Thermal and spectroscopic investigation of new binuclear Pt(II) complexes with carboxylic acids

The thermal decomposition of the binuclear Pt(II) complexes with acetate, propionate, valerate and izovalerate ligands were studied by TG and DTA techniques. The Pt(II) complex with acetic acid (PtAA) was stable up to 343.15 K, Pt(II) complex with propionic acid (PtPrA) was stable up to 323.15 K, Pt(II) complex with valeric acid (PtVA) was stable up to T=313.15 K and Pt(II) complex with isovaleric acid (PtIvA) was stable up to 408.15 K. The PtAA complex was investigated again after a year by thermogravimetric analysis. After the thermal decomposition of the Pt(II) complexes with carboxylic acids, only in the PtVA complex and PtAA complex (investigated after a year) the final residue contains only platinum, while in the rest complexes the solid residue was a mixture of platinum and platinum carbides (PtC₂, Pt₂C₃).     

Thermal Analysis of Manganese(II) Complexes With Glycine

The thermal decomposition behaviour of the manganese(II) complexes with glycine: Mn(gly)Cl₂(H₂O)₂, Mn(gly)₂Cl₂, Mn(gly)Br₂(H₂O)₂, Mn(gly)₂Br₂(H₂O)₂ was investigated by means of TG-DTG-DTA, Hi-Res-TA and DSC techniques. The evolved gas analysis was carried out by means of the coupled TG-FTIR system. Heating of the complexes results first in the release of water molecules. Next, the multi-stage decomposition process with degradation of glycine ligand occurs. Water, carbon dioxide and ammonia were detected in the gaseous products of the complexes decomposition. The temperature of NH₃ evolution from the complexes is higher than from free glycine. The final residue in the air atmosphere is Mn₂O₃ which transforms into Mn₃O₄ at 930°C. In a nitrogen atmosphere, the complexes decompose into MnO. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study of the thermal decomposition on Pt(II) complexes with cycloalkanespiro-5′-hydantoins

The thermal decomposition of the Pt(II) complexes with cyclobutane-and cycloheptanespiro-5′-hydantoins were studied by TG and DTA techniques. The Pt(II) complex with cyclobutanespiro-5′hydantoin (PtCBH) was stable up to 115°C (388 K) and Pt(II) complex with cycloheptanespiro-5′-hydantoin (PtCHTH) was stable up to 150°C (423 K). After the thermal decomposition of PtCBH the solid residue was platinum, while the decomposition of PtCHTH gave a mixture of platinum carbides (PtC₂, Pt₂C₃).     

Spectral and thermal studies of new Co(II) and Ni(II) hexaaza and octaaza macrocyclic complexes

The macrocyclic complexes of Co(II) and Ni(II) having chloride or thiocyanate ions in the axial position have been synthesized and characterized. These complexes are synthesised by the template condensation of o-phenylenediamine or 2,3-butanedionedihydrazone with the appropriate aldehydes in NH₄OH solution in the presence of the metal ions, Co(II) and Ni(II). The complexes were characterized by spectroscopic methods (IR, UV-Vis and ESR) and magnetic measurements as well as thermal analysis (TG and DTA). The results obtained are commensurate with the proposed formulae. Spectral studies indicate that these complexes have an octahedral structure. From conductivity measurements the complexes are non-electrolytes. The kinetic of the thermal decomposition of the complexes was studied and the thermodynamic parameters are reported.     

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.     

Theoretical studies of complexes between Hg(II) ions and l‐cysteinate amino acids

In this study, ab initio and density functional theory methods have been used to understand the structures and thermodynamic stabilities of complexes formed between l ‐cysteine and mercury (II) ions in neutral aqueous solution. To better understand the interaction between sulfur and mercury (II) ion, the MP2, B3LYP, M06‐2X, and TPSS methods have been used to optimize [HgSH_x]^2?x, x = 1–4, complexes and compared to benchmark QCISD(T) structures. Furthermore, energies from these same methods are compared to CCSD(T)/CBS(2,3) energies. From these benchmark calculations, the M06‐2X method was selected to optimize l ‐cysteinate‐Hg(II) complexes and the MP2 method for estimating complex energies. l ‐cysteinate‐mercury (II) ion complexes are formed primarily by forming a bond between cysteinate sulfur and the mercury ion. Stable complexes of l ‐cysteinate and mercury can be formed in 1:1, 2:1, 3:1, and 4:1 ratios. Each complex is stabilized further by interaction between carboxylate oxygen and mercury as well as hydrogen bonding among complex cysteinate ligands. The results indicate that at high cysteinate to Hg(II) ratios high‐coordinate complexes can be present but at lower ratios the 2:1 complex should be dominant. © 2013 Wiley Periodicals, Inc.     

Synthesis and characterization of novel water-soluble zinc(II) Schiff-base complexes derived from amino acids and salicylaldehyde-5-sulfonates

New water-soluble zinc(II) Schiff-base complexes derived from amino acids (glycine, L-phenylalanine, and L-valine) and salicylaldehyde-5-sulfonates (sodium salicylaldehyde-5-sulfonate and sodium 3-methoxy-salicylaldehyde-5-sulfonate) have been synthesized. The complexes were characterized by elemental analysis, IR, electronic, ¹H?NMR, and ¹³C?NMR spectra. In the IR spectra of the complexes, the large difference between the asymmetric ν_as(COO) and symmetric ν_s(COO) carboxylate stretch, Δν(ν_as(COO)–ν_s(COO)) of 199–247?cm^?1, indicates monodentate coordination of the carboxylate group. Spectral data showed that in these complexes the ligand is a tridentate ONO moiety, coordinating to the metal through its phenolic oxygen, imine nitrogen, and carboxyl oxygen.     

Synthesis,molecular geometry,spectroscopic studies and thermal properties of Co(II) complexes

Co(II) complexes (1‐4) were prepared and characterized by elemental analyses, infrared spectra, spectral studies, magnetic susceptibility measurements, X‐ray diffraction analysis and thermogravimetric analysis (TGA). The X‐ray diffraction patterns of Co(II) complexes were observed many peaks which indicate the polycrystalline nature. The thermodynamic parameters were calculated by using Coats–Redfern and Horowitz–Metzger methods. The bond length, bond angle and quantum chemical parameters of the Co(II) complexes were studied and discussed. The Co(II) complexes were tested against various Gram‐positive bacteria, Gram‐negative bacteria and fungi. It was found that the Co(II) complex (1) has more antifungal activity than miconazole (antifungal standard drug) against P. italicum at all concentration. The Co(II) complex ( 2 ) has more antibacterial activity than the penicillin against K. pneumoniae at all concentration. The interaction between Co(II) complexes and calf thymus DNA show hypochromism effect. The relationship between the values of HOMO–LUMO energy gap (?E) and the values of intrinsic binding constant (K_b) is revealed increasing of HOMO–LUMO energy gap accompanied by the decrease of K_b.     

Thermal stability and kinetic studies of new dinuclear copper(II) complexes with octaazamacrocyclic and multidonor bidentate ligands

The thermal properties of four copper(II) complexes with N,N′,N″,N-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane (tpmc) and several bidentate ligands N,S (thiosemicarbazide and thiourea) or N,O donors (semicarbazide and urea), of the general formula [Cu₂(X)tpmc](ClO₄)₄, have been investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC). The thermal stability order can be recognized for the examined complexes, depending on coordinated bidentate bridging N,S or N,O ligand. Kinetic data demonstrated first-order thermal decomposition. A plausible mechanism has been proposed which explains the major products of the degradation.     

Synthesis and characterization of water-soluble zinc(II) Schiff-base complexes derived from amino acids and 3-formyl-4-hydroxybenzyl-triphenylphosphonium chloride

Tridentate Schiff-base ligands derived from condensation of 3-formyl-4-hydroxybenzyl-triphenylphosphonium chloride with glycine, L-alanine, L-valine, L-leucine and L-phenylalanine in the presence of Zn(OAc)₂ · 2H₂O form five new water-soluble Zn(II) complexes, which were characterized by elemental analyses, IR, electronic absorption and ¹H, ¹³C NMR spectroscopies. In the IR spectra of the complexes, the difference between the asymmetric and the symmetric carboxylate stretching frequencies is larger than ～210 cm^?1, which implies that the carboxylate groups are monodentate. UV-Vis electronic absorption studies show that Zn(II) functions as a trap for the Schiff-base intermediate. Schiff-base complexes formation were confirmed by the appearance of new signals in the ¹H NMR for the azomethine hydrogen at ～8 ppm and condensed L-amino acids at 3.4–3.8 ppm (C(3)–H). These complexes are formed through coordination of the ONO from the carboxyl, imino and phenoxy groups of the ligands to Zn(II).     

Effect of type and position of the anions on the thermal decomposition of some copper(II) complexes

A number of copper(II) complexes of some aromatic diamines have been prepared and characterized. The thermal stabilities of the complexes were studied and discussed in terms of covalent bond character, chelate ring size and angle strain. On the other hand, the effective role of the anions on the decomposition pathways was also considered. Moreover, the nature of interaction of the solvent of crystallization has also been investigated.

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Zusammenfassung Es wurde eine Anzahl von Kupfer(II)-komplexen einiger aromatischer Diamine hergestellt und beschrieben. Die thermische Stabilität der Komplexe wurde als Funktion des kovalenten Bindungscharakters, der Chelatringgröße und der Winkelspannung untersucht und diskutiert. Andererseits wurde auch der Einfluß der Anionen auf den Zersetzungsweg in Erwägung gezogen. Außerdem wurde auch die Wechselwirkung zwischen Lösungsmittel und Kristallisierung untersucht.

     

Kinetics of thermal decomposition of manganese(ii) oxalate

The kinetics of manganese(II) oxalate thermal decomposition in the helium atmosphere was studied on the basis of isothermal measurements in the temperature range from 608 to 623 K. Manganese(II) oxide, MnO, was found to be the final product of reaction. The Avrami-Erofeev kinetic equation was used to describe all the experimental data in the range of decomposition degrees from 0.1 to 0.9. The determined activation energy equals 184.7 kJ mol^-1 with standard deviation ±5.2 kJ mol^-1. The estimated value of parameter n is 1.9 with standard deviation ±0.01 what suggests that the rate limiting step of MnC₂O₄ decomposition is the nucleation of new MnO phase and that the rate of nuclei growth is rising during decomposition. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydration of copper(II) amino acids complexes

Hydration of the copper(II) bis‐complexes with glycine, serine, lysine, and aspartic acid was studied by DFT and MD simulation methods. The distances between copper(II) and water molecules in the 1st and 2nd coordination shells, the average number of water molecules and their mean residence times in the hydration shells were calculated. Good agreement was observed between the values obtained and those found by DFT and NMR relaxation methods. Influence of the functional groups of the ligands and the cis–trans isomerism of the complexes on the structural and dynamical parameters of the hydration shells was displayed and explained. Analysis of the MD trajectories reveals the competition for a copper(II) axial position between water molecules or water molecules and the functional chain groups of the ligands and confirms the suggestion on the pentacoordination of copper(II) in such complexes. MD simulations show that only one axial position of Cu(II) is basically occupied at each time step while in average the coordination number more than 5 is observed. © 2017 Wiley Periodicals, Inc.     

The effect of the water vapor pressure on the kinetics of thermal dehydration of manganese(II) formate dihydrate

The effect of the water vapor pressure on the thermal dehydration of manganese(II) formate dihydrate was studied by means of isothermal gravimetry under various water vapor pressure, ranging from 4.6 to 24.4 torr. The kinetics of dehydration was described by a two-dimensional phase-boundary model,R ₂. The rate of dehydration decreased with increasing atmospheric water vapor pressure, but the Smith-Topley phenomenon was not observed for the present dehydration. The activation energy and the frequency factor for the dehydration were 110–170 kJ·mol⁻¹ and 10¹⁰–10¹⁶ cm·s⁻¹, respectively. These values increased with increasing water vapor pressure, and were much larger than those reported for the dehydration in vacuum.     

Synthesis, thermal and other studies of 2,4'-bipyridine-dichloroacetato complexes of Mn(II), Co(II), Ni(II) and Cu(II)

Four new mixed ligand complexes were prepared by the reaction of title metal dichloroacetates and 2,4'-bipyridine. The general formulae of synthesized compounds are M(2,4'-bpy)₂(CCl₂HCOO)₂·nH₂O (where M(II)=Mn, Co, Ni, Cu; 2,4'-bpy=2,4'-bipyridine, n=2 or 4). The complexes have been isolated from aqueous media and characterized by chemical analysis, molar conductance (in MeOH, DMSO and DMF), magnetic, IR and VIS spectral studies. The nature of metal(II)-ligand coordination is discussed. The thermal behaviour of obtained complexes was studied by thermal analysis and TG-MS techniques in air. IR, X-ray powder diffraction and thermoanalytical data were used for the determination of solid intermediate products of the thermal decomposition. The principal volatile products of thermal decomposition of complexes were proved by mass spectroscopy: H₂O⁺, CO⁺ ₂, HCl⁺ ₂, Cl⁺ ₂, NO⁺ and other. This revised version was published online in July 2006 with corrections to the Cover Date.     

A thermal decomposition study on cobalt(II) complexes of 1,2-bis(IMINO-4'-antipyrinyl)ethane

The phenomenological, kinetic and mechanistic aspects of thermal decomposition of perchlorate, nitrate, chloride, bromide and iodide complexes of cobalt(II) with the Schiff base 1,2-bis(imino-4'-antipyrinyl)ethane (GA) have been studied by TG and DTG analyses. The kinetic parameters like the activation energy, pre-exponential factor and entropy of activation were calculated. The decomposition reactions follow 'random nucleation with one nucleus on each particle - Mampel model'. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis,spectral and thermal properties of macrocyclic zinc(II) complexes

The new zinc ternary complexes [Zn(cyclen)NO₃]ClO4 (I), [Zn₂(cyclen)₂(m-nic)](ClO₄)₃ (II), [Zn₂(cyclen)₂(m-pic)](ClO₄)₃ (III) (cyclen=1,4,7,10-tetraazacyclododecane; nic=nicotinic acid; pic=picolinic acid) were synthesized and their spectral and thermal properties were investigated. The compounds were characterized by elemental analysis, IR spectroscopy and TG/DTG, DTA methods. Moreover, the way of coordination of pyridinecarboxylate anions was proposed on the basis of the spectral data and consequently proved with results of X-ray structure analysis. This revised version was published online in August 2006 with corrections to the Cover Date.     

TG,DTA and electrical conductance properties of some Cu(II) AND Mn(II) bisazo- dianils complexes

The TG and DTA of a new series of Mn(II) and Cu(II) complexes with a number of newly prepared bisazo-dianil ligands were studied in the temperature range (20-700°C). The TG and DTG curves display to main steps, the first one within the temperature range (25-330°C) correspond to the elimination of water or and ethanol from the complexes. The second step within the range (350-625°C) is due to the decomposition of the complexes yielding the metal oxides as the final product. The rate constants of the dehydration and decomposition reactions were determined, from which some kinetic parameters were evaluated. The DTA curves show that the dehydration of the metal complexes is an endothermic reaction. In all cases the anhydrous metal complexes undergo exothermic decomposition reactions to give the metal oxide. The thermodynamic parameters (ΔE, ΔH, ΔS, ΔG) for the occurring processes are calculated. The electrical conductivities of the solid complexes were measured and the activation energy of the complex and its free ligand are also calculated. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis and DNA cleavage properties of ternary Cu(II) complexes containing histamine and amino acids

The ternary complexes of [Cu^II(Hist)(Tyr)]⁺1 and [Cu^II(Hist)(Trp)]⁺2 have been synthesized, structurally characterized and their DNA binding and cleavage abilities probed. The intrinsic binding constants (K_b) for complexes/CT-DNA were also determined (K_b = 2.7 × 10² for complex 1 and K_b = 2.2 × 10² for complex 2). These complexes exhibit their nuclease activity on plasmid DNA, which seems to depend on the nature of the aromatic moiety. The DNA hydrolytic cleavage rate constants were also determined for complexes 1 and 2, which are 0.91 and 0.79 h⁻¹, respectively.     

Hydrolytic cleavage of DNA by quercetin manganese(II) complexes

Quercetin manganese(II) complexes were investigated focusing on its DNA hydrolytic activity. The complexes successfully promote the cleavage of plasmid DNA, producing single and double DNA strand breaks. The amount of conversion of supercoiled form (SC) of plasmid DNA to the nicked circular form (NC) depends on the concentration of the complex as well as the duration of incubation of the complexes with DNA. The maximum rate of conversion of the supercoiled form to the nicked circular form at pH 7.2 in the presence of 100 μM of the complexes is found to be 1.32 × 10⁻⁴ s⁻¹. The hydrolytic cleavage of DNA by the complexes was supported by the evidence from free radical quenching, thiobarbituric acid-reactive substances (TBARS) assay and T4 ligase ligation.