Showing papers in "Transition Metal Chemistry in 2000"

Complexes of a tridentate ONS Schiff base. Synthesis and biological properties

Abstract: Several new complexes of a tridentate ONS Schiff base derived from the condensation of S-benzyldithiocarbazate with salicylaldehyde have been characterised by elemental analyses, molar conductivity measurements and by i.r. and electronic spectra. The Schiff base (HONSH) behaves as a dinegatively charged ligand coordinating through the thiolo sulphur, the azomethine nitrogen and the hydroxyl oxygen. It forms mono-ligand complexes: [M(ONS)X], [M=NiII, CuII, CrIII, SbIII, ZnII, ZrIV or UVI with X = H2O, Cl]. The ligand produced a bis-chelated complex of composition [Th(ONS)2] with ThIV. Square-planar structures are proposed for the NiII and CuII complexes. Antimicrobial tests indicate that the Schiff base and five of the metal complexes of CuII, NiII, UVI, ZnII and SbIII are strongly active against bacteria. NiII and SbIII complexes were the most effective against Pseudomonas aeruginosa (gram negative), while the CuII complex proved to be best against Bacillus cereus (gram positive bacteria). Antifungal activities were also noted with the Schiff base and the UVI complex. These compounds showed positive results against Candida albicans fungi, however, none of them were effective against Aspergillus ochraceous fungi. The Schiff base and its zinc and antimony complexes are strongly active against leukemic cells (CD50 = 2.3–4.3 μg cm−3) while the copper, uranium and thorium complexes are moderately active (CD50 = 6.9–9.5 μg cm−3). The nickel, zirconium and chromium complexes were found to be inactive.

In vitro and in vivo antitumour studies of a new thiosemicarbazide derivative and its complexes with 3d-metal ions

Abstract: A new ligand, 1-(2-furanthiocarbo)-3-thiosemicarbazide (H2ftsc), prepared from thiosemicarbazide and carboxymethyl-2-furandithioate, forms complexes [Mn(ftsc)(H2O)2], [Pd(ftsc)] · 2H2O, [M(Hftsc)(acac)2] (M = CoIII or CrIII), [M(Hftsc)2(acac)] (M = MnIII or FeIII) and [Zn(Hftsc)2] · 2H2O, which were characterized by elemental analyses, magnetic susceptibility, i.r., electronic and n.m.r. spectral data. The Mossbauer spectra of [Fe(Hftsc)2(acac)] at 298 K and 80 K suggest the presence of high-spin iron(III) with an S = 5/2 state. In vivo and in vitro antitumour activity of the ligand and the complexes have been screened towards several tumour cell-lines.

Coordination chemistry and biological activity of two tridentate ONS and NNS Schiff bases derived from S-benzyldithiocarbazate

Abstract: Two tridentate Schiff bases having ONS and NNS donor sequences were prepared by condensing S-benzyldithiocarbazate (NH2NHCSSCH2Ph) (SBDTC) with pyridine-2-carboxaldehyde and salicylaldehyde, respectively. Complexes of these ligands with NiII, ZnII, CrIII, CoII, CuII, and SnII were studied and characterized by elemental analyses and various physico-chemical techniques. NiII, CuII, ZnII and SnII complexes were four-coordinate while the CrIII, SrIII and CoIII complexes were six-coordinate. The ONS Schiff base was moderately active against leukemia, while its zinc, antimony and cobalt complexes were strongly active against leukemic cells with DC50 = 0.35–5.00.

Synthesis, spectral and antimicrobial activity studies of o-aminoacetophenone o-hydroxybenzoylhydrazone complexes

Abstract: Coordination compounds of MnII, CoII, NiII, CuII, ZnII, CdII and HgII ions with o-aminoacetophenone o-hydroxybenzoylhydrazone (AAOHBH) were synthesized and characterized by elemental analyses, molar conductivity, magnetic moments (at ca. 25 °C) and spectral (i.r., u.v., n.m.r. and m.s.) studies. The i.r. spectra show that the ligand acts in a monovalent bidentate, neutral bidentate and/or neutral tridentate fashion, depending on the metal salt used and the reaction medium. Tetrahedral structures are proposed for both CoII and NiII complexes and square planar for CuII complexes on the basis of magnetic and spectral evidence. The complex formation in solution was investigated potentiometrically and spectrophotometrically. Spectral studies in solution show that the ligand can be used for the microdetermination of CoII ion within a metal concentration up to 46.3 p.p.m. The electrical conductivity of AAOHBH and its metal complexes was determined. The tendency of AAOHBH to form complexes with CoII, NiII, CuII, CdII and HgII ions in 50% aqueous-dioxane was studied by pH measurements.

Synthesis, spectroscopic, magnetic and biological activity studies of copper(II) complexes of an antipyrine Schiff base

Abstract: The Schiff base, 4-(2-pyrrolylmethylideneamino)antipyrine (HPAP), (1), and its copper(II) complexes were synthesized and characterized by elemental analysis and by physical and spectral methods such as i.r., u.v.–vis., 1H-n.m.r., 13C-n.m.r. and e.s.r. as well as by molar conductance and magnetic moment determinations. Both the bis-ligand, [(HPAP)2Cu]X2 (4, 5), [(PAP)2Cu] (6), and the dimer, [(PAP)Cu]2X2 (2, 3), complexes were isolated. In these complexes, the Schiff base acts as a bidentate or tridentate neutral or monobasic ligand. Interaction of the isolated [(PAP)Cu]2Cl2 (2), with strong coordinating organic bases was studied and the resultant adducts, [(PAP)CuLs]Cl; Ls = pyridine (7), α-picoline (8), β-picoline (9), γ-picoline (10) or n-propylamine (11), were isolated and characterized. Biological activity screening was studied and an activity correlation coefficients matrix was constructed for HPAP and the copper(II) complexes against gram-positive, gram-negative and fungi species. The copper content, structure of the complex as well as the degree of exposure of the metal center control the biological activity of the isolated complexes.

Nuclease activity of 2-substituted heteroaromatic thiosemicarbazone and semicarbazone copper(II) complexes

Abstract: Copper(II) Schiff base complexes derived from furan-2-carboxaldehyde, 2-furylmethyl ketone, thiophene-2-carboxaldehyde and methyl-2-thienyl ketone with semicarbazide and thiosemicarbazide have been prepared and characterized by analytical, i.r., electronic, e.s.r. and c.v. spectral data. The electronic spectral d–d band position varies from 744–415 nm in pyridine and 872–371 nm in DMF. E.s.r. g∥ values lie between 2.1439 and 2.3149 at LNT. All complexes undergo quasi-reversible one-electron electrochemical reduction (CuIII/CuII) in the 0.42–0.52 V potential range. The electron transfer is much faster in thiosemicarbazone complexes compared to semicarbazone complexes. All these copper(II) complexes showed increased nuclease activity in presence of oxidant.

Unusual rate inhibition of manganese(II) assisted oxidation of citric acid by chromium(VI) in the presence of ionic micelles

Abstract: The kinetics and mechanism of citric acid oxidation by CrVI; catalyzed by MnII, has been studied in H2O and in the presence of anionic and cationic surfactants. A linear correlation between k obs −1 and [MnII]−1 was found, satisfying the Michaelis–Menten kinetics. The rate-determining step is the decomposition of complex HCrO4–citric acid–MnII formed between citric acid–MnII and CrVI. Based on kinetic data, a one-step three-electron oxidation mechanism has been proposed. The rate decreased with increase in concentration of the cationic surfactants cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB), while anionic sodium dodecyl sulphate (SDS) had no effect on the rate. The data have been interpreted in terms of reaction in the aqueous phase. The effect of added anions, such as chloride, bromide, nitrate, and sulphate, has been studied and discussed. The activation parameters (ΔH ‡ and ΔS ‡) were significantly affected by the presence of 10.0 × 10−4 mol dm−3 of CTAB or CPB.

Transition metal orotic acid complexes

Abstract: Complexes of orotic acid with transition metals (Cu2+, Mn2+, VO2+, Zn2+, Hg2+, Cd2+, Fe3+, Cr3+, and Ag+) have been prepared and characterized by elemental, conductivity, magnetic measurements, i.r., n.m.r. and diffuse reflectance spectra. The ligand, in its monoanion form, coordinates through the carboxylic group to the metal. The Co2+ complex was also isolated under alkaline conditions and studied.

Copper(II), nickel(II), cobalt(II) and oxovanadium(IV) complexes of substituted β-hydroxyiminoanilides

Abstract: Complexes of the general formula, ML2 [M = CuII, NiII, CoII and OVIV; L = 1,2,3,5,6,7,8,8a-octahydro-3-hydroxyimino-N-(4-X-phenyl)-l-phenyl-5-(phenylmethylene)-2-naphthalenecarboxamide (X = H, Me, OMe, Cl)] have been prepared and characterized on the basis of elemental analysis, magnetic moments and i.r., e.p.r. and electronic spectra. These metal complexes contain the N4 chromophore with the ligand coordinating through nitrogens of the azomethine and deprotonated anilide functions. C.v. measurements indicate that the copper(II) complexes are quasi-reversible in acetonitrile solution. Square planar and square pyramidal structures are assigned respectively to the copper(II) and oxovanadium(IV) complexes, whereas tetrahedral geometry is assigned to the nickel(II) and cobalt(II) complexes. Deprotonated anilide nitrogen is involved in coordination and the presence of an electron-donating group para to the anilide function decreases the ΔE values of the d–d transitions while the value is found to increase when electron-withdrawing groups are substituted. Line spacing in the e.p.r. spectra of the copper(II) and oxovanadium(IV) complexes increases when methyl group is para to the anilide group, and decreases when this group is replaced by methoxy or chloro. The ν(C–N) of the anilide group and the ν(C-N) of the azomethine function of the oxime metal complexes are metal-sensitive and the blue shift for the above stretching frequencies follows the order: copper(II) > oxovanadium(IV) > nickel(II) ≈ cobalt(II).

Synthesis, spectral and cytotoxicity studies of palladium(II) and platinum(II) amino acid Schiff base complexes

Abstract: Novel PdII and PtII complexes of substituted o-hydroxyacetophenone-glycine have been synthesized, and characterized by conductivity measurements, i.r., electronic and 1H-n.m.r. spectra. The spectral data indicate that the ligands are monobasic bidentate, coordinating through imino nitrogen and the carboxylate group. A four coordinate square planar configuration has been proposed for all the complexes. The ligands, as well as their PdII and PtII complexes, exhibit potent cytotoxic activity against Ehrlich ascites tumour cells in vitro, but appear to be more active in vivo.

Nuclease activity of mixed ligand complexes of copper(II) with heteroaromatic derivatives and picoline

Abstract: New picoline adducts with carbamic acid [(furan-2-yl)methylene]hydrazide–CuII (CFMH) (1); thiocarbamic acid [(furan-2-yl)methylene]hydrazide–CuII (TFMH) (2); carbamic acid [(furan-2-yl)ethylidene]hydrazide–CuII (CFEH) (3), thiocarbamic acid [(furan-2-yl)ethylidene]hydrazide–CuII (TFEH) (4); carbamic acid [(thiophene-2-yl) methylene]hydrazide–CuII (CTMH) (5), thiocarbamic acid [(thiophene-2-yl)methylene]hydrazide–CuII (TTMH) (6), carbamic acid [(thiophene-2-yl)ethylidene]hydrazide–CuII (CTEH) (7), thiocarbamic acid [(thiophene-2-yl)ethylidene]hydrazide–CuII (TTEH) (8) have been prepared and characterized by analytical, i.r., electronic, e.s.r. and c.v. spectral data. The electronic spectra suggest distorted octahedral geometry for all the picoline adducts. E.s.r. g ∥ values lie between 2.251–2.286 at l.n.t. All the adducts undergo a quasi-reversible one-electron reduction in the range +0.47 to +0.51 V versus s.c.e., attributable to the CuIII/CuII redox couple. The electron transfer is much faster in the semicarbazone complexes than in the thiosemicarbazone complexes. All adducts showed increased nuclease activity in the presence of oxidant; the nuclease activity is compared with that of the parent copper(II) complexes.

Alternating ferromagnetic and antiferromagnetic interactions in the azido-bridged copper(II) chain compound [Cu(phen)(N3)2]n

Abstract: Single crystals of a copper(II) chain compound**, [Cu(phen)(N3)2] n (phen = 1,10-phenanthroline), were obtained and its crystal structure was determined by X-ray diffraction methods. The complex crystallizes in the space group P1¯ and is made up of neutral chains of copper(II) ions bridged by two azide groups exhibiting an asymmetrical tri-dentate μ(1,1,3) coordination mode. The copper atoms have a distorted CuN6 octahedral environment: the basal plane is built of two nitrogen atoms from a chelating phen molecule and two azide nitrogens from one bridging and one terminal azide, whereas two nitrogens from two bridging azides fill the axial positions. The intrachain copper(II)–copper(II) separation is 3.396(1) and 5.700(1) A. The magnetic behavior was investigated in the 5–300 K range. Weak intrachain alternating antiferromagnetic (J = −6.56 cm−1) and ferromagnetic (αJ = 12.76 cm−1) interactions were observed.

Nickel(II) and copper(II) complexes of macrocyclic and acyclic Schiff-base ligands derived from new asymmetrical tripodal tetraamines and 2,6-diacetylpyridine

Abstract: The asymmetrical tripodal 4,2,2′-tetraamine N{(CH2)4NH2}{(CH2)2NH2}2 bee, 3,2,2′-tetraamine N{(CH2)3NH2} {(CH2)2NH2}2 pee, and 3,3′,2-tetraamine N{(CH2)3NH2}2{(CH2)2NH2} ppe ligands have been prepared. In the presence of CuII or NiII ions, these ligands condense with 2,6-diacetylpyridine. In some cases, cyclization occurs and new isomers of CR-type with a pendant primary amine group are formed. In the other cases ring closure does not occur and coordinated acyclic hexadentate ligands have been isolated. At room temperature and in absolute methanol the latter acyclic complexes are usually the only products. I.r., u.v.–vis., reflectance spectra and magnetic moments for the complexes were recorded.

Kinetics and mechanism of the color removal from congo red with hydrogen peroxide catalyzed by supported zirconium oxide

Abstract: The kinetics of the oxidative color removal from congo red dye using H2O2 in conjunction with transition metal ions supported on ZrO2 were studied. The rate of reaction is first order on H2O2, the catalyst, and in congo red. It attains a limiting rate at higher concentrations of reagent. Also, the rate of reaction decreases with increasing [H+], due to protonation of the substrate amino groups, as well as to the low deprotonation constant of H2O2 in acid medium. Addition of KCl to the mixture increased the rate of reaction. The catalytic activity of the catalysts lies in the following order: AgI > CuII > HgII > CoII > MnII > FeIII > NiII > ZrO2 which is correlated with the redox potential, mg loading and % surface content of the supported metal ions. A probable mechanism for the oxidation processes has been suggested, which is consistent with the experimental results.

Ruthenium(II) 2-hydroxybenzophenone N(4)-substituted thiosemicarbazone complexes

Abstract: New ruthenium(II) complexes with 2-hydroxybenzophenone N(4)-substituted (Me, Ph and/or piperidyl) thiosemicarbazones have been prepared and characterised by elemental analysis, molar conductivity, thermal analysis, spectroscopy (i.r., 1H-n.m.r. and u.v.–vis.) and by cyclic voltammetry. The thiosemicarbazones coordinate to ruthenium(II) as mononegative tridentate ligands via the deprotonated hydroxyl group, N1 nitrogen and thione sulphur centres. The redox properties, nature of the electrode processes and the stability of the complexes towards oxidation in CH2Cl2 are discussed. The change in the E 1/2 values of the complexes can be related to the basicity of the N(4)-substituents. All the complexes display an irreversible one-electron charge-transfer couple in the potential range studied.

1,2-Bis-(2-benzimidazolyl)-1,2-ethanediol and 1,4-bis-(2-benzimidazolyl)-1,2,3,4-butanetetraol PdCl2 complexes

Abstract: The 1,2-bis-(2-benzimidazolyl)-1,2-ethanediol (EH2) and 1,4-bis-(2-benzimidazolyl)-1,2,3,4-butanetetraol (TH4) ligands form 4-coordinate mono- and bi-metallic complexes with PdCl2, respectively. In Pd(EH2)Cl2 the ligand acts as a bidentate through two of the nitrogen atoms. On the other hand, in Pd2(TH4)Cl4 the ligand coordinates to two palladium atoms through both bis-benzimidazole nitrogen atoms and two oxygen atoms of the hydroxy groups, forming two different isomers. The complexes were characterised by analytical data, magnetic susceptibility, molar conductivity, and also by i.r., 1H- and 13C-n.m.r. spectra.

Catalytic activity of a zirconium(IV) oxide surface supported with transition metal ions

Abstract: The kinetics of H2O2 decomposition have been investigated using ZrO2 supported with transition metal ions including CuII, AgI, HgII, CoII, MnII, NiII and FeIII. At pH = 6.8, the reaction rate exhibits a first order dependence on the initial H2O2 concentration at low concentrations. The order of activity of the different catalysts is strongly dependent on the [H2O2]0 used. The reaction proceed via the formation of the peroxo-intermediate which has an inhibiting effect on the reaction rate. The rate increases with increasing pH, and attains a limiting rate at higher pH's. A reaction mechanism is proposed involving liberation of HO2 radicals from the peroxo-intermediate as the rate-determining step.

Crystal structures and voltammetric behavior of three copper(II) complexes derived from bulky Schiff bases

Abstract: Three Schiff base copper(II) complexes have been prepared and characterized by elemental analysis, mass spectra, i.r., electronic spectra, μeff and X-ray crystal structures. Cyclic voltammetry studies on the complexes indicate a dependence of the cathodic potentials upon electronic effects, but independence on the solid state structure.

Mixed ligand complexes involving aminoacid dithiocarbamates, substituted phosphines and nickel(II)

Abstract: Mixed ligand complexes involving four aminoacid dithiocarbamates (RR′dtc = glydtc− (R = H; R′ = H), methdtc− (R = H; R′ = C3H7S), sardtc− (R = Me; R′ = H), trydtc− (R = H; R′ = C9H8N), substituted phosphines [PPh3, Ph2PCH2CH2PPh2(dppe)] and nickel(II) are reported. All are diamagnetic. Thermal analyses of the complexes are in keeping with the proposed formulae. Thermal decomposition of the dithiocarbamate moiety proceeds through the formation of Ni(SCN)2. PPh3 and dppe are lost in the initial decomposition stages.

Nickel(II), copper(II), palladium(II) and platinum(II) complexes of bidentate SN ligands derived from S-alkyldithiocarbazates and the X-ray crystal structures of the [Ni(tasbz)2] and [Cu(tasbz)2] · CHCl3 complexes

Abstract: New complexes of general empirical formula, [M(NS)2] · nCHCl3 (M = NiII, CuII, PdII or PtII; NS = anionic form of the thiophene-2-aldehyde Schiff bases of S-methyl- and S-benzyldithiocarbazate; n = 0, 1) have been synthesized and characterized by physico-chemical techniques. Magnetic and spectroscopic evidence support a square-planar structure for these complexes. The crystal structures of the [Ni(tasbz)2] and [Cu(tasbz)2] · CHCl3 complexes (tasbz = anionic form of the thiophene-2-aldehyde Schiff base of S-benzyldithiocarbazate) have been determined by X-ray diffraction. Both complexes have a trans-planar structure in which the two Schiff base ligands are coordinated to the metal(II) ion as uninegatively charged bidentate ligands via the thiolate sulfur and the azomethine nitrogen atoms.

Correlation between i.r. spectra and thermal decomposition of cobalt(II), nickel(II), copper(II) and mercury(II) complexes with piperidinedithiocarbamate and pyrrolidinedithiocarbamate

Abstract: The thermal decomposition of pyrrolidinedithiocarbamate and piperidinedithiocarbamate complexes of CoII, NiII, CuII and HgII have been studied by thermogravimetry and differential scanning calorimetry. The decomposition intermediates and final products were identified by their X-ray diffraction patterns. The i.r. spectra are discussed in terms of the thermal decomposition pathways.

Soft template synthesis in copper(II)–dithiooxamide–methanal, copper(II)–dithiooxamide–ethanal and copper(II)–dithiooxamide–propanone triple systems in a copper(II)hexacyanoferrate(II) gelatin-immobilized matrix

Abstract: Novel complexing processes in the CuII–dithiooxamide–methanal, CuII–dithiooxamide–ethanal and CuII–dithiooxamide–propanone triple systems proceeding under specific conditions, to copper(II)hexacyanoferrate(II) gelatin-immobilized matrix systems in contact with aqueous-alkaline (pH ∼ 12) solutions containing dithiooxamide and methanal, ethanal or propanone, have been studied. It has been shown that template synthesis leading to the formation of macrocyclic coordination compounds (2,8-dithio-3,7-diaza-5-oxanonandithioamide-1,9)copper(II), (2,8-dithio-3,7-diaza-4,6-dimethyl-5-oxanonandithio-amide-1,9)copper(II) and (4,4′,6-trimethyl-2,8-dithio-3,7-diazanonen-6-dithioamide-1,9)copper(II), respectively, takes place under such conditions. Dithiooxamide, methanal, ethanal and propanone act as ligand synthons in these processes.

Copper(II) complexes of 2-pyridineformamide N(4)-methylthiosemicarbazone

Abstract: Reduction of 2-cyanopyridine by sodium in dry MeOH in the presence of N(4)-methylthiosemicarbazide produces 2-pyridineformamide N(4)-methylthiosemicarbazone, HAm4M. Copper(II) complexes have been prepared and characterized by molar conductivities, magnetic susceptibilities and spectroscopic techniques. Coordination is via the pyridyl nitrogen, imine nitrogen and thione or thiolato sulfur, when coordinating as the neutral or anionic ligand, respectively.

Coordination chemistry and biological activity of bidentate and quadridentate nitrogen–sulfur donor ligands and their complexes

Abstract: The ligand S-benzyldithiocarbazate (SBDTC) acts as a bidentate sulfur–nitrogen chelating agent. The reaction of SnII or SbIII with SBDTC under alkaline conditions gives complexes of composition [Sn(SBDTCA)2] · 2H2O and [Sb(SBDTCA)Cl2 · 2H2O]. A quadridentate Schiff base of SBDTC with benzil, having a donor sequence SNNS, yields complexes, [Cd(SNNS)] and [Zr(O)(SNNS) · H2O]. The ligands and the complexes have been characterized by elemental analyses, i.r., u.v.–vis., molar conductance measurements and 1H-n.m.r. spectroscopy. SBDTC, SnII and SbIII complexes and the SNNS Schiff base together with its CdII and ZrIV complexes display significant antifungal, antibacterial and anti-cancer activity. The SnII complex and the SNNS free Schiff base were very effective against Melanoma (skin cancer cells). The SBDTC and its SnII complex were also very effective against Renal carcinoma (kidney cancer cells). The results have been compared with those of the uncomplexed metal salts and the free ligands. The minimum concentrations for the evaluation of the above activities for CD50 of the samples were in the 1.0–15 μg cm−3 range.

New ruthenium(III) complexes containing tetradentate Schiff bases and their antibacterial activity

Abstract: Ruthenium(III) complexes, [RuX(EPh3)(LL′)] (X = Cl, Br; E = P, As; LL′-acactet, dbm-tet, dbm-o-ph), have been synthesised by reacting [RuCl3(PPh3)3], [RuCl3(AsPh3)3], [RuBr3(AsPh3)3] or [RuBr3(PPh3)2(MeOH)] with tetradentate Schiff bases such as bis(acetylacetone)tetramethylenediimine (H2acactet), bis(dibenzoylmethane)tetramethylenediimine (H2dbmtet) and bis(dibenzoylmethane)-o-phenylenediimine (H2dbm-o-ph) All the complexes have been characterised by elemental analysis, ir, electronic spectra, epr, magnetic moment and cyclic voltammetric data and an octahedral structure has been tentatively proposed These new complexes have been tested for their antibacterial activities

Low-temperaturic template synthesis of macrocyclic cobalt(III) chelates with (N,N,S,S)-donor atomic ligands in the cobalt(II)–dithiooxamide-formaldehyde and cobalt(II)–dithiooxamide-glyoxal systems in the Co2[Fe(CN)6]-gelatin-immobilized matrices

Abstract: The complexing processes in the triple cobalt(II)–dithiooxamide-formaldehyde and cobalt(II)–dithiooxamide-glyoxal systems taking place in the cobalt(II)hexacyanoferrate(II) gelatin-immobilized matrix in contact with aqueous alkaline solutions (pH ca. 12) containing (dithiooxamide + formaldehyde) and (dithiooxamide + glyoxal), have been studied. Template synthesis leading to macrocyclic coordination compounds with tetradentate N,N,S,S-donor ligands-(2,8-dithio-3,7-diaza-5-oxanonan-dithioamide-1,9) and (2,7-dithio-3,6-diazaoctadien-3,5-dithioamide-1,8) with CoII–CoIII redox-process occurs under these specific conditions where dithiooxamide, formaldehyde and glyoxal are the ligand synthons.

Rhodium(I) carbonyl complexes of triphenylphosphine chalcogenides and their catalytic activity

Abstract: Rhodium(I) carbonyl complexes [Rh(CO)2ClL] where L = Ph3PO, Ph3PS and Ph3PSe, were synthesized and characterized by elemental analysis, i.r. and by 1H-, 13C- and 31P-n.m.r. spectroscopy. The vBD;(CO) band frequencies in the complexes follow the order: Ph3PO > Ph3PS > Ph3PSe, in keeping with the hard/soft nature of the interactions. The complexes undergo oxidative additions with electrophiles such as MeI, PhCH2Cl and I2 to give, e.g. [Rh(CO)(COMe)ClIL] which react with PPh3 to give trans-[Rh(CO)Cl(PPh3)2]. The catalytic activity of the [Rh(CO)2ClL] complexes in carbonylation of MeOH is higher than that of the well-known [Rh(CO)2I2]− species.

Structural studies on iminophosphine ligands and their palladium complexes

Abstract: The crystal and molecular structures of the iminophosphine o-(Ph2P)C6H4CH=NC6H4OMe-4 (1) and its palladium complexes [Pd(η3-C3H5){o-(Ph2P)C6H4CH=NC6H4OMe-p}]BF4 (2) and [Pd(η2-fn){o-(Ph2P)C6H4CH=NC6H4OMe-4}] [fn = fumaronitrile, (3)] have been determined by X-ray analysis. In the free ligand (1), the planar imino group of E configuration is oriented, relative to the PPh2 unit, so that the CH=N hydrogen atom points towards phosphorus, with the nitrogen atom on the opposite side. In (2) and (3) the iminophosphine behaves as a P,N-chelate ligand, this coordination mode being achieved by the imino group rotation of 169.3 ° and 145.3 °, respectively, around its bond with the ortho disubstituted phenyl ring. Complex (2) shows a structural disorder with two different orientations of the allyl ligand. The trigonal planar coordination around the central metal in complex (3) involves the P- and N-donor atoms of (1) and the η2-bound olefin, with a marked lengthening of the olefinic carbon-carbon bond. In both the complexes, the chelate six-membered ring of the iminophosphine with palladium is not coplanar with the N-Pd-P coordination plane, the imino carbon atom and the ortho disubstituted phenyl group lying on the same side out of the N-Pd-P plane, whereas the N-substituent and one of the PPh2 groups are on the opposite side. The 1H-n.m.r. spectra at low temperatures of (2) and (3), and of [Pd(η2-tmetc){o-(Ph2P)C6H4CH=NCMe3}] [tmetc = tetramethyl ethylenetetracarboxylate, (4)] are interpreted on the basis of a non-rigid conformation of the chelate iminophosphine, which undergoes a fast dynamic process whereby the N- and P-substituents move above and below the coordination plane.

Binuclear bis(β-diketonato) complexes of ruthenium(III) containing triphenylphosphine or triphenylarsine

Abstract: Stable bis(β-diketonato) bridged binuclear complexes prepared by reacting [RuX3(EPh3)3] (X = Cl or Br; E = P or As) with (RCO)(MeCO)CH–Y–CH(COR)(COMe) [R = Me or Ph; Y = (CH2)6, (CH2)10] in a 2:1 molar ratio in benzene, have been characterised by elemental analyses, i.r., electronic, e.p.r. and cyclic voltammetry. The oxidation state of the metal ion in these complexes is confirmed as + 3 by electrochemical and by e.p.r. measurements. The complexes belong to a low-spin d5 configuration. An attempt has been made to ascertain the effect of the length of the bridging ligand on the electron transfer processes by cyclic voltammetry in these binuclear complexes. Based on the above studies an octahedral geometry has been tentatively proposed. The new complexes have been subjected to the antifungal activity studies.

Synthesis and structure of nickel(II) and palladium(II) carbene complexes containing the 1,3-diallylimidazolidin-2-ylidene ligand

Abstract: Trans-carbene complexes of nickel(II) and palladium(II) with 1,3-diallylimidazolidin-2-ylidene (LAllyl) were prepared and characterized by i.r., n.m.r. and mass spectra. The structure of two complexes were determined by single crystal X-ray diffraction techniques.