Formation and dissociation kinetics of Cu(II) and Ni(II) complexes with N2S2-macrocycles

The kinetics of the formation and dissociation of the Cu(2+) and Ni(2+) complexes with a series of N(2)S(2) macrocycles, in which the ring size and the geometry of the arrangement of the donor groups have been varied, have been measured at 25 [degree]C and I= 0.5 (KNO(3)). Both the deprotonated (L) and the monoprotonated (LH(+)) form of the ligands are reactive species in the formation step. In their deprotonated form, first bond formation, in some cases supported by an ICB effect, is rate determining, independently of the ring size. In the monoprotonated form, we find slower rates, due to the charge repulsion and/or conformation changes induced by hydrogen bonds. In contrast the mechanism of the dissociation is very dependent on the ring size. The complexes with the smaller rings react as flexible open-chain ligands directly with H(+). In contrast, the complexes with the larger rings react in a similar way as rigid ligands: first the metal amine bond slowly dissociates so that the free electron pair of the amine can take the "out conformation" and then it is protonated. The 14-membered macrocycle L(3) forms complexes in which the metal ions are ideally coordinated so that their dissociation becomes extremely slow.     

Mechanisms of sensitization of lanthanide(III)-based luminescence in transition metal/lanthanide and anthracene/lanthanide dyads

Four sets of dyads are discussed, in all of which near-infrared emitting lanthanide(III) ions such as Nd(III), Er(III) or Yb(III) are energy-acceptors which provide sensitized luminescence following energy-transfer from an antenna group. In three sets of dyads the antenna (energy-donor) group is a luminescent transition metal fragment; in the fourth the antenna is an anthracene group. A combination of photophysical studies and calculations has been used to understand the mechanisms by which energy-transfer to the lanthanide(III) ion occurs. Although definitive answers are not possible in every case due to the presence of several possible energy-transfer pathways, the relative contributions of Förster-type, Dexter-type and redox-mediated energy-transfer pathways have been analysed. Interesting results include (i) the demonstration of pure Dexter energy-transfer over 20 Å in a Ru(II)/Nd(III) dyad, and (ii) the demonstration of a redox-based mechanism for energy-transfer in anthracene/Ln(III) dyads in which the first step is photoinduced electron-transfer from the excited anthracene chromophore to a diimine ligand on the lanthanide(III) to generate a charge-separated state.     

Antitumor activity of transition metal(II) complexes with all- trans retinoic acid

Five complexes of transition metals with all-trans retinoic acid (HRA) have been prepared and characterized by elemental analysis, molar conductance, t.g.–d.t.a, i.r., and u.v.-vis. spectroscopy, and 1H-n.m.r. spectrometry. The general formula of these complexes is ML2 ·nH2O where L=RA, M=MnII, CoII, NiII, CuII, ZnII, and n=3 or 4. They have been studied for their antitumour activity against human bladder cancer line EJ (EJ cells) with respect to proliferation, induce differentiation, P21 and mutation P53 expressions in vitro.     

Structural features of copper(II) and lanthanide(III) tartratogermanate(IV) complexes

Four heterometallic tartratogermanate complexes, namely [Cu₂Ge₂(Tart)₃(H₂O)₁₀] _n · 3nH₂O and (H₃O)[LnGe₂(Tart)₃(H₂O)₆] · nH₂O (Ln³⁺ = Gd, n = 3.5; Tm, n = 3; Yb, n = 3), have been prepared via the reaction between germanium tetrachloride and D-tartaric acid (H₄Tart) in aqueous acetic acid. All complexes contain {Ge₂(Tart)₃} _n ^4n- polymer chains. The Cu²⁺ and Ln³⁺ atoms coordinate only Tart carbonyl oxygen atoms.     

Monopropionate analogues of DOTA4- and DTPA5-: kinetics of formation and dissociation of their lanthanide(III) complexes

The replacement of an acetate function of the macrocyclic DOTA4-(DO3A-Nprop4-) or the acyclic DTPA5- in terminal position (DTTA-Nprop5-) has been recently shown to result in a significant increase of the water exchange rate on the Gd3+ complexes, which makes these chelates potential contrast agents for MRI applications. Here, two novel and straightforward synthetic routes to H4DO3A-Nprop are described. Protonation constants of DO3A-Nprop4- and stability constants with several alkaline earth and transition metal ions have been determined by potentiometry. For each metal, the thermodynamic stability constant is decreased in comparison to the DOTA chelates. The formation reaction of LnDO3A-Nprop- complexes (Ln=Ce, Gd and Yb) proceeds via the rapid formation of a diprotonated intermediate and its subsequent deprotonation and rearrangement in a slow, OH- catalyzed process. The stability of the LnH2DO3A-Nprop* intermediates is similar to those reported for the corresponding DOTA analogues. The rate constants of the OH- catalyzed deprotonation step increase with decreasing lanthanide ion size, and are slightly higher than for DOTA complexes. The kinetic inertness of GdDTTA-Nprop2- was characterized by the rates of its exchange reactions with Zn2+ and Eu3+. The rate of the reaction between GdDTTA-Nprop2- and Zn2+ increases with Zn2+ concentration, while it is independent of pH, implying that the exchange takes place predominantly via direct attack of the metal ion on the complex. In the Eu3+ exchange, the rate decreases with increasing concentration of the exchanging ion which is accounted for by the transitional formation of a dinuclear GdDTTA-NpropEu+ species. The kinetic inertness of the monopropionate GdDTTA-Nprop2- is decreased in comparison to GdDTPA2-: all rate constants, characterizing the dissociation reaction via either proton- or metal-catalyzed pathways being higher by 1-2 orders of magnitude. Similarly, a study of the acid-catalyzed dissociation of the macrocyclic CeDO3A-Nprop- showed a partial loss of the kinetic inertness with regard to the tetraacetate derivative CeDOTA-.     

Equilibrium and formation/dissociation kinetics of some Ln(III)PCTA complexes

The protonation constants () of 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene-3,6,9-triacetic acid (PCTA) and stability constants of complexes formed between this pyridine-containing macrocycle and several different metal ions have been determined in 1.0 M KCl at 25 degrees C and compared to previous literature values. The first protonation constant was found to be 0.5-0.6 log units higher than the value reported previously, and a total of five protonation steps were detected (log = 11.36, 7.35, 3.83, 2.12, and 1.29). The stability constants of complexes formed between PCTA and Mg2+, Ca2+, Cu2+, and Zn2+ were also somewhat higher than those previously reported, but this difference could be largely attributed to the higher first protonation constant of the ligand. Stability constants of complexes formed between PCTA and the Ln3+ series of ions and Y3+ were determined by using an "out-of-cell" potentiometric method. These values ranged from log K = 18.15 for Ce(PCTA) to log K = 20.63 for Yb(PCTA), increasing along the Ln series in proportion to decreasing Ln3+ cation size. The rates of complex formation for Ce(PCTA), Eu(PCTA), Y(PCTA), and Yb(PCTA) were followed by conventional UV-vis spectroscopy in the pH range 3.5-4.4. First-order rate constants (saturation kinetics) obtained for different ligand-to-metal ion ratios were consistent with the rapid formation of a diprotonated intermediate, Ln(H(2)PCTA)(2+). The stabilities of the intermediates as determined from the kinetic data were 2.81, 3.12, 2.97, and 2.69 log K units for Ce(H(2)PCTA), Eu(H(2)PCTA), Y(H(2)PCTA), and Yb(H(2)PCTA), respectively. Rearrangement of these intermediates to the fully chelated complexes was the rate-determining step, and the rate constant (k(r)) for this process was found to be inversely proportional to the proton concentration. The formation rates (k(OH)) increased with a decrease in the lanthanide ion size [9.68 x 10(7), 1.74 x 10(8), 1.13 x 10(8), and 1.11 x 10(9) M(-1) s(-1) for Ce(PCTA), Eu(PCTA), Y(PCTA), and Yb(PCTA), respectively]. These data indicate that the Ln(PCTA) complexes exhibit the fastest formation rates among all lanthanide macrocyclic ligand complexes studied to date. The acid-catalyzed dissociation rates (k1) varied with the cation from 9.61 x 10(-4), 5.08 x 10(-4), 1.07 x 10(-3), and 2.80 x 10(-4) M(-1) s(-1) for Ce(PCTA), Eu(PCTA), Y(PCTA), and Yb(PCTA), respectively.     

Thermal analysis of lanthanide(III) and Y(III) complexes with 4-hydroxy-3-methoxybenzoic acid

Summary A procedure for the extrapolation of accelerated thermo-oxidative ageing tests to lower temperatures is proposed. The procedure involves a deconvolution of the global process into high- and low-temperature components where the extrapolation to low temperatures is carried out using the low-temperature component. The method was tested on stabilized and unstabilized polyisoprene rubber and was found to produce realistic estimations of the length of the induction period of oxidation so giving a more accurate estimation of the service life. However, to obtain the low-temperature values of the adjustable kinetic parameters, very low heating rates are required (0.04 K min^-1, 0.1 K min^-1) making the measurement process time consuming. Using this method, more realistic estimates of the durability of a material are obtained.     

Photo and electroluminescence of lanthanide(III) complexes

Major classes of coordination compounds used as electroluminescent materials are surveyed, and their advantages and disadvantages are discussed. The strategy of the directed synthesis of lanthanide(III) complexes promising for use as electroluminescent materials is formulated. The results of studies dealing with the design of electroluminescent devices based on europium(III), terbium(III), and thulium(III) complexes are considered.     

4-Cyanoaniline complexes with transition metal(II) halides

Summary Coordination compounds formed by the interaction of manganese(II), cobalt(II), nickel(II) and copper(II) chloride and bromide with 4-cyanoaniline (4-CA) have been prepared and characterized by molar conductance, magnetic susceptibilities, electronic and i.r. spectral measurements down to 200 cm^–1 in the solid state. The isolated complexes are M(4-CA)₂X₂ except for nickel(II) bromide which is NI(4-CA)₄Br₂. I.r. spectra, indicate that 4-CA, though a potentially bidentate ligand, nevertheless acts only as a terminally aniline (NH₂) bonded monodentate ligand in all the complexes. Tentative stereochemistries of the complexes have been suggested in the solid state.     

Spin transition in iron(III) and iron(II) complexes

The main stages of the studies on the spin transitions in iron(III) and iron(II) complexes are considered. The types of the spin transitions and the factors responsible for the latter are reported. The problems arising during experiments in this field are discussed.     

Decarboxylation syntheses of transition metal organometallics. III polyfluorophenylplatinum(II) complexes with nitrogen donor ligands

Summary The platinum(II) carboxylates,trans-Pt(O₂CR)₂(py)₂ and Pt(O₂CR)₂bpy (R=C₆F₅,p-HC₆F₄,m-HC₆F₄, oro-HC₆F₄; bpy=2,2-bipyridyl), have been prepared by reactions oftrans-Pt(OH)₂(py)₂ or Pt(OH)₂bpy with the appropriate polyfluorobenzoic acids, whilst [Pt(py)₄](O₂CC₆F₅)₂ has been obtained from reaction oftrans-PtCl₂(py)₂ with thallous pentafluorobenzoate in pyridine at room temperature. In boiling pyridine, the platinum(II) polyfluorobenzoates undergo either decarboxylation givingtrans-PtR₂(py)₂ and PtR₂bpy (R= C₆F₅,p-HC₆F₄, orm-HC₆F₄) complexes or substitution, giving [Pt(py)₄](O₂CC₆F₄H-o)₂ and [Ptbpy(py)₂](O₂CC₆F₄H-o)₂. Reactions oftrans-PtX₂(py)₂ and PtX₂bpy (X=Cl or Br) with appropriate thallous polyfluorobenzoates in boiling pyridine have yielded the complexestrans-PtR₂(py)₂, PtR₂bpy, PtCl(R)bpy (R=C₆F₅,p-HC₆F₄, orm-HC₆F₄ in each case),trans-PtCl(R)(py)₂ (R = C₆F₅ orm-HC₆F₄),trans-PtBr(C₆F₅)(py)₂, and PtBr(C₆F₅)bpy. The complexestrans-PtR₂(py)₂ (R=C₆F₅ orp-HC₆F₄) have also been prepared from potassium tetrachloroplatinate(II) and the appropriate thallous polyfluorobenzoate in boiling py, andtrans-Pt(C₆F₅)₂(py)₂ has been similarly obtained fromcis-PtCl₂(py)₂ and C₆F₅CO₂Tl. Significant decarboxylation was not observed on reaction oftrans-PtCl₂(py)₂ or PtCl₂bpy with thallous 2,3,4,5-tetrafluorobenzoate.Part II, ref. 4;Preliminary communication, ref. 3;     

Thermal properties of lanthanide(III) complexes with 5-amino-1,3-benzenedicarboxylic acid

The complexes of yttrium(III) and lanthanides(III) with 5-amino-1,3-benzenedicarboxylic acid form two isostructural series of compounds and have the general formula Ln₂(C₈H₅O₄N)₃·nH₂O, where n = 13 for Y, La-Er and n=9 for Tm, Yb, Lu. They are insoluble in water and stable at room temperature. On heating in air or inert gas atmosphere they lose all water molecules in several steps. The anhydrous compounds are stable to about 400°C and next decompose to oxides.     

Formation and dissociation kinetics and crystal structures of nickel(II)-macrocyclic tetrathiaether complexes in acetonitrile. Comparison to nickel(II)-macrocyclic tetramines

Complex formation and dissociation rate constants have been independently determined for solvated nickel(II) ion reacting with eight macrocyclic tetrathiaether ligands and one acyclic analogue in acetonitrile at 25 degrees C, mu = 0.15 M. The macrocyclic ligands include 1,4,8,11-tetrathiacyclotetradecane ([14]aneS4) and seven derivatives in which one or both ethylene bridges have been substituted by cis- or trans-1,2-cyclohexane, while the acyclic ligand is 2,5,9,12-tetrathiatridecane (Me2-2,3,2-S4). In contrast to similar complex formation kinetic studies on Ni(II) reacting with corresponding macrocyclic tetramines in acetonitrile and N,N-dimethylformamide (DMF), the kinetics of complex formation with the macrocyclic tetrathiaethers show no evidence of slow conformational changes following the initial coordination process. The differing behavior is ascribed to the fact that such conformational changes require donor atom inversion, which is readily accommodated by thiaether sulfurs but requires abstraction of a hydrogen from a nitrogen (to form a temporary amide). The latter process is not facilitated in solvents of low protophilicity. The rate-determining step in the formation reactions appears to be at the point of first-bond formation for the acyclic tetrathiaether but shifts to the point of chelate ring closure (i.e., second-bond formation) for the macrocyclic tetrathiaether complexes. The formation rate constants for Ni(II) with the macrocyclic tetrathiaethers parallel those previously obtained for Cu(II) reacting with the same ligands in 80% methanol-20% water (w/w). By contrast, the Ni(II) dissociation rate constants show significant variations from the trends in the Cu(II) behavior. Crystal structures are reported for the Ni(II) complexes formed with all five dicyclohexanediyl-substituted macrocyclic tetrathiaethers. All but one are low-spin species.     

Synthesis and properties of lanthanide(III) complexes with 4-hydroxy-3,5-dimethoxybenzoic acid

Complexes of yttrium(III) and lanthanides(III) with 4-hydroxy-3,5-dimethoxybenzoic (syringic) acid were obtained as solids with metal to ligand mole ratio of 1: 3. The compounds were characterized by elemental analysis, IR spectroscopy, X-ray diffraction patterns, solubility, and thermal studies. The complexes are sparingly soluble in water and stable at room temperature. Compounds of light lanthanides (from La to Nd) are hydrated and they crystallize in a triclinic system. When heated, they lose water molecules in one step and in the next step they decompose to oxides. Complexes of yttrium and other lanthanides are anhydrous and crystallize in a monoclinic system. They are stable up to 300°C and then decompose to oxides. As the coordination number of lanthanide ions is usually equal to 9 or 8, one can suppose that hydroxy or methoxy groups take part in the coordination of these metal ions.     

Formation and dissociation kinetics of Eu(III) complexes with H5do3ap and similar dota-like ligands

Complexation kinetics of the europium(III)-H₅do3ap complex (1,4,7,10-tetraazacyclododecane-1,4,7-triacetic-10-(methylphosphonic acid)) was studied at 25 °C and I = 0.1 M KCl and compared with the analogous H₄dota-like ligands. The mechanism of the formation reactions between the europium(III) ion and H₃do3a, H₄dota and H₄dota analogs having one methylphosphonic (H₅do3ap) or phosphinic acid pendant arms with a propionate side chain (H₅do3ap^PrA) was proposed on the basis of TRLIFS measurements. The experimental data of the dissociation kinetics of the europium(III) complexes with H₅do3ap and H₅do3ap^PrA ligands show that there is no change in reactivity of the complexes due to the side chain of the phosphinic acid bifunctional chelate. The TRLIFS study of the proton-assisted decomplexation reaction of the europium(III) complexes with H₃do3a, H₄dota, H₅do3ap and H₅do3ap^PrA demonstrates different behaviour influenced by a change in the number of water molecules during the reaction. The advantages and disadvantages of the TRLIFS methodology as a new experimental technique for simultaneous evaluation of kinetics and reaction mechanisms are discussed.     

Study of the effects of concentration and pH on the dissociation kinetics of Fe(II)-fulvic acid complexes

The effects of reagent concentration and the pH in the kinetic behavior of the dissociation of Fe(II)-fulvic acid complexes were studied using a spectrophotometric technique. The results show that this behavior is not strongly affected by the concentration of fulvic acid, the concentration of the metal cation on the ratio of these concentrations and that variations in pH are more important in the dissociation process. A possible explanation based in the relative influence of proton concentration on the stability of the complexes is proposed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 63–67,1998.     

Reaction of lanthanide(II) and lanthanide(III) phenylethynyl cuprates with acetyl chloride

Praseodymium and ytterbium phenylethynyl cuprates [(PhC≡C)₃Cu]₃Pr₂(THF)₆ and {[(PhC≡C)₃Cu]·Yb(THF)₂}₂ react with acetyl chloride in tetrahydrofuran with elimination of phenylethynylcopper and formation of alkoxides [PhC≡C-CCl(CH₃)O] _n Ln (n = 3, Ln = Pr; n = 2, Ln = Yb). Then praseodymium alkoxide forms ester [methyl (phenylethynyl)chloromethylethanoate] and praseodymium chloride, alkoxy derivative. Itterbium alkoxide is oxidized to unsymmetrical dialkoxyitterbium chloride PhC≡C-CH(CH₃)-O-Yb(Cl)-O-CCl(CH₃)C≡CPh·2THF.     

Kinetics and mechanism of acid catalysed dissociation of some octahedral complexes of cobalt(III) and chromium(III)

Summary The kinetics of dissociation of glycinepentaamminecobalt(III) and tetraaquomonoacetylacetonatochrormium(III) ions in moderately strong perchloric acid media have been investigated spectrophotometrically. From the dependence of the rate on various acidity functions and the observed isokinetic and free energy relationships, both the complexes appear to react by an associative process involving interaction of the conjugate acid form of the substrate complex and H₃O⁺.     

Mixed metal hydroxycarboxylic acid complexes. Spectrophotometric study of complexes of U(VI) with In(III), Cu(II), Zn(II) and Cd(II)

The formation of mixed metal complexes between uranium (VI), as the central metal ion, and aluminium (III), indium (III), copper (II), zinc (II) and cadmium (II), as the additional metal ions, with a hydroxycarboxylic acid chosen between citric, tartaric or malic, has been studied using spectrophotometric methods.The effect of pH has been examined, and the results show that at pH=4 stable complexes are formed for most of the systems. At this pH the method of mole ratio and Job's method of continuous variations, were employed to determine the stoichiometry of the mixed metal complexes. Al(III), In(III) and Cu(II) showed a high tendency to form mixed metal complexes with U(VI), while the formation of complexes is uncertain for Cd(II) and Zn(II). The ratio of the ligand to the total metal ion has been found to be 21 and metal:metal ratios of 11 and 12 have been observed.Represents part of the Ph.D. thesis submitted by Emanuel Manzurola to Ben Gurion University of the Negev.     

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.