Photophysical Properties and OLED Applications of Phosphorescent Platinum(II) Schiff Base Complexes

The syntheses, crystal structures, and detailed investigations of the photophysical properties of phosphorescent platinum(II) Schiff base complexes are presented. All of these complexes exhibit intense absorption bands with λ_max in the range 417–546 nm, which are assigned to states of metal‐to‐ligand charge‐transfer (¹MLCT) ¹[Pt(5d)→π*(Schiff base)] character mixed with ¹[lone pair(phenoxide)→π*(imine)] charge‐transfer character. The platinum(II) Schiff base complexes are thermally stable, with decomposition temperatures up to 495 °C, and show emission λ_max at 541–649 nm in acetonitrile, with emission quantum yields up to 0.27. Measurements of the emission decay times in the temperature range from 130 to 1.5 K give total zero‐field splitting parameters of the emitting triplet state of 14–28 cm^?1. High‐performance yellow to red organic light‐emitting devices (OLEDs) using these platinum(II) Schiff base complexes have been fabricated with the best efficiency up to 31 cd A^?1 and a device lifetime up to 77 000 h at 500 cd m^?2.     

The Preparation, Characterization and Biological Activity of Palladium(II) and Platinum(II) Complexes of Tridentate NNS Ligands Derived from S-methyl- and S-benzyldithiocarbazates and the X-ray Crystal Structure of the [Pd(mpasme)Cl] Complex

New complexes of general formula, [M(NNS)Cl] (M = Pd^II, Pt^II; NNS = anionic forms of the 6-methyl-2-formylpyridine Schiff bases of S-methyl- and S-benzyldithiocarbazates) have been prepared and characterized by a variety of physico-chemical techniques. Based on conductance and spectral evidence, a square-planar structure is assigned to these complexes. The crystal and molecular structure of the [Pd(mpasme)Cl] complex (mpasme=anionic form of the 6-methyl-2-formylpyridine Schiff base of S-methyldithiocarbazate) has been determined by X-ray diffraction. The complex has a distorted square-planar geometry with the ligand coordinated to the palladium(II) ion via the pyridine nitrogen atom, the azomethine nitrogen atom and the thiolate sulfur atom; the fourth coordination position around the palladium(II) ion is occupied by the chloride ligand. The distortion from a regular square-planar geometry is ascribed to the restricted bite angle of the ligand. Both the Schiff bases exhibit strong cytotoxicity against the human ovarian cancer (Caov-3) cell lines, the S-methyl derivative being two times more active than the S-benzyl derivative. The [Pt(mpasme)Cl] complex is moderately active but the palladium(II) complex is weakly active against this cancer. None of the complexes of Hmpsbz are active against Caov-3. The Schiff base, Hmpasme exhibits moderate activity against the bacteria, MRSA, P. aeruginosa and S. typhimurium but is inactive against B. subtilis. Coordination of the ligand with palladium(II) substantially reduces its activity. The Schiff base, Hmpasbz and its palladium(II) and platinum(II) complexes are inactive against these bacteria. The Schiff bases and their palladium(II) and platinum (II) complexes are inactive against the pathogenic fungi, C. albican, Aspergillus ochraceous and Saccharomyces cerevisiae.     

Metallosurfactant Schiff base cobalt(III) coordination complexes. Synthesis,characterization, determination of CMC values and biological activities

Twelve surfactant Schiff base ligands were synthesized from salicylaldehyde and its chloro-, bromo- and methoxy- derivatives by condensation with long-chain aliphatic primary amines, and a number of mixed ligand cobalt(III) surfactant Schiff base coordination complexes of the type [Co(trien)A]²⁺ were synthesized from the corresponding dihalogeno complexes by ligand substitution. The Schiff bases and their complexes were characterized by physico-chemical and spectroscopic methods. The complexes form foams in aqueous solution upon shaking. The critical micelle concentration (CMC) values of the complexes in aqueous solution were obtained from conductance measurements. Specific conductivity data (at 303–323 K) served for the evaluation of the thermodynamics of micellization ( \Updelta G_\textm⁰ \Updelta G_{\text{m}}^{0} , \Updelta H_\textm⁰ \Updelta H_{\text{m}}^{0} , \Updelta S_\textm⁰ \Updelta S_{\text{m}}^{0} ). The complexes were tested for its antimicrobial activity.     

Synthesis and structures of platinum(II) mixed ligand complexes with purine or piyrimidine bases of DNA and imidazole derivatives. Part 2

Summary Platinum(II) mixed ligand complexes with either purine or pyrimidine and imidazole derivatives were prepared and characterized by i.r., Raman and electronic spectroscopy. The compounds had the general formula [PtL¹L²Cl₂], where L¹ = adenine, guanine, hypoxanthine, cytosine, 2-aminopyrimidine; L² =N-methylimidazole,N-ethyl-imidazole orN-propylimidazole. The platinum(II) complexes had a square planar structure withcis-halogens. Purine or pyrimidine and imidazole derivatived bases acted as monodentate ligands coordinated via the N(7) of purine and N(3) of pyrimidine and imidazole derivatives.     

The Synthesis and Characterization of s‐Triazine‐Cored Tripodal Structure and Its Salen/Salophen‐Bridged Fe/Cr(III) Capped Complexes

A novel Schiff base compound was synthesized, and its complexation properties with Fe(III) and Cr(III) were investigated. Tripodal ligand was synthesized by the reaction of s‐triazine and 4‐hydroxybenzaldehyde. Then a Schiff base involving 8‐hydroxyquinoline was synthesized by the reaction of 5‐aminomethyl‐8‐hydroxyquinoline ( QN ) and 2,4,6‐tris(p‐formylphenoxy)‐1,3,5‐triazine ( TRIPOD ) in methanol/chloroform media. The obtained Schiff base ( QN-TRIPOD ) was then reacted with four trinuclear Fe(III) and Cr(III) complexes including tetradentate Schiff bases N ,N ′‐bis(salicylidene)ethylenediamine (salenH₂)/bis(salicylidene)‐o‐phenylenediamine (SalophenH₂). The synthesized ligand and complexes were characterized by means of elemental analysis carrying out ¹H NMR, FTIR spectroscopy, thermal analyses, and magnetic susceptibility measurements. Finally, metal ratios of the prepared complexes were determined by using atomic adsorption spectrometry.     

Schiff Base Complexes of Rhodium(I) with Tridentate N-Methyl-S-methyldithiocarbazate Ligands

Schiff bases derived from the condensation of β-diketones with N-methyl-S-methyldithiocarbazates yield cis dicarbonyl complexes Rh(CO)₂ (Schiff) on reaction with [Rh(μ-Cl)(CO)₂]₂. Those derived from aromatic aldehydes form trans dicarbonyl complexes. These complexes with excess of triphenylphosphine give only Rh(CO)(PPh₃)(Schiff). cis-1,5-cyclooctadiene (COD) reacts with cis dicarbonyl complexes to yield the carbonyl-free product Rh(COD)(Schiff); similar reactions have not been observed in the case of trans-dicarbonyl complexes. Oxidative addition of bromine to these complexes yields dibromo derivative in which the Schiff base acts as bidentate chelate. Rh(PPh₃)₂(Schiff) complexes have been obtained from the reaction of above Schiff bases with Rh(PPh₃)₃Cl. The structures of these new complexes have been determined based on IR and ¹H NMR spectra.     

Structural Studies with Antimicrobial and Antifertility Activity of a Monofunctional Bidentate Ligand with its Boron(III), Palladium(II), and Platinum(II) Complexes

The reaction of the sulfur donor Schiff base ligand, 7-nitro-3-(indolin-2-one) hydrazinecarbo-thioamide, with phenyldihydroxyboron in benzene, palladium(II)chloride, and platinum(II) chloride, in ethanol, gave the mononuclear tetracoordinated and hexacoordinated complexes. The Schiff base ligand coordinated to the boron atom in 1:1 and 1:2 molar ratios and to the palladium and platinum metals in only 1:2 molar ratios in the presence of an acidic and basic medium. Tentative structural conclusions are drawn for reaction products based upon elemental analysis, electrical conductance, and spectral (electronic, infrared, ¹ H NMR, ¹³ C NMR, and ¹¹ B NMR) data. The antifertility activity of the ligand and its nonmetal/metal complexes are discussed with a comparative study in an effective manner.     

Antimicrobial and anticancer activities of Schiff base ligand and its transition metal mixed ligand complexes with heterocyclic base

A new Schiff base ligand (HL) was prepared via a condensation reaction of quinoline‐2‐carboxaldhyde with 2‐aminophenol in a molar ratio of 1:1. Its transition metal mixed ligand complexes with 1,10‐phenanthroline (1,10‐phen) as co‐ligand were also synthesized in a 1:1:1 ratio. HL and its mixed ligand complexes were characterized using elemental analysis, infrared, ¹H NMR, mass and UV–visible spectroscopies, molar conductance, magnetic measurements, solid reflectance, thermal analysis, electron spin resonance and X‐ray diffraction. Molar conductance measurements showed that all complexes have an electrolytic nature, except Cd(II) complex. From elemental and spectral data, the formulae [M(L)(1,10‐phen)(H₂O)]Cl_x?nH₂O (where M = Cr(III) (x = n = 2), Mn(II) and Ni(II) (x = 1, n = 2), Fe(III) (x = n = 2), Co(II), Cu(II) and Zn(II) (x = 1, n = 2)) and [Cd(L)(1,10‐phen)Cl]?3H₂O for the metal complexes have been proposed. The geometric structures of complexes were found to be octahedral. Powder X‐ray diffraction reflected the crystalline nature of the complexes; however, the Schiff base is amorphous. HL and its mixed ligand complexes were screened against Gram‐positive bacteria (Streptococcus pneumoniae and Bacillus subtilis) and Gram‐negative bacteria (Pseudomonas aeruginosa and Escherichia coli). Antifungal activity was determined against Aspergillus fumigatus and Candida albicans, the data showing that most complexes had activity less than that of the Schiff base while Mn(II), Fe(III) and Ni(II) complexes showed no significant antifungal activity. The anticancer activity of HL and its metal complexes was also studied against breast and colon cell lines. The metal complexes showed IC₅₀ higher than that of HL, especially the Cu(II) complex which showed the highest IC₅₀ against breast cell line.     

Biocidal and catalytic efficiency of ruthenium(III) complexes with tridentate Schiff base ligands

The reaction of the Schiff bases (obtained by condensing isatin with o‐aminophenol/o‐aminothiophenol/o‐aminobenzoic acid) with [RuX₃(EPh₃)₃] (where X = Cl/Br; E = P/As) in benzene afforded new, air‐stable Ru(III) complexes of the general formula [Ru(L)X(EPh₃)₂] (L = dianion of tridentate Schiff bases). In all these reactions, the Schiff base ligand replaces one triphenylphosphine/triphenylarsine and two chlorides/bromides from the ruthenium precursors. The complexes were characterized by elemental analyses, spectral (FT–IR, UV–vis, ¹H and ¹³C NMR for the ligands, and EPR) and electrochemical studies. All the metal complexes exhibit characteristic LMCT absorption bands in the visible region. The catalytic reactivity proved these complexes to be efficient catalysts in the oxidation of alcohols and C? C coupling. All the complexes were screened for their biocidal efficiency against bacteria such as Staphylococcus epidermidis and Escherichia coli and fungi such as Botrytis cinerea and Aspergillus niger at 0.25, 0.50 and 1% concentrations. Copyright © 2010 John Wiley & Sons, Ltd.     

Metal chelates of ligands containing the ONS donor grouping,part I. Metal chelates of Schiff bases derived from fluorinatedβ-diketones and thiosemicarbazide

Summary The Schiff bases RC(OFl)=CFlC(CF₃)=NNlJC(S)NH₂ (R = 2-thienyl, Ph,p-BrC₆H₄,p-MeC₆H₄,p-MeOC₆H₄,m-McOC₆H₄, -naphthy], Prⁱ) have been prepared by condensation of fluorinated -diketones with thiosemicarbazide. By the loss of one or two protons from their tautomeric iminothiol form RC(OH)=CHC(CF₃)=NN=C(SH)NH₂ the Schiff bases act as (i) doubly negatively charged ONS tridentate or (ii) singly negatively charged NS bidentate ligands, respectively. The Schiff bases give dimeric µ₂-dithiolo-bridged complexes M(ONS)₂ (M = Ni, Pd, and Pt). The thiolo-bridges in the nickel complexes can be split by reaction with pyridine to give the monomeric compounds Ni(ONS)py, whereas the palladium and platinum complexes are unreactive towards pyridine. When R = 2-thienyl orp-BrC₆H₄, 1:2 complexes of the type M(HONS)₂ (M = Pd or Pt) were isolated. With copper(II) the Schiff bases yield the complexes Cu^II(ONS). Cu^I(HONS) which are considered to have a polymeric structure involving -thiolo-bridges.     

Spectral,magnetic, biological,and thermal studies of metal(II) complexes of some unsymmetrical Schiff bases

New nickel(II) and copper(II) complexes with unsymmetrical Schiff bases derived from aromatic 2-hydroxy aldehydes were synthesized and characterized by elemental analyses, melting points, ¹H-NMR, magnetic susceptibility, thermogravimetric analysis, differential scanning calorimetry (DSC), infrared (IR), and electronic spectral measurements. Comparison of IR spectra of the Schiff bases and their metal complexes indicated that the Schiff bases are tetradentate, coordinated via the two azomethine nitrogens and the two phenolic oxygens. Magnetic moments and electronic spectral data confirm square-planar geometry for the complexes. Thermal studies reveal a general decomposition pattern, whereby the complexes decomposed partially in a single step due to loss of part of the organic moiety. A single endothermic profile, corresponding to melting point, was observed from the DSC of all complexes, except those whose ligand contained the nitro group, which decomposed exothermally without melting. The Schiff bases and their complexes were screened in vitro against 10 human pathogenic bacteria. The metal(II) complexes exhibited higher antibacterial activity than their corresponding Schiff bases.     

Spectroscopic characterization and electrochemical studies of ruthenium(II) carbonyl complexes containing bidentate Schiff bases and triphenylphosphine or a nitrogen heterocycle

Reactions of ruthenium(II) carbonyl complexes of the type [RuHCl(CO)(PPh₃)₂(B)] [B?=?PPh₃, pyridine (py), piperidine (pip) or morpholine (mor)] with bidentate Schiff base ligands derived from the condensation of 2-hydroxy-1-naphthaldehyde with aniline, o-, m- or p-toluidine in a 1?:?1 mol ratio in benzene resulted in the formation of complexes formulated as [RuCl(CO)(L)(PPh₃)(B)] [L?=?bidentate Schiff base anion, B?=?PPh₃, py, pip, mor]. The complexes were characterized by analyses, IR, electronic and ¹H NMR spectroscopy, and cyclic voltammetric studies. In all cases, the Schiff bases replace one molecule of phosphine and a hydride ion from the starting complexes, indicating that Ru–N bonds in the complexes containing heterocyclic nitrogenous bases are stronger than the Ru–P bond to PPh₃. Octahedral geometry is proposed for the complexes.     

Synthesis,characterization, antibacterial,and thermal studies of unsymmetrical Schiff-base complexes of cobalt(II)

Cobalt(II) complexes of a new series of unsymmetrical Schiff bases have been synthesized and characterized by their elemental analyses, melting points, magnetic susceptibility, thermogravimetric analysis, differential scanning calorimetry, infrared (IR), and electronic spectral measurements. The purity of the ligands and the metal complexes are confirmed by microanalysis, while the unsymmetrical nature of the ligands was further corroborated by ¹H-NMR. Comparison of the IR spectra of the Schiff bases and their metal complexes confirm that the Schiff bases are tetradentate and coordinated via N₂O₂ chromophore. The magnetic moments and electronic spectral data support square-planar geometry for the cobalt(II) complexes. The complexes were thermally stable to 372.3°C and their thermal decomposition was generally via the partial loss of the organic moiety. The Schiff bases and their complexes were screened for in vitro antibacterial activities against 10 human pathogenic bacteria and their minimum inhibitory concentrations were determined. Both the free ligands and cobalt(II) complexes exhibit antibacterial activities against some strains of the microorganisms, which in a number of cases were comparable with, or higher than, that of chloramphenicol.     

Schiff base supported mononuclear organotin(IV) complexes: Syntheses,structures and fluorescence cell imaging

Three mononuclear organotin(IV) complexes supported by Schiff bases have been synthesized. The complexes [(C₆H₅)₂Sn(L)] ( 1 ), [(t‐Bu)₂Sn(L)] ( 2 ) and [(t‐Bu)₂Sn(L')] ( 3 ) (L, L' = deprotonated Schiff bases) were obtained in good yield by the reaction of Schiff bases H ₂ L or H ₂ L′ with corresponding diorganotin dichlorides respectively. All newly synthesized complexes were characterized by means of FT‐IR spectroscopy, elemental analysis and multinuclear (¹H, ¹³C and ¹¹⁹Sn) NMR spectroscopy. In addition, single crystal X‐ray diffraction analyses were employed to establish the solid state molecular structures of these complexes. The structures of 1 – 3 reveal that all complexes are mononuclear with a five‐coordinated tin(IV) centre in it. The absorption and emission properties of all complexes have been investigated. Moreover, cytotoxicity and fluorescence cell imaging studies of theses complexes have been performed.     

Biomolecular docking,antimicrobial and cytotoxic studies on new bidentate schiff base ligand derived metal (II) complexes

Three new metal complexes [Cu(L)₂] (1), [Co(L)₂] (2) and [Zn(L)₂] (3) have been prepared by the reaction of hydrated salts of metal (II) acetate with new Schiff base ligand HL, [2‐((4‐(dimethylamino)phenylimino)methyl)‐4,6‐di‐t‐butylphenol] and characterized by different physico‐chemical analyses such as elemental analysis, single XRD, ¹H NMR, FTIR and UV–Vis spectroscopic techniques. Their biomolecular docking, antimicrobial and cytotoxicity studies have also been demonstrated. The proposed structure of Schiff base ligand HL and complex 2 are confirmed by Single crystal X‐ray crystallography study. This analysis revealed that metal (II) complexes remain in distorted tetrahedral coordination environments. The electronic properties such as HOMO and LUMO energies are carried out by gaseous phase DFT/B3LYP calculations using Gaussian 09 program. Complex 1 showed a good binding propensity to the DNA and HSA, during the assessment of docking studies. Schiff base ligand HL and its metal (II) complexes, 1–3 screened for their in vitro antimicrobial activities using the disc diffusion method against selected microbes. Complex 1 shows higher antimicrobial activity than complexes 2, 3 and Schiff base ligand HL. According to the results obtained from the cytotoxic studies, Schiff base ligand HL and its metal (II) complexes 1–3 have better cytotoxicity against MCF‐7 cell lines with potency higher than the currently used chemotherapeutic agent cyclophosphamide.     

Synthesis,characterization and antifungal activity of glycylglycine Schiff base complexes of 3d transition metal ions

Summary Two new Schiff bases, N-4-hydroxysalicylidene-glycylglycine (K·GGRS·H₂O), N-O-vanillal-glycylglycine (K· GGVS·3H₂O) and their manganese(II), cobalt(II), nickel(II) and copper(II) complexes have been synthesized and characterized by elemental analysis, t.g.a., molar conductance, i.r. and u.v. spectral studies. The ¹³Cn.m.r. spectrum of one of the Schiff base ligands has been recorded. The results show that the ligand is coordinated to the central metal ion via amide nitrogen, imino nitrogen, phenolic oxygen and carboxyl oxygen to form a quadridentate complexes. Some of the complexes exhibit strong inhibitory action towards Candida albicans and Cryptococcus neoformans.     

New diorganotin(IV) complexes with some Schiff bases derived from β-diketones: synthesis,spectral properties,thermal analysis,and antibacterial activity

The Schiff bases H₂L^a, H₂L^b, and H₂L^c have been prepared from the reaction of 2-amino-4-chlorophenol with acetylacetone, benzoylacetone, and dibenzoylmethane, respectively. Organotin(IV) complexes [SnPh₂(L^a)] (1), [SnPh₂(L^b)] (2), [SnPh₂(L^c)] (3), and [SnMe₂(L^c)] (4) have been synthesized from the reaction of SnPh₂Cl₂ and SnMe₂Cl₂ with these Schiff bases. The synthesized complexes have been characterized by elemental analysis and FT-IR, ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy. Spectroscopic data suggest the Schiff bases are completely deprotonated and coordinated tridentate to tin via imine nitrogen and phenolic and enolic oxygen atoms; the coordination number of tin is five. Thermal decomposition of the complexes has been studied by thermogravimetry. The in vitro antibacterial activities of the Schiff bases and their complexes have been evaluated against Gram-positive (Bacillus subtilis and Staphylococcus aureus) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria. H₂L^a, H₂L^c, and all complexes exhibited good activities and have potential as drugs.     

Ruthenium(II) complexes containing bidentate Schiff bases and their antifungal activity

The reactions of ruthenium(II) complexes, [RuHCl(CO)(PPh₃)₂(B)] [B = PPh₃, pyridine (py) or piperidine (pip)], with bidentate Schiff base ligands derived by condensing salicylaldehyde with aniline, o-, m- or p-toluidine have been carried out. The products were characterised by analytical, i.r., electronic, ¹H-n.m.r. and ³¹P-n.m.r. spectral studies and are formulated as [RuCl(CO)(L)(PPh₃)(B)] (L = Schiff base anion; B = PPh₃, py or pip). An octahedral structure has been tentatively proposed for the new complexes. The Schiff bases and the new complexes were tested in vitro to evaluate their activity against the fungus Aspergillus flavus.     

New copper (II) complexes of tridentate dibasic ONO donor ligands derived from salicylaldehyde or substituted salicylaldehydes ando-hydroxybenzylamine

Summary Copper(II) complexes with the Schiff bases derived from Salicylaldehyde and its 5-chloro-, 5-bromo-, 5-nitro-, 3-ethoxy- and 3,5-dichloro derivatives, or from 2-hydroxy-1-naphthaldehyde ando-hydroxybenzylamine, have been synthesized and characterized on the basis of elemental analysis, i.r. and electronic spectra and magnetic susceptibility measurements. The Schiff bases behave as tridentate dibasic O, N and O donor ligands and form complexes with 11 metal: ligand stoichiometry which exhibit subnormal magnetic moments ( _eff=0.88–0.98 B.M.) and are involved in strong antifer-romagnetic exchange (–J=482–525 cm^–1). The complexes exhibit a d-d band atca. 1600 cm^–1. A dimeric structure with aminophenolic oxygen atoms as the bridging atoms is proposed on the basis of i.r. and magnetic data.     

Synthesis and characterization of biologically active new Schiff bases containing 3‐functionalized 1,2,4‐triazoles and their zinc(II) complexes: crystal structure of 4‐bromo‐2‐[(E)‐(1H‐1,2,4‐triazol‐3‐ylimino)‐ methyl]phenol

Biologically active triazole Schiff bases ( L ¹  L ³ ) derived from the reaction of 3‐amino‐1,2,4‐triazole with chloro‐, bromo‐ and nitro‐ substituted salicylaldehydes and their Zn(II) complexes (1–3) have been synthesized and characterized by their physical, spectral and analytical data. Triazole Schiff bases potentially act as tridentate ligands and coordinate with the Zn(II) metal atom through salicylidene‐O, azomethine‐N and triazole‐N. The complexes have the general formula [M(L‐H)₂], where M = zinc(II) and L = ( L ¹ – L ³ ), and observe an octahedral geometry. The Schiff bases and their Zn(II) complexes have been screened for in‐vitro antibacterial, antifungal and brine shrimp bioassay. The biological activity data show the Zn(II) complexes to be more potent antibacterial and antifungal than the parent simple Schiff bases. Copyright © 2011 John Wiley & Sons, Ltd.