Luka J. Bjelica

Transition metal complexes with the thiosemicarbazide-based ligands—III. Synthesis, physico-chemical properties and voltammetric characterization of some FeIII complexes with ter- and quadridentate S-methylisothiosemicarbazide derivatives

Abstract Several high-spin Fe III complexes of the type Fe(HL)Cl 2 and Fe(L)Cl (HL = monoanion of terdentate NNO ligand and L = dianion of quadridentate ONNO ligand, respectively), based on the condensation products of S-methylisothiosemicarbazide and different aromatic 2-hydroxy-aldehydes, have been prepared and characterized by elemental analysis, conductivity and magnetic measurements, IR and electronic spectra, as well as by cyclic voltammetry. For all solid complexes a pentacoordinated structure is proposed, while in DMF solutions hexacoordination is suggested. Differences in some physico-chemical properties, arising from structural changes in the coordinated ligand, are discussed.

Synthesis, physicochemical properties and voltammetric characterization of some new Fe(III) complexes with semicarbazone-based ligands

Abstract Several bis(ligand) octahedral complexes of iron(III) with salicylaldehyde semi-, thiosemi-, and S-methylthiosemi- carbazones have been synthesized and characterized by elemental analysis, conductivity and magnetic measurements, electronic and IR spectra, as well as by linear sweep and cyclic voltammetry. General procedures for the syntheses of all types of complexes have been established, giving better defined reaction conditions. Physicochemical properties of the novel complexes have been related to those of the already known compounds of the same type.

Transition metal complexes with the thiosemicarbazide-based ligands—XXIII. Synthesis, physicochemical properties and voltammetric characterization of iron(III) complexes with terdentate and quadridentate thiosemicarbazide derivatives

Abstract Two iron(III) complexes with the terdentate ONS and ONN ligands benzoylacetone thiosemi- and S-methylisothiosemicarbazone, respectively, of the general formula [Fe(HL)Cl2], were synthesized. Besides, the iron(III) complexes of the general formula [Fe(L)Cl] involving the quadridentate ONNO ligands N(1)-benzoylisopropilidene-N(4)-salicylidene (5-chloro-, 3,5-dichloro-, or 5-nitro-salicylidene) S-methylisothiosemicarbazide were also prepared. The complexes were characterized by elemental analysis, molar conductivity and magnetic measurements, IR and electronic spectra, as well as by cyclic voltammetry. It was found that the complexes are high-spin pentacoordinated. In addition, a detailed voltammetric study in DMF solutions has shown that the electrochemical processes are frequently accompanied by various chemical reactions.

Activation of glassy carbon electrode in aqueous and non-aqueous media

Abstract By recording the cyclic voltammograms at a freshly polished and electrochemically pretreated (ex situ) Tokai gce for the ferric/ferrous reaction in water, water + DMF, and water + ethanol, it was established that the activating effect of electrochemical pretreatment decreases with increasing content of the organic solvent in the solution.

Electrochemistry of iron(III) complexes with salicylaldehyde thiosemicarbazone and its S-methyl derivative

Abstract A detailed electrochemical study of Fe(III) chelate complexes with salicylaldehyde thiosemicarbazone (H2L1) and its S-methyl derivative (H2L2), of general formulae Fe(HL)Cl2, [Fe(HL)2]Cl, Fe(HL)L and Li[FeL2] was carried out at a glassy carbon electrode in a DMF + LiCl system. Both the cation and anion of the supporting electrolyte affect the behaviour of the complexes significantly: Li+ by forming ion pairs with the reduced bis(ligand) anions and Cl− via replacement of HL− in corresponding complexes. In addition, H+ plays an important role in both the heterogeneous and homogeneous processes. While all complex species are reduced in a one-electron process, those containing the L2− form can also be oxidized. The H2L1 complexes are more easily reduced/oxidized than the analogous H2L2 complexes. Chemical reactions associated with electron transfer processes make the overall behaviour of the compounds rather complex. All heterogeneous and homogeneous reactions are presented in a common reaction scheme, and the overall mechanism is discussed.

Photocatalytic Degradation of Herbicide Quinmerac in Various Types of Natural Water

The efficiency of the photocatalytic degradation of the herbicide quinmerac in aqueous TiO2 suspensions was examined as a function of the type of light source, TiO2 loading, pH, temperature, electron acceptors, and hydroxyl radical (•OH) scavenger. The optimum loading of catalyst was found to be 0.25 mg mL−1 under UV light at pH 7.2, with the apparent activation energy of the reaction being 13.7 kJ mol−1. In the first stage of the reaction, the photocatalytic degradation of quinmerac (50 μM) followed approximately a pseudo-first order kinetics. The most efficient electron acceptor appeared to be H2O2 along with molecular oxygen. By studying the effect of ethanol as an •OH scavenger, it was shown that the heterogeneous catalysis takes place mainly via •OH. The results also showed that the disappearance of quinmerac led to the formation of a number of organic intermediates and ionic byproducts, whereas its complete mineralization occurred in about 120 min. The reaction intermediates (7-chloro-3-methylquinoline-5,8-dione, three isomeric phenols hydroxy-7-chloro-3-methylquinoline-8-carboxylic acids, and 7-chloro-3-(hydroxymethyl)quinoline-8-carboxylic acid) were identified and the kinetics of their appearance/disappearance was followed by LC–ESI–MS/MS. Tentative photodegradation pathways were proposed and discussed. The study also encompassed the effect of quality of natural water on the rate of removal of quinmerac.

Transition metal complexes with the thiosemicarbazide-based ligand—XVI. Novel iron(IV) complexes with pentane-2,4-dione bis(s-methylisothiosemicarbazone)

Abstract Several square-pyramidal iron(IV) complexes with the quadridentate ligand pentane-2,4-dione bis(S-methylisothiosemicarbazone) (H3L) of the type [Fe(L)X], where X = Cl, Br, NCO or NCS, were synthesized and their physicochemical characteristics, together with those of previously reported [Fe(L)I] and [Fe(L)]2O, are described. The complexes were characterized by elemental analysis, molar conductivity and magnetic measurements, IR and electronic spectra. In addition, cyclic voltammetry is used to study the redox behaviour of the complexes in their DMF solutions and especially of the dimermonomer equilibria influenced by the acidity of the solution.

Application of an indicating system of bismuth electrodes for the determination of organic bases and acids in nonaqueous solutions

ZusammenfassungTertiäre Amine und Salze organischer Säuren werden durch Titration mit einer Lösung von Perchlorsäure quantitativ bestimmt. Das verwendete Indicatorsystem besteht aus einem Paar polarisierter oder nichtpolarisierter Wismutelektroden. Das gleiche System wurde auch angewandt auf die titrimetrische Bestimmung von Mono- und Polycarbonsäuren mit einer starken Base. Die Ergebnisse stimmen gut mit denen der potentiometrischen bzw. katalytisch-thermometrischen Methode überein.SummaryTertiary amines and salts of organic acids have been titrated by means of perchloric acid applying a biamperometric indicating system consisting of a polarised or unpolarised pair of bismuth electrodes. Also, mono- and polycarboxylic acids, alone and in mixtures, have been determined with a strong base using the same end-point detection technique. The results obtained are in good agreement with those of potentiometry or catalytic thermometry.

Complexes of iron(III) with benzoylacetone 1-naphthoylhydrazone

Abstract One mono(ligand) and three bis(ligand) octahedral complexes (cationic, anionic and non-electrolyte type) of iron(III) and benzoylacetone 1-naphthoylhydrazone have been prepared and characterized by elemental analysis, conductivity measurements, IR and electronic spectra, as well as by linear sweep and cyclic voltammetry. It has been found that formation of these complexes can be explained by the nature of this tridentate (ONO) ligand, taking part in coordination as both a mono- and a dianion.

Voltammetry of some novel Fe(III) complexes with tetradentate ONNO ligands: The axial ligand effect

Abstract The electrochemistry of some novel Fe(III) complexes of the type Fe(L)Cl involving several tetradentate ligands based on the bis-condensation products of S-methylisothiosemicarbazide with two either identical or different aldehydes (salicylaldehyde, its derivatives, or 2-hydroxy-1-naphthaldehyde), was studied in DMF solutions at a GC electrode. All complexes undergo a two-step one-electron reduction which is usually complicated by chemical reactions. In solutions containing Cl− (either from the complex, or added as LiCl), the Cl−-DMF ligand exchange reaction takes place and is especially pronounced for the Fe(II) oxidation state. The stability of the chloride-containing complexes was discussed in detail in view of the coordinated ligand effect and the oxidation state of the central atom. Some relevant kinetic parameters are calculated.