Ahmed H. Osman

Synthesis, Characterization, and Photochemical Studies of Some Copper Complexes of Schiff Bases Derived from 3‐Hydrazino‐6‐methyl[1,2,4]triazin‐5(4H)one

Abstract Cu(II) complexes of new bidentate and tridentate Schiff bases derived from the condensation of 3‐hydrazino‐6‐methyl[1,2,4]triazin‐5(4H)one and aromatic aldehyde derivatives were synthesized and characterized. The structure of the complexes proposed according to elemental analyses, molar conductance, IR UV‐Visible absorption spectra is square‐planar. The thermodecomposition kinetics of the complexes were investigated under non‐isothermal condition. TG and DTG curves indicated that the complexes decompose in three to six steps. The photochemical behavior of the complexes depends on the substituted group on the aromatic aldehyde. A mechanism has been suggested to account for the recorded results.

AN INVESTIGATION OF THE Cu(II) COMPLEXES OF CERTAIN CEPHALOSPORIN ANTIBIOTICS: SPECTRAL, THERMAL, AND PHOTOCHEMICAL STUDIES

ABSTRACT The following Cu(II) complexes of some cephalosporin antibiotics were synthesized and characterized: [Cu(ATB)Cl]ċ-xH2O, [Cu(ATB)2]ċxH2O and [Cu(ATB)2]ċxH2, where HATB=cephalexin, cephapirin, cefamandole, cefuroxime or cefotaxime, H2ATB=ceftazidime and x=1–4. The stoichiometries and structures of the complexes were deduced from their elemental analyses, IR and electronic spectra and thermal decomposition. Thermal stabilities of the complexes were discussed and kinetic parameters were calculated using the Coats-Redfern and Horowitz-Metzger equations. The photochemical behaviour of the complexes was investigated. Upon irradiation, the Cu(II) complex of cefamandole underwent two competitive processes, one is photodegradation, the other is intramolecular hydrogen abstraction, as indicated from the spectral changes. The remaining studied Cu(II) complexes behave similar to their corresponding free antibiotics.

SPECTRAL, THERMAL, AND PHOTOCHEMICAL STUDIES ON CERTAIN FIRST, SECOND, AND THIRD GENERATION CEPHALOSPORIN ANTIBIOTICS AND THEIR CD(II) COMPLEXES

ABSTRACT The reactions of six cephalosporin antibiotics with cadmium chloride afforded the corresponding Cd(II) complexes. The antibiotics are: cephalexin, cephapirin, cefamandole, cefuroxime, cefotaxime, and ceftazidime. Their Cd(II) complexes are of the general formulas Cd(ATB)ClċxH2O, Cd(ATB)2ċ-xH2O and Cd2(ATB)Cl2ċxH2O where ATB=the respective antibiotic, x=1–3. The complexes have been characterized on the basis of elemental analyses, IR, electronic and 1H NMR spectroscopy, thermal decomposition and photochemical behaviour. Thermogravimetry and derivative thermogravimetry (TG-DTG) have been used to study the stabilities and the thermal decomposition processes of the antibiotics and their Cd(II) complexes. In some cases, the decomposition steps could be correlated with the proper decomposition products, where possible activation energies and order of the decomposition reaction have been calculated from the thermal data. The photochemical behaviour of the antibiotics under investigation and their Cd(II) complexes have been studied. Cephalexin and cefamandole show similar behaviour upon irradiation with light of 298 nm, i.e., an appearance of a new band at long wavelength attributable to the formation of a photocyclization product. The Cd(II) complex of cephalexin exhibits high light sensitivity. Mechanisms of the photolysis of the free antibiotics and Cd-complexes are suggested.

Thermal and photochemical behaviour of Zn(II) complexes of some cephalosporins

Zn(II) complexes of some cephalosporin antibiotics namely cephalexin, cephapirin, cefamandole, cefuroxime, cefotaxime and ceftazidime were synthesised and characterized. The stoichiometrics and the mode of bonding of the complexes were deduced from their elemental analysis, IR and electronic spectroscopies. Thermal stabilities and the photochemical behaviour of the complexes were studied. The Zn(II) complex of cephalexin exhibited a high light sensitivity. The remaining Zn(II) complexes behaved similarly to their free antibiotics, upon irradiation.

Mixed benzohydroxamato-acetylacetonato metal complexes: spectral, thermal and photochemical behaviour

SummaryBis(acetylacetonato)VOII,−CoII,−NiII,−CuII,−ZnII, −UO2II and tris(acetylacetonato)FeIII react with benzohydroxamic acid to yield the corresponding mixed ligand complexes as a result of displacement of one acetylacetone molecule. Intermolecular association may be the reason for six-coordination geometry around the metal ions. A t.g.a. study of the complexes shows, in most cases, initial loss of alcohol and water molecules associated with the complexes; subsequent decomposition steps are characterised by very sharp weight loss. The photochemical stability of the complexes has been studied. Intraligand excitation causes a decomposition in the case of FeIII and VOII-complexes but no detectable effect for CoII, NiII, CuII, ZnII, or UO2II-complexes.

THERMAL STABILITY AND KINETIC STUDIES OF COBALT (II), NICKEL (II), COPPER (II), CADMIUM (II) AND MERCURY (II) COMPLEXES DERIVED FROM N-SALICYLIDENE SCHIFF BASES

The thermal properties of a number of Schiff base metal complexes in nitrogen atmosphere have been investigated by thermogravimetry (TG) and differential thermogravimetry (DTG). The kinetic analyses of the thermal decomposition were studied using the Coats-Redfern and Horowitz-Metzger equations. The obtained kinetic parameters show the kinetic compensation effect.

Optical outer-sphere ligand to metal charge transfer in bis(N-ethylsalicylaldiminato)nickel(II)/tris(oxalato)ferrate(III)

A mixture of [Ni(Et-sal)2] (= bis(N-ethylsalicylaldiminato)nickel(II)) and [Fe(Ox)3]3− (tris-(oxalato)fcrrate(III) ion) displays longwavelength absorption at λmax=472 nm. This new absorption band is assigned to an outer-sphere LMCT transition from the coordinated ethylsalicylaldimine of [Ni(Et-sal)2] to Fe(III) of [Fe(Ox)3]3−. Mixing free ethylsalicyldimine or [M(Et-sal)2] (where M = Co(II), Cu(II) or Zn(II)) and [Fe(Ox)3]3− also shows the same phenomenon; the maximum of the new absorption band is independent on the nature of the metal.

SYNTHESIS AND INTRAMOLECULAR EXCITED STATE ELECTRON TRANSFER OF [Co(NH3)5-CEPHALEXIN]2+ COMPLEX

ABSTRACT [Co(NH3)5-cephalexin]2+ has been synthesized and characterized by elemental analyses, IR and UV-Visible spectroscopy as well as photochemical and thermal studies. The electronic spectrum of the complex in DMF shows two bands at 358 and 267 nm, which are assigned to intraligand charge transfer and π-π* transitions, respectively. The fluorescence of the cephalexin is quenched by excited state electron transfer to Co(III). As a consequence, the cephalexin is oxidized while Co(III) is reduced to Co(II) ion with quantum yield (φ)=0.03±0.002, at exciting wave length (λ irr)=298 nm. A reaction mechanism is proposed. The thermal decomposition of the complex was studied in static air. On the basis of the thermogravimetric curves, some decomposition could be correlated with the proper decomposition products.