Polarography of metal-gallic complexes

The polarographic behavior of metal ions in perchlorate media containing gallic acid is described. Tungsten(VI) forms a complex with gallic acid which yields a single wave in these media, useful in the polarographic determination of tungsten. Evidence for complexation of chromium(III), copper(II), iron(III), molybdenum(VI), uranium(VI), vanadium(V), tungsten(VI), praseodymium(III), samarium(III), neodymium(III) and gadolinium(III) is obtained and the behavior of these metal ions is summarized.     

Acid-base equilibrium of aqua-chromium-dioxolene complexes aimed at formation of oxo-chromium complexes

A series of aqua-Cr(III)-dioxolene complexes, [Cr(OH(2))(3,5-Bu(2)SQ)(trpy)](ClO(4))(2) (1s), [Cr(OH(2))(3,5-Bu(2)Cat)(trpy)]ClO(4) (1c), [Cr(OH(2))(3,6-Bu(2)SQ)(trpy)](ClO(4))(2) (2), [Cr(OH(2))(Cat)(trpy)]ClO(4) (3), [Cr(OH(2))(Cl(4)Cat)(trpy)]ClO(4) (4), [Cr(OH(2))(3,5-Bu(2)SQ)(Me(3)-tacn)](ClO(4))(2) (5), [Cr(OH(2))(Cat)(Me(3)-tacn)]ClO(4) (6), and [Cr(OH(2))(Cl(4)Cat)(Me(3)-tacn)]ClO(4) (7) (Bu(2)SQ = di-tert-butyl-o-benzosemiquinonate anion, Bu(2)Cat = di-tert-butylcatecholate dianion, Cat = catecholate dianion, Cl(4)Cat = tetrachlorocatecholate dianion, trpy = 2,2':6',2' '-terpyridine, and Me(3)-tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane), were prepared. On the basis of the crystal structures, redox behavior, and elemental analyses of these complexes, dioxolene in 1c, 3, 4, 6, and 7 coordinated to Cr(III) as the catechol form, and the ligand in 1s, 2, and 5 was linked to Cr(III) with the semiquinone form. All the aqua-Cr(III) complexes reversibly changed to the hydroxo-Cr(III) ones upon dissociation of the aqua proton, and the pK(a) value of the aqua-Cr(III) complexes increased in the order 6 > 3 approximately 1c > 7 > 5 approximately 4 > 1s. Hydroxo-Cr(III)-catechol complexes derived from 1c, 3, 4, 6, and 7 did not show any signs of dissociation of their hydroxy proton. On the other hand, hydroxo-Cr(III)-semiquinone complexes were reduced to hydroxo-Cr(III)-catechol in H(2)O/THF at pH 11 under illumination of visible light.     

Dinuclear cyano-bridged CoIII-FeII complexes as precursors for molecular mixed-valence complexes of higher nuclearity

The preparation and characterization of a series of trinuclear mixed-valence cyano-bridged Co(III)-Fe(II)-Co(III) compounds derived from known dinuclear [[L(n)Co(III)(mu-NC)]Fe(II)(CN)(5)](-) complexes (L(n)() = N(5) or N(3)S(2) n-membered pendant amine macrocycle) are presented. All of the new trinuclear complexes were fully characterized spectroscopically (UV-vis, IR, and (13)C NMR). Complexes exhibiting a trans and cis arrangement of the Co-Fe-Co units around the [Fe(CN)(6)](4-) center are described (i.e., cis/trans-[{L(n)Co(III)(mu-NC)](2)Fe(II)(CN)(4)](2+)), and some of their structures are determined by X-ray crystallography. Electrochemical experiments revealed an expected anodic shift of the Fe(III/II) redox potential upon addition of a tripositively charged [Co(III)L(n)] moiety. The Co(III/II) redox potentials do not change greatly from the di- to the trinuclear complex, but rather behave in a fully independent and noncooperative way. In this respect, the energies and extinction coefficients of the MMCT bands agree with the formal existence of two mixed-valence Fe(II)-CN-Co(III) units per molecule. Solvatochromic experiments also indicated that the MMCT band of these compounds behaves as expected for a class II mixed-valence complex. Nevertheless, its extinction coefficient is dramatically increased upon increasing the solvent donor number.     

Energy transfer in solution of lanthanide complexes

The lanthanides with their well-defined energy levels provide an excellent basis to study different Ln(III)-specific energy transfer processes in a variety of chemical environments. The studies concerning intramolecular and intermolecular energy transfer processes with participation of Ln(III) ions and a variety of ligand groups in solution are reviewed. Phenomena of energy transfer from ligands to Ln(III) ions, resulting consequently in a great enhancement of the Ln(III) ion luminescence (ligand sensitized luminescence), as well as from Ln(III) to other species and between Ln(III) ions are presented.     

Metal complexes of isonicotinic acid hydrazide

Complexes of platinum(IV), ruthenium(III), rhodium(III), iridium(III), gold(III), dioxouranium(II), zinc(II), cadmium(II), mercury(II) and manganese(II) with isonicotinic acid hydrazide were prepared and characterized on the basis of analytical, conductometric, magnetic susceptibility and spectral data. Platinum(IV) ruthenium(III), rhodium(III), iridium(III), dioxouranium(II) and manganese(II) form six-coordinate complexes while gold(III), zinc(II), cadmium(II) and mercury(II) form four coordinate complexes.     

Iron complexes of 5,10,15,20-tetraphenyl-21-oxaporphyrin

The iron complexes of 5,10,15,20-tetraphenyl-21-oxaporphyrin (OTPP)H have been investigated. Insertion of iron(II) followed by one-electron oxidation yielded a high-spin, six-coordinate (OTPP)Fe(III)Cl(2) complex. The reduction of (OTPP)Fe(III)Cl(2) has been accomplished by means of moderate reducing reagents producing high-spin five-coordinate (OTPP)Fe(II)Cl. The molecular structure of (OTPP)Fe(III)Cl(2) has been determined by X-ray diffraction. The iron(III) 21-oxaporphyrin skeleton is essentially planar. The furan ring coordinates in the eta(1) fashion through the oxygen atom, which acquires trigonal geometry. The iron(III) apically coordinates two chloride ligands. Addition of potassium cyanide to a solution of (OTPP)Fe(III)Cl(2) in methanol-d(4) results in its conversion to a six-coordinate, low-spin complex [OTPP)Fe(III)(CN)(2)] which is spontaneously reduced to [OTPP)Fe(II)(CN)(2)](-) by excess cyanide. The spectroscopic features of [OTPP)Fe(III)(CN)(2)] correspond to the common low-spin iron(III) porphyrin (d(xy))(2)(d(xz)d(yz))(3) electronic configuration. Titration of (OTPP)Fe(III)Cl(2) or (OTPP)Fe(II)Cl with n-BuLi (toluene-d(8), 205 K) resulted in the formation of (OTPP)Fe(II)(CH(2)CH(2)CH(2)CH(3)). (OTPP)Fe(II)(n-Bu) decomposes via homolytic cleavage of the iron-carbon bond to produce (OTPP)Fe(I). The EPR spectrum (toluene-d(8), 77 K) is consistent with a (d(xy))(2)(d(xz))(2)(d(yz))(2)(d(z)(2)(1)(d[(x)(2)-(y)(2)])(0) ground electronic state of iron(I) oxaporphyrin (g(1) = 2.234, g(2) = 2.032, g(3) = 1.990). The (1)H NMR spectra of (OTPP)Fe(III)Cl(2), (OTPP)Fe(III)(CN)(2), ([(OTPP)Fe(III))](2)O)(2+), and (OTPP)Fe(II)Cl have been analyzed. There are considerable similarities in (1)H NMR properties within each iron(n) oxaporphyrin-iron(n) regular porphyrin or N-methylporphyrin pair (n = 2, 3). Contrary to this observation, the pattern of downfield positions of pyrrole resonances at 156.2, 126.5, 76.3 ppm and furan resonance at 161.4 ppm (273 K) detected for the two-electron reduction product of (OTPP)Fe(III)Cl(2) is unprecedented in the group of iron(I) porphyrins.     

Synthesis and electrochemical properties of bipyrimidine bridged triruthenium complexes

A new μ(4)-bpym-bridged dimer of an oxoacetao-triruthenium complex with carbonyl, [{Ru(3)O(CH(3)COO)(5)(CO)(py)}(2)(μ(4)-bpym)], was synthesized. The complex possesses two stable mixed-valence states associated with Ru(3)(III,III,II)/Ru(3)(III,II,II) and Ru(3)(III,III,III)/Ru(3)(III,III,II). The IR-spectroelectrochemistry reveals ν(CO) spectra in five oxidation states, Ru(3)(III,III,III)-Ru(3)(III,III,III) to Ru(3)(III,II,II)-Ru(3)(III,II,II) and both the mixed-valence states show a spectrum indicating medium interaction between the Ru(3) units.     

Stability constants of polymer-metal complexes

Conditional stability constants of metal complexes with synthesized copolymers are studied by potentiometric titration. Linear copolymers are found to form more stable complexes than cross-linked sorbents with analogous functional groups. The stability of these complexes decreases in the order Th(IV) > Fe(III) ≈ La(III) > Cu(II).     

Hydroxide complexes of lanthanides-VI

Experiments performed previously with cerium(III), samarium and gadolinium have been extended to conditions of high pC(H) in order to discover any amphoteric character. Up to pC(H) 14.6, the solubility of gadolinium hydroxide and of cerium(III) hydroxide does not increase, so the previously reported constants hold up to this pC(H). The solubility of samarium hydroxide increases at high pC(H), and the value log ( *)beta(4) = -36.7 can be deduced. This should be added to the previously reported set, now applicable up to pC(H) 14.5.     

Insulin-enhancing vanadium(III) complexes

Simple, high-yield, large-scale syntheses of the V(III) complexes tris(maltolato)vanadium(III), V(ma)3, tris(ethylmaltolato)vanadium(III), V(ema)3, tris(kojato)vanadium(III) monohydrate, V(koj)3-H2O, and tris(1,2-dimethyl-3-hydroxy-4-pyridinonato)vanadium(III) dodecahydrate, V(dpp)3-12H2O, are described; the characterization of these complexes by various methods and, in the case of V(dpp)3-12H2O, by an X-ray crystal structure determination, is reported. The ability of these complexes to normalize glucose levels in the STZ-diabetic rat model has been examined and compared with that of the benchmark compound BMOV (bis(maltolato)oxovanadium(IV)), an established insulin-enhancing agent.     

Heterobismetal complexes of [26]hexaphyrin(1.1.1.1.1.1)

Au(III)Cu(III) and Au(III)Rh(I) heterobismetal complexes of meso-aryl-substituted [26]hexaphyrin were rationally prepared from a monometal Au(III) complex. The Au(III)Cu(III) complex is an aromatic molecule with a rectangular shape, while Au(III)Rh(I) complexes are out-of-plane macrocycles, being either aromatic or antiaromatic depending upon the number of conjugated pi electrons. The 26pi Au(III)Rh(I) complex was converted into an aromatic and planar 26pi Au(III)Rh(III) complex via double C-H bond activation upon refluxing in pyridine.     

Liquid chromatography of xanthate complexes

Summary The chromatographic behaviour of As(III), Sb(III), Bi(III), Se(II), Te(II) and Ni(II)xanthate complexes is seriously affected by decomposition effects. Polar stationary and mobile phases acting as Lewis bases cause decomposition of the complexes by displacing the xanthate ligands. Separation of the xanthate complexes without decomposition is possible if reversed phases, especially CN- or DIOL-modified reversed phases, are used.     

Unique crown thioether complexes of f elements: the crystal structure of U(III) and La(III) complexes of 1,4,7-trithiacyclononane

The crystal structures of the first U(III) complex of a crown thioether and of its La(III) analog have been determined; a stronger M-S interaction is observed for U(III) with respect to La(III) and Ce(III) in solution and in the solid state.     

Photoelectron spectroscopy of metal β-diketonato complexes

The electronic structures of yttrium(III), gadolinium(III) and ytterbium(III) tris-2,2,6,6-tetramethyl-3,5-heptanedione (tmhd) complexes have been investigated by HeI and HeII photoelectron spectroscopy (UPS), UDFT and OVGF calculations. We discuss metal-ligand bonding in the series of metal β-diketonato complexes on the basis of empirical arguments. The photoionization cross-sections and orbital energies of metal atoms must both be taken into account in order to rationalize changes in relative band intensities of the HeI/HeII spectra.     

Some lanthanide metal complexes of n-isonicotinamidosalicylaldimine

Trivalent lanthanide complexes of the type K[ML ₂] whereM=La(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III) and Dy(III) and H₂ L=N-isonicotinamidosalicyladimine, have been prepared and characterised. The nephelauxetic ratio (β), covalency (δ) and bonding parameter (b ²) of K[NdL ₂] have been calculated. Infrared spectral studies reveal that N-isonicotinamidosalicylaldimine acts as a dibasic tridentate ligand. A coordination number six has been proposed for the lanthanide metal ions.     

Gadolinium(III) complexes as MRI contrast agents: ligand design and properties of the complexes

Magnetic resonance imaging is a commonly used diagnostic method in medicinal practice as well as in biological and preclinical research. Contrast agents (CAs), which are often applied are mostly based on Gd(III) complexes. In this paper, the ligand types and structures of their complexes on one side and a set of the physico-chemical parameters governing properties of the CAs on the other side are discussed. The solid-state structures of lanthanide(III) complexes of open-chain and macrocyclic ligands and their structural features are compared. Examples of tuning of ligand structures to alter the relaxometric properties of gadolinium(III) complexes as a number of coordinated water molecules, their residence time (exchange rate) or reorientation time of the complexes are given. Influence of the structural changes of the ligands on thermodynamic stability and kinetic inertness/lability of their lanthanide(III) complexes is discussed.     

Highly luminescent lanthanide complexes of 1-hydroxy-2-pyridinones

The synthesis, X-ray structure, stability, and photophysical properties of several trivalent lanthanide complexes formed from two differing bis-bidentate ligands incorporating either alkyl or alkyl ether linkages and featuring the 1-hydroxy-2-pyridinone (1,2-HOPO) chelate group in complex with Eu(III), Sm(III), and Gd(III) are reported. The Eu(III) complexes are among some of the best examples, pairing highly efficient emission (Phi tot (Eu) approximately 21.5%) with high stability (pEu approximately 18.6) in aqueous solution, and are excellent candidates for use in biological assays. A comparison of the observed behavior of the complexes with differing backbone linkages shows remarkable similarities, both in stability and photophysical properties. Low temperature photophysical measurements for a Gd(III) complex were also used to gain insight into the electronic structure and were found to agree with corresponding time-dependent density functional theory (TD-DFT) calculations for a model complex. A comparison of the high resolution Eu(III) emission spectra in solution and from single crystals also revealed a more symmetric coordination geometry about the metal ion in solution due to dynamic rotation of the observed solid state structure.     

pH-metric studies on some ternary complexes of lanthanones

Stepwise mixed ligand complex formation has been cited for the formation of 111,Ln(III)—NTA—catechol ternary complexes potentiometrically [whereLn(III)=La(III), Pr(III) or Nd(III)]. The results of titration curves indicate the formation of 11,Ln(III)—NTA complexes in beginning and the addition of catechol, takes place later on in the higher buffer region. The relative stability of these ternary complexes in terms of metal ion has been reported as La(III)< 相似文献   

Photophysical and structural properties of cyanoruthenate complexes of hexaazatriphenylene

The tritopic bridging ligand hexaazatriphenylene (HAT) has been used to prepare the mono-, di-, and trinuclear cyanoruthenate complexes [Ru(CN)(4)(HAT)](2-) ([1](2-)), [{Ru(CN)(4)}(2)(mu(2)-HAT)](4-) ([2](4-)), and [{Ru(CN)(4)}(3)(mu(3)-HAT)](6-) ([3](6-)). These complexes are of interest both for their photophysical properties and ability to act as sensitizers, associated with strong MLCT absorptions; and their structural properties, with up to 12 externally directed cyanide ligands at a single "node" for preparation of coordination networks. The complexes are strongly solvatochromic, with broad and intense MLCT absorption manifolds arising from the presence of low-lying pi* orbitals on the HAT ligand, as confirmed by DFT calculations; in aprotic solvents [3](6-) is a panchromatic absorber of visible light. Although nonluminescent in fluid solution, the lowest MLCT excited states have lifetimes in D(2)O of tens of nanoseconds and could be detected by time-resolved IR spectrosocopy. For dinuclear [2](4-) and trinuclear [3](6-) the TRIR spectra are indicative of asymmetric MLCT excited states containing distinct Ru(III) and Ru(II) centers on the IR time scale. The complexes show red (3)MLCT luminescence as solids and in EtOH/MeOH glass at 77 K. Ln(III) salts of [1](2-), [2](4-), and [3](6-) form infinite coordination networks based on Ru-CN-Ln bridges with a range of one-, two-, and three-dimensional polymeric structures. In the Yb(III) and Nd(III) salts of [3](6- )the complex anion forms an 8-connected node. Whereas all of the Gd(III) salts show strong (3)MLCT luminescence in the solid state, the Ru-based emission in the Nd(III) and Yb(III) analogues is substantially quenched by Ru --> Ln photoinduced energy transfer, which results in sensitized near-infrared luminescence from Yb(III) and Nd(III).     

Columinescence effect in macromolecular complexes of Eu(III) and Tb(III)

The effect of Y(III) and Gd(III) coactivator ions on the intensity of Eu(III) and Tb(III) luminescence in monomer and polymer mixed-metal complexes was studied. Isomorphic replacement of Eu(III) and Tb(III) ions by Y(III) and Gd(III) ions in macromolecular complexes led to sensitization of Eu(III) and Tb(III) ion luminescence. A mechanism of columinescence was suggested. It involves a charge transfer and the ligand orbitals and the vacant orbitals of Eu(III) and Tb(III) ions and coactivators.