is longer than M-N by 0.029 Å. The average chelate angles N-M-O in the complexes are: N-Ni-O 95.12°; N-Pd-O 95.68°; N-Cu-O 93.88°.     

Synthesis, characterization, biological and thermal behaviour of Co(II), Ni(II) and Cu(II) complexes with Schiff bases having coumarin moieties

A series of Co(II), Ni(II) and Cu(II) complexes have been synthesized with Schiff bases derived from 5-amino-1,3,4-thiadiazole-2-thiol and 8-formyl-7-hydroxy-4-methylcoumarin/8-acetyl-7-hydroxy-4-methylcoumarin. The chelation of the complexes has been proposed in the light of analytical, spectral (IR, UV–Vis), ESI-mass, magnetic, ESR and thermal studies. The measured molar conductance values indicate that the complexes are non-electrolytes. TG and DTA provide the useful information about the coordination of water molecules to the metal ion and the stability of the complexes. TG and DTA curves show that the Co(II) complexes decomposition takes place in two stages corresponds to loss due to water molecules and Schiff base moiety. Whereas, Ni(II) and Cu(II) complexes decomposition took place in three steps corresponding to the loss of coordinated water molecules, 1,3,4-thiadiazole moiety and coumarin moiety, respectively. The Schiff bases and their complexes have been screened for their antibacterial and antifungal activities. The results of these studies show the metal complexes to be more antibacterial and antifungal as compared to the uncomplexed coumarins.     

Synthesis and Characterization of Luminescent Cyclometalated Platinum(II) Complexes of 1,3‐Bis‐Hetero‐Azolylbenzenes with Tunable Color for Applications in Organic Light‐Emitting Devices through Extension of π Conjugation by Variation of the Heteroatom

A series of luminescent cyclometalated platinum(II) complexes of N^C^N ligands [N^C^N=2,6‐bis(benzoxazol‐2′‐yl)benzene (bzoxb), 2,6‐bis(benzothiazol‐2′‐yl)benzene (bzthb), and 2,6‐bis(N‐alkylnaphthoimidazol‐2′‐yl)benzene (naphimb)] has been synthesized and characterized. Two of the platinum(II) complexes have been structurally characterized by X‐ray crystallography. Their electrochemical, electronic absorption, and luminescence properties have been investigated. In dichloromethane solution at room temperature, the cyclometalated N^C^N platinum(II) complexes exhibited rich luminescence with well‐resolved vibronic‐structured emission bands. The emission energies of the complexes are found to be closely related to the electronic properties of the N^C^N ligands. By varying the electronic properties of the cyclometalated ligands, a fine‐tuning of the emission energies can be achieved, as supported by computational studies. Multilayer organic light‐emitting devices have been prepared by utilizing two of these platinum(II) complexes as phosphorescent dopants, in which a saturated yellow emission with Commission International de I′Eclairage coordinates of (0.50, 0.49) was achieved.     

DNA binding and topoisomerase II inhibitory activity of water-soluble ruthenium(II) and rhodium(III) complexes

Water-soluble piano-stool arene ruthenium complexes based on 1-(4-cyanophenyl)imidazole (CPI) and 4-cyanopyridine (CNPy) with the formulas [(eta6-arene)RuCl2(L)] (L = CPI, eta6-arene = benzene (1), p-cymene (2), hexamethylbenzene (3); L = CNPy, eta6-arene = benzene (4), p-cymene (5), hexamethylbenzene (6)) have been prepared by our earlier methods. The molecular structure of [(eta6-C6Me6)RuCl2(CNPy)] (6) has been determined crystallographically. Analogous rhodium(III) complex [(eta5-C5Me5)RhCl2(CPI)] (7) has also been prepared and characterized. DNA interaction with the arene ruthenium complexes and the rhodium complex has been examined by spectroscopic and gel mobility shift assay; condensation of DNA and B-->Z transition have also been described. Arene ruthenium(II) and EPh3 (E = P, As)-containing arene ruthenium(II) complexes exhibited strong binding behavior, however, rhodium(III) complexes were found to be Topo II inhibitors with an inhibition percentage of 70% (7) and 30% (7a). Furthermore, arene ruthenium complexes containing polypyridyl ligands also act as mild Topo II inhibitors (10%, 3c and 40%, 3d) in contrast to their precursor complexes. Complexes 4-6 also show significant inhibition of beta-hematin/hemozoin formation activity.     

Kinetics of zinc(II) cloride extraction with tributyl phosphate

The equilibrium and rate of solvent extraction of zinc chloride complexes from HCl solutions into benzene solutions of tributyl phosphate (TBP) have been studied. The extracted species are discussed in the light of the results. The extraction was found to be first order with respect to both Zn(II) and TBP, and zero order for HCl. The rate-controlling steps are discussed and the rate constants for these reactions are calculated.     

Luminescent Platinum(II) Complexes of 1,3‐Bis(N‐alkylbenzimidazol‐ 2′‐yl)benzene‐Type Ligands with Potential Applications in Efficient Organic Light‐Emitting Diodes

A series of luminescent platinum(II) complexes of tridentate 1,3‐bis(N‐alkylbenzimidazol‐2′‐yl)benzene (bzimb) ligands has been synthesized and characterized. One of these platinum(II) complexes has been structurally characterized by X‐ray crystallography. Their electrochemical, electronic absorption, and luminescence properties have been investigated. Computational studies have been performed on this class of complexes to elucidate the origin of their photophysical properties. Some of these complexes have been utilized in the fabrication of organic light‐emitting diodes (OLEDs) by using either vapor deposition or spin‐coating techniques. Chloroplatinum(II)? bzimb complexes that are functionalized at the 5‐position of the aryl ring, [Pt(R‐bzimb)Cl], not only show tunable emission color but also exhibit high current and external quantum efficiencies in OLEDs. Concentration‐dependent dual‐emissive behavior was observed in multilayer OLEDs upon the incorporation of pyrenyl ligand into the Pt(bzimb) system. Devices doped with low concentrations of the complexes gave rise to white‐light emission, thereby representing a unique class of small‐molecule, platinum(II)‐based white OLEDs.     

EPR study on ligand-exchange reaction between bis(diethyldiselenocarbamato)copper(II) and some bis(acetylacetonato)copper(II) complexes

The paper is a study on the formation and properties of mixed-chelate copper(II) complexes, in which one ligand is strongly covalently bound diselenocarbamate (dsc), and the other belongs to a series of differently substituted acetylacetonates (acac), all forming weak covalent bonds. Thenoyltrifluoro- and trifluoro- substituted acetylacetonates only partly form mixed-chelate complexes, stable in toluene, benzene or dichloromethane, but gradually decomposing in chloroform or carbontetrachloride by analogy with Cu(Et(2)dsc)(2) behavior in these solvents. Hexafluoro-acetylacetonato copper(II) completely turns into a mixed-chelate Cu(dsc)(hfacac), which remains unchanged for more than 8 months of monitoring in all solvents used. The stability of Cu(dsc)(hfacac) is attributed to the reduced remaining negative charge on selenium atom embarrassing the formation of weak D-A complex with haloalkanes. The obtained EPR parameters suggest significant lowering of the contribution of the 4s AO of copper(II) in the mixed-chelate complexes. It is shown that Cu(acac)(2) does not react with Cu(Et(2)dsc)(2).     

Protolytic dissociation of copper(II) and nickel(II) dipyrrolylmethenates in benzene solutions of acetic acid

Protolytic dissociation of copper(II) and nickel(II) dipyrrolylmethenates in benzene solutions of acetic acid has been studied. The results have completed the knowledge of kinetics of dipyrrolylmethene complexes dissociation in acidic medium. The effect of the nature of complex forming atom, ligand, and other factors on the complexes kinetic stability has been analyzed.     

Complexes of Cu(II), Ni(II), Co(II), and Ag(I) Metals with 1,4-Bis(3-Phenyl Triazenil) Benzene

Moscow University Chemistry Bulletin - New complexes of Cu(II), Ni(II), Co(II) and Ag(I) with 1,4-bis(3-phenyl triazenyl) benzene are obtained. Using the methods of IR, EPR, electron spectroscopy,...     

Effect of photostability of mercury(II) dithizonate on photoacoustic spectroscopic determination of trace mercury

The solvent effect on the photostability of Hg(II) dithizonate in daylight and under laser irradiation has been confirmed and benzene found to be the best solvent to use in photometric work with Hg(II) dithizonate. A 1:1 v/v mixture of benzene and carbon tetrachloride is recommended for use in the laser-induced photoacoustic spectrometric determination of Hg(II) dithizonate. A detection limit of 0.8 ng/ml has been attained, together with a linear dynamic range of 3 orders of magnitude. Coupled with a concentration factor of 50 obtained by extraction, the method shows promise for the detection of Hg(II) at the 5-pg/ml level in water.     

Separation of zinc(II), cadmium(II) and mercury by solvent extraction using thiocarbohydrazide and the complexing agent

The extraction behaviour is reported of zinc(II), cadmium(II) and mercury(II) complexes of thiocarbohydrazide in benzene, chloroform, carbon tetrachloride, di-isopropyl ether, ethyl acetate, amyl acetate, and amyl alcohol. The separation of the three elements has been achieved by the use of various masking agents, as well as by making use of the effect ofpH on their extractability. This work was carried out under CSIR (India) Scheme No. 1 (450/69 GAU. II.     

Syntheses and structures of ytterbium(II) hydride and hydroxide complexes: similarities and differences with their calcium analogues

The Yb(II) hydride complex (DIPP-nacnac)YbH x THF (3-Yb, DIPP-nacnac = CH{(CMe)(2,6-iPr(2)C(6)H(3)N)}(2)) was prepared by a mild metathesis reaction of (DIPP-nacnac)Yb[N(SiMe(3))(2)].THF with PhSiH(3). 3-Yb crystallizes as a dimer with bridging hydride ions, and its geometry is similar to that of the analogue calcium hydride complex (3-Ca). 3-Yb is well soluble in benzene and remarkably stable in solution at room temperature. Ligand exchange to the homoleptic Yb(II) complexes takes place at higher temperatures (3-Yb is less stable than the analogue 3-Ca). The soluble hydride complexes 3-Ca and 3-Yb are catalysts for the hydrosilylation of 1,1-diphenylethylene, but differences in the product distributions are observed. Slow hydrolysis of (DIPP-nacnac)Yb[N(SiMe(3))(2)].THF gave reduction of water and unidentified Yb(III) complexes. Fast hydrolysis at low temperature, however, resulted in the first Yb(II) hydroxide complex, (DIPP-nacnac)Yb(OH) x THF (4-Yb, 20% yield), which is a dimer with bridging hydroxide ions in the solid state. The crystal structure is isomorphous to that of the calcium analogue 4-Ca. 4-Yb is well soluble in benzene and considerably more stable against ligand exchange and formation of homoleptic species than 3-Yb.     

X-ray structurally characterized Mo (VI), Fe (III) and Cu (II) complexes of amide-imine conjugate: (bio)catalytic and histidine recognition studies

An amide-imine conjugate, (E)-N′-((2-hydroxybenzen-1-yl) methylene)-4-methylbenzohydrazide (H₂L^PTASAL), derived from 4-methyl-benzoic acid hydrazide (PTA) and 2-hydroxybenzaldehyde is used to prepare Mo (VI), Cu (II) and Fe (III) complexes. The X-ray structurally characterized complexes have been explored as catalyst for amine assisted asymmetric ring opening (ARO) of epoxide, carbon-heteroatom cross-coupling and ethyl benzene oxidation. In addition, their catecholase like activities have thoroughly been investigated. Moreover, the Cu (II) complex selectively recognizes histidine by fluorescence spectroscopy.     

Structural studies and photochromism of mercury(II)-iodo complexes of (arylazo)imidazoles

Neat reaction between HgI2 and 1-methyl-2-(phenylazo)imidazole (Pai-Me) under microwave irradiation has isolated a novel compound whose structure shows intercalated HgI2 in the layers of Pai-Me. They exist independently in interpenetrated arrays. In a solution phase study, the same reaction has synthesized an iodo-bridged azoimidazole-Hg(II) complex, [Hg(RaaiR')(mu-I)(I)]2 (RaaiR' = 1-alkyl-2-(arylazo)imidazole). The structures have been characterized by X-ray diffraction studies. Chloro-bridged Hg(II) complexes of azoimidazoles, [Hg(RaaiR')(mu-Cl)(Cl)]2, are also known. These complexes upon irradiation with UV light show trans-to-cis isomerization. The reverse transformation, cis-to-trans isomerization, is very slow with visible light irradiation. Quantum yields (phi t-->c) of trans-to-cis isomerization are calculated, and the free ligand shows higher phi than their Hg(II) complexes. The cis-to-trans isomerization is a thermally induced process. The activation energy (Ea) of cis-to-trans isomerization is calculated by controlled temperature reaction. The Ea's of free ligands are much higher than that of halo-bridged Hg(II)-azoimidazole complexes. Chloro-bridged Hg(II) complexes show lower Ea's than those of iodo-bridged complexes. DFT calculation has been adopted to rationalize the experimental results.     

Effect of composition and structure of cobalt(II) complexes with oxyaldiminopropylaerosils on their catalytic activity in the decomposition of ozone

The composition, structure, and catalytic activity in low-temperature ozone decomposition were described for cobalt(II) complexes with oxyaldiminopropyl ligands achored to aerosil A-300 differing in the nature and position of the benzene ring substituent. The effect of the geometry of the coordination unit and electronic effects of the benzene ring substituents on the catalytic activity of the cobalt(II) complexes in ozone decomposition were established.     

Linear and star-shaped polynuclear Ru(II) complexes of 2-(2'-pyridyl)benzimidazolyl derivatives: syntheses, photophysical properties and red light-emitting devices

Two new star-shaped ligands with a 1,3,5-triphenylbenzene core, tmpb (1,3,5-tris[p-2-(2'-pyridyl)benzimidazolylphenyl]benzene), and a 2,4,6-tris(p-biphenyl)-1,3,5-triazine core, tmbt (2,4,6-tris[p-2-(2'-pyridyl)benzimidazolylbiphenyl]-1,3,5-triazine), have been synthesized. Their corresponding trinuclear Ru(II) complexes [Ru3(tmpb)(bpy)6](PF6)6 (3) and [Ru3(tmpt)(bpy)6](PF6)6 (4) have been obtained. Two dinuclear linear Ru(II) complexes with previously reported ligands bmb (1,4-bis[2-(2'-pyridyl)benzimidazolyl]benzene) and bmbp (4,4'-bis[2-(2'-pyridyl)benzimidazolyl]biphenyl) and formulae [Ru2(bmb)(bpy)4](PF6)4 (1) and [Ru2(bmbp)(bpy)4](PF6)4 (2) have also been synthesized. Photophysical and electrochemical properties of the new compounds have been investigated. All four compounds display a characteristic metal-to-ligand-charge transfer (MLCT) absorption band and emit a red light when excited at the maximum of the MLCT band with emission maximum at 624, 629, 623 and 625 nm, respectively in neat films at ambient temperature. The emission quantum efficiency of the four complexes in neat films was determined to be 0.15, 0.17, 0.04 and 0.05, respectively. Light emitting devices based on these four compounds were fabricated by spin-casting the compound as a neat film to an ITO substrate, followed by the deposition of an aluminium metal layer. All devices emit a deep red light and the device behavior resembles that of a light emitting electrochemical cell. The EL maximum of the devices 1, 2, 3, and 4 is at 637, 657, 678, and 655 nm, respectively. All four devices have a fast response time when a sufficiently high voltage is applied. The device based on 2 is the brightest with a maximum luminance of 133 cd m(-2) at 7 V. The performance of devices based on 1, 2, and 4 is in general much more efficient than the device based on [Ru(bpy)3](PF6)2, which was fabricated and evaluated under the same experimental conditions as for the devices based on 1-4.     

Aggregation properties of bis(salicylaldiminato)zinc(II) Schiff-base complexes and their Lewis acidic character

The synthesis, characterization, (1)H NMR, optical absorption and fluorescent properties of a series of amphiphilic Schiff-base bis(salicylaldiminato)zinc(II) complexes are reported. Detailed (1)H NMR, DOSY NMR, optical absorption and fluorescence spectroscopy studies indicate the existence of aggregate species in solutions of non-coordinating solvents. The degree of aggregation is related to the nature of the bridging diamine. Chloroform solutions of complexes where the bridging diamine contains a naphthalene or the pyridine nucleus are always characterized by the presence of defined dimer aggregates, whereas oligomeric aggregates are likely formed by complexes where the bridging diamine contains a benzene ring. In coordinating solvents or in the presence of coordinating species, a complete deaggregation of the complexes occurs, because of the axial coordination to the Zn(II) ion, accompanied by considerable changes in the (1)H NMR and optical absorption spectra. The effect of the alkyl chains length seems to play a minor role in the aggregation properties, as noticed by (1)H NMR data, optical absorption and fluorescence spectra, which remain almost unaltered on changing the chain length.     

Spectroscopic studies on chromium(III), manganese(II), cobalt(II), nickel(II) and copper(II) complexes with hexadentate nitrogen-sulfur donor [N(2)S(4)] macrocyclic ligand

Complexes of transition metals have been synthesized with hexadentate ligand (2,6-bis(((2-mercaptophenyl)thio)methyl)pyridinato)metal(II). These complexes have been synthesized via the two step template reaction by using the benzene dithiol, 2,6-bis(chloro)methyl pyridine and corresponding metal salt as key raw materials. The structures of the complexes have been elucidated on the basis of elemental analysis, molar conductance measurements, magnetic susceptibility measurements, IR, electronic and EPR spectral studies. All of the complexes were found to possess six-coordinated geometry and are of high spin type.