NMR study of intramolecular processes in EDTA metal complexes

The kinetics of the intramolecular acetate scramblings occurring in thirteen ethylenediaminetetraacetate (EDTA) complexes has been studied by analyzing the modification observed in the NMR spectra of their D₂O solutions, when temperature is changed. The experimental results indicate that the Δ, Λ conversion is a fast process on the NMR time scale for each of the complexes considered, whereas the nitrogen inversion occurs at an observable rate in the case of the Cd(II), In(III), Sc(III), Y(III) and Lu(III) chelates and is too rapid in the other complexes. Computer analysis of the experimental NMR spectra has been performed in order to obtain enthalpy, entropy and free energy of activation concerning the N inversion of the cited chelates. Twist and bond breaking mechanisms are discussed with reference to both scrambling processes.     

An NMR study of the complexes of Zn(II) and Cd(II) ions with tris(dimethylamino)phosphine sulphide: Ligand exchange kinetics

The preparation of the complex species [Cd(TDPS)₄](ClO₄)₂ and [Zn(TDPS)₄](ClO₄)₂ (TDPS = tris(dimethylamino)phosphine sulphide)     

Dioxouranium(VI) complexes of some sulphur donor ligands

Complexes of uranyl chloride and uranyl nitrate of the type UO₂X₂·2L and [UO₂X₂2L′], where X = Cl or NO₃ and L = N,N′-tetramethylthiourea (TMTU); N,N′-dimethylthiourea (DMTU); monomethylthiourea (MMTU), monoethylthiourea (METU), pyridine-2-thiol (PYT) and L′ = 4,6-dimethylpyrimidine-2-thiol (PYMT), have been prepared. The complexes were characterised on the basis of IR spectroscopy and by elemental analysis. In some cases Raman spectra are also reported.     

Palladium(II) malonato complexes with some heterocyclic ligands

Palladium(II) malonato complexes with heterocyclic ligands have been synthesized and characterized by spectroscopic and biological studies. The compoun     

Structural features of some organotin(IV) complexes of semi- and thio-semicarbazones

Some five- and six-coordinated di and tri-n-butyl tin(IV) semi- and thio-semi carbazates have been synthesized. The characterization of these complexes, by IR, NMR (¹H, ¹³C, ¹¹⁹Sn), ¹¹⁹Sn), ¹¹⁹Sn Mössbauer and Mass spectroscopies along with X-ray diffraction, reveals that complexes of biionic ligands of the type Bu₂Sn L″ are five-coordinated having trigonal bipyramidal geometry. However, complexes of monoionic ligands of the type Bu₂SnL′₂ are six-coordinated in a distorted cis-octahedral geometry and Bu₃SnL′ are five-coordinated with a trigonal bipyramidal structure. X-ray structural studies on the compound Bu₂Sn(O.C₆H₄.CH:N.N.CS.NH₂), show that it crystallizes in a monoclinic lattice with a = 16.90 Å, b = 9.71 Å, c = 8.60 Å, and β = 103°45′.     

Binary,ternary and quaternary complexes invloved in the systems pyridoxamine-glycine-imidazole with some bivalent metal ions

Equilibrium-based computer models using MINIQUAD-75 program were utilized to determine the stoichiometry and formation constants involved in the systems pyridoxamine(Pm)-glycine (Gly)-imidazole (lmd) with CO(II), Ni(II), Cu(II), Zn(II) and Cd(II) metal ions. The data were obtained from potentiometric pH titration of the various binary and ternary quaternary systems under physiological-like conditions (0.15 M NaNO₃-37°C). Various composition ratios of metal and ligands were used. The ligand concentrations did not exceed 4 times the concentration of metal ion in the binary systems and 4 times of the metal ions in ternary systems. In case of the quaternary systems only imidazole concentrations were two or four times the concentrations of metal ions keeping those of other ligands equal to that of metal ions. The stability constants of the quaternary species are discussed in terms of binary and ternary constants as are the effect of ring size on the stability of mixed ligand species. In addition, electrostatic as well as statistical effects also are mentioned and the biological implications of these model equilibria are described.     

Formation equilibria of copper(II) complexes with some pyridinols in various solvents

Complexation of copper(II) with two different pyridinols in three solvents has been studied by visible spectrophotometry and flow-microcalorimetry. The influence of the solvent on tautomeric equilibrium of the ligand, on distribution, on stability and on formation enthalpies of the main complex species is discussed.     

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.     

Multinuclear magnetic resonance and related studies on some organotin(IV) complexes of dithiocarbazates

Synthesis, characterization and geometrical features of pentacoordinated dibutyltin(IV) dithiocarbazate complexes of the type n-Bu₂Sn L (where L = dianion of $\text{S}$-methyl-B-N (2-hydroxy-phenyl) methylene and methyl dithiocarbazate are described. These are obtained as viscous oils from the reactions of n-Bu₂SnO with equimolar proportions of the ligands in benzene. On the basis of UV, IR, NMR (¹H, ¹³C, ¹¹⁹Sn) spectra along with the mass spectral fragmentation pattern a trigonal bipyramidal geometry is proposed. The N atom probably occupies the axial site, while the remaining two donor atoms O and S and the dibutyl groups rest in an equatorial plane. These complexes are active against P.388 Lymphocyte leukaemia system.     

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].     

Preparations,structures and thermal decomposition of some bis(pentafluorobenzoato)dioxouranium(VI) complexes

Reaction Of UO₂(O₂CCH₃)₂ with pentafluorobenzoic acid yields UO₂(O₂CC₆F₅)₂, which has been converted into the solvated complexes UO₂(O₂CC₆F₅)₂L₂·S [L₂ = 2,2′-bipyridyl (bpy), S = 0.33 (PhH) or 0.07 (t-BuOH); L = Ph₃PO, S = t-BuOH; L = Ph₃AsO, S = 0.40 (t-BuOH)] and the solvent free UO₂(O₂CC₆F₅)₂L₂ [L₂ = bpy; L = Ph₃PO]. The crystal structure of UO₂(O₂CC₆F₅)₂bpy (orthorhombic, space group P2₁2₁2₁; a = 18.45(2), b = 18.94(2), c = 7.069(8) Å, Z = 4] reveals distorted hexagonal bipyramidal stereochemistry with a trans UO₂ group, chelating pentafluorobenzoate ligands, and chelating 2,2′-bipyridyl, which is significantly displaced from the hexagonal plane. The structure of UO₂(O₂CC₆F₅)₂(OPPh₃)₂·t-BuOH [rhombohedral, space group R3; a = 21.51(3) Å, α = 117.28(5)°, Z = 3] shows trans UO₂, pseudo trans Ph₃PO ligands, and one unidentate and one disordered chelating pentafluorobenzoate ligand, whilst t-BuOH could not be located because it is highly disordered. Relationships between ν (CO₂) frequencies and the carboxylate coordination are discussed, and UO₂(O₂CC₆F₅)₂(OAsPh₃)₂.0.40 (t-BuOH) is considered to have stereochemistry similar to that of the phosphine oxide complex. The complexes undergo decarboxylation in dimethyl sulphoxide yielding pentafluorobenzene and carbonatodioxouranium(VI) species not UO₂(C₆F₅)₂ derivatives.     

Synthesis,characterization and photochemistry of some monometallic and bimetallic 2,2′-bipyrimidine complexes of chromium and tungsten carbonyls

Synthesis, electronic absorption spectra, ¹³C NMR and photochemistry are reported for the complexes M(CO)₄bpym (M = Cr or W) and [W(CO)₄]₂bpym. The electronic absorption spectra indicate, for these complexes, that the lowest lying metal-to-ligand (L) charge transfer (MLCT) excited state is lower in energy than the ligand field (LF) excited states. The ¹³C NMR spectra showed that the chemical shifts of C(5) and C(6) for the M-bpym complexes move downfield with respect to that of the free ligand, bpym, while C(4) moves upfield upon complexation. Small, wavelength-dependent quantum yields for loss of CO were obtained upon irradiation. These quantum yields were an order of magnitude larger for the Cr-bpym complex than for the W complexes (Φ = 2.4 x 10^?2 quanta/min for Cr-bpym, 2.5 x 10^?3 quanta/min for W-bpym and 1.1 x 10^?3 quanta/min for W-bpym-W, λ_irr = 366 nm).     

Synthesis and circular dichroism studies of some cobalt(III) complexes containing 2,2′ bipyridine, 1,10 phenanthroline,and some optically active amino acids

Two series of cobalt(III) complexes were synthesized and spectrally analyzed, [Co(2,2′-bipyridyl)₂(aa)]I₂ and [Co(1,10-phenanthroline)₂(aa)]I₂ (where the letters aa refer to an optically active, bidentate amino acid). The following amino acids were used: l-alanine, glycine, l-leucine, l-phenylalanine, and l-proline.This research is an analogue to the chemical systems studied by Mason et al.^1,2 They investigated complexes such as [Co(phen)₃]³⁺, [Co(dipy)₃]³⁺, [Co(phen)₂(dipy)]³⁺, [Co(dipy)₂(phen)]³⁺, [Co(phen)₂(ox)]²⁺, and [Co(dipy)₂(ox)]²⁺. The series of [Co(dipy)₂(na)]²⁺ and [Co(phen)₂(na)]²⁺ complexes, where the letters na refer to a non-optically active, bidentate ligand, have exhibited exciton-splitting. We used optically active amino acids to ascertain whether or not the exciton-splitting phenomenon would occur when a non-optically active ligand was substituted by an optically active amino acid. In addition, a series of optically active amino acids was selected with the intention of determining whether small differences among the amino acid ligands would affect the circular dichroism (CD) spectra of the different complexes and if the formation of these complex ions would be steroselective.     

Photochemical production of chromate(VI) ions from some chromium(Ill) complexes

Complexes of the type [Cr(CN)_6-X(OH)_X]^3- were found to produce the chromate(VI) ions upon exposure to UV radiation in alkaline medium. The quantum yields are reported and possible mechanism is discussed.     

Synthesis,physicochemical properties and voltammetric characterization of some new Fe(III) complexes with semicarbazone-based ligands

Several bis(ligand) octahedral complexes of iron(III) with salicylaldehyde semi-, thiosemi-, and S-methylthiosemi- carbazones have been synthesized and characterized by elemental analysis, conductivity and magnetic measurements, electronic and IR spectra, as well as by linear sweep and cyclic voltammetry. General procedures for the syntheses of all types of complexes have been established, giving better defined reaction conditions. Physicochemical properties of the novel complexes have been related to those of the already known compounds of the same type.     

Metal complexes of some asymmetric diaminodiamide ligands—III1,2: Rates of conversion from octahedral to square planar complexes of Ni(II)

Dissociation of the two amide protons from complexes of asymmetric diaminodiamides with Ni(II) in aqueous solution occurs under moderately basic conditions. The loss of the protons is accompanied by a conversion of the complex from octahedral to square planar. The rates of conversion for complexes NiL²⁺ were measured spectrophotometrically and were found to depend linearly on [OH^?]. The diaminodiamide ligands used 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). The rates varied in the order SS-DAEN > DGEN > SRS-DAPN > R-DGPN ≈ SSS-DAPN.     

Manganese(II) and copper(II) complexes of some nitrogenoxygen and nitrogensulphur donor ligands

Manganese(II) and copper(II) complexes of the type M(ligandH)₂ with some nitrogenoxygen and nitrogensulphur donor ligands (HL) viz. phenylpyruvic acid semicarbazone (ppysc), 4-methylphenylpyruvic acid semicarbazone (4-mppysc), phenylpyruvic acid thiosemicarbazone (ppytsc) and 4-methylphenyl pyruvic acid thiosemicarbazone (4-ppytsc), have been synthesised. All the complexes have been characterised by magnetic moment measurements, IR electronic and electron spin resonance special studies. All the ligands behave as tridentate.     

Adduct formation of some tris(N,N dialkyldithiocarbamato)Cr(III) complexes with iodine

Spectrophotometric studies of dichloromethane solutions containing iodine and some Cr(S₂CNR₂)₃ complexes (where R₂NCS^?₂ are: OC₄H₈NCS^?₂ = modtc; (C₂H₅)₂NCS^?₂ = Et₂dtc; (C₆H₅CH₂)₂NCS^?₂ = Bz₂dtc) have shown the formation of 1:1 adducts whose spectral features were studied and which suggested that charge-transfer interaction involving iodine and a sulphur atom of a coordinated dithiocarbamato ligand occurred.A new BASIC non-linear least-squares program which performs an optimization of the absorbance data taken at several wavelengths was devised to evaluate reliable formation constants.The thermodynamic parameters have been calculated and compared with those obtained in the same conditions as above by a reinvestigation of the known 1:1 complex formation of iodine with the corresponding tetraalkylthiuram-disulphides, where the donor site is also the sulphur atom of the thiocarbonyl group. The ?ΔH° values related to the Cr(dtc)₃ · I₂ complexes are about 2 kcal lower than those of thiuram disulphides, showing a lowering of the donor strength of the thiocarbonyl sulphur as a consequence of the coordination to the metal.     

Cyanoalkyl complexes of transition metals . : II. Preparation and properties of some platinum complexes containing phosphorus as a donor atom

cis-PtCl(CH₂CN)(PPh₃)₂ was obtained by the reaction of Pt(PPh₃)₄ with ClCH₂CN in acetone. A solution of Pt(PPh₃)₄ and ClCH₂CN in benzene was heated under reflux to give trans-PtCl(CH₂CN)(PPh₃)₂. The reaction of the trans-isomer with Br^?, I^?, Ph₂PCH₂CH₂ PPh₂, Ph₂PCH₂CH₂AsPh₂ and cisPh₂PCHCHPPh₂ has been examined. The trans-influence of a ligand trans to the CH₂CN group seems to be indicated by the ²J(PtH) of the CH₂CN protons. The τ values of trans-PtX(CH₂CN)(PPh₃)₂ and PtX(CH₂ CN)(PP) (X = Cl, Br, I) are related by a linear function.