QTAIM study of transition metal complexes with cyclophosphazene-based multisite ligands II. Cobalt(II) complexes

[(CoLCl)CoCl₃], [(CoMeLCl)CoCl₃], [(CoLBr)CoBr₃], [CoLBr]⁺ and [CoMeLBr₂] complexes, L = hexakis(2-pyridyloxy)cyclotriphosphazene, MeL = hexakis(4-methyl-2-pyridyloxy)cyclotriphosphazene, in the most stable high spin states are investigated at DFT level of theory using hybrid B3LYP functional. The exchange coupling parameter evaluated using a broken symmetry treatment increases with the ligands mass. Electron density is evaluated in terms of QTAIM (Quantum Theory of Atoms-in-Molecule) topological analysis of electron density. The bonds of central Co atoms with phosphazene nitrogens are shorter, stronger and more polar than with the aromatic pyridine nitrogens and their higher ellipticities may be explained by the π contribution from the phosphazene ring. The atomic charges of phosphazene nitrogens are ca. twice more negative than at the pyridine ones.     

Gas-phase negative ions of platinum metal fluorides. II. Electron affinity of platinum metal hexafluorides

Reactions of platinum metal hexafluoride negative ions were studied by Knudsen cell mass spectrometry. The electron affinities were measured for OsF₆(5.93±0.28 eV), IrF₆ (6.50±0.38 eV), PtF₆(7.00±0.35 eV), and RuF₆ (6.47±0.31 eV).The relevant data on electron affinities of platinum metal hexafluorides are discussed.     

Thermal degradation of transition metal carbonyl complexes. Part II

The thermal degradation of three monosubstituted hexacarbonyl complexes, M(CO)₅py (where M=Cr, Mo, and W; py=pyridine) has been studied by thermogravimetry (TG) and differential scanning calorimetry (DSC) and their results reported. It was found that for each of the three complexes studied, the starting material M(CO)₆ was formed which immediately sublimed unchanged with or without concomitant loss of carbonyl (CO) ligands to give the first large weight loss step. This was closely followed by the volatilisation of the pyridine ligands and at higher temperatures the loss of further CO ligands. The enthalpy changes associated with the above-mentioned steps are reported. The conversion of M(CO)₅py to M(CO)₆ and other products was confirmed by the analysis of residue after pyrolysis in a tube furnace under conditions similar to those observed in TG experiments.

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Zusammenfassung Der thermische Abbau von drei monosubstituierten Hexacarbonylkomplexen der allgemeinen Formel M(CO)₅py (mit M=Cr, Mo und W; py=Pyridin) wurden mittels TG und DSC untersucht. Von jeder der drei Komplexe wird die Ausgangssubstanz M(CO)₆ erhalten, die sofort unverändert mit oder ohne gleichzeitigem Verlust an Carbonyl (CO)-Liganden sublimiert und die erste große Gewichtsverluststufe ergibt. Diesem Schritt folgt gleich die Verflüchtigung des Pyridinliganden und bei höheren Temperaturen die Abgabe weiterer CO-Liganden. Die mit den genannten Schritten einhergehenden Enthalpieveränderungen werden mitgeteilt. Die Umwandlung von M(CO)₅py zu M(CO)₆ und anderen Produkten wurden durch Analyse des Rückstandes nach der Pyrolyse in einem Röhrenofen unter ähnlichen Bedingungen wie in den TG-Versuchen bestätigt.

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()₅, M=, , =. , , , . , . . , .

     

Thermal and chromatographic behaviour of metal complexes. Part II. Complexes of platinum(II) with dipeptide ester

Experimental measurements of the rate of reduction of particles of Carol Lake and Kiruna ores have been made using pure hydrogen and pure carbon monoxide and mixtures of these two gases. The temperature range covered was 773–1143 K and throughout this range the reduction rate with hydrogen was greater than that with carbon monoxide. A retracting core model was found to best fit the experimental data even when granules of 9 × 10^?4 m diameter were used. Reduction with gas mixtures of hydrogen and carbon monoxide give rates intermediate between those of the pure gases.     

Mixed metal complexes in solution. Part 4. Formation and stability of heterobinuclear complexes of cadmium(II)-citrate with some bivalent metal ions in aqueous solution

Summary The systems, Cd-Ni-citrate, Cd-Mn-citrate and Cd-Zn citrate have been investigated pH-metrically at 25°C and I = 0.1 mol dm^–3 (KNO₃).As previously found for analogous citrate systems (namely for Cu-Ni-, Cu-Zn- and Ni-Zn-citrate) the existence of mixed metal complexes of the type [MM(cit)₂H_–2]^4– has been shown. In addition, the species [MM(cit)₂H_–1]^3– was also found to be present for Cd-Ni- and Cd-Zn-citrate systems The significance of the formation of such species is discussed.The existence of mixed metal complexes is also discussed in connection with the transport and the absorption of metal ions in biological systems.     

Preliminary study of selenium and mercury distribution in some porcine tissues and their subcellular fractions by NAA and HG-AFS

Selenium and mercury distribution in porcine tissues and their subcellular fractions from a mercury-polluted area of Guizhou Province and from a not mercury-exposed area of Beijing in China have been studied with neutron activation analysis and hydride generation-atomic fluorescence spectrometry. Both the selenium and mercury levels are higher in Guizhou porcine tissues and their subcellular fractions than those in Beijing. These two elements are highly enriched in kidney and liver of Guizhou pig, while selenium is only enriched in the kidney of Beijing pig. Exposure of mercury may result in redistribution of Se and Hg in vivo. The Hg/Se molar ratio of the subcellular fractions is very low in the case of relatively low mercury level and gradually reaches to a high constant value with increasing level of mercury, which implies that selenium and mercury may form some special complexes in the organisms. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal behaviour of transition metal complexes of dithiocarbazic esters. II

A thermal study (simultaneous TG and DTA measurements) was carried out on the dithiocarbazic ester complexes M[N³CH₂R₁N²C¹(S)SCH₃]₂, where M=Ni, Pt; R₁=C₆H₅. The following disproportionation reaction occurs in the solid state: II is formed through deprotonation of the CH₂ group bound to N³, whereas III is formed through protonation of N³.The influence of inductive and/or steric effects on the mechanism of this reaction is discussed, taking into account the electrochemical and X-ray data on the complexes Pt[NRNC(S)SR']₂ with differentR substituents: R=H, Ph, CH₂Ph, CH₂C₅H₁₁, CH(CH₃)₂, C(CH₃)₃; R=CH₃, CH₂Ph.These results accord with the behaviour of the same complexes in solution.

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Zusammenfassung Dithiokarbamidsäureesterkomplexe M[N³CH₂R₁N²C¹(S)SCH₃]₂ mit M=Ni, Pt und R₁=C₆H₅ wurden thermisch untersucht. Im festen Zustand spielt sich folgende Disproportionierungsreaktion ab: II wird durch Deprotonierung der an N³ gebundenen CH₂ Gruppe und III durch Protonierung des Atoms N² gebildet. Unter Zuhilfenahme der elektrochemischen und Röntgendaten der Komplexe Pt[NRNC(S)SR']₂ mit verschiedenen Substituenten R: R=H, Ph, CH₂Ph, CH₂C₅H₁₁, CH(CH₃)₂, C(CH₃)₃ und R=CH₃ bzw. CH₂Ph wurde der Einfluß von induktiven und/or sterischen Effekten auf den Reaktionsmechanismus diskutiert. Diese Ergebnisse stehen in Übereinstimmung mit dem Verhalten der Komplexe in Lösung.

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M[N³CH₂R₁N²C¹(S)SCH₃]₂, M= Ni, Pt,R ₁=C₆H₅. : II CH₂ , N³, III N². () , Pt[NRNC(S)SR]₂, R= , aR= . .

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We thank prof. A. La Ginestra for many helpful discussions on the various aspects of this work.     

Estrogen-derived steroidal metal complexes: agents for cellular delivery of metal centers to estrogen receptor-positive cells

Targeted cellular delivery of drugs to specific tissues is an important goal in biomedical chemistry. Achieving this requires harnessing and applying molecular-level recognition events prevalent in (or specific to) the desired tissue type. Tissues rich in estrogen receptors (ERs), which include many types of breast cancer, accumulate molecules that have high binding affinities for these receptors. Therefore, molecules that (i) bind to the ER, (ii) have favorable cellular transport properties, and (iii) contain a second functionality (such as a center that may be used for diagnostic imaging or medical therapy) are exciting synthetic targets in the field of drug delivery. To this end, we have prepared a range of metallo-estrogens based on 17alpha-ethynylestradiol and examined their binding to the ER both as isolated receptor and in whole cell assays (ER positive MCF-7 cells). Estrogens functionalized with metal binding units are prepared by palladium-catalyzed cross-coupling reactions and a wide range of metal centers introduced readily. All the compounds prepared and tested exhibit effective binding to the estrogen receptor and are delivered across the cell membrane into MCF-7 cells. In the whole cell assays, despite their monocationic nature, the palladium and platinum complexes prepared exhibit similar (and even enhanced) receptor binding affinities compared to their corresponding neutral free ligands. It is unprecedented for a higher ER binding affinity to be observed for a cationic complex than for its metal-free ligand.     

Semi-empirical LCAO-xα theory for transition metal complexes. II. Application to ionization potentials

Ionization potentials for 17 nd-transition metal complexes are calculated by a semi-empirical LCAO-Xα theory excluding (n + 1)s and (n + 1)p atomic orbitals. The results agree well with both photoelectron data and discrete-variational Xα results, which include the (n + 1) atomic orbitals. Implications of the (n + 1)-atomic orbital exclusion are noted. Also, new assignments for photoelectron spectra of VCl₃0, MnCl₃O, CrCl₂O₂, and MoCl₂O₂ are proposed.     

Infrared multiple-photon dissociation spectroscopy of group II metal complexes with salicylate

Ion trap tandem mass spectrometry with collision‐induced dissociation, and the combination of infrared multiple‐photon dissociation (IRMPD) spectroscopy and density functional theory (DFT) calculations, were used to characterize singly charged, 1:1 complexes of Ca²⁺, Sr²⁺ and Ba²⁺ with salicylate. For each metal‐salicylate complex, the CID pathways are: (a) elimination of CO₂ and (b) formation of [MOH]⁺ where M = Ca²⁺, Sr²⁺ or Ba²⁺. DFT calculations predict three minima for the cation‐salicylate complexes which differ in the mode of metal binding. In the first, the metal ion is coordinated by O atoms of the (neutral) phenol and carboxylate groups of salicylate. In the second, the cation is coordinated by phenoxide and (neutral) carboxylic acid groups. The third mode involves coordination by the carboxylate group alone. The infrared spectrum for the metal‐salicylate complexes contains a number of absorptions between 1000 and 1650 cm^–1, and the best correlation between theoretical and experimental spectra is found for the structure that features coordination of the metal ion by phenoxide and the carbonyl O of the carboxylic acid group, consistent with the calculated energies for the respective species. Copyright © 2011 John Wiley & Sons, Ltd.     

Thermal decomposition of metal complexes: II. Mixed complexes of iron(II) iodide with 1,10-phenanthroline,and 4,7-disubstituted-1,10-phenanthrolines

The thermal behavior of the Fe(II) iodide mixed complexes with 1,10-phenanthroline and 4,7-disubstituted phenanthrolines in nitrogen atmosphere is investigated.In order to determine to what extent small changes in ligand field symmetries influence the “activation energy” E_a, this energy is determined. The results are discussed in relation to the changes of the σ and π bonds.     

Transition metal complexes with thiosemicarbazide-based ligands. Part 56. Square-pyramidal complexes of copper(II) with 2-acetylpyridine S-methylisothiosemicarbazone

The article describes the synthesis and single-crystal X-ray analysis of two sulfato and one thiocyanato copper(II) complex with 2-acetylpyridine S-methylisothiosemicarbazone (HL) of the formulae [Cu(HL)SO₄(H₂O)]·H₂O (1), [Cu₂(HL)₂(μ-SO₄)₂]·2H₂O (2) and [Cu(HL)(NCS)(SCN)] (3), as well as the structure of the protonated ligand H₂L⁺I⁻. Complexes 1 and 2 were obtained from the reaction of aqueous/methanolic CuSO₄·5H₂O and ethanolic/methanolic H₂L⁺I⁻ solutions, respectively. Complex 3 was synthesized by the reaction of methanolic solutions of Cu(ClO₄)₂·6H₂O, the ligand and NH₄SCN, with the addition of triethyl orthoformate. All three complexes have a slightly deformed square-pyramidal structure (τ_av = 0.15) with the tridentate NNN neutral ligand in the basal plane. In complexes 1 and 3 the apical position is occupied by the oxygen atom of the monodentate SO₄ group, or the sulfur atom of the SCN group. Thanks to the hydrogen bonds, complex 3 may be thought of as having a pseudo-dimeric structure. In the authentic centrosymmetric dimer 2, the oxygen atoms of both SO₄ groups occupy also the apical position of both coordination polyhedra, as well as an equatorial position. Complexes 1 and 3 have μ_eff values characteristic of magnetically isolated mononuclear Cu(II) complexes. In contrast to them, complex 2 has a μ_eff value of 1.57 BM, which is in agreement with its dinuclear structure. All the complexes, in addition to the X-ray analysis and magnetic measurements, were characterized by IR and UV–Vis spectroscopy and by thermal analysis.     

Preparation and reactivity of metal-containing monomers. 24. Equilibrium in solutions of metal(II) complexes with methacroylacetone

Stability constants of Mg, Ca, Sr, Ba Mn, Co, Ni, Cu, and Zn complexes with the polymerizable ligand methacrylacetone have been determined in aqueous-dioxane solutions at an ionic strength of =0.1 at 22°C. The methacroylacetone was shown to contain 30% in the enol form using the pH-meter method. The stability sequence of the transition-metal complexes corresponds to the Irving — Williams stability series for ligands of low molecular weight; for the alkaline-earth metals the stability of the complexes increases with increase in ionic radius. Methacroylacetone-based chelates are significantly less stable than their analogs with unsubstituted acetylacetone.Institute of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka. I. I. Mechnikov Odessa State University, 270000 Odessa. Odessa Institute of Physical Chemistry, Ukrainian Academy of Sciences, 270050 Odessa. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 9, pp. 2066–2073, September, 1992.     

Investigation of the interaction of olefin-bonded transition metal complexes by gas chromatography. II. Phosphine complexes of Cu(II)

Summary Packings consisting of chemically bonded diphenylphosphine complexes with CuCl₂ and CuBr₂ were synthesized and their retention parameters determined. The packings investigated are capable of specific interactions with electron-donating compounds and are characterized by particularly high selectivity in relation to cis and trans isomers allowing their complete separation.Part 1: see ref. [1]     

Determination of stability constants of valinomycin complexes with ammonium and alkali metal ions by capillary affinity electrophoresis

Capillary affinity electrophoresis (CAE) has been employed to investigate quantitatively the interactions of valinomycin, macrocyclic depsipeptide antibiotic ionophore, with univalent cations, ammonium and alkali metal ions, K(+), Cs(+), Na(+), and Li(+), in methanol. The study involved measuring the change in effective electrophoretic mobility of valinomycin while the cation concentrations in the BGE were increased. The corresponding apparent stability (binding) constants of the valinomycin-univalent cation complexes were obtained from the dependence of valinomycin effective mobility on the cation concentration in BGE using a nonlinear regression analysis. The calculated apparent stability constants of the above-mentioned complexes show the substantially higher selectivity of valinomycin for K(+) and Cs(+) ions over Li(+), Na(+), and NH(4)(+) ions. CAE proved to be a suitable method for the investigation of both weak and strong interactions of valinomycin with small ions.