Oxidation of copper(II)-coordinated diethylenetriamine by hexacyanoferrate(III) ion. A kinetic investigation

The stoichiometry and kinetics of the reaction between [Cu(dien)(OH)]⁺ and [Fe(CN)₆]³⁻ in aqueous alkaline medium are described. The rate equation − (d[Fe(III)]/dt = {k₁[OH⁻]²[[Cu(dien)(OH)]⁺] + k₂[OH⁻] × [[Cu(dien)(OH)]⁺]²}([Fe(III)]/[Fe(II)]) (Fe(III) = [Fe(CN)₆]³⁻; Fe(II) = [Fe(CN)₆]⁴⁻, the 4:4:1 OH⁻/Fe(III)/[Cu(dien)(OH)]⁺ stoichiometric ratio and the nature of the ultimate products identified in the reaction solution suggest the fast formation of a doubly deprotonated Cu(III)-diamido complex which slowly undergoes an internal redox process where the ligand is oxidised to the Schiff base H₂NCH₂CH₂NCHCHNH.The [[Cu(dien)(OH)]⁺]² term in the rate equation is explained with the formation of a transient μ-hydroxo mixed-valence Cu dimer. A two-electron internal reduction of the Cu(III) complex yielding a Cu(I) intermediate is suggested to account for the presence of monovalent copper in a precipitate which forms at relatively high reactant concentrations and in the absence of dioxygen.     

Preparation,structure and properties of dicyano silver complexes of the M(en)3Ag2(CN)4 and M(en)2Ag2(CN)4 type

Complexes of the M(en)₃Ag₂(CN)₄ (M = Ni, Zn, Cd) and M(en)₂Ag₂(CN)₄ (M = Ni, Cu, Zn, Cd) type were prepared and identified by elemental analysis, infrared spectroscopy, measurement of magnetic susceptibility, and X-ray powder diffractometry. The crystal structures of Ni(en)₃Ag₂(CN)₄ (I) and Zn(en)₂Ag₂(CN)₄ (II) were determined by the method of monocrystal structure analysis. Complex I crystallizes in the space group C2/c, a = 1.2639(5), b = 1.3739(4), c = 1.2494(4) nm, β = 113.25(4)°, D_m = 1.86(1), D_c = 1.86 gcm⁻³ Z = 4, R = 0.0429. The crystal structure of I consists of complex cations [Ni(en)₃]²⁺ and complex anions [Ag(CN)₂]⁻. Complex II crystallizes in the space group I2/m, a = 0.9150(3), b = 1.3308(4), c = 0.6442(2) nm, β = 95.80(3)°, D_m = 2.14(1), D_c = 2.15 gcm⁻³, Z = 2, R = 0.0334. Its crystal structure consists of infinite, positively charged chains of the [-NCAgCNZn- (en)₂]_nⁿ⁺ type and isolated [Ag(CN)₂]⁻ anions. The atoms of Ag are positioned parallely to the z axis and the AgAg distance is equal to 0.3221(2) nm.     

Cobalt(II) and nickel(II) complexes with nitrogen-sulfur tripod ligands. Crystal and molecular structure of the five-coordinate complex bromotris(2-tert-butylthioethyl)aminecobalt(II) hexafluorophosphate (NS3Br donor set)

The tripod ligands tris(2-alkylthioethyl)amine, with alkyl = ethyl, iso-propyl, and tert-butyl, give with cobalt(II) and nickel(II) halides high-spin complexes with formulae [MLX₂], [MLX]Y, and [MLX]₂[MX₄] (where X = Cl, Br, I; Y = BPh₄, PF₆). The nickel complexes are either six- or five-coordinate: the coordination number decreases as the bulkiness of the alkyl group bound to the sulfur is increased. All the cobalt complexes contain the five-coordinate cation [CoLX]⁺. The crystal and molecular structure of the [Co(NS₃-t-Bu)Br]PF₆ complex has been determined by standard X-ray methods, and refined to R = 0.061. The crystals are monoclinic, space group P2¹/n. The unit cell dimensions are: a = 27.420 (2), b = 11.923 (4), c = 17.082 (1) Å, β = 102.40 (1)°, Z = 8. The complex cation has a trigonal bipyramidal geometry with the nitrogen and bromine atoms at the apexes, and the three sulfur atoms in the equatorial plane. The tetrahedral distortion is relatively small (mean BrCoS angle = 98.5°), and similar to that found for the [Co (Me₆tren)Br]Br complex [Me₆tren = tris(2-dimethylaminoethyl)amine).     

The structures of bis(1H,5H-S-methylisothiocarbonohydrazidium) di-μ-chloro-octachlorodibismuthate(III) tetrahydrate and tris(1H-S-methylisothiocarbonohydrazidium) esachlorobismuthate(III)

The structures of bis(1H⁺,5H⁺-S-methylisothiocarbonohydrazidium) di-μ-chlorooctachlorodibismuthate(III) tetrahydrate: (C₂H₁₀N₄S)₂(Bi₂Cl₁₀)· 4H₂O (compound [I]) and of tris(1H⁺-S-methylisothiocarbonohydrazidium) esachlorobismuthate(III): (C₂H₉N₄S)₃(BiCl_5.67I_0.33) (compound [II]) were determined from single crystal X-ray diffractometer data. Both compounds crystallize as triclinic (P ); crystals [I] with Z = 1 formula unit in a cell of constants: A = 10.621(3), B = 9.989(5), C = 7.439(3) Å, α = 88.31(2), β = 84.51(2), γ = 68.88(2)°, final R = 0.0427 for 2229 unique reflections with I 2σ(I); crystals [II] with Z = 2 and cell dimensions: A = 14.109(4), B = 12.209(9), C = 8.206(7) Å, α = 103.54(3), β = 104.95(2), γ = 81.96(2)°, final R = 0.0411 for 3637 unique reflections (1 2σ(I)). The structure of [I] is built up of diprotonated organic cations, water molecules and dinuclear centrosymmetric [Bi₂Cl₁₀]⁴⁻ anions held together by N-HCl, N-HO, O-HCl hydrogen bonds and Van der Waals interactions. The [Bi₂Cl₁₀]⁴⁻ complex consists of two edge-sharing octahedra in which three pairs of bonds of similar length are observed (Bi-Cl_av = 2.602(5), 2.712(4), 2.855(5) Å). The structure of [II] consists of monoprotonated cations and [BiCl_5.67I_0.33]³⁻ anions held together by a tridimensional network of hydrogen bonds. Each bismuth atom is octahedrally surrounded by six chlorine atoms, one of which is statistically substituted by a iodine atom.     

Structural isomerism involving an ambidentate ligand: the synthesis and characterization of diselenocyanato [bis(diphenylphosphino)methane] palladium(II) and cyano(selenocyanato) [diphenyl(diphenylphosphinomethyl)phosphine selenide] palladium(II)

The reaction, at 25 °C in methanol, between [Pd(SeCN)₄]²⁻ and bis(diphenylphosphino)methane (dpm) has been found to produce cyano(selenocyanato) [diphenyl(diphenylphosphinomethyl) phosphine selenide]palladium(II), [Pd(dpmSe)(CN)(SeCN)], wherein the cyanide group is trans to an Se atom which has been inserted into one PdP bond, and the selenocyanate group is trans to the unchanged diphenylphosphino group. The structure has been confirmed by the results of a single crystal X-ray diffraction study. The structural isomer, [Pd(dpm)- (SeCN)₂], of the foregoing complex has also been prepared by the reaction of Pd(C₂H₃O₂)₂ with dpm, followed by reaction with KSeCN. Heating the [Pd(dpm)(SeCN)₂] isomer converts it into [Pd- (dpmSe)(CN)(SeCN)]. A mechanism is proposed for the isomerization which involves an intramolecular selenium atom insertion.     

Three Co(III)-Fe(II) complexes based on hexacyanoferrates: Syntheses, spectroscopic and structural characterizations

Red or orange crystals of [Co(NH₃)₆]₂Cl₂[Fe(CN)₆] · 4H₂O (1), [Co(en)₃]₂Cl₂[Fe(CN)₆] · 2H₂O (2) and [Co(en)₃]₄[Fe(CN)₆]₃ · 21.6H₂O (3) were isolated from the aqueous systems Co³⁺-L_N-[Fe(CN)₆]⁴⁻ (L_N = NH₃, en = 1,2-diaminoethane). In all isolated samples the combination of Mössbauer (δ values were from the range −0.07 to −0.08 mm/s) and IR spectra (ν(CN) stretching vibrations in the range 2015-2047 cm⁻¹) confirms the presence of low spin Fe(II) in [Fe(CN)₆]⁴⁻ anions. X-ray structure analyses corroborate the ionic character of all studied compounds. These contain diamagnetic [Co(NH₃)₆]³⁺ (1) or [Co(en)₃]³⁺ (2 and 3) complex cations and diamagnetic [Fe(CN)₆]⁴⁻ complex anions. In compounds 1 and 2 chloride anions are present, too. All three compounds contain water of crystallization, in compound 3 as many as 21.6 molecules per formula unit.     

High-temperature spin-crossover in coordination compounds of iron(II) with tris(pyrazol-1-yl)methane

Novel mononuclear Fe(II) complexes of tris(pyrazol-1-yl)methane [Fe{HC(pz)₃}₂]²⁺ with and p-sulfonatothiacalix[4]arene (TCAS⁴⁻) as counterions were obtained. The compounds were characterized by magnetic susceptibility method, IR and UV-Vis spectroscopy. The structure of [Fe{HC(pz)₃}₂]SiF₆ has been analyzed by single-crystal X-ray diffraction. The ¹H NMR spectroscopy measurements of [Fe{HC(pz)₃}₂]₂(TСAS) in aqueous solution reveal the outer sphere inclusion of [Fe{HC(pz)₃}₂]²⁺ into the cyclophanic cavity of TCAS⁴⁻. The temperature induced spin-crossover ¹А₁ ⇔ ⁵Т₂, accompanied by thermochromism, has been revealed from the temperature dependence of μ_eff and IR spectra for both complexes. The comparative analysis of magnetochemical and spectroscopy data elucidates the effect of the cyclophanic counterion on the physico-chemical properties of Fe(II) complex.     

Kinetics and mechanism of the reaction between 1,2-diaminopropanetetra-acetatoferrate(III) and cyanide ion

The present study examines the kinetics and mechanism of the system [FePDTA(OH)]²⁻ + 5CN⁻ ⇌ [Fe(CN)₅OH]³⁻ + PDTA⁴⁻ at pH= 11.0±0.02, I= 0.25 M and temperature = 25 ± 0.1 °C. The reaction has been studied spectrophotometrically at 395 nm (λ_max of [Fe(CN)₅OH]³⁻). The data show that the reaction has three distinguishable stages; the first stage is formation of [Fe(CN)₅OH]³⁻, the second is conversion of [Fe(CN)₅OH)]³⁻ to [Fe(CN)₆]³⁻ and last is reduction of [Fe(CN)₆]³⁻ to [Fe(CN)₆]³⁻ by the released ligand, viz., PDTA. The first reaction shows variable order dependence on cyanide concentration, one at high cyanide concentration and two at low cyanide concentration. The second reaction exhibits first order dependence on the concentration of [Fe(CN)₅OH]³⁻ as well as cyanide. The reverse reaction between [Fe(CN)₅OH]³⁻ and PDTA is first order in [Fe(CN)₅OH]³⁻ and PDTA, and inverse first order in cyanide. On the basis of forward and reverse rate studies, a five-step mechanism has been proposed for the first reaction.     

Platinum(IV) isocyanide complexes

Neutral and cationic platinum(IV) isocyanide complexes of the type [PtCl₄(CNR)₂], [PtCl₄(CNR) (PMe₂Ph)], [PtCl₃(CNR)(PMe₂Ph)₂]⁺, [PtCl₂(CNR)₂ (PMe₂Ph)₂]²⁺, where R = methyl, t-butyl, cyclohexyl, p-tolyl, have been prepared by chlorine addition to the corresponding platinum(II) derivatives. The complexes [PtCl₂(CN)₂(CNR)₂] and [PtCl₂(CN)(CNR) (PMe₂Ph)₂]⁺ (R = t-butyl), are also reported. The cationic t-butylisocyanide derivatives are noteworthy in the way they readily lose the t-butyl cation at room temperature to give the corresponding cyano complexes. The compounds have been characterized by elemental analysis, molecular weights and conductivity measurements, and their i.r. and n.m.r. data are discussed in relation to structures and to the nature of the platinum-isocyanide bond.     

Mechanisms for acceleration of halide anation reactions of platinum(IV) complexes. REOA versus ligand assistance and platinum(II) catalysis Without central ion exchange

Chloride anation of trans-Pt(CN)₄ClOH₂⁻ has been studied with and without Pt(CN)₄²⁻ present at 25.0°C by use of stopped-flow and conventional spectrophotometry and a 1.00 M perchlorate medium. The rate law in the absence of Pt(CN)₄²⁻ is Rate=(p₁ + p₂ [H⁺] ) [Cl⁻]² [complex]/(1 + q [Cl₋]) with p₁=(3.0 ± 0.1) × 10⁻⁵ M⁻²s⁻¹, p₂=(3.6 ± 0.1) × 10⁻⁵ M⁻³ s⁻¹ and q=(0.62 ± 0.02) M⁻¹. It is compatible with a chloride assistance via an intermediate of the type Cl-Cl-Pt(CN)₄···OH₂²⁻, in which the reactivity of the aqua ligand is enhanced due to a partial reduction of the platinum. This mechanism of halide assistance is in principle the same as the modified reductive elimination oxidative addition (REOA) mechanism proposed by Poë, in which the intermediate is not split into free halogen, platinum(II) and water, and in which electron transfer not necessarily involves complete reduction to platinum(II). To avoid confusion with complete reductive eliminations, reactions without split of the intermediates are here termed halide-assisted reactions. The pH-dependence indicates acid catalysis via a protonated intermediate ClClPt(CN)₄···OH₃⁻.The Pt(CN)₄²⁻accelerated path has the rate law Rate=

[Cl-] [Pt(CN)₄²⁻] [complex] where k=(39.9±0.5) M⁻² s⁻¹ and K_a=(4.0±0.2)10⁻² M is the protolysis constant of trans-Pt(CN)₄ClOH²⁻.Reaction between PtCl₅OH₂⁻ and chloride is accelerated by Pt(CN)₄²⁻ and gives PtCl₆²⁻ as the reaction product. The rate law is Rate=k [Cl⁻] [Pt(CN)₄²⁻] [PtCl₅OH₂⁻] with k=(5.6 ± 0.2)10⁻³ M⁻² s⁻¹ at 35.0°C and for a 1.50 M perchlorate acid medium. The reaction takes place without central ion exchange. Alternative mechanisms with two consecutive central ion exchanges can be excluded. The role of Pt(CN)₄²⁻ in this reaction is very similar to that of the assisting halide in the halide assisted anations. [p ]Reaction between trans-Pt(CN)₄ClOH₂⁻ and PtCl₄²⁻ gives Pt(CN)₄²⁻ and PtCl₅OH₂⁻ as products and has the rate law Rate=k[PtCl₄²⁻] [trans-Pt(CN)₄ClOH₂⁻] with k=(3.32 ± 0.02) M⁻¹ s⁻¹ at 25 °C for a 1.00 M perchloric acid medium. The formation of an aqua complex as the primary reaction product and the rate independent of [Cl⁻] shows that formation of a bridged intermediate of the type Pt(II)Cl₄ClPt(IV)(CN)₄OH₂³⁻ is formed in the initial reaction step, not five-coordinated PtCl₅³⁻.     

Syntheses and structures of photochromic molybdenum(II) and rhodium(II) complexes with 1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene

Four novel Mo(II) and Rh(II) complexes with cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene (cis-dbe) or closed-dbe were synthesized and characterized. Employing [M(O₂CCF₃)₄] (M = Mo, Rh) with cis-dbe or closed-dbe afforded complex [Mo₂(O₂CCF₃)₄(cis-dbe)](benzene) (1), [Rh₂(O₂CCF₃)₄(cis-dbe)](benzene) (2), [{Mo₂(O₂CCF₃)₄}₂(closed-dbe)] (3), and [Rh₂(O₂CCF₃)₄(closed-dbe)](p-xylene) (4). The structures of four metal complexes were revealed by X-ray crystallographic analyses and the correlation between the crystal structures and the photochromic performance was discussed. In all complexes, two cyano groups of the ligand bridged two dimetal carboxylates to give a 1-D zigzag infinite chain structure. Upon irradiation with 405 nm light, complex 1 turned into reddish purple from yellow, and the color reverted to initial yellow on exposure to 563 nm light, indicating the reversible cyclization/ring-opening reaction in the crystalline phase. However, the Rh(II) complex 2 did not display similarities in reaction induced by light, which is attributable to the lower ratio of photoactive anti-parallel conformers compared with complex 1 and coordination effect of metal ions on photochromism of diarylethenes. The complexes of Rh(II) ions did not exhibit the expected reversible photoinduced behavior.     

Photoproducts from the photolysis of tris(bipyridine)ruthenium(II) chloride in dimethylformamide

Six photoproducts were observed in the photolysis of [Ru(bpy)₃]²⁺ in N,N-dimethylformamide (DMF) in the presence of chloride ions. The primary products were cis-[Ru(bpy)₂Cl₂] and cis-[Ru(bpy)₂-(DMF)Cl]⁺. The remaining ruthenium products, which were thermally unstable to varying degrees, were cis-[Ru(bpy)₂Cl₂]⁺, [Ru(bpy)₃]⁺, and a binuclear species we have tentatively identified as [Ru(bpy)₂Cl]₂ⁿ⁺ (n = 3 or 4).     

Low-dimensional compounds containing cyano groups. XIX. Crystal structure, spectroscopic, thermal and magnetic properties of {[Cu(tn)2]3[Pt(CN)4]2}[Pt(CN)4] (tn = 1,3-diaminopropane) complex

Violet prismatic crystals of {[Cu(tn)₂]₃[Pt(CN)₄]₂}[Pt(CN)₄] (tn = 1,3-diaminopropane) were crystallized from the water-methanol solution containing CuCl₂·2H₂O, tn and K₂[Pt(CN)₄]·3H₂O. Prepared complex was characterized using elemental analysis, infrared and UV-Vis spectroscopy, magnetic measurement and thermal analysis. X-ray analysis revealed an ionic character of the complex containing mononuclear square planar [Pt(CN)₄]²⁻ complex anions and penta-nuclear [Cu(tn)₂-Pt(CN)₄-Cu(tn)₂-Pt(CN)₄-Cu(tn)₂]²⁺ complex cations. The inner Cu(II) atom of the complex cation is hexa-coordinated, whereas two crystallographically equivalent peripheral Cu(II) atoms are penta-coordinated in the shape of a deformed square pyramid. Four v(CN) absorption bands observed in the IR spectrum are in agreement with the higher number of crystallographically different cyano groups and a broad highly asymmetric band observed in the reflectance UV-Vis spectrum is consistent with the presence of both hexa- and penta-coordinated Cu(II) atoms in the structure. The temperature dependence of the inverse susceptibility suggests the presence of a weak antiferromagnetic exchange coupling between Cu(II) ions. The complex is stable up to 210 °C when its two-stage thermal decomposition starts.     

Light-induced electron-transfer reactions. Part 2. Kinetics of the intra-molecular redox decomposition of tris(oxalato)-cobaltate(III) by irradiation with visible light of aqueous solution containing tris(2,2′-bipyridine)ruthenium(II) ion

The rate of the intra-molecular redox decomposition of the tris(oxalato)cobaltate(III) ion [Co(Ox)₃]^3? is greatly accelerated by irradiation with visible light of aqueous acidic solutions containing the tris(2,2′-bipyridine)ruthenium(II) ion [Ru(bpy)₃]²⁺. The rate of the light-induced reaction in hydrochloric acid with an acidity range 0.05–0.18 mol dm^?3 is of zero-order with respect to the [Co(Ox)₃]^3? ion concentration and is proportional to the light-intensity irradiated and also essentially to the [Ru(bpy)₃]²⁺ ion concentration. Moreover, the rate is independent not only of the oxalate ion concentrations, but also of the acidity over the range 0.05–0.18 mol dm^?3 hydrochloric acid. The ionic-strength dependence, as well as temperature dependence, were extremely small. The [Ru(bpy)₃]²⁺ concentration does not change during the occurrence of the reaction and the tris(2,2′-bipyridine)ruthenium(II) ion acts as a homogeneous catalyzer. However, a dramatic indication that the situation was rather different was found in the stronger acid solutions of 0.5 or 1.0 mol dm^?3 hydrochloric acid, in which the [Ru(bpy)₃]²⁺ concentration decreased greatly immediately after the initiation of reaction and then increased up to the initial concentration. Such a decrease at the initial stage of the reaction disappeared by addition of oxalate before the start of the reaction. A chain mechanism of reaction is proposed to account for these results.     

Crystal structures and coordination-site exchange reactions of palladium(II) and platinum(II) complexes containing tris[2-(tert-butylthio)ethyl]amine

Palladium(II) and platinum(II) complexes, [PdX(NS₃ ¹Bu)]BPh₄ (X=Cl, Br, I; NS₃ ¹Bu=tris[2-(tert-butylthio)ethyl]amine) and [PtCl(NS₃ ¹Bu)]BPh₄, were prepared, and their structures were determined by X-ray analyses. The geometry around the palladium and platinum atoms is square planar. The NS₃ ¹Bu ligand functions as a tridentate ligand and one sulfur atom is not coordinated to the metal. The ¹H NMR spectrum of [PdCl(NS₃ ¹Bu)]BPh₄ in acetone-d₆ exhibited a dynamic behavior. At 20°C the spectrum showed a singlet signal at 1.60 ppm that can be assigned to tert-butyl protons, whereas at −70°C three singlet signals were observed at 1.36, 1.61, and 1.70 ppm with an intensity ratio of 1: 0.25: 2. The signals at 1.36 and 1.70 ppm are assigned to the tert-butyl protons in the square-planar structure, and these signals are consistent with the X-ray structure. The signal at 1.61 ppm can be assigned to the tert-butyl protons in a trigonal-bipyramidal structure where the three tert-butyl groups are magnetically equivalent. Thus, we concluded that the coordination-site exchange occurred via a trigonal-bipyramidal intermediate. The square-planar and trigonal-bipyramidal species of [PdCl(NS₃ ¹Bu)]BPh₄ are in equilibrium in acetone-d₆. The equilibrium was shifted toward the square-planar species on decreasing the temperature. The ¹H NMR spectra for [PdX(NS₃ ¹Bu)]BPh₄ (X=Cl, Br, and I) were similar to one another at the same temperature, suggesting that the site-exchange process is insensitive to the kind of coexisting halogen ligand. The site exchange reaction of [PtCl(NS₃ ¹Bu)]BPh₄ seems to occur more slowly than that of the palladium(II) analogue.     

Complexes of d(+)-biotin with Pd(II) and Pt(II)

The reactions of d(+)-biotin with K₂MX₄, where M = Pd(II) or Pt(II) and X = Cl or Br have been studied in acidic, neutral or alkaline aqueous solutions. Complexes of the type trans-M(Bio)₂X₂ have been isolated for both metals and characterized with elemental analyses, conductivity measurments, ir spectra, ¹Hnmr and ¹³Cnmr spectra. The complex of the type [Pd(Bio)Cl₂]₂ has also been isolated from DMF solutions. The results indicate that d(+)-biotin coordinates exclusively through its sulfur atom with these metals in all the complexes in the present study, in the solid state or in solution.     

Preparation, structural, magnetic and thermal properties of two heterobimetallic cyano-bridged nickel(II)-copper(II)/platinum(II) coordination polymers

Two unique bimetalic Pt(II) coordination polymers of composition [Ni(hydeten)₂Pt(CN)₄] (Ni-Pt) and [Cu(hydeten)₂Pt(CN)₄] (Cu-Pt) [hydeten = N-(2-hydroxyethyl-ethylenediamine) or 2-(2-aminoethylamino)ethanol] have been synthesized and structurally characterized by various methods in this study. The crystal structure of Cu-Pt was determined by single-crystal X-ray diffraction analysis. The structure of Cu-Pt forms of infinite 2,2-TT type [-Cu(hydeten)₂-NC-Pt(CN)₂-CN-] chains containing paramagnetic copper atoms bridged by tetracyanoplatinate species. In this complex, Cu(II) centers display an axially elongated octahedron with two chelating hydeten molecules in the equatorial positions and N-bonded bridging cyano groups in the axial positions, whereas Pt(II) centers are four coordinate with four cyanide-carbon atoms in a square-planar arrangement. The decrease of the moments of these complexes in temperature range of 50 305 K can assigned to the antiferromagnetic interactions in the structures. The thermal decomposition of Cu-Pt comprise of five distinguished stages, while the thermal decomposition of Ni-Pt take place four different stages.     

Homoleptic copper(II) and copper(I) complexes of 5,6-dihydro-5,6-epoxy-1,10-phenanthroline. Six-coordinate copper(I) in solution

Reaction of 5,6-dihydro-5,6-epoxy-1,10-phenanthroline (L) with Cu(ClO₄)₂·6H₂O in methanol in 3:1 M ratio at room temperature yields light green [CuL₃](ClO₄)₂·H₂O (1). The X-ray crystal structure of the hemi acetonitrile solvate [CuL₃](ClO₄)₂·0.5CH₃CN has been determined which shows Jahn-Teller distortion in the CuN₆ core present in the cation [CuL₃]²⁺. Complex 1 gives an axial EPR spectrum in acetonitrile-toluene glass with g_|| = 2.262 (A_|| = 169 × 10⁻⁴ cm⁻¹) and g_⊥ = 2.069. The Cu(II/I) potential in 1 in CH₂Cl₂ at a glassy carbon electrode is 0.32 V versus NHE. This potential does not change with the addition of extra L in the medium implicating generation of a six-coordinate copper(I) species [CuL₃]⁺ in solution. B3LYP/LanL2DZ calculations show that the six Cu-N bond distances in [CuL₃]⁺ are 2.33, 2.25, 2.32, 2.25, 2.28 and 2.25 Å while the ideal Cu(I)-N bond length in a symmetric Cu(I)N₆ moiety is estimated as 2.25 Å. Reaction of L with Cu(CH₃CN)₄ClO₄ in dehydrated methanol at room temperature even in 4:1 M proportion yields [CuL₂]ClO₄ (2). Its ¹H NMR spectrum indicates that the metal in [CuL₂]⁺ is tetrahedral. The Cu(II/I) potential in 2 is found to be 0.68 V versus NHE in CH₂Cl₂ at a glassy carbon electrode. In presence of excess L, 2 yields the cyclic voltammogram of 1. From ¹H NMR titration, the free energy of binding of L to [CuL₂]⁺ to produce [CuL₃]⁺ in CD₂Cl₂ at 298 K is estimated as −11.7 (±0.2) kJ mol⁻¹.     

Number of binding sites of DNA and polynucleotides with tris(2,2'-dipyridyl)ruthenium(II) cations

The binding of tris(2,2′-bipyridyl)ruthenium(II) cations [Ru(bpy)] with single- and double-stranded (ss and ds) DNA, and the polynucleotides poly(A), poly(C), poly(G), poly(I), poly(I) · poly(C), and poly(U), was studied in aqueous solution. Steady-state electrical conductivity measurements with the polynucleotides, ssDNA, and dsDNA reveal that approximately three nucleotides offer one binding site. This may be compared with the ratio [nucleotide]/[Mg²⁺] of 2.4 : 1 for dsDNA. After laser excitation (353 nm), the luminescence of Ru(bpy) bound to nucleic acids shows two decay components. The contribution of the fast component, which is interpreted as resulting from quenching processes of the absorbed ruthenium complex, exhibits a maximum with increasing [nucleotide]/[Ru(bpy)] at a ratio of about three to one. Bound Ru(bpy) can be released from the strand by addition of NaClO₄ [half-concentration: 2.5 and ≤ 10 mM for poly(U) and dsDNA, respectively].     

One-dimensional coordination polymers made of transition metal-nitronyl nitroxide radical with dicyanoaurate(I) bridges

Three 1-D transition metal-nitronyl nitroxide radical complexes with dicyanoaurate(I) bridges, [M(NIT3py)₂][Au(CN)₂]₂ [NIT3py = 2-(3′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, M = Mn, Co, Zn (1-3)], were synthesized and structurally characterized. Three compounds are all isostructural in monoclinic, C2/c space group with Z = 4. The [Au(CN)₂]⁻ anions link [M(NIT3py)₂] units via μ₂-bridging mode, leading to a linear coordination chain. The M(II) ion adopts a distorted octahedral geometry with four N atoms from [Au(CN)₂]⁻ groups and two pyridyl-N atoms from NIT3py ligands. The magnetic behavior shows that the couplings are both weak antiferromagnetic between Mn(II) and NIT3py and between Co(II) and NIT3py.