Preparation,spectroscopic characterization and X-ray crystal and molecular structures of nickel(II), copper(II) and zinc(II) complexes of the Schiff base formed from isatin and S-methyldithiocarbazate (Hisa-sme)

Complexes of general formula, [M(isa-sme)₂] · n(solvate) [M = Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺; isa-sme = monoanionic form of the Schiff base formed by condensation of isatin with S-methyldithiocarbazate; n = 1 or 1.5; solvate = MeCN, DMSO, MeOH or H₂O] have been synthesized and characterized by a variety of physicochemical techniques. An X-ray crystallographic structure determination of the [Ni(isa-sme)₂] · MeCN complex reveals a six-coordinate, distorted octahedral geometry. The two uninegatively charged, tridentate, Schiff base ligands are coordinated to the nickel(II) ion meridionally via the amide O-atoms, the azomethine N-atoms and the thiolate S-atoms. By contrast, the crystal structure of [Zn(isa-sme)₂] · MeOH shows a four-coordinate distorted tetrahedral geometry. The two dithiocarbazate ligands are coordinated as N, S bidentate chelates with the amide O-atom not coordinated. The structure of the copper(II) complex [Cu(isa-sme)₂] · DMSO is complicated and comprises two different complexes in the asymmetric unit, one four- and the other five-coordinate. The four-coordinate copper(II) has a distorted (flattened) tetrahedral geometry as seen in the Zn(II) analogue whereas the five-coordinate copper(II) has a distorted square-pyramidal geometry with one ligand coordinated to the copper(II) ion as a tridentate (N, S, O) ligand and the other coordinated as a bidentate N, S chelate. EPR spectroscopy indicates that in solution only one form is present, that being a distorted tetrahedral complex.     

A ratiometric fluorescent chemodosimeter for Cu(II) in water with high selectivity and sensitivity

Coumarin derivative 1 was synthesized as an efficient ratiometric chemodosimeter for the detection of Cu(II) in 99% water/DMSO (v/v) at pH 7.0. Mechanism studies suggested that 1 formed a complex with Cu(II) at 2:1 ratio accompanied by quenching of green fluorescence at 524 nm; when the solution was heated to 50 °C for 30 min, Cu(II)-promoted hydrolysis of coumarin lactone moiety of 1 occurred with bright blue fluorescence at 451 nm emerged. With fluorescence intensity ratio detection at 451 nm and 524 nm, 1 features an excellent sensitivity with the detection limit of 15 nmol L⁻¹ toward Cu(II) and a good selectivity over other metal ions.     

Cu(II) and Pd(II) complexes of N-(2-hydroxybenzyl)aminopyridines

N-(2-Hydroxybenzyl)aminopyridines (Lⁱ) react with Cu(II) and Pd(II) ions to form complexes in the compositions Cu(Lⁱ)₂(CH₃COO)₂ · nH₂O (n = 0, 2, 4), Pd(Lⁱ)₂Cl₂ · nC₂H₅OH (n = 0, 2) and Pd(L²)₂Cl₂ · 2H₂O. In the complexes, the ligands are neutral and monodentate which coordinate through pyridinic nitrogen. Crystal data of the complexes obtained from 2-amino pyridine derivative have pointed such a coordinating route and comparison of the spectral data suggests the validity of similar complexation modes of other analog ligands. Cu(II) complex of N-(2-hydroxybenzyl)-2-aminopyridine (L¹), [Cu(L¹)₂(CH₃COO)₂] has slightly distorted square planar cis-mononuclear structure which is built by two oxygen atoms of two monodentate carboxylic groups disposed in cis-position and two nitrogen atoms of two pyridine rings. The remaining two oxygen atoms of two carboxylic groups form two Cu and H bridges containing cycles which joint at same four coordinated copper(II) ion. IR and electronic spectral data and the magnetic moments as well as the thermogravimetric analyses also specify on mononuclear octahedric structure of complexes [Cu(L²)₂(CH₃COO)₂ · 2H₂O] and [Cu(L³)₂(CH₃COO)₂ · 4H₂O] where L² and L³ are N-(2-hydroxybenzyl)-2- or 3-aminopyridines, respectively.     

Spectroscopic,structure and DFT studies of copper(II) and palladium(II) complexes of pyridine-2-carboxaldehyde-2-pyridylhydrazone: A chromogenic agent for palladium(II)

A heterocyclic hydrazone ligand, pyridine-2-carboxaldehyde-2-pyridylhydrazone, HL, 1, was investigated as a new chromogenic agent for selective detection of Pd²⁺. The ligand HL, 1, undergoes 1:1 complexation with Pd²⁺ and Cu²⁺ to form complexes [Pd(L)Cl], 1a and [Cu(HL)Cl₂], 1b respectively. The complex 1a gives a characteristic absorption peak at 536 nm with distinct reddish-pink coloration. The change in color can easily be distinguished from other metal complexes by the naked eye. No obvious interference was observed in the presence of other metal ions (Na⁺, K⁺, Mg²⁺, Ca²⁺, Al³⁺, Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Sn²⁺, Hg²⁺, Pb²⁺). The association constants, K_ass (UV–Vis), were found to be 5.52 ± 0.004 × 10⁴ for 1a and 4.94 ± 0.006 × 10⁴ for 1b at 298 K. On excitation at 295 nm, the ligand HL, 1 strongly emits at 372 nm due to an intraligand ¹(π–π^∗) transition. Upon complexation the emission peaks are blue shifted (λ_ex 295 nm, λ_em 358 nm for 1a and λ_ex 295 nm, λ_em 367 nm for 1b) along with a quenching (F/F₀ 0.32 for 1a and 0.88 for 1b) in the emission intensity. DFT and TDDFT calculations were highly consistent with the spectroscopic behavior of the ligand and complexes. The molecular structure of the complex 1b has been determined by single crystal X-ray diffraction studies.     

Liquid chromatographic determination of cis-platin as platinum(II) in pharmaceutical preparation, serum and urine samples of cancer patients

Spectrophotometric and high performance liquid chromatographic (HPLC) methods have been developed for the determination of cis-platin and carboplatin based on the pre-column derivatization of platinum(II) with 2-acetylpyridine-4-phenyl-3-thiosemicarbazone. The complex was extracted in chloroform with molar absorptivity of 2.2 × 10⁴ L mol⁻¹ cm⁻¹ at 380 nm. The complex eluted from a Phenomenex C-18 (150 mm × 4.6 mm i.d.) column with methanol:water:acetonitrile:tetrabutyl ammonium bromide (1 mM) (44:30:25:1, v/v/v/v) with a flow rate of 1 ml/min and UV detection at 260 nm. Ruthenium(IV) and selenium(IV) also separated completely. The linear calibration curve was with 0.5-12.5 μg/ml and detection limit of 10 ng/ml platinum(II).The analysis of cis-platin and carboplatin injections by spectrophotometric and HPLC methods indicated relative standard deviation (R.S.D.) of 0.66-2.1%. The method was used for the determinations of cis-platin in serum and urine of cancer patients after chemotherapy and platinum contents were found 148-444 and 50-90 ng/ml with R.S.D. of 0.3-3.0 and 0.6-2.4% for the serum and urine, respectively. The recovery of platinum(II) from serum was 97% with R.S.D. 2.2%.     

Novel nickel(II) and copper(II) complexes with phenoxy-imidazole ligands: Syntheses, crystal structures and norbornene addition polymerization

The novel nickel(II) (1) and copper(II) (2) complexes bearing 2′-(4′,6′-di-tert-butylhydroxy-phenyl)-1,4,5-triphenyl imidazole ligand have been synthesized and characterized. The molecular structure analyses of complexes 1 and 2 indicated that Ni(II) centre in 1 adopts a distorted tetrahedral coordination geometry with a dihedral angle of 85.2° between Ni(1)O(1)N(1) plane and Ni(1)O(1A)N(1A) plane, while the Cu(II) centre in 2 represents a distorted square planar coordination geometry with a cis-N₂O₂ arrangement of the donor atoms, the dihedral angle being 32° between Cu(1)O(1)N(1) plane and Cu(1)O(1A)N(1A) plane. After activation with methylaluminoxane (MAO), both Ni(II) and Cu(II) complexes can be used as catalysts for the addition polymerization of norbornene (NB). The polynorbornenes (PNBs) are produced with very high polymerization activity (10⁸ g PNB mol⁻¹ Ni h⁻¹) for Ni(II) complex and moderate catalytic activity (10⁵ g PNB mol⁻¹ Cu h⁻¹) for Cu(II) complex, respectively. The high molecular weight polynorbornenes (10⁶) are obtained for complexes 1 and 2. Moreover, the distinct effects of polymerization temperature and Al/M ratio on catalytic activities and molecular weights of polymers are discussed.     

Highly selective determination of total mercury(II) sub microgram per liter by β-cyclodextrin polymer solid-phase spectrophotometry using 1,3-di-(4-nitrodiazoamino)-benzene

A highly selective β-cyclodextrin polymer solid-phase spectrophotometric (β-CDPSPS) method is described for the determination of total mercury(II) sub microgram per liter. The methods are based on the chromogenic reaction of mercury(II) with 1,3-di-(4-nitrodiazoamino)-benzene (DNAAB) loaded on β-cyclodextrin polymer (β-CDP). In pH 10.0 borax buffer, Hg(II)-DNAAB complex on β-CDP gives a positive peak at 445 nm and a negative one at 545 nm. The absorbance was measured at two peaks and the net absorbance (A_s) was calculated between the difference of positive and negative peaks. The apparent molar absorptivity is 1.1 × 10⁷ l mol⁻¹ cm⁻¹ (82-fold of it in solution) for 100 ml sample and the linear range of the determination is 0.062-250 μg l⁻¹. The selectivity for coexistent ions was greatly improved, only silver(I) interfered with the mercury determination and the amount of the others was reduced 25-1000 times compared to previous solution method. The interference caused by silver(I) can be eliminated using tri-n-octylmethylammonium bromide as masking agent. The detection limit and the quantification limit were found to be 0.024 and 0.062 μg l⁻¹, respectively. The relative standard deviation of ten replicate determinations of 5.0 μg mercury(II) in 100 ml sample was of 2.4%. The method was validated by analyzing the water and soil reference materials and successfully applied to the determination of mercury(II) in locally collected water and dust samples.     

Extractive spectrophotometric determination of palladium with N,N,N',N'-tetra(2-ethylhexyl)-thiodiglycolamide T(2EH)TDGA

A precise, sensitive and selective method for the spectrophotometric determination of palladium (II) using N,N,N′,N′-tetra(2-ethylhexyl) thiodiglycolamide T(2EH)TDGA as an extractant is described. Palladium (II) forms yellow colored complex with T(2EH)TDGA which exhibits an absorption maximum at ∼300 nm. The colored complex obeys Beer's law in the concentration range 1.0-15.0 μg ml⁻¹ of palladium with a molar absorptivity of 1.29 × 10⁵ M⁻¹ cm⁻¹. The effects of various experimental parameters have been studied to establish the optimum conditions for the extraction and determination of palladium. The precision of the method has been evaluated and the relative standard deviation has been found to be less than 0.5%. The method has been successfully applied to the determination of palladium in simulated high level liquid waste (SHLW) solution.     

Synthesis and properties of 6,6′-dithienyl-4,4′-bipyrimidine and its hetero- and homo-leptic Ru(II) complexes

Hetero- and homo-leptic Ru(II) complexes of a new 4,4′-bipyrimidine ligand, th₂bpm (6,6′-di(2″-thienyl)-4,4′-bipyrimidine), have been synthesized and characterized. The parent ligand th₂bpm has electron rich thiophene units on the periphery of a bidentate ligand which is capable of binding to metal ions. The heteroleptic complex of th₂bpm [Ru(bpy)₂th₂bpm]²⁺ (bpy = 2,2′-bipyridine) exhibits a Ru-to-bpm metal-to-ligand charge transfer (MLCT) absorption centered at 547 nm and a Ru-to-bpy MLCT absorption centered at 438 nm. The assignment of the low energy absorption is supported by the relative ease of electrochemical reduction of the new complex as compared to [Ru(bpy)₃]²⁺. The homoleptic complex, [Ru(th₂bpm)₃]²⁺, exhibits a Ru-to-bpm MLCT absorption at slightly higher energy (544 nm). Both complexes are emissive at room temperature in fluid solution and 5 is one of the lowest energy emitters based on tris-bidentate Ru(II) complexes known (λ_max = 770 nm). The luminescence spectra is red-shifted compared to [Ru(bpy)₃]²⁺ and this effect is ascribed to the delocalization in the acceptor ligand.     

Interaction between quercetin-copper(II) complex and DNA with the use of the Neutral Red dye fluorophor probe

The interaction of quercetin-Cu(II) complex with calf thymus DNA was investigated with the use of Neutral Red (NR) dye as a spectral probe by the application of UV-vis spectrophotometry, cyclic voltammetry and synchronous fluorescence spectroscopy. The results showed that both quercetin-Cu(II) complex and the NR molecule can intercalate into the double helix of the DNA. The 2:1 quercetin:Cu(II) complex (estimated binding constant = 2.85 × 10⁹) is stabilized by intercalation in the DNA (binding constant, K_{[quercetin-Cu(II)-DNA]} = (1.82 ± 0.20) × 10⁵ M⁻¹), and displaces the NR dye from the NR-DNA complex in a competitive reaction. Cyclic voltammetry studies confirm the intercalation reaction and show that the ratio (K_R/K_O) of binding constants for the reduced and oxidized forms of the metal complex is 2.05. Furthermore, the alternative least squares (ALS) method was applied to resolve a complex two-way array of the absorption spectra data. This yielded the equilibrium concentration profiles of each component in the reaction (NR, NR-DNA and quercetin-Cu(II)) as well as the corresponding pure spectra. The extracted profiles showed that at equilibrium the [NR-DNA] and [NR] trends decreased and increased symmetrically, respectively, with approximately linear behaviour being observed below 10 × 10⁻⁶ mol L⁻¹ of the added quercetin-Cu²⁺ complex. Thereafter, these trends converged asymptotically. The free [quercetin-Cu(II)] trend-line at equilibrium was linear over the whole range of the complex added. It was possible to estimate the approximate value of the equilibrium constant of the exchange process (approximately 5 × 10⁻¹) involving the intercalation of the quercetin-Cu(II) complex. It was also found that about 35% of the bound complex was unaccounted by the intercalation reaction, presumably being stabilized at an alternative site.     

Solid phase selective separation and preconcentration of Cu(II) by Cu(II)-imprinted polymethacrylic microbeads

Ion-imprinted polymer (IIP) particles are prepared by copolymerization of methacrylic acid as monomer, trimethylolpropane trimethacrylate as crosslinking agent and 2,2′-azo-bis-isobutyronitrile as initiator in the presence of Cu(II), a Cu(II)-4-(2-pyridylazo)resorcinol (Cu(II)-PAR) complex, and PAR only. A batch procedure is used for the determination of the characteristics of the Cu(II) solid phase extraction from the IIP produced. The results obtained show that the Cu(II)-PAR IIP has the greatest adsorption capacity (37.4 μmol g⁻¹ of dry copolymer) among the IIPs investigated. The optimal pH value for the quantitative preconcentration is 7, and full desorption is achieved by 1 M HNO₃. The selectivity coefficients (S_Cu/Me) for Me = Ni(II), Co(II) are 45.0 and 38.5, respectively. It is established that Cu(II)-PAR IIPs can be used repeatedly without a considerable adsorption capacity loss. The determination of Cu(II) ions in seawater shows that the interfering matrix does not influence the preconcentration and selectivity values of the Cu(II)-PAR IIPs. The detection and quantification limits are 0.001 μmol L⁻¹ (3σ) and 0.003 μmol L⁻¹ (6σ), respectively.     

Kinetic determination of cysteine and thiosulphate by inhibition of Hg(II) catalyzed ligand substitution reaction

The sulphur containing inhibitors (I), cysteine (Cys) and sodium thiosulphate (THS), have been found to inhibit Hg(II) catalyzed exchange of cyanide in hexacyanoferrate(II) by nitroso-R-salt (NRS). The inhibitory effect of both the ligands are attributed to their binding tendencies with Hg(II) leading to the formation of catalyst-inhibitor (C-I) complex. The reactions have been followed spectrophotometrically in aqueous medium at 720 nm by noting the increase in absorbance of the green colour product, [Fe(CN)₅NRS]³⁻ at pH 6.50 ± 0.02, temp 25.0 ± 0.1 °C and ionic strength (μ) 0.1 M (KNO₃). A most plausible mechanistic scheme involving the role of analytes (inhibitors) has been proposed. The values of equilibrium constants for complex formation between catalyst-inhibitor (K_CI), catalyst-substrate (K_S) and Mechaelis-Menton constant (K_m) have been computed from the kinetic data. The linear calibration curves have been established between absorbance and inhibitor concentrations under specified conditions. Cys and THS have been determined in the range 1-5 × 10^− 7 M and 4.9-16.9 × 10^− 7 M respectively. The detection limits have been computed to be 1 × 10^− 7 M and 4.9 × 10^− 7 M for Cys and THS, respectively.     

Flow-injection determination of hydrogen peroxide based on fluorescence quenching of chromotropic acid catalyzed with Fe(II)

Flow-injection analysis system (FIA system), which was based on Fe(II)-catalyzed oxidation of chromotropic acid with hydrogen peroxide, was developed for the determination of hydrogen peroxide. The chromotropic acid has a fluorescence measured at λ_em = 440 nm (emission wavelength) with λ_ex = 235 nm (excitation wavelength), and the fluorescence intensity at λ_em = 440 nm quietly decreased in the presence of hydrogen peroxide and Fe(II), which was caused by Fe(II)-catalyzed oxidation of chromotropic acid with hydrogen peroxide. By measuring the difference of fluorescence intensity, hydrogen peroxide (1.0 × 10⁻⁸-1.0 × 10⁻³ mol L⁻¹) could be determined by the proposed FIA system, whose analytical throughput was 40 samples h⁻¹. The relative standard deviation (RSD) was 1.03% (n = 10) for 4.0 × 10⁻⁸ mol L⁻¹ hydrogen peroxide. The proposed FIA technique could be applied to the determination of hydrogen peroxide in rain water samples.     

Structural characterization of five-coordinate copper(II), nickel(II), and cobalt(II) thiocyanato complexes derived from bis(2-(3,5-dimethyl-1-pyrazolyl)ethyl)amine

The reaction of M(ClO₄)₂·6H₂O with NH₄NCS in presence of the organic sterically hindered bis(2-(di-3,5-dimethyl-1-pyrazolyl)ethyl)amine (bedmpza) afforded the five-coordinate mononuclear dithiocyanato-M(II) complexes [M(bedmpza)(NCS)₂]·xMeOH (1: M = Cu²⁺, x = 0; 2: M = Ni²⁺, x = 0; 3: M = Co²⁺, x = 0.84). The compounds which proved to be non-electrolytes were characterized by IR and UV-Vis spectroscopy and their molecular structures were determined by single-crystal X-ray crystallography. In these complexes, the five-coordinate geometry was achieved by the three N-donors of the ligand bedmpza and two N atoms of the terminal thiocyanato ligands. The Cu(II) complex exists in two polymorphs 1-I and 1-II: an intermediate five-coordinate geometry with the two thiocyanato ligands are arranged as cisoid in 1-I and distorted square pyramidal geometry with the thiocyanato ligands are in transoid orientation in 1-II. Although the later geometry was also observed in the nickel complex 2, distorted trigonal bipyramidal geometry was found in 3. Each complex forms hydrogen bonds of type N-H?S from the secondary amine N(3) donor atoms to the adjacent terminal S(1) acceptor atoms of the thiocyanate group. The thermal behavior of the two polymorphs 1-I and 1-II were similar and no significant differences were observed between the two complexes.     

Synthesis,spectroscopy, electrochemistry,and methylation reaction of the dithiolate-based cobalt(II) complex derived from tert-butyl N-(2-mercaptoethyl)carbamate

A dithiolate-containing a carbamate mononuclear cobalt(II) complex namely, [Co(Boc-S)₂] (1), was obtained by the reaction of a methanolic solution of cobalt(II) nitrate hexahydrate with two equimolar amounts of the deprotonated form of tert-butyl N-(2-mercaptoethyl)carbamate (Boc-SH). The cobalt(II) complex (1) was characterized in the solid state and in solution by using FT–IR, Raman, UV–visible, and EI–mass spectroscopies, as well as thermal and X-ray diffraction studies. Spectral data showed that the carbamate (Boc-SH) acts as a mono-anionic bidentate ligand coordinating the cobalt(II) ion through two imine nitrogen and two deprotonated thiolate sulfur donor atoms in a distorted tetrahedral geometry. The thermoanalytical data evidence that the complex is stable up to 165 °C and undergoes complete decomposition, resulting in CoO. TEM imaging of the oxide residue shows its nano size clusters, suggesting that the complex (1) may be used as a precursor for nano-oxides. X-ray powder diffraction patterns evidence an isomorphism among the complex. The redox behavior of the cobalt(II) complex was also investigated by cyclic voltammetry. The reaction of the dithiolate cobalt(II) complex (1) with methyl iodide appears to occur intramolecularly with the cobalt-bound dithiolate, forming the cobalt(II)-bound dithioether complex [Co(Boc–SCH₃)₂]I₂ (2), as a dication complex with a clean second-order reaction of 13.24 × 10⁻² M⁻¹·s⁻¹.     

Synthesis,crystal structures and spectroscopic properties of two Zn(II) Schiff’s base complexes of pyridoxal

Two mononuclear zinc(II) complexes, [ZnL¹H₂Cl]Cl·2H₂O (1·Cl·2H₂O) and [ZnL²HCl]·H₂O (2·H₂O) (L¹H₂ and L²H₂ are N,N′-bis(pyridoxylidene)ethylenediamine and N,N′-bis(pyridoxylidene)1,3-propanediamine, respectively) have been synthesized and characterized by elemental analysis, FT-IR, fluorescence spectroscopy, TG–DTA and single crystal X-ray diffraction studies. The Zn(II) ion in complex 1 have a square pyramidal geometry with appreciable distortion towards trigonal bipyramid, whereas in 2 it has a geometry which is near the midpoint of square pyramid and trigonal bipyramid. The zinc atom is coordinated by two imine nitrogens, two phenolic oxygens and one chloride ion. The Zn(II) complexes show emission at 462 nm when excited at their lowest energy absorption at 372 nm.     

Synthesis,thermal stability and structural characterisation of iron(II) phthalocyanine complex with 4-cyanopyridine

A new complex of bis-axially coordinated iron(II) phthalocyanine by 4-cyanopyridine (4-CNpy) has been obtained in crystalline form as an adduct with two 4-CNpy molecules. The [FePc(4-CNpy)₂] · 2(4-CNpy) crystallises in the monoclinic system, space group P2₁/c with two molecules in the unit cell. The iron(II) coordinates four isoindole nitrogen atoms of the almost planar phthalocyaninato(2−) macroring and axially two nitrogen atoms of 4-CNpy molecules. The coordination polyhedron around the Fe(II) atom approximates to a tetragonal by-pyramid. Four equatorial Fe–N bonds are shorter (1.936(2) Å) than two axial Fe–N bonds (2.027(2) Å). The centrosymmetric FePc(4-CNpy)₂ molecules form alternating sheets parallel to the bc crystallographic plane and solvated 4-CNpy molecules that are anti-parallel oriented by their polar cyano groups are located between the sheets of FePc(4-CNpy)₂ molecules. Ligation of the intermediate-spin iron(II) phthalocyanine by 4-CNpy molecules leads to the low spin Fe(II) complex. The importance of the d(π) → π^∗(Pc) back donation is manifested in the difference between the values of C–N isoindole and C–N azamethine bond lengths of the Pc macrocycle. The thermal analysis of the crystals of [FePc(4-CN)₂] · 2(4-CNpy) shows two steps responsible for a loss of solvated (∼170 °C) and coordinated (∼235 °C) 4-CNpy molecules.     

Thermochromism in nickel(II) complexes: thermal, solid state H NMR and single crystal X-ray analysis of bis-(N,N-dimethyl-1,2-ethanediamine) nickel(II) perchlorate

The complex bis-(N,N-dimethyl-1,2-ethanediamine) nickel(II) perchlorate undergoes a first-order thermochromic phase transition at ca. 476 K, changing its color from orange to red. The room temperature X-ray crystal structure determination showed that the nickel ion possesses a square-planar geometry with two five membered chelate rings, in the δλ conformation, forming the NiN₄ chromophore. The broad-line ¹H NMR indicates the onset of a dynamic disorder of diamine chelate rings at the phase transition temperature region, while T₁ measurement of ¹H affords the activation energy of the puckering metal chelate rings to be 26 kJ mol⁻¹. The electronic spectrum revealed that a weakening of ligand field around the nickel is associated with the phase transition.     

UV-visible spectroscopic and electrochemical study of the complex formation between Fe(II) and 5-amino-1,10-phenantroline (5-Aphen) in aqueous solution

The system Fe(II)-5-Aphen-H₂O was studied. The spectroscopic and electrochemical results show that only one stable complex between Fe(II) and 5-Aphen forms, having a 1:3 stoichiometric ratio. The spectrophotometry study allowed determination of the formation constant of the complex (log β₃ = 23.42 ± 0.06). Also, the stability of the complex was evaluated as a function of pH; it was found that it decomposed at low pH values depending on the concentration and a pseudo-first order kinetics constant associated with k′ = 0.011 min⁻¹. The results are in agreement with the electrochemical behaviour observed in the system, which indicated that at pH 1.33 the destruction of the complex [Fe(5-Aphen)3]²⁺ took place as a function of time; however, when the experiments were carried out at pH 6.19 the complex was stable. The thermodynamic data obtained through the use of MEDUSA allowed construction of predominance zone diagrams of the system Fe(II)-5-Aphen-H₂O under the experimental conditions used. The thermodynamic results represented in the PZD describe the experimental behaviour reported in this work.     

Catalytic efficacy of Schiff-base copper(II) complexes: Synthesis,X-ray structure and olefin oxidation

Three copper(II) Schiff-base complexes, [Cu(L¹)(H₂O)](ClO₄) (1), [Cu(L²)] (2) and [Cu(L³)] (3) have been synthesized and characterized [where HL¹ = 1-(N-ortho-hydroxy-acetophenimine)-2-methyl-pyridine], H₂L² = N,N′-(2-hydroxy-propane-1,3-diyl)-bis-salicylideneimine and H₂L³ = N,N′-(2,2-dimethyl-propane-1,3-diyl)-bis-salicylideneimine]. The structure of complex 1 has been determined by single crystal X-ray diffraction analysis. In complex 1, the copper(II) ion is coordinated to one oxygen atom and two nitrogen atoms of the tridentate Schiff-base ligand, HL¹. The fourth coordination site of the central metal ion is occupied by the oxygen atom from a water molecule. All the complexes exhibit high catalytic activity in the oxidation reactions of a variety of olefins with tert-butyl-hydroperoxide in acetonitrile. The catalytic efficacy of the copper(II) complexes towards olefin oxidation reactions has been studied in different solvent media.