Kinetic analysis of thermogravimetric data on some nickel(II) N-alkyldithiocarbamates

Thermogravimetric and derivative thermogravimetric curves of some complexes [Ni(S₂CNHR)₂] (R=Me, Et, Prⁱ, Buⁱ, Bu^t, Bz,p-MePh,p-MeOPh,p-ClPh,p-NO₂Ph) in a dynamic nitrogen atmosphere were studied to determine their modes of decomposition. All these complexes show similar TG profiles. The weight losses in the main decomposition stages indicate conversion of the nickel(II) dithiocarbamates to sulphide. Reaction orders were estimated via the shape characteristics of the corresponding derivative thermogravimetric curves and kinetic analysis of the thermogravimetric data was performed by using the Coats-Redfern and Horowitz-Metzger methods.

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Zusammenfassung Im Stickstoffstrom wurden TG- und DTG-Kurven einiger Komplexe [Ni(S₂CNHR)₂] mit R=Me, Et, Prⁱ, Buⁱ, Bu^t, Bz,p-MePh,p-MeOPh,p-ClPh undp-NO₂Ph ermittelt, um Art und Weise ihrer Zersetzung zu bestimmen. Alle diese Komplexe zeigen ähnliche TG-Proflle. Die Gewichtsverluste der Hauptzersetzungsschritte weisen auf eine Umwandlung der Nickel(II)dithiokarbamate in Sulfide hin. Aus dem Verlauf der korrespondierenden DTG-Kurven wurde auf die Reaktionsordnung geschlossen und unter Anwendung der Coats-Redfern und Horowitz-Metzger Methoden wurde eine kinetische Analyse der TG-Daten durchgeführt.

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[Ni(S₂CNHR)₂], R=Me, Et, i-Pr, i-, t-Bu, Bz, p-MePh, p-MeOPh, p-ClPh p-NO₂Ph, . . . , - -.

     

Mass spectral and thermogravimetric studies of some iron(III) binuclear complexes with bridging thiuram disulfide ligands

Mass spectral and thermal studies by TG and DTG of some iron(III) binuclear complexes of the general type Fe₂(R₂dtc)₂(tds)X₂X/ have been carried out to determine their modes of decomposition. Fragmentation patterns are given and possible mechanisms are discussed.

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Zusammenfassung Massenspektrometrische und thermische Untersuchungen (TG und DTG) einiger zweikerniger Eisen(III)-Komplexe des allgemeinen Typs (R₂dtc)₂(tds)X₂X₂ wurden ausgeführt, um deren Zersetzungsmechanismus zu ermitteln. Fragmentspektren werden angegeben und mögliche Mechanismen diskutiert.

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- ( ) Fe₂(R₂dtc)₂(tds)X₂X₂ . .

     

Thermal decomposition of some homobinuclear dihalide-bridged iron(III) complexes

Thermal studies by TG and DTG on some homobinuclear dihalide-bridged iron(III) complexes of the general type [Fe(S₂CNR₂)₂X]₂(}-X ₂) were carried out in air and nitrogen atmospheres. The apparent activation energies were determined by graphical methods and the TIN temperatures were calculated from the TG profiles. Finally, a possible mechanism of the decomposition is suggested on the basis of the pyrolysis and mass spectral data.

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Zusammenfassung Einige homobinukleare Eisen(III)-Komplexe mit Dihalidbrücken der allgemeinen Formel [Fe(S₂CNR₂)₂X]₂(–X₂) wurden mittels TG und DTG in Luft und Stickstoffatmosphäre untersucht. Die scheinbaren Aktivierungsenergien wurden nach graphischen Methoden aus den TG-Profilen bestimmt. Ein möglicher, auf pyrolytischen und massenspektrometrischen Daten basierender Zersetzungsmechanismus wird vorgeschlagen.

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[Fe(S₂CNR₂)₂X]₂ (-₂) . , . - .

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Thanks are due to Dr. G. Karagiannidis, Laboratory of Organic Chemical Technology, Aristotelian University, for technical assistance.     

Four-coordinated palladium(II) and platinum(II) complexes containing the Lewis-acid {M(S2CNHR)(PR3′)} group combined with a variety of other ligands

A new series of four-coordinated Pd(II) and Pt(II) complexes in which the Lewis-acid (14-electron) {M(S₂CNHR)(PR₃′)} group is combined with a variety of other ligands (such as RHNCS₂^?, I^?, SCN^?, SnCl₂I^?) has been synthesised and studied. The structures of the new compounds are discussed in relation to their specroscopic, magnetic and thermal properties. In the case of [M(S₂CNHR)₂(PR₃′)] complexes both the spectroscopic data (IR, ¹H NMR, UV-Vis) and their thermal behaviour strongly suggest the coexistence of two kinds of gem-disulphide ligands, one acting as a bidentate ligand and the other one as a unidentate. Also it was confirmed that the chemical behaviour of the bis(N-alkyldithiocarbamato) complexes of Pd(II) and Pt(II) towards tertiary phosphines is similar to that of the isoelectronic xanthate complexes rathe than to the bis(N,N-dialkyldithiocarbamato) complexes.     

Chemical stability and reactivity of the 1∶1 and 2:1 halobis(N,N-dialkyldithiocarbamato)iron(III): Molecular halogen loose associations

EHMO-SCCC calculations have been used to probe the molecular orbital interactions of 1:1 and 21 charge-transfer complexes of halobis(N,N-dialkyldithiocarbamato)iron(III) complexes with molecular halogens, treated as super molecules. The molecular orbital structure of the compounds is being described in essentially the same way to that successfully applied in the cases of-, -gs, and n- CT complexes. It is found that all types of orbital interactions (- and/or type) have a destabilizing effect on the complexes; hence, the forces of attachment have to be of the charge-transfer and van der Waals type, to offset this molecular orbital-based repulsion. The relative stability of the compounds is broadly discussed in terms of the calculated binding energies, which are found to depend on the nature of both constituent molecules. Moreover, orbital populations, two-center energy terms, and computed atomic charges of the super molecules, as compared to those of the constituent molecules, provide adequate information on the mechanism of the charge-transfer processes occurring upon complexation. It is important that weak bonding interactions between the constituent molecules do exist, but surprisingly directly, between the molecular halogens and the iron(III) central atoms, and not via the apical halogeno ligands. These bonding interactions, although not responsible for the stability of the compounds, account well for the observed magnetic behavior of the dimeric (21) complexes and are of key importance in promoting intramolecular electron-transfer reactions responsible for the oxidation of half of the dithio ligands into the thiuram disulfides observed in some of the reactions of the iron(III) halobisdithiocarbamates with molecular halogens.     

Structural properties and potential reactivity of substituted 3- aroyldithiocarbazates

A series of substituted 3-aroyldithiocarbazates has been synthesized and studied. The corresponding acid dissociation constants have been determined potentiometrically. Semiempirical PM3 molecular orbital calculations suggest the existence of several tautomeric forms of the compounds. Geometrical parameters, proton affinities, and static reactivity indices have been examined. Structural properties and protonation sites are well described by calculations. The strong correlations between the pK _a values and the Hammett constants as well as the N(3) calculated proton affinities indicate that the N(3) atom is the most probable protonation site. The thermodynamics of the protonation process are mainly controlled by HOMO-LUMO rather than electrostatic interactions. According to PM3 results, 3-aroyldithiocarbazic acid should be quite stable in the gas phase, while a mechanism for its decomposition in solution is proposed.