Thermoanalytical and IR-spectral Investigation of Mg(II) Complexes with Heterocyclic Ligands

Thermogravimetry (TG), differential thermal analysis (DTA) and other analytical methods have been applied to the investigation of the thermal behaviour and structure of the complexes Mg(pc)(na)₃⋅3H₂O (I), Mg(pc)(py)₂⋅2H₂O (II),Mg(pc)(pic)₂⋅2H₂O (III) and Mg(pc)(caf)₂⋅4H₂O (IV), where pc=2,6- pyridinedicarboxylate, na=nicotinamide,py=pyridine, pic=γ-picoline and caf=caffeine. The thermal decomposition of these compounds is multi-stage processes. The chemical composition of the complexes, the solid intermediates and the resultant products of thermolysis have been identified by means of elemental analysis and complexometric titration. Schemes of destruction of these complexes are suggested. Heating of these compounds first resulted in a release of water molecules. In complexes I, II and IV the loss of the molecular ligands (na, py and caf) occur (on the TG curves) in one step (-2na, -2py and -2caf) and in complex III in two steps (-pic, -pic). The final product of the thermal decomposition was MgO. The thermalstability of the complexes can be ordered in the sequence: IV<I<III<II. Nicotinamide, pyridine, γ-picoline and caffeine were co-ordinated to Mg(II) through the N atom of the respective heterocyclic ring. IR data suggested a unidentate co-ordination of carboxylates to Mg(II) in complexes I–IV. This revised version was published online in July 2006 with corrections to the Cover Date.     

Studies on Some Nickel(II) and Cobalt(II) Mixed Ligand Complexes of Arylsalicyl-Aldimine and Other Ligands

Several new mixed ligand complexes of Ni(II) and Co(II) of p-tolylsalicylaldimine (Sal-TH) or p-anisylsalicylaldimine (Sal-AH) with 8-hydroxyquinoline (HOx), benzohydroxamic acid (BH₂) or α-picoline (α-pic) have been synthesized. The complexes have the general formulae: [M(Sal-T)L],[M(Sal-A)L]⋅H₂O or [Ni(Sal-T)₂(α-pic)₂]⋅H₂O where M=Ni(II) or Co(II), Sal-T=p-tolylsalicylaldiminate, Sal-A=p-anisylsalicylaldiminate, L=8-hydroxyquinolinate or benzohydroxamate and α-pic=α-picoline. Analytical, conductivity and spectral data support a square planar structure for Co(II) complexes and octahedral structure for Ni(II) complexes. The thermal behaviour of the complexes has been studied by TG and DTG techniques. It was proposed that the decomposition of the complexed Schiff base takes place via a radical mechanism while for 8-hydroxyquinolinate or benzohydroxamate via proton transfer. Kinetic parameters of the thermal decomposition process have been computed by means of Coats-Redfern and Horowitz-Metzger methods. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal and spectral studies of palladium(II) complexes

Palladium(II) complexes of type [Pd(L)Cl₂] [where L=2-aminopyridine-N-thiohydrazide (L¹), (2-aminopyridine-N-thio)-1,3-propanediamine (L²), benzaldehyde 2-aminopyridine-N-thiohydrazone (L³) and salicylaldehyde-2-aminopyridine-N-thiohydrazone (L⁴)] have been synthesized. The thiohydrazide, thiodiamine and thiohydrazones can exist as thione-thiol tautomer and coordinate as a bidentate N-S ligand. The ligands found to act in bidentate fashion. The complexes have been characterized by elemental analysis, IR, mass, electronic, ¹H NMR spectroscopic studies, and TG/DTA study. Antifungal studies of some complexes were also carried out. Various kinetic and thermodynamic parameters like order of reaction (n), activation energy (E _a), apparent activation entropy (S ^# ) and heat of reaction (ΔH) have also been carried out for one complex.     

Substitutions of organopalladium(II) species with benzimidazole derivatives

The [Pd(cod)(cotl)]ClO₄ complex (cod = cycloocta-1,5-diene; cotl = cyclooctenyl, C₁₈H₁₃ ^–) undergoes substitutions with new Schiff base ligands containing benzimidazole L [L = 2-(2-N-n-propylidenephenyl)benzimidazole (L¹); 2-(2-N-i-propylidenephenyl)benzimidazole (L²); 2-(2-N-n-butylidenephenyl)benzimidazole (L³); 2-(2-N-i-butylidenephenyl)benzimidazole (L⁴)]. Facile displacement of cod by L occurs to produce complexes of the type [Pd(cotl)L]ClO₄· nMe₂CO (n= 0; L = L¹, L² or L³; n= 2, L = L⁴). Dihalobridge complexes of the type [Pd(cotl)X]₂(X = Cl or Br) undergo halogen-bridge cleavage with L¹–L⁴ to give mononuclear complexes of the type Pd(cotl)LX · nH₂O (n= 2, X = Cl, L = L¹; n= 0, X = Br, L = L¹; n= 0, X = Cl, L = L²; n= 0, X = Cl or Br, L = L³; n= 0, X = Cl, L = L⁴; n= 2, X = Br, L = L⁴) and a binuclear complex [Pd(cotl)Br]₂L². The complexes were characterised by physical properties, i.r., ¹H- and ¹³C-n.m.r. spectral techniques and by mass spectra. Probable structures have been proposed.     

Thermal decomposition of nickel(II), palladium(II), and platinum(II) complexes of <Emphasis Type="Italic">N</Emphasis>-allyl-<Emphasis Type="Italic">N</Emphasis>′-pyrimidin-2ylthiourea

Thermal decomposition of Ni(II), Pd(II), and Pt(II) complexes of N-pyrimidin-2ylthiourea (AllPmTu) have been studied by TG, DTG, and DTA and by electron impact (EI) mass spectra. The complexes have the molecular formulae as [Ni(AllPmTu)Cl₂(H₂O)], [Ni(AllPmTu)₂Cl₂(H₂O)₂], and [M(AllPmTu)Cl₂], where M = Pd^II or Pt^II, and [Pt(AllPmTu)₂]. The TG curves show that Ni(II) complexes decompose in three stages to yield NiO as a residue, while Pd(II) and Pt(II) decompose in two stages to yield MS residues. The initial mass losses correspond to elimination of allylamine for Pd(II) and Pt(II) complexes but, allyisothiocyanate for both Ni(II) complexes revealing that sulfur atom of thiourea part is involved in coordination to Pd(II) and Pt(II) but does not to Ni(II). Kinetic parameters (E ^#, n, ΔH ^#, ΔS ^#, ΔG ^#) of the decomposition stages are determined and correlated with bonding and structural properties of the complexes. The EI mass spectra of the complexes show fragments corresponding to the evolved and intermediate species.     

Heteroleptic tri-<Emphasis Type="Italic">tert</Emphasis>-butoxysilanethiolate complexes of manganese(II)

The thermal behavior of Mn(II) silanethiolate series [Mn(SR)₂L(MeOH)_n], where R=SSi(OBut)₃, L=heterocyclic nitrogen base and n=0, 1 or 2 has been comparatively investigated using differential scanning calorimetry (DSC), thermogravimetry (TG) and TG-infrared spectoscopy (IR) techniques. The TG curves indicate the differences in the thermal decomposition due to presence of distinct N-donor ligands and labile MeOH molecules coordinated to the central atom. The first step on the TG curves (60–110°C) corresponds to the elimination of alcohol from respective complexes. The main step (150–350°C) can be assigned to the decomposition of the complexes yielding Mn₃O₄ and silica as the main final products, identified by X-ray diffraction patterns.     

Synthesis, spectral and thermal studies on dicarboxylate-bridged palladium(II) coordination polymers. Part I

The synthesis and thermal behavior of the new [Pd(fum)(bipy)] _n ·2nH₂O (1), [Pd(fum)(bpe)] _n ·nH₂O (2) and [Pd(fum)(pz)] _n ·3nH₂O (3) {bipy = 4,4′-bipyridine, bpe = 1,2-bis(4-pyridyl)ethene and pz = pyrazine} fumarate complexes are described in this work as well their characterization by IR and ¹³C CPMAS NMR spectroscopies. TG curves showed that the compounds released organic ligands and lattice water molecules in the temperature range of 46–491 °C. In all the cases, metallic palladium was identified as the final residue.     

Palladium(II) complexes with 1-allyl-3-(2-pyridyl)thiourea: Synthesis and spectroscopic characterization

New Pd(II) complexes with 1-allyl-3-(2-pyridyl)thiourea (APTU) of the formulas [Pd(C₉H₁₁N₃S)Cl₂] (I) and [Pd(C₉H₁₁N₃S)₂]Cl₂ (II) were obtained and examined by UV-Vis, IR, and 1H NMR spectroscopy. The conditions for the complexation reactions were optimized. The instability constants and molar absorption coefficients of these complexes were calculated. Comparison of the characteristic bands in the UV-Vis and IR spectra of the complexes and free APTU revealed that the ligand in both complexes is coordinated to the metal atom in the thione form in the bidentate chelating mode through the S atom of the thiourea group and the pyridine N atom. In the UV-Vis spectra of the complexes, the charge transfer bands (π → π* Py) and n → π* (C=N_Py), (C=S) experience hypsochromic shifts by 450–470 cm⁻¹ caused by the coordination of APTU to the metal ion, which gives rise to ligand-metal charge-transfer bands (C=N_Py → Pd, n → π* (C=S)) and (SPd). The protons in the 6-, 4-, and 3-positions of the pyridine ring and the thiourea NH proton in the chelate ring are most sensitive to the complexation.     

Mixed-ligand complexes of tris(acetylacetonato)iridium(III) with <Emphasis Type="Italic">N</Emphasis>-heterocyclic ligands: synthesis and crystal structure

A series of mixed-ligand complexes of tris(acetylacetonato) iridium(III) with N-heterocyclic ligands, namely [bis(acac-O,O′)(acac-C³)Ir(L)], where acac = acetyacetonato; L = 2-picoline (1), 3-picoline (2), 4-picoline (3), have been synthesized via the reaction of [bis(acac-O,O′) (acac-C³)Ir(H₂O)] with the corresponding ligand, respectively. Molecular structures of all complexes were determined by using single-crystal X-ray diffraction. The results reveal that these complexes have slightly distorted octahedral coordination geometries.     

The coordination chemistry ofN,N′-ethylenebis(2-acetylpyridine imine) andN,N′-ethylenebis(2-benzoylpyridine imine); two potentially tetradentate ligands containing four nitrogen atoms

Summary New complexes of the general formulae [ML_A(H₂O)₂]-Cl₂ (M=Ni or Cu), [ML_AX₂] (M=Co or Cu; X=Cl or Br), [NiL_ABr₂]·H₂O, [ML_A] [MCl₄] (M=Pd or Pt), [NiL_B(H₂O)₂]Cl₂·2H₂O, [ML_BCl₂] (M=Co, Ni, Cu, Pd or Pt; X=Cl or Br) and [ML_B] [MCl₄] (M=Pd or Pt), where L_A=N,N-ethylenebis(2-acetylpyridine imine) and L_B=N, N-ethylenebis(2-benzoylpyridine imine), have been isolated. The complexes were characterized by elemental analyses, conductivity measurements, t.g./d.t.g. methods, magnetic susceptibilities and spectroscopic (i.r., far-i.r., ligand field,¹Hn.m.r.) studies. Monomeric pseudo-octahedral stereochemistries for the Co^II, Ni^II and Cu^II complexes andcis square planar structures for the compounds [ML_BX₂] (M=Pd or Pt; X=Cl or Br) are assigned in the solid state. The molecules L_A and L_B behave as tetradentate chelate ligands in the Co^II, Ni^II, Cu^II and Magnus-type Pd^II and Pt^II complexes, bonding through both the pyridine and methine nitrogen atoms. A bidentateN-methine coordination of the Schiff base L_B is assigned in the [ML_BX₂] complexes (M=Pd or Pt; X=Cl or Br). The anomalous magnetic moment values of the Co^II complexes are discussed.     

Fluxional rearrangement in congested ruthenium(II) complexes containing pyrimidine- and/or pyridine-based dithioether ligands

The solvento species obtained by the treatment of cis-RuCl₂(N,N-L)₂ [L = di-2-pyridyl sulfide (dps), di-2-pyrimidyl sulfide (dprs)] with AgPF₆, reacted with dithioethers L′ [L′ = 2,6-bis(2-pyridylthiomethyl)pyridine (pytmp), 2,6-bis(2-pyrimidylthiomethyl)pyridine (prtmp) and 2,6-bis{2-(4-methyl)pyrimidylthiomethyl} pyridine (mprtmp)] to afford the compounds [Ru(N,N-L)₂(N,S-L′)][PF₆]₂. The ¹H NMR spectra indicate that L′ is chelated through S and N atoms with the formation of a four-membered ring. As a consequence, the ruthenium and sulfur atoms are stereogenic centers with ∆ and Λ and (R) and (S) configurations, respectively. NMR spectra, at low temperatures, show that two invertomers, of similar abundance, as enantiomeric couples ∆S, ΛR and ∆R, ΛS are present. In the methylene region, four AB systems are observed that in both the species contain two non-equivalent methylene groups. Variable-temperature NMR spectra and EXSY experiments show that the sulfur inversion produces an exchange between the invertomers. The one-dimensional band-shape analysis of the exchanging methylene signals showed that the energy barriers for the process are in the 43–52 kJ mol⁻¹ range. The possible mechanisms of the sulfur inversion are discussed.     

Non-isothermal Studies on Mechanism And Kinetics of Thermal Decomposition of Cobalt(II) Oxalate Dihydrate

Thermal decomposition of CoC₂O₄⋅2H₂O was studied using DTA, TG, QMS and XRD techniques. It was shown that decomposition generally occurs in two steps: dehydration to anhydrous oxalate and next decomposition to Co and to CoO in two parallel reactions. Two parallel reactions were distinguished using mass spectra data of gaseous products of decomposition. Both reactions run according toAvrami–Erofeev equation. For reaction going to metallic cobalt parameter n=2 and activation energy is 97±14 kJ mol^–1. It was found that decomposition to CoO proceeds in two stages. First stage (0.12<α_II<0.41) proceeds according to n=2, with activation energy 251±15 kJ mol^–1 and second stage (0.45<α_II<0.85) proceeds according to parameter n=1 and activation energy 203±21 kJ mol^–1. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cyclooctenyl complexes of palladium(II) with multidentate N-heterocycles

[Pd(cod)(cotl)]ClO₄ (cod = 1,5-cyclooctadiene, cotl = cyclooctenyl, C₈H₁₃ ^–) undergoes substitutions with multidentate N-heterocycles: 1,3-bis(benzimidazolyl)benzene (L¹), 1,3-bis(1-methylbenzimidazol-2-yl)benzene (L²), 2,6-bis(benzimidazolyl)pyridine (L³) and 2,6-bis(1-methylbenzimidazol-2-yl)pyridine (L⁴) to yield mono/binuclear complexes: [Pd(cotl)(L¹)(OClO₃)], [Pd(cotl)(L)]ClO₄ (L = L² or L³) and [Pd(cotl)₂(L⁴)](ClO₄)₂. Dihalobridged binuclear complexes [PdX(cotl)]₂ (X = Cl or Br) undergo halogen bridge cleavages with the multidentate N-heterocycles to form binuclear complexes of the type [PdX(cotl)₂L] (X = Cl or Br; L = L¹, L², L³ or L⁴). The complexes were characterized by elemental analyses, ¹H-, ¹³C-n.m.r., i.r., far-i.r. and FAB-mass spectral studies.     

Thermoanalytical behaviour of carbaryl and its copper(II) and zinc(II) complexes

Non-isothermal techniques, i.e. thermogravimetry (TG) and differential scanning calorimetry (DSC), have been applied to investigate the thermal behaviour of carbaryl (1-naphthyl-N-methylcarbamate = 1-Naph-N-Mecbm) and its complexes, M(1-Naph-N-Mecbm)₄X₂, where M = Cu, X = Cl, NO₃ and CH₃COO and M = Zn, X = Cl. Carbaryl and Zn(1-Naph-N-Mecbm)₄Cl₂ complex exhibit two-stage thermal decomposition while the copper(II) complexes exhibit three and four-stage decomposition in their TG curves. The nature of the metal ion has been found to play highly influential role on the nature of thermal decomposition products as well as energy of activation ‘E*’. The presence of different anions does not seem to alter the thermal decomposition patterns. The complexes display weak to medium intensity exothermic and endothermic DSC curves, while the free ligand exhibits two endothermic peaks. The kinetic and thermodynamic parameters namely, the energy of activation ‘E*’, the frequency factor ‘A’ and the entropy of activation ‘S*’ etc. have been rationalized in relation to the bonding aspect of the carbaryl ligand. The nature and chemical composition of the residues of the decomposition steps have been studied by elemental analysis and FTIR data.     

Thermal and spectroscopic investigation on N,N-dimethylbenzylamine based cyclopalladated compounds containing isonicotinamide

Synthesis, spectroscopic characterization and thermal analysis of the [Pd(dmba)(Cl)(iso)] (1), [Pd(dmba)(NCO)(iso)] (2), [Pd(dmba)(N₃)(iso)] (3) and [Pd(dmba)(Br)(iso)] (4) (dmba = N,N′-dimethylbenzylamine; iso = isonicotinamide) compounds are described in this work. The complexes were investigated by infrared spectroscopy (IR), differential thermal analysis (DTA) and thermogravimetry (TG) and the residues of the thermal decomposition were identified as Pd^o by X-ray powder diffraction. The thermal stability order of the complexes varied as [Pd(dmba)(Cl)(iso)] (1) > [Pd(dmba)(Br)(iso)] (4) > [Pd(dmba)(NCO)(iso)] (2) > [Pd(dmba)(N₃)(iso)] (3).     

Thermal behaviour and spectroscopic studies of complexes of some divalent transitional metals with 2-benzoil-pyridil-izonicotinoylhydrazone

New complexes of 2-benzoyl-pyridil-isonicotinoylhydrazone (L) with Cu(II), Co(II), Ni(II) and Mn(II), having formula of type [ML₂] SO₄·xH₂O (M = Cu²⁺, Co²⁺, Ni²⁺, x = 2 and M = Mn²⁺, x = 3), have been synthesised and characterised. All complexes were characterised on the basis of elemental analyses, IR spectroscopy, UV–VIS–NIR, EPR, as well as thermal analysis and determination of molar conductivity and magnetic moments. The thermal behaviour of complexes was studied using thermogravimetry (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The structure of L hydrazone was established by X-ray study on single crystal. The ligand works as tridentate NNO, being coordinated through the azomethine nitrogen, the pyridine nitrogen and carbonylic oxygen. Heats of decomposition, ΔH, associated with the exothermal effects were also determined.     

Synthesis and characterisation of some complexes of manganese(II) and iron(II) picrates with heterocyclic amines

Summary Complexes of manganese(II) and iron(II) picrates with various bidentate (L) and monodentate (L) heterocyclic bases have been synthesised; their compositions have been established as [ML₃]A₂ (1), [ML₂ · 2 H₂O]A₂ (2), [ML₆]A₂ (3) and [ML4 · 2 H₂O]A₂ (4), where M = Fe^II and Mn^II, L = 2,2-bipyridyl (bipy) and 1,10-phenanthroline (phen) in (1), A = picrate anion; M = Mn^II, L = bipy and phen in (2); M = Fe^II, L = pyridine (py), 4-picoline (4-pic) and 3-picoline (3-pic) in (3); M = Mn^II, L = py, 4-pic, quinoline (quin) and 2,6-lutidine (2,6-lut) in (4) and also M = Fe^II, L = quin and 2,6-lut.     

Synthesis and thermal decomposition kinetics of La(III) complexwith unsymmetrical Schiff base ligand

A new unsymmetrical solid Schiff base (LLi) was synthesized using L-lysine, o-vanillin and 2-hydroxy-l-naphthaldehyde. Solid lanthanum(III) complex of this ligand [LaL(NO₃)]NO₃·2H₂O have been prepared and characterized by elemental analyses, IR, UV and molar conductance. The thermal decomposition kinetics of the complex for the second stage was studied under non-isothermal condition by TG and DTG methods. The kinetic equation may be expressed as: dα/dt=Ae^−E/RT(1−α)². The kinetic parameters (E, A), activation entropy ΔS ^# and activation free-energy ΔG ^# were also gained.     

Preparation of ferrites from the thermal decomposition of magnesium and calcium <Emphasis Type="Italic">tris</Emphasis>(succinato)ferrates(III) precursors

The complexes of general formula Ln(btfa)₃L, where Ln=Eu or Tb, btfa=4,4,4-trifluoro-1-phenyl-1,3-butanedione, L=1,10-phenanthroline (phen) or 2,2-bipyridine (bipy), were synthesized by reacting the corresponding metal chloride with the proper β-diketone and the other ligand. The complexes were obtained in the powder form and were characterized by photoluminescence and TG. Their thermal decomposition was studied by non-isothermal thermogravimetric techniques. The Eu(btfa)₃bipy complex presented the highest thermal stability and it melts before being decomposed. The complex Eu(btfa)₃phen presented the largest activation energy for a heating rate of 5°C min^–1.     

Thermal Investigations of M[La(C2O4)3]⋅xH2O (M=Cr(III) and Co(III))

The complexes M[La(C₂O₄)₃]⋅xH₂O (x=10 for M=Cr(III) and x=7 forM=Co(III)) have been synthesized and their thermal stability was investigated. The complexes were characterized by elemental analysis, IR, reflectance and powder X-ray diffraction (XRD) studies. Thermal investigations using TG, DTG and DTA techniques in air of chromium(III)tris(oxalato)lanthanum(III)decahydrate, Cr[La(C₂O₄)₃]⋅10H₂O showed the complex decomposition pattern in air. The compound released all the ten molecules of water within ∼170°C, followed by decomposition to a mixture of oxides and carbides of chromium and lanthanum, i.e. CrO₂, Cr₂O₃, Cr₃O₄, Cr₃C₂, La₂O₃, La₂C₃, LaCO, LaCrO_x (2<x<3) and C at ∼1000°C through the intermediate formation of several compounds of chromium and lanthanum at ∼374, ∼430 and ∼550°C. Thecobalt(III)tris(oxalato)lanthanum(III)heptahydrate, Co[La(C₂O₄)₃]⋅7H₂O becomes anhydrous around 225°C, followed by decomposition to Co₃O₄, La₂(CO₃)₃ and C at ∼340°C and several other mixture species of cobalt and lanthanum at∼485°C. The end products were identified to be LaCoO₃, Co₃O₄, La₂O₃, La₂C₃, Co₃C, LaCO and C at ∼ 2>1000°C. DSC studies in nitrogen of both the compounds showed several distinct steps of decomposition along with ΔH and ΔSvalues. IR and powder XRD studies have identified some of the intermediate species. The tentative mechanisms for the decomposition in air are proposed. This revised version was published online in August 2006 with corrections to the Cover Date.