K. K. Mohammed Yusuff

Thermal and spectral studies of 1-benzyl-2- phenylbenzimidazole complexes of cobalt(II)

Abstract Cobalt(II) complexes of 1-benzyl-2-phenylbenzimidazole (BPBI), of general formula [Co(BPBI) 2 X 2 ] (X ≡ Cl − Br − , I − or NCS − ), have been synthesized and characterized. A tetrahedral structure has been suggested for these complexes. The complexes were subjected to a systematic TG/DTG/DTA analysis. All the complexes decompose just after melting, and the decomposition process consists essentially of two stages. The final residue in all cases was found to be CoO. The mass loss data indicate the formation of intermediate complexes with approximate compositions [Co(BPBI)Cl 2 ], [Co(BPBI)Br 2 ], [Co(BPBI)I] and [Co(BPBI) 0.5 (NCS) 2 ] at the end of the first stage of decomposition. The kinetic parameters were calculated using the Coats-Redferw equation. In all the complexes except the bromo complex, the E a values for the second stage of decomposition were found to be much higher than those for the first stage. The anomalously smaller E a and Δ S values exhibited by the bromo complex for the second stage of decomposition indicate catalytic activity for the intermediate bromo complex.

Intrazeolite cobalt(II), nickel(II) and copper(II) complexes of 3-formylsalicylic acid for oxidation reactions

Y zeolite encapsulated Co(II), Ni(II) and Cu(II) complexes of 3-formylsalicylic acid were synthesized and characterized by chemical analyses, SEM, XRD, surface area, pore volume and IR, reflectance and EPR spectroscopy with a view to confirm the encapsulation of complexes and to arrive at the composition, structure and geometry of encapsulated complexes. The analytical data indicate a composition corresponding to the binuclear complex of 3-formylsalicylic acid. The characterization data show the absence of extraneous complexes, retention of zeolite crystalline structure and encapsulation in the cavities. The shift of carbonyl-stretching frequencies of both the aldehyde and carboxylate groups of 3-formylsalicylic acid suggests binuclear coordination in the encapsulated complexes. Tetrahedral, octahedral and tetrahedrally distorted square planar symmetries are tentatively assigned to the encapsulated complexes of Co(II), Ni(II) and Cu(II) ions, respectively. Encapsulated Cu(II) complex is catalytically very efficient as compared to other complexes for the partial oxidation of benzyl alcohol and ethylbenzene and is stable to be recycled without much deterioration.

Preparation and Use of Nano Zinc Oxide in Neoprene Rubber

Zinc oxide (ZnO) of nanometer particle size was prepared by solid-state pyrolytic method. TEM, XRD, and surface area studies showed that the prepared zinc oxide had particle size in the range of 15–30 nm and surface area in the range of 12–30 m2/g. This nano zinc oxide was used as a curing agent in neoprene rubber. The optimum dosage of ZnO was found to be low compared to commercial ZnO. The cure characteristic and mechanical properties were compared with those containing conventional ZnO. It was found that a low dosage of zinc oxide was enough to give equivalent curing and mechanical properties compared to one containing a higher dosage (5 phr) of commercial zinc oxide in neoprene rubber.

Thermal decomposition kinetics of iron(III), cobalt(II), nickel(II) and copper(II) complexes of a Schiff base derived from quinoxaline-2-carboxaldehyde and glycine

Quinoxaline-2-carboxalideneglycine complexes of iron(III), cobalt(II), nickel(II) and copper(II) complexes were subjected to a systematic TG/DTG analysis. The decomposition process consists of two stages for all these complexes. Kinetic parameters were evaluated for each of these stages using the Coats-Redfern equation. The rate of decomposition at the second stage seems to have a bearing on the catalytic effect of the metal oxides formed during this stage.AbstractКомплексы хиноксалин-2-карбоксалиденглицина с железом(III) ковальтом(II), никелем(II) и медью(II) были подвергнуты систематическому анализу ТГ/ДТГ. Процесс разложения для всех комплексов состоит из двух стадий. На основе уравнения Котс-Рэдферна были рассчитаны кинетические параметры каждой ступени. Скорость разложения на второй стадии, по-видимому, оказывает влияние на каталитические свойства окислов металла, образующихся на этой стадии.

Reaction of Dihydrazinium Ethylenediaminetetraacetate with Nitrates of Co(II), Ni(II), Cu(II) and Zn(II)

Abstract The dihydrazinium ethylenediaminetetraacetate, (N2H5)2 (H2edta) reacts with metal nitrates to form complexes of the type, N2H5[M(Hedta)˙H2O], where M = Co(II), Ni (II), Cu(II) or Zn (II). These complexes were characterised by analytical data, conductivity and magnetic susceptibility measurements, electronic and infrared spectroscopy and thermal analyses. The complexes are 1:1 electrolytes in aqueous solution.

New Complexes of Iron(III), Cobalt(II), Nickel(II) and Copper(II) with the Schiff Base Derived from Quinoxaline-2-carboxaldehvde and Glycine

Abstract New complexes of iron(III), cobalt(II), nickel(II) and copper(II) with the Schiff base derived from quino-xaline-2-carboxaldehyde and glycine have been synthesized and characterised using elemental analyses, solid state infrared and electronic spectra, magnetic measurements and TG studies. The complexes have the general formulae, [M2(QCG)C1(OH)2(H2o)4] for the Co(II), Ni(II), and Cu(II), and [Fe2(QCG)Cl(OH)4(H2O)2] for the Fe(III) complexes (where QCG = quinoxaline-2-carboxal-ideneglycine). A dimeric structure involving Cl and OH bridges has been proposed for these complexes.

Studies on Some Transition Metal Complexes of Schiff Bases Derived from Quinoxaline-2-carboxaldehyde

Two series of transition metal complexes of Schiff bases derived from quinoxaline‐2‐carboxaldehyde with semicarbazide (QSC) and furfurylamine (QFA) were synthesised and characterised by elemental analyses, molar conductance and magnetic susceptibility measurements, IR, electronic and EPR spectral studies. The QSC complexes have the general formula [M(QSC)Cl2]. A tetrahedral structure has been assigned for the Mn(II), Co(II) and Ni(II) complexes and a square‐planar structure for the Cu(II) complex. The QFA complexes have the formula [M(QFA)2Cl2]. An octahedral structure has been assigned for these complexes. All of the complexes exhibit catalytic activity towards the oxidation of 3,5‐di‐tert‐butylcatechol (DTBC) to 3,5‐di‐tert‐butylquinone (DTBQ) using atmospheric oxygen. The cobalt(II) complex of the ligand QFA was found to be the most active catalyst.

Synthesis and Characterization of Some New Transition Metal Complexes of the Schiff Base Derived from Quinoxaline-2-Carboxaldehyde and 2-Aminophenol

Abstract Some new transition metal complexes of the Schiff base quinoxaline-2-carboxalidene-2-aminophenol (HQAP) have been synthesized and characterized by elemental analyses, conductance and magnetic measurements and IR and UV-Visible spectral studies. The complexes have the following empirical formulae: [Mn(QAP)2], [Fe(QAP)2Cl], [Co(QAP)2], [Ni(QAP)2] and [Cu(QAP)2]. A tetrahedral structure has been assigned for the manganese(II), cobalt(II), nickel(II) and copper(II) complexes. For the iron(III) complex an octahedral dimeric structure has been suggested. Referee I: M. D. Johnson Referee II: W. Wacholtz

Determination of the nature of the diperiodatocuprate(III) species in aqueous alkaline medium through a kinetic and mechanistic study on the oxidation of iodide ion

AbstractThe nature of the diperiodatocuprate(III) (DPC) species present in aqueous alkaline medium has been investigated by a kinetic and mechanistic study on the oxidation of iodide by DPC. The reaction kinetics were studied over the 1.0 × 10−3–0.1 mol dm−3 alkali range. The reaction order with respect to DPC, as well as iodide, was found to be unity when [DPC] ≪ [I−]. In the 1.0 × 10−3–1.0 × 10−2 mol dm−3 alkali region, the rate decreased with increase in the alkali concentration and a plot of the pseudo-first order rate constant, kversus 1/[OH−] was linear. Above 5.0 × 10−2 mol dm−3, a plot of kversus [OH−] was also linear with a non-zero intercept. An increase in ionic strength of the reaction mixtures showed no effect on k at low alkali concentrations, whereas at high concentrations an increase in ionic strength leads to an increase in k. A plot of 1/kversus [periodate] was linear with an intercept in both alkali ranges. Iodine was found to accelerate the reaction at the three different alkali concentrations employed. The observed results indicated the following equilibria for DPC.[Cu(H2IO6)2]3- ⇋ [Cu(H2IO6)]- + H2IO63- [Cu(H2IO6)] + OH- ⇋ [Cu(HIO6)]- + H2OA suitable mechanism has been proposed on the basis of these equilibria to account for the kinetic results.

Synthesis, Characterization and Cytotoxicity of New Complexes of Cobalt(III), Nickel(II) and Copper(II) with Quinoxaline-2-carboxaldehyde Thiosemicarbazone

Abstract New quinoxaline-2-carboxaldehyde thiosemicarbazone (H-QTSC) complexes of cobalt(III), nickel(II) and copper(II) have been prepared and characterized on the basis of elemental analyses, molar conductance, magnetic susceptibility, and electronic and infrared spectral data. Analytical and molar conductance data suggest that the complexes have the formulae [Co(QTSC)2IX, [Ni(H-QTSC)2(OAc)X] and [Cu(QTSC) (OAc) (H2O)]2 (where X = Cl or Br and OAc = acetate). The magnetic and spectral data suggest a distorted octahedral geometry for the complexes. The copper complex appears to be dimeric with bridging acetate groups. The ligand acts as a uninegative tridentate NNS donor in the cobalt and copper complexes, while it acts as a neutral bidentate NS donor in the nickel complexes. The cytotoxicity of the cobalt(III) complexes were determined in vitro as well as in tissue culture. The chloro complex was found to have greater cytotoxic activity than the bromo complex. Referee I: G. Dyer Referee II: A. Pidcock