Shaker L. Stefan

Determination of some lanthanide ions by conductometric and spectrophotometric measurements of their hydrazo-5-pyrazolone complexes

Abstract A series of complexes of 1-phenyl-3-methyl-4( x -phenylhydrazo)-5-pyrazolone [where x = 2-OCH 3 (i), 2-COOH (ii), 2-OH-5-Cl (iii), 2-OH-5-CH 3 (iv), and 2-SO 3 Na-4-CH 3 (v)] with trivalent lanthanide ions, Ln (III) were investigated and used for determination of these ions by conductometric and spectral measurements. The results indicate the probable formation of 1:1 and 1:2 chelates (metal:ligand). Solid chelates were isolated and their structures established by elemental analysis and infrared spectral data. The hydrazo stretching frequency of NHN = appeared in the range 1535 to 1520 cm −1 , the carbonyl band from 1670 to 1650 cm −1 , ν M − N from 575 to 565 cm −1 , and ν M − O from 530 to 510 cm −1 . Ln (III) coordinate with hydrazo-5-pyrazolone derivatives to form chelate rings with benzenoid type resonance through π-bonding from the metal to the ligand. The Yb 3+ complexes with 2-hydroxy-5-methyl (iv) derivative were also investigated in solutions by spectrophotometric studies and were very useful in the microdetermination of this element.

METAL COMPLEXES OF NOVEL SYMMETRICAL SCHIFF BASE LIGANDS

Two novel symmetrical Schiff base ligands, H2L1 and H2L2, with tetradentate N2O2 and pentadentate N3O2 coordinating sites were prepared by the reaction of the aldehyde 2-methyl-7-formyl-8-hydroxy-quinoline with 1,3-diaminopropane or diethylenetriamine, respectively, in the molar ratio 2:1. Cu(II), Ni(II), Co(II), Mn(II), Fe(III) and VO(IV) complexes of both ligands were synthesized. The ligands and their metal complexes were characterized by elemental analyses, IR, UV-Vis, ESR, NMR and mass spectra and also by magnetic moment measurements. Both ligands behave as tetradentate ones when coordinating metal cations. The ligand H2L1 has a smaller cavity than the ligand H2L2, thus the former ligand yielded mononuclear products, through chelation of one ligand molecule to a metal cation, while the latter ligand yielded binuclear products, through the coordination of two metal cations to two ligand molecules. Each of the Fe(III) cations was coordinated to three halves of both ligand molecules yielding also a mononuclear product with ligand H2L1 and a binuclear product with ligand H2L2. Either mononuclear or binuclear complex molecules link together forming polymeric chains. The mononuclear and binuclear complex forms were well manifested in the ESR spectra of the vanadyl complexes. The polymeric structures of the metal complexes led to an enhanced decrease of their magnetic moments through antiferromagnetic exchange between neighbouring metal cations.

SCHIFF BASE COMPLEXES DERIVED FROM SALICYLALDEHYDE WITH AMINE, [Ni(1,2-pn)2Cl2]·3H2O AND [Cu(1,2-pn)2]SO4·2H2O, AS COMPLEX LIGANDS

Schiff base complexes known as complex ligands were prepared by the condensation of dichlorobis(1,2-diaminopropane)nickel(II), [Ni(1,2-pn)2Cl2]·H2O, or bis(1,2-diaminopropane)copper(II) sulphate, [Cu(1,2-pn)2]SO4·H2O, with salicylaldehyde producing the Schiff base complex ligands [ML] (M = Ni or Cu). The complex ligands [ML] act as bidentate ligands through the bridged di-μ-phenoxy oxygen atoms. These Schiff base complexes react with transition metal ions yielding homo- and heteronuclear complexes of the types [MLM′Cl2] or [(ML)2M′Cl2], [(ML)2M′]Cl2, [(ML)2M′](ClO4)2 and [(ML)2M′(NO3)2](NO3)n, M = Ni or Cu; M′ = Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Ce(III) and Th(IV). The complexes were characterized by elemental analyses, thermal analyses, IR, visible and ESR spectra, magnetic susceptibility measurements as well as mass spectra. Magnetic moments were altered by the introduction of additional metal cations besides the one already present in the complex ligands. The M′ cations were linked to the outer phenoxo oxygen atoms in the [NiL]·½H2O and [CuL]·H2O complex ligands. All homo- and hetero bi- and tri-nuclear complexes show antiferromagnetic interactions which are attributed to inter- or intramolecular interactions of the metal cations. Mass spectra of the complex ligands and selected homo- and hetero bi- and trinuclear complexes support the formula weights of these complexes. Visible and ESR spectra as well as magnetic moments indicated that the parent mononuclear complex ligands [ML] have square-planar geometry. The binuclear and trinuclear complexes have similar or different geometries, octahedral or square-planar. The octahedral configuration is completed by chlorine atoms, nitrate groups and/or solvent molecules.

Synthesis and Characterization of Oxotitanium(IV) and Oxovanadium(IV) Complexes of Arylbis(5-hydroxy-3-methyl-1-phenyl-4-pyrazolyl)methane Ligands

Abstract The interactions of oxotitanium(IV) and oxovanadium(IV) with arylbis (5-hydroxy-3-methyl-1-phenyl-4-pyrazolyl)methane (ArBPyM) ligands containing enolic oxygen donors, have been studied with ir spectroscopy, thermogravi-metric measurements and elemental analysis. The results indicate the probable formation of dimeric complexes (metal: ligand ratio = 1:1) through bridging sulfato ligand. Application of differential thermal analysis allowed determination of the mechanism of thermal decomposition of the complexes.

Structure-stability relationships of some ortho-hydrazopyrazolone derivatives with divalent metal ions

Abstract Acid dissociation constants (p K H ) of a series of five compounds (I to V) of substituted 5-pyrazolone dyes have been determined potentiometrically in 75% ( v v ) dioxane/water at 30 °C and M ionic strength. The stability constants of their 1:1 and 1:2 chelates with six divalent metal ions M 2+ have also been determined. The effect of substituents on the hydrazo-moiety of the ligand was discussed. Data were correlated and the results were used to explain the stabilization of such chelates by dative π bonding between M 2+ and the ligands.

Kinetics and mechanisms of the catalyzed decomposition of hydrogen peroxide by ethylenebis(oxyethylenedinitrilo)tetracetate complex of iron(III)

Abstract The rate of decomposition of H2O2 in the presence of Fe(III)-y complex (y is ethylenebis(oxyethylenedinitrilo)tetraacetic acid (EGTA) anion) was investigated under variable conditions of pH and temperature, various water-miscible solvents, and different concentrations of H2O2, [Fe-y]−, and acetate ions. The following rate law holds: Rate = ( k 1 K 3 K 4 [ H + ] ) [ Fe -y( OH )] 2− [ H 2 O 2 ] at pH less than 9.80, and Rate = ( k 2 K 5 [ H + ] K 3 ) [ Fe -y (OH) 2 ] 3− [OOH] − at pH above 9.80. The values of k1K4and k2K5 at 25 °C were found to be 1523 and 0.747 M−1 S−1, respectively. Activation enthalpy and activation entropy for this reaction were determined from Arrhenius plots and found to be Δ H ∗ = 34.38 K J mol −1 and Δ S ∗ = −167.2 J K −1 mol −1 .

Structure-stability relationships of some meta- and para-hydrazopyrazolone derivatives with trivalent lanthanide ions

Abstract Acid dissociation constants (pKH) of a series of 10 compounds (I to X) of substituted 5-pyrazolone dyes have been determined potentiometrically in 75% (v/v) dioxane-water at 30 °C and

Synthesis and Properties of Some New Double-Metal Aroxide Complexes

Abstract A new series of double-metal aroxocobaltate(II) tetra-hydrofurane complexes of the type ˙ nTHF (X = o-NO2, o-Cl, o-Br, m-Cl, p-Br, 2,4-dichloro, 2,6-dichloro and 2,4-dimethyl; n = 1,3,4 or 5) was synthesized by the reaction of anhydrous CoBr2 with the sodium salt of the corresponding phenol (abbreviated as NaOAr) as a monodentate ligand. The blue violet crystalline and very airsenstive compounds show good solubilities in some organic solvents, eliminate THF in vacuo at a temperature between 80 and 120°C/0.8 torr to yield the corresponding THF-free complexes. Electronic spectra (VIS and NIR) and magnetic measurements at 297°K point to a prefered tetrahedral configuration of cobalt(II) in these complexes.

Kinetics and mechanism of oxidation of ethylenediaminetetraacetate by manganese(VII) solution

Abstract The kinetics of oxidation of ethylenediaminetetraacetic acid (EDTA) by MnO4− in acidic medium have been investigated. The order of reaction was found to be two in MnO4− and one in EDTA, and inversely first order in H+. Mn(II) was found to retard the reaction velocity. A mechanism of the reaction was proposed with the rate law rate = − d[ MnO 4 − ] dt = [ kKK 1 H + ] + k 3 K 2 ] [ H 4 Y ][ MnO 4 − ] 2 The values of kK1 and k3K2 were evaluated at different temperatures. Activation parameters ( ΔE ∗ and ΔS ∗ ) for the acid-dependent and acid-independent rate constants were found to be 16.56 and 2.21 °K cal mol−1 for Δ E ∗ , −14.62and −64.45 e.u. for Δ S ∗ , respectively.