Thermochemistry of adducts of some bivalent transition metal bromides with pyridine

The compounds [MBr₂(py)₂] (where M is Mn(II), Co(II), Ni(II), Cu(II) or Zn(II); py = pyridine) were synthesized and characterized by melting points, elemental analysis, thermal analysis and electronic and IR spectroscopy. The enthalpies of dissolution of the adducts, metal(II) bromides and pyridine in 25% (v/v) 1.2 M aqueous HCl in methanol were measured and by using thermochemical cycles, the following thermochemical parameters for the adducts have been determined: the standard enthalpies for the Lewis acid/base reactions (Δ_rH^θ), the standard enthalpies of formation (Δ_fH^θ), the standard enthalpies of decomposition (Δ_DH^θ), the lattice standard enthalpies (Δ_MH^θ) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (Δ_rH^θ(g)). The mean bond dissociation enthalpies of the M(II)-nitrogen bonds have been estimated as well as the enthalpies of the adducts formation in the gaseous phase.     

Thermochemistry of adducts of some bivalent transition metal bromides with 4-chloroaniline

The compounds [MBr₂(p-clan)₂] (where M is Mn(II), Fe(II), Co(II), Ni(II), Cu(II) or Zn(II); p-clan = 4-chloroaniline) were synthesized and characterized by melting points, elemental analysis, thermal analysis and electronic and IR spectroscopy. The enthalpies of solution of the adducts, metal(II) bromides and 4-chloroaniline in methanol, 1.2 M aqueous HCl or 25% (v/v) 1.2 M aqueous HCl in methanol were measures and by using thermochemical cycles, the following thermochemical parameters for the adducts have been determined: the standard enthalpies for the Lewis acid/base reactions (Δ_rH°), the standard enthalpies of formation (Δ_fH°), the standard enthalpies of decomposition (Δ_DH°), the lattice standard enthalpies (Δ_MH°) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (Δ_rH°(g)). The mean bond dissociation enthalpies of the metal(II)-nitrogen coordinated bonds and the enthalpies of adduct formation in the gaseous phase have been estimated.     

Thermochemistry of adducts of some transition metals(II) bromides with pyridine N-oxide

The compounds [MBr₂(pyNO)_n] (where M: Mn, Fe, Co, Ni, Cu or Zn; pyNO is pyridine N-oxide and n=2, 3 or 6) were synthesized and characterized by melting points, elemental analysis, thermal analysis and electronic and IR spectroscopy. The enthalpies of dissolution of the adducts, metal(II) bromides and pyNo in methanol were measured and by using thermochemical cycles, the following thermochemical parameters for the adducts have been determined: the standard enthalpies for the Lewis acid/base reactions (Δ_rH^θ), the standard enthalpies of formation (Δ_fH^θ), the standard enthalpies of decomposition (Δ_DH^θ), the lattice standard enthalpies (Δ_MH^θ) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (Δ_rH^θ(g)). The mean bond dissociation enthalpies of the M(II)-oxygen bonds () have been estimated.     

Thermochemistry of piperidine adducts of some bivalent transition metal bromides

The adducts [MBr₂(pipd) _n ] (where M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), or Zn(II); pipd = piperidine; n = 1/2, 1, or 3/4) were synthesized and characterized by melting points, elemental analysis, thermal studies, and IR and electronic spectroscopy. From calorimetric studies in solution, the standard enthalpies of formation and several other thermochemical parameters of them were determined. The mean standard enthalpies of the metal–nitrogen bonds were calculated, as well as the enthalpies of the adduct formation in the gaseous phase. Using the values obtained for the enthalpies of reaction, the acidity order of the salts is obtained: FeBr₂ > MnBr₂ and CoBr₂ > NiBr₂. Comparing with pyridine adducts, the ligand piperidine is more basic than the ligand pyridine: pipd > py.     

Stability of bivalent metal complex with L-hydroxyproline

Potentiometric titration of L-hydroxyproline with NaOH solution at 30° ±0.1°C in a medium of constant ionic strenth, =0.1M (KNO₃) gave the stepwise formation constants of the complexes formed between Mn(II), Co(II) and Zn(II) ions. The values were logK ₁=3.45; logK ₁=4.58, logK ₂=4.03; logK ₁=5.08, logK ₂=4.66; for Mn(II), Co(II) and Zn(II) complexes. The order of stability constant is in accordance with theIrving-Williams series.

---

Die Stabilität bivalenter metall-komplexe mit L-hydroxyprolin

Zusammenfassung Potentiometrische Titration von L-Hydroxyprolin in NaOH-Lösung bei 30±0,1°C und einer konstanten Ionenstärke von =0,1M-KNO₃ ergab stufenweise die Bildungskonstanten der entsprechenden Komplexe mit Mn(II), Co(II) und Zn(II). Die Werte sind logK ₁=3,45; logK ₁=4,58, logK ₂=4,03; logK ₁=5,08, logK ₂=4,66; für Mn(II); Co(II); Zn(II). Die Reihenfolge der Stabilität der Komplexe ist im Einklang mit derIrving-Williams-Reihung.

     

Metal chelates of some transition and non-transition metal ions with Schiff base derived from isatin witho-phenylenediamine

Summary New Cr(III), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II) chelates of the Schiff base derived from isatin witho-phenylenediamine have been synthesized and characterized on the basis of elemental analyses, electronic, IR and¹H NMR spectra, and also by aid of molar conductivity and magnetic moment measurements. It has been found that the Schiff base behaves as ONNO tetradentate dibasic ligand forming chelates with 1:1 (metal:ligand) stoichiometry. Square planar environment is suggested for nickel(II) chelate. All the metal chelates show non-electrolytic behaviour.

---

Metallchelate einiger Übergangs- und Nichtübergangsmetallionen mit Isatin-o-Phenylendiamin-Schiff-Basen

Zusammenfassung Es wurden neue Chelate von Cr(III), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) und Pb(II) mit Schiff-Basen aus Isatin undo-Phenylendiamin hergestellt und mittels Elementaranalysen, Elektronen-, IR- und¹H-NMR-Spektroskopie, sowie durch Messung der molaren Leitfähigkeit und der magnetischen Momente charakterisiert. Es wurde festgestellt, daß sich die Schiff-Base als vierzähniger zweibasischer ONNO-Ligand verhält, wobei 1:1-stöchiometrische Metall:Ligand-Komplexe gebildet werden. Für das Nickel(II)-Chelat wird eine quadratisch-planare Geometrie vorgeschlagen. Alle untersuchten Metallchelate zeigen ein nicht-elektrolytisches Verhalten.

     

EXAFS studies on the methanol and ethanol solutions of cobalt(II) bromides

The results of an EXAFS investigation of methanol and ethanol solutions of CoBr₂ are reported. The curve fitting analysis gives the coordination numbers and the Co–Br and Co-solvent distances. The results for both 0.2M and 3.8M CoBr₂ in ethanol show the existence of [CoBr₂(C₂H₅OH)₂] as the dominant species, although a considerable amount of octahedral species also exists in the solutions. In 0.2 and 3.3M CoBr₂ methanol solutions, the dominant species are [Co(CH₃OH)₆]²⁺ and [CoBr(CH₃OH)₅]⁺, respectively.     

Solid-state compounds of 2-methoxybenzylidenepyruvate with some bivalent metal ions

Solid-state M-2-MeO-BP compounds, where M represents bivalent Mn, Fe, Co, Ni, Cu, Zn and 2-MeO-BP is 2-methoxybenzylidenepyruvate have been synthesized. Simultaneous thermogravimetry-differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), X-ray powder diffractometry, infrared spectroscopy, elemental analysis and complexometry were used to characterize and to study the thermal stability and thermal decomposition of these compounds. The results led to information about the composition, dehydration, crystallinity and thermal decomposition of the isolated compounds.     

Synthesis and further reactivity studies of some transition metal gallyl complexes

Reactions of the anionic gallium(I) heterocycle salt, [K(tmeda)][Ga(DAB)] (DAB = {N(Dip)C(H)}₂; Dip = C₆H₃Prⁱ₂-2,6), with a series of groups 6-9 and 11 metal halide complexes have given rise to the metal gallyl complexes, [CpCr(IMes){Ga(DAB)}] (IMes = :C{(Mes)NC(H)}₂; Mes = mesityl), [M(tmeda){Ga(DAB)}₂] (M = Mn, Fe or Co) and [Cu(dppe){Ga(DAB)}] (dppe = 1,2-bis(diphenylphosphino)ethane). The majority of the complexes have been crystallographically characterized. The reactivity of the previously reported copper(I) gallyl complex, [(IPr)Cu{Ga(DAB)}] (IPr = :C{(Dip)NC(H)}₂), towards a variety of unsaturated substrates has been explored. Three crystallographically characterized complexes have arisen from this phase of the study, viz. [(IPr)CuCCPh], [(IPr)Cu{Ga(DAB)}(CNBu^t)] and [(IPr)Cu{κ¹-OC(O)C(CNHDip)(NHDip)}]. The results of these investigations show that the reactivity of [(IPr)Cu{Ga(DAB)}] is significantly different to that of related copper boryl complexes.     

Synthesis,coordination behavior,and investigations of pharmacological effects of some transition metal complexes with isoniazid Schiff bases

Two isoniazid Schiff bases, N-isonicotinamido-2-furanketimine (INH-F¹) and N-isonicotinamido-5-methyl-2-furanketimine (INH-F²), possessing potential N and O coordination sites have been prepared by the reaction of isoniazid with 2-acetylfuran and 2-acetyl-5-methylfuran, respectively. Complexes of Pd(II) and Pt(II) have been prepared and characterized by elemental analyses, melting point determinations and electronic, infrared, ¹H NMR, ¹³C NMR spectral studies, and X-ray powder diffraction studies. In all the complexes, the monobasic bidentate nature of the ligand is evident. Antibacterial and antifungal studies of these compounds against various pathogenic bacterial and fungal strains have been carried out. Both the ligands and their metal chelates were active against all the microbial strains investigated. However, the chelates were found to be more active than the ligands. The antimycobacterial activity of the ligands and their metal complexes has been evaluated against Mycobacterium smegmatis, which showed clear enhancement in this activity upon metal complexation with Schiff bases.     

Synthesis,characterization and biocidal activities of some metal(II) complexes with diacetyl salicylaldehyde acyldihydrazones

Complexes of diacetyl salicylaldehyde oxalic acid dihydrazone, CH₃COC(CH₃)= NNHCOCONHN=CHC₆H₄(OH),(dsodh) and diacetyl salicylaldehyde malonic acid dihydrazone CH₃COC(CH₃)=NNHCOCH₂CONHN=CHC₆H₄(OH), (dsmdh) of general compositions [M(L)]Cl, [M′(L)Cl], [M(L′)]Cl and [M′(L′)Cl] (where M?=?Co(II), Cu(II), Zn(II), Cd(II) and M′?=?Ni(II); HL?=?dsodh and HL′?=?dsmdh) were prepared and characterized by elemental analyses, molar conductance, magnetic moments, electronic, ESR and infrared spectra and X-ray diffraction data. The magnetic moments and electronic spectra indicate six-coordinate octahedral geometry for Co(II) and square planar geometry for Ni(II) complexes. The ESR spectral data of Cu(II) complexes in DMF solution reveal a tetragonally distorted octahedral geometry. Both ligands bond through >C=O, >C=N and deprotonated phenolate groups in all octahedral complexes and through >C=N and deprotonated phenolate groups in Ni(II) square planar complexes. The lattice parameters for Cu(dsodh) and Co(dsmdh) correspond to an orthorhombic and Ni(dsodh) corresponds to a tetragonal crystal lattice.

The complexes show significant antifungal activity against a number of pathogenic fungi viz. Stemphylium, Myrothecium and Alternaria. The antibacterial activity was studied against Pseudomonas fluorescence (gram ?ve) and Clostridium thermocellum (gram +ve).     

Synthesis and spectral characterization of Schiff-base complexes derived from alanine and 2-acetylpyridine with some divalent metal acetates

Schiff-base complexes [ML(H₂O)₂(Ac)]nH₂O (M?=?Co(II), Ni(II) and Zn(II); L?=?Schiff-base ligand derived from 2-acetylpyridine and alanine and n?=?1–3/2) were synthesized and characterized by elemental analysis, spectral (FTIR, UV/Vis, MS, ¹H-NMR), thermal (TGA), conductance and magnetic moment measurements. The results suggest octahedral geometry for all the isolated complexes. IR spectra show that the ligand coordinates to the metal ions as mononegative tridentate through pyridyl nitrogen, azomethine nitrogen and carboxylate oxygen after deprotonation of the hydroxyl group. Semi-empirical calculations PM3 and AM1 have been used to study the molecular geometry and the harmonic vibrational spectra to assist the experimental assignments of the complexes.     

Calculation of transition metal compounds using an extension of the CNDO-formalism

A recently developed extension of the CNDO-method is used to study the electronic structure of a number of binuclear transition metal carbonyls and carboxylates with fourfold or quasi-fourfold symmetry. The results are compared to those available from nonempirical calculations. Special attention is paid to the nature of the metal-metal bond. Connections with qualitative MO-considerations allow a fairly general discussion of metal-metal bonding in binuclear transition metal complexes with basic fourfold symmetry. A few, up to now unknown, but possibly existing, complexes are considered.     

On nd bonding in the transition metal trimers: comparison of Sc3 and Y3

CASSCF/CCI calculations are presented for the low-lying states of Y₃. Comparison of the wave functions for Y₃ and Sc₃ indicates substantial 4d-5p hybridization in Y₃, but little 3d-4p hybridization in Sc₃. The increased 4d-5p hybridization leads to stabilization of 4d bonding with respect to 4d bonding for equilateral triangle Y₃, and also leads to 4d-5p bonding for linear geometries. These effects lead to a different ordering of states for equilateral triangle geometries and a smaller excitation energy to the linear configuration for Y₃ as compared to Sc₃.     

Characterization of mixed ligand complexes of some bivalent transition metal imides with polyamines

Complexes of the types [Cu(imide)₂(Am)] (imide = deprotonated malonimide, succinimide, glutarimide and phthalimide; Am = dipyridyl and o-phenanthroline), [M(imide)₂(Am)₂] (M = Ni(II) and Co(II); imide = deprotonated malonimide, glutarimide and phthalimide) and Na₂[M(succ)₄(Am)] (succ = deprotonated succinimide) have been prepared and characterised on the basis of IR, electronic spectra, conductance and magnetic measurements. The order of bonding power of these imides is malonimide ≈ phthalimide > succinimide > glutarimide.     

A pH-stat study of the reaction of some transition metal cations with disodium ethylenedinitrilotetraacetate (EDTA) and its analytical application

The pH-stat titration technique is an autonomous and very powerful tool for performing and monitoring chelatometric titrations of metal cations with great accuracy, poorly known, however, and seldom exploited. Based on measurement of the amount of strong base required to keep the pH of the test solution at a selected value during stepwise known additions of ethylenedinitrilotetraacetate (EDTA), it requires a glass electrode as the only sensor and is easily implemented on potentiometric titrators. It was introduced a quarter of century ago on an empirical basis for a very peculiar purpose (determination of calcium in diary products), but only very recently it was generalised and its fundamentals were thoroughly examined. In this work, pH-static titrations of some transition metal cations of analytical relevance (Co²⁺, Cu²⁺, Mn²⁺, Zn²⁺) were thoroughly investigated in the acid pH range between 2.3 and 5 or 7 (the highest pH depending on the metal hydroxide or carbonate solubility). The results at higher acidity showed unsuspected properties of such chelation reactions. At moderately acid pH (generally ≥4), indeed, pH-static titrations yield results of high precision and accuracy. On decreasing pH, however, the reaction stoichiomety deviates more and more from the 1:1 ratio between chelating agent and cation, seemingly because of formation of binuclear complexes, an occurrence very seldom mentioned in the current literature. The optimal titration conditions for each metal are defined, and directions for establishing a laboratory protocol for quantitative determinations are given.