Photosubstitution in some cyanide complexes of chromium(III)(1)

Photosubstitution by OH^? ligand was concluded from a photochemical study of the [Cr(CN)₆]^3? and [Cr(CN)₅OH]^3? complexes in alkaline medium. Photoaccelerated aquation was found to proceed in the case of aquocyanochromates(III): [Cr(CN)₅H₂O]^2? and [Cr(CN)₃(H₂O)₃].     

Formation of Cu(II)—dicyandiamide complexes in neutral and acidic aqueous solutions

This work presents spectroscopic studies and electrochemical characterization of Cu(II)—dicyandiamide (DCDA) complex formation. The range of conditions leading to the precipitation of the complex is significantly larger than that presented in the literature. In all cases the stoichiometry of the compound is: [Cu(DCDA)₂(SO₄)(H₂O)₅). The spectroscopic data suggest that DCDA is a monodentate ligand forming a bond with Cu²⁺ via the nitryl nitrogen. Electroreduction of this complex is a two-step process occurring through a Cu(I)—DCDA intermediate.     

Metal complexes of some asymmetric diaminodiamide ligands—II. Stabilities of complexes of nickel(II) in aqueous solution

Equilibria between a series of asymmetric diaminodiamides and Ni(II) in aqueous solution have been studied by potentiometric and spectrophotometric methods. The ligands were S,R,S- and S,S,S-N,N′-dialanylpropylenediamine (DAPN), S,S-N,N′-dialanylethylenediamine (DAEN), R-N,N′-diglycylpropylenediamine (DGPN), and N,N′-diglycylethylenediamine (DGEN). At lower values of pH the complexes NiL²⁺ and in some cases NiL²⁺₂ were formed. Spectral data indicated that both of these were octahedral. At higher pH the two amide protons were lost and square planar complexes were formed. The diastereomeric DAPN ligands showed stereoselectivity in the equilibrium constants for deprotonation and formation of the square planar complexes. Comparison of optical rotatory dispersion curves and absorption spectra for the various complexes permits partial assignment of structures.     

Solvent complexes of the type [FeIII(CN)5L]n−

The title complexes have been prepared in situ by photolyzing the [Fe(CN)₅NO]^2? ion in some aliphatic alcohols, formamide and its derivatives, pyridine, acetonitrile and dimethylsulphoxide. Characterization of the complexes was made on the basis of three pieces of evidence: (i) the spectral properties, (ii) the presence of the titratable hydrogen in the complexes with protogenic solvents, and (iii) the anation reaction with the N₃^? and NCS^? ions.     

C3-bonded hetero-β-diketonates of palladium(II)

Reactions of PdL₂ complexes, where LH = benzoylacetone, dibenzoyl methane, or dipivaloyl methane, with pyridine and neat β-diketones (L ¹H trifluoroacetylacetone, hexafluoroacetylacetone, thenoyltrifluoroacetone and pivaloyltrifluoroacetone) in toluene resulted in the formation of central carbon (C³) bonded hetero-β-diketonate complexes of the formula [Pd(L)(C³-L′)py]. These were characterized by microanalyses, IR and ¹H NMR spectral data.     

Structural dependencies of pyramidal inversion at sulphur and selenium in thio- and seleno- ether complexes of palladium(II) and platinum(II): A nuclear magnetic resonance study

Total NMR band shape fitting methods have provided accurate energy data for inversion barriers at sulphur and selenium in complexes of types cis-[MX₂L] (M = Pd^II, Pt^II; X = Cl, Br, I; L = MeS(CH₂)₂SMe, MeS(CH₂)₃SMe, o-(SMe)₂C₆H₃Me, cis-MeSCH=CHSMe) and [PtXMe{MeE(CH₂)₂E′Me}] (E= E′= S or Se and E = S, E′= Se; X = Cl, Br, I). Barrier energies were found to decrease by 10–12 kJ mol^?1 in going from aliphatic through aromatic to olefinic ligand back-bone. This can be explained in terms of (3p - 2p) π conjugation between the inverting centre and the ligand back-bone. The effects of ligand ring size, nature of halogen atom and the metal oxidation state on the barrier energies are discussed.     

Palladium(II) and platinum(II) complexes in MN2x2 chromophores

Some Pd(II) and Pt(II) halide complexes with 2-bromo- and 2-chloro-1,3,4-thiadiazoles have been prepared and characterized by electronic, NMR, Raman and IR spectroscopy, and by thermogravimetric analysis and conductivity measurements. All of the complexes appear to have square-planar stereochemistry with MN₂x₂ (X = Cl or Br) chromophores. Two of them are present in the cis configuration while for all the others unambiguous trans configurations are observed.     

Some mixed-ligand palladium(II) complexes and comparison of their photosensitizing ability with analogous platinum(II) complexes

Three new palladium(II) complexes of formula [Pd(bipy)(XX)] [where bipy is 2,2′-bipyridine and XX are dianions of catechol (CAT), 4-tert-butylcatechol (BCAT) and 3,4-dimercaptotoluene (DMT)] have been prepared and characterized by physical methods. A ligand-ligand charge-transfer band in each complex was observed between 16–21 kK (ε_max = 1500–2200 1 mol^?1 cm^?1) which is negatively solvochromic. These palladium(II) complexes in dimethylformamide photosensitize the formation of singlet oxygen and their ability to photosensitize triplet oxygen (³O₂) to singlet oxygen (¹O₂) are compared with analogous platinum(II) complexes. In addition, 2,2′-bipyridine-platinum(II) complex of 3,4-dimercaptotoluene also undergoes self-sensitized photooxidation.     

ESR studies on the reactions of sulphite radical anion,SO3.̄−, with nitroalkane compounds in aqueous solutions

The reactions of the sulphite radical anion, SO₃^{$\text{.}\text{?}$?} (generated from the Ti³⁺-H₂O₂-Na₂SO₃ system at pH 9), in aqueous solutions with some nitroalkane compounds were investigated by using a rapid-mixing flow technique coupled with electron spin resonance (ESR) which can detect the radicals having a lifetime of 5–100 ms. The SO₃^{$\text{.}\text{?}$?} radical added to the double bond of CN in the nitroalkane aci-anions which are the main form of nitroalkanes in aqueous alkaline solutions. From the observed hyperfine splitting constants of the SO₃^{$\text{.}\text{?}$?} adducts of nitroalkane aci-anions, the preferred conformation of the adducts was deduced.     

Ion pair association of complexes of La3+ and Nd3+ with Br− and NO3− in N,N-dimethylacetamide

The formation constants and the respective variations of enthalpy were obtained by means of calorimetric titration of the lanthanides La³⁺ and Nd³⁺ with bromide and nitrate in N,N-dimethylacetamide. These thermochemical data were calculated for the 1:1 and 1:2 species which are less stable than the corresponding species obtained with chloride. The order of stability Cl^? > Br^?>NO₃^? was established for both species of La³⁺, and the order Br^?>Cl^?>LNO₃^? for 1:1 species of Nd³⁺. NdCl₂⁺ and NdBr₂⁺ species were not detected. Our results support the view that the metal-anion interactions involve inner sphere species.     

Preparation of cationic (keto-stabilized phosphonium or sulphonium ylide)(η5-cyclopentadienyl)(triphenylphosphine)palladium(II) complexes

In the presence of AgClO₄, chloro(η⁵-cyclopentadienyl)(triphenylphosphine)palladium(II) was treated with triphenylphosphonium benzoylmethylid     

Thermal and photochemical production of chromate(VI) ions from some complexes containing the “CrNO”2+ group

Results are reported for the oxidation of complexes of the type [Cr(CN)_5?x(H₂O)_xNO]^x?3 by molecular oxygen in alkaline medium. In the case of the [Cr(CN)₅NO]^3? complex the reaction proceeded photochemically, whereas in othe cases the thermal oxidation was also observed. The influence of pH, CN^? concentration and energy of radiation was investigated.     

Four-coordinated palladium(II) and platinum(II) complexes containing the Lewis-acid {M(S2CNHR)(PR3′)} group combined with a variety of other ligands

A new series of four-coordinated Pd(II) and Pt(II) complexes in which the Lewis-acid (14-electron) {M(S₂CNHR)(PR₃′)} group is combined with a variety of other ligands (such as RHNCS₂^?, I^?, SCN^?, SnCl₂I^?) has been synthesised and studied. The structures of the new compounds are discussed in relation to their specroscopic, magnetic and thermal properties. In the case of [M(S₂CNHR)₂(PR₃′)] complexes both the spectroscopic data (IR, ¹H NMR, UV-Vis) and their thermal behaviour strongly suggest the coexistence of two kinds of gem-disulphide ligands, one acting as a bidentate ligand and the other one as a unidentate. Also it was confirmed that the chemical behaviour of the bis(N-alkyldithiocarbamato) complexes of Pd(II) and Pt(II) towards tertiary phosphines is similar to that of the isoelectronic xanthate complexes rathe than to the bis(N,N-dialkyldithiocarbamato) complexes.     

Tetrahedral metal complexes of [MW12O40]-type (MAlIII, ZnII) with dodecatungstate as tetrahedral ligand

Tetrabutylammonium salts of 12-heteropolytungstates with central metal ions in a tetrahedral oxygen environment, MW₁₂O₄₀ (MAl, Zn), have been prepared and their spectroscopic data (IR, UV and MCD) presented. IR studies in acetonitrile solution suggest that the tetrahedral structure around AlO₄ moiety is largely distorted, whereas the ZnO₄ moiety retains excellent tetrahedral symmetry.     

Can the pentazole anion (N5−) be isolated and/or trapped in metal complexes?

The 1,3-dipolar cycloreversion pathway of the pentazole anion (N₅^?) to the azide anion (N₃^?) plus dinitrogen (N₂) has been investigated using ab initio methods. At the MP4SDQ/6–31 + G* level of theory plus zero-point energy contributions, the pentazole anion is predicted to lie at 31 kcal mol^?1 above the N₃^? + N₂ system but the energy barrier for decomposition is 22 kcal mol^?1. This indicates that the pentazole anion could be isolated in an inert matrix at low temperature. Comparison between extended Hückel calculations on the (N₅)M(CO)₃ and (C₅H₅)M(CO)₃ complexes (with M = Fe²⁺, Mn⁺ and Cr) suggests that the N₅^? complexes would be formed if the fragments could be brought together. Predicted vibrational frequencies of the N₅^? anion are also reported.     

New biimidazole and bibenzimidazole derivatives: mono and binuclear palladium(II) or platinum(II) complexes and heterobinuclear palladium(II)-rhodium(I) or platinum(II)-rhodium(I) complexes

Novel neutral biimidazolate or bibenzimidazolate palladium(II) and platinum(II) complexes of the type M(NN)₂(dpe) [M = Pd, Pt; (NN)₂^2? = BiIm^2?, BiBzIm^2?. dpe = 1,2-bis(diphenylphosphino) ethane] have been obtained by reacting MCl₂(dpe) with TI₂(NN)₂. Complexes M(NN)₂(dpe) which are Lewis bases react with HClO₄ or [M(dpe)(Me₂CO)₂](ClO₄)₂ to yield, respectively, mononuclear cationic complexes of general formula [M{H₂(NN)₂](dpe) (M = Pd, Pt; H₂(NN)₂ = H₂BiIm, H₂BiBzIm) and homobinuclear palladium(II) or platinum(II) cationic complexes of the type [M₂{μ - (NN)₂}(dpe)₂](ClO₄)₂. Reactions of M(BiBzIm)(dpe) with [Rh(COD) (Me₂CO)_X](ClO₄) render similar heterobinuclear palladium(II)-rhodium(I) and platinum(II)-rhodium(I) cationic complexes, of general formula [(dpe)M(μ-BiBzIm)Rh(COD)](ClO₄) (M = Pd, Pt; COD = 1,5-cyclooctadiene). Di- and mono-carbonyl derivatives [(dpe)M(μ-BiBzIm)Rh(CO)L](ClO₄) (M = Pd, Pt; L = CO, PPh₃) have also been prepared. The structures of the resulting complexes have been elucidated by conductance studies and IR spectroscopy.     

NMR (195Pt and 13C) contribution to the study of some Pt(II), Pt(IV) and mixed-valence thioamido complexes

The ¹⁹⁵Pt and ¹³C chemical shifts (δ_Pt and δ_c) are reported for platinum(II), platinum(IV) and class II mixed-valence complexes, with general formula [PtL₄]X₂, cis- and trans-PtL₂X₂, PtL₂X₄ and Pt₂L₄X₆ (where L may be thiourea, 2-imidazolidine-thione, tetrahydro 2-pyrimidinethione, thiocaprolactam, pyridine-2-thione and tetramethylthiourea, and X may be Cl or Br). The ¹⁹⁵Pt chemical shifts can be understood in view of ¹³C data in terms of variations of electronegativities and σ-donor abilities of ligands attached to platinum.     

Spectroscopic and biological studies on palladium(II) complexes with N-ethyl and N-propylimidazole

Palladium(II) halide complexes with N-ethylimidazole (N-EtIm) and N- propylimidazole (N-PropIm) with general formulae Pd(L)₂X₂ and Pd(L)₄X₂ (X = Cl, Br, I) were prepared and characterized by spectroscopic methods and conductivity measurements. These complexes are diamagnetic and have square planar stereochemistry. The Pd(L₂)X₂ derivatives, are non-conductors, and have trans-structures except for the cis-Pd(N-EtIm)₂Br₂. The biological activity of water soluble Pd(II) compounds is also reported.     

Copper(II) complexes of diaminodiamides in aqueous solution

The basicity constants of N,N′-bis(β-carbamoylethyl)ethylenediamine, N,N′-bis(β-carbamoylethyl)trimethylenediamine, N,N′-bis(β-carbamoylethyl)-1,2-propylenediamine, and N,N′-bis-(β-carbamoylethyl)-2-hydroxyltrimethylenediamine were determined potentiometrically in 0.10 mol dm^?3 NaNO₃ at 25.0°C. The formation of Cu(II) complexes of these ligands and the CuO to CuN bond rearrangements at the two amide sites of these complexes were investigated quantitatively by potentiometric and spectrophotometric techniques under the same conditions. Electronic spectra of the Cu(II) complexes of these ligands and their deprotonated species formed in aqueous solution were measured and discussed.     

Magnetic and electronic characterization of 2:1 copper(II) complexes of a series of aminocarboxylic acids

Copper(II) complexes with L-(—)-proline, pipecolinic acid, picolinic acid, anthranilic acid, 4-chloranthranilic acid, 3,5,-dichloroanthranilic acid, 4-nitroanthranilic acid, N-phenyl-anthranilic acid, and flufenamic acid anions were prepared and characterized. The copper complexes of the anions of proline, pipecolinic acid, and picolinic acid are soluble in polar solvents and display frozen solution EPR spectra with axial resonance parameters. The copper complexes of the ring-substituted anthranilates are highly insoluble or only slightly soluble in a few solvents. The EPR spectra of the copper-doped zinc(II) analogues of these complexes display various degrees of rhombicity in their EPR parameters. The N-substituted anthranilates form insoluble complexes in aqueous solution which readily dissolve in organic solvents and undergo dimerization.