| 1. |
- Banyai, I., et al.
(författare)
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Cyanide exchange on Tl(CN)(4)(-) in aqueous solution studied by Tl-205 and C-13 NMR spectroscopy
- 2001
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Ingår i: European Journal of Inorganic Chemistry. - 1434-1948 .- 1099-1948. ; :7, s. 1709-1717
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Tidskriftsartikel (refereegranskat)abstract
- Dynamics of cyanide exchange between Tl((CN)-C-13)(4)(-) and (CN-)-C-13 was studied by means Tl-205 and C-13 NMR. The rate law consists of two parts: w = k(CN)[Tl(CN)(4)(-)][CN-] + k(OH)[Tl(CN)(4)(-)][CN-][OH-] with k(CN) = 9.7(+/-0.4) x 10(6) M(-1)s(-1) and k(OH) = 5.4(+/-0.4) x 10(10) M(-2)s(-1). It was shown that the exchange between the two cyano species can be studied, not only by C-13 NMR, but also by Tl-205 NMR using the heteronuclear carbon-thallium scalar coupling as an indicator, despite the fact that only one Tl site is present in the system. The reaction mechanism is discussed in terms of an associative interchange mechanism, I-A. Penetration of the incoming cyanide ion into the coordination sphere of Tl(CN)(4)(-) Tl(CN)(4)(OH)(-) is suggested to be the rate-determining step for the two parallel reactions paths. Possible reasons for the strong labilizing effect of the cyanide ligand is discussed in the light of thermodynamic and structural data. The possibility of detection of an exceptional exchange reaction, namely cyanide exchange between two Tl(CN)(4)(-) entities by a direct encounter was theoretically settled, but found to be too slow to be detected.
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| 2. |
- Bodor, A., et al.
(författare)
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F-19 NMR study of the equilibria and dynamics of the Al3+/F- system
- 2000
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 39:12, s. 2530-2537
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Tidskriftsartikel (refereegranskat)abstract
- A careful reinvestigation by high-field F-19 NMR (470 MHz) spectroscopy has been made of the Al3+/F- system in aqueous solution under carefully controlled conditions of pH, concentration, ionic strength (I), and temperature. The F-19 NMR spectra show five distinct signals at 278 K and I = 0.6 M (TMACl) which have been attributed to the complexes AlFi(3-i)+(aq) with i less than or equal to 5. There was no need to invoke AlFi(OH)(j)((3-i-j)+) mixed complexes in the model under our experimental conditions (pH less than or equal to 6.5), nor was any evidence obtained for the formation of AlF63-(aq) at very high ratios of F-/Al3+. The stepwise equilibrium constants obtained for the complexes by integration of the F-19 signals are in good agreement with literature data given the differences in medium and temperature. In I = 0.6 M TMACl at 278 K and in I = 3 M KCl at 298 K the log K-i values are 6.42, 5.31, 3.99, 2.50, and 0.84 (for species i = 1-5) and 6.35, 5.25, and 4.11 (for species i = 1-3), respectively. Disappearance of the F-19 NMR signals under certain conditions was shown to be due to precipitation. Certain 19F NMR signals exhibit temperature- and concentration-dependent exchange broadening. Detailed line shape analysis of the spectra and magnetization transfer measurements indicate that the kinetics are dominated by F- exchange rather than complex formation. The detected reactions and their rate constants are AlF22+ + *F- reversible arrow AIF*F2+ + F- (k(02) = (1.8 +/- 0.3) x 10(6) M-1 s(-1)), AlF30 + *F- reversible arrow (AlF2F0)-F-* + F- (k(03) = (3.9 +/- 0.9) x 10(6) M-1 s(-1)), and AlF30 + H*F reversible arrow AlF2*F-0 + HF (k(03)(H) = (6.6 +/- 0.5) x 10(4) M-1 s(-1)). The rates of these exchange reactions increase markedly with increasing F- substitution. Thus, the reactions of AlF2+(aq) were too inert to be detected even on the T-1 NMR time scale, while some of the reactions of AlF30(aq) were fast, causing large line broadening. The ligand exchange appears to follow an associative interchange mechanism. The cis-trans isomerization of AlF2+(aq), consistent with octahedral geometry for that complex, is slowed sufficiently to be observed at temperatures around 270 R. Difference between the Al3+/F- system and the much studied Al3+/OH- system are briefly commented on.
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| 3. |
- Jalilehvand, F., et al.
(författare)
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New class of oligonuclear platinum-thallium compounds with a direct metal-metal bond. 5. Structure determination of heterodimetallic cyano complexes in aqueous solution by EXAFS and vibrational spectroscopy
- 2001
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 40:16, s. 3889-3899
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Tidskriftsartikel (refereegranskat)abstract
- The structures of three closely related heterodimetallic cyano complexes, [(NC)(5)Pt-Tl(CN)(n)](n-) (n = 1-3), formed in reactions between [Pt-II(CN)(4)](2-) and Tl-III cyano complexes, have been studied in aqueous solution. Multinuclear NMR data ((TI)-T-205, Pt-195, and C-13) were used for identification and quantitative analysis. X-ray absorption spectra were recorded at the Pt and TlLIII edges. The EXAFS data show, after developing a model describing the extensive multiple scattering within the linearly coordinated cyano ligands, short Pt-Tl bond distances in the [(NC)(5)Pt-Tl(CN)(n)](n-) complexes: 2.60(1), 2.62(1), and 2.64(1) Angstrom for n = 1-3, respectively. Thus, the Pt-Tl bond distance increases with increasing number of cyano ligands on the thallium atom. In all three complexes the thallium atom and five cyano ligands, with a mean Pt-C distance of 2.00-2.01 Angstrom, octahedrally coordinate the platinum atom. In the hydrated [(NC)(5)Pt-Tl(CN)(H2O)(4)](-) species the thallium atom coordinates one cyano ligand, probably as a linear Pt-TI-CN entity with a Tl-C bond distance of 2.13(1) Angstrom, and possibly four loosely bound water molecules with a mean Tl-O bond distance of about 2.51 Angstrom. In the [(NC)(5)Pt-Tl(CN)(2)](2-) species, the thallium atom probably coordinates the cyano ligands trigonally with two TI-C bond distances at 2.20(2) Angstrom, and in [(NC)(5)Pt-Tl(CN)(3)]Tl3- coordinates tetrahedrally with three TI-C distances at 2.22(2) Angstrom. EXAFS data were reevaluated for previously studied mononuclear thallium(III)-cyano complexes in aqueous solution, [Tl(CN)(2)(H2O)(4)](+), [Tl(CN)(3)(H2O)], and [Tl(CN)(4)](-), and also for the solid K[TI(CN)(4)] compound. A comparison shows that the TI-C bond distances are longer in the dinuclear complexes [(NC)(5)Pt-TI(CN)(n)](n-) (it = 1-3) for the same coordination number. Relative oxidation states of the metal atoms were estimated from their Pt-195 and (TI)-T-205 chemical shifts, confirming that the I(NC)5Pt-TI(CN),]n- complexes can be considered as metastable intermediates in a two-electron-transfer redox reaction from platinum(II) to thallium(III). Vibrational spectra were recorded and force constants from normal-coordinate analyses are used for discussing the delocalized bonding in these species.
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| 4. |
- Jalilehvand, F., et al.
(författare)
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Tl-Pt(CN)(5) in the solid state - A multimethod study of an unusual compound containing inorganic wires
- 2001
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Ingår i: Chemistry - A European Journal. - 0947-6539 .- 1521-3765. ; 7:10, s. 2167-2177
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Tidskriftsartikel (refereegranskat)abstract
- The crystal and molecular structure of a polycrystalline powder with a metal-metal bond and the composition TlPt(CN)(5) has been determined by combining results from X-ray powder diffraction (XRD), extended X-ray absorption fine structure (EXAFS) and vibrational spectroscopic studies. The XRD data gave the tetragonal space group P4/nmm (No. 129). with a = 7.647(3), c = 8.049(3) Angstrom, Z = 2, and well-determined positions of the heavy metal atoms. The Pt-Tl bond length in the compound is 2.627(2) Angstrom. The platinum atom coordinates four equivalent equatorial cyano ligands, with a fifth axial CN ligand and a thallium atom completing a distorted octahedral coordination geometry. The Tl-Pt(CN)(5) entities are linked together in linear -NC-Pt-Tl-NC-Pt-Tl chains through the axial cyano ligand. These linear wires are the essential structural features and influence the properties of the com-pound. A three-dimensional network is formed by the four equatorial cyano ligands of the platinum atom that form bridges to the thallium atoms of neighbouring antiparallel chains. The platinum atom and the five nitrogen atoms from the bridging cyano groups form a distorted octahedron around the thallium atom. EXAFS data were recorded at the Pt and Tl L-III edges for a more complete description of the local structure around the Pt and Tl atoms. The excessive multiple scattering was evaluated by means of the FEFF program. Raman and infrared absorption spectroscopy reveal strong coupling of the vibrational modes of the TlPt(CN)(5) entities, in particular the metal - metal stretching mode, which is split into four Raman and two IR bands. Factor group theory shows that a structural unit larger than the crystallographic unit cell must be used to assign vibrational bands. Intra- and intermolecular force constants have also been calculated. The compound exhibits red luminescence at 700+/- 3 nm in glycerol and has a corresponding excitation maximum at 240 nm. X-ray photoelectron spectra (XPS) show that the metal atoms have intermediate oxidation states, Pt3.2+ and Tl1.6+, between those in the parent Pt-II and Tl-III species and the decomposition products, Pt-IV and Tl-I. The solid compound TlPt(CN)(5) is stable to 520 degreesC. However in presence of water, a two-electron transfer between the metal atoms results in the cleavage of the metal-metal bond at 80 degreesC, forming a Pt-IV pentacyanohydrate complex and a monovalent thallium ion.
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| 5. |
- Nagy, P., et al.
(författare)
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Kinetics and mechanism of formation of the platinum-thallium bond : The (CN)(5)Pt-Tl(CN)(3) (3-) complex
- 2003
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 42:21, s. 6907-6914
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Tidskriftsartikel (refereegranskat)abstract
- Formation kinetics of the metal-metal bonded [(CN)(5)PtTl(CN)(3)](3-) complex from Pt(CN)(4)(2-) and Tl(CN)(4)(-) has been studied in the pH range-of 5-10, using standard mix-and-measure spectrophotometric technique at pH 5-8 and stopped-flow method at pH > 8. The overall order of the reaction, Pt(CN)(4)(2-) + Tl(CN)(4)(-) reversible arrow [(CN)(5)PtTl(CN)(3)](3-), is 2 in the slightly acidic region and 3 in the alkaline region, which means first order for the two reactants in both cases and also for CN- at high pH. The two-term rate law corresponds to two different pathways via the Tl(CN)(3) and Tl(CN)(4)(-) complexes in acidic and alkaline solution, respectively. The two complexes are in fast equilibrium, and their actual concentration ratio is controlled by the concentration of free cyanide ion. The following expression was derived for the pseudo-first-order rate constant of the overall reaction: k(obs) = (k(1)(a)[Tl(CN)(4)(-)] + (k(1)(a)/K-f))(1/(1 + K-p[H+]))[CN-](free) + k(1)(b) [Tl(CN)(4)(-)] + (k(1)(b)/K-f), where k(1)(a) and k(1)(b) are the forward rate constants for the alkaline and slightly acidic paths, K-f is the stability constant of [(CN)(5)PtTI(CN)(3)](3-), and K-p is the protonation constant of cyanide ion. k(1)(a) = 143 +/- 13 M-2 s(-1), k(1)(b) = 0.056 +/- 0.004 M-1 s(-1), K-f = 250 +/- 54 M-1, and log K-p = 9.15 +/- 0.05 (l = 1 M NaClO4, T = 298 K). Two possible mechanisms were postulated for the overall reaction in both pH regions, which include a metal-metal bond formation step and the coordination of the axial cyanide ion to the platinum center. The alternative mechanisms are different in the sequence of these steps.
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| 6. |
- Nagy, P., et al.
(författare)
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Kinetics and mechanism of platinum-thallium bond formation : The binuclear (CN)(5)Pt-Tl(CN) (-) and the trinuclear (CN)(5)Pt-Tl-Pt(CN)(5) (3-) complex
- 2004
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 43:17, s. 5216-5221
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Tidskriftsartikel (refereegranskat)abstract
- Formation kinetics of the metal-metal bonded binuclear [(CN)(5)Pt-TI(CN)](-) (1) and the trinuclear [(CN)(5)Pt-TI-Pt(CN)(5)](3-) (2) complexes is studied, using the standard mix-and-measure spectrophotometric method. The overall reactions are Pt(CN)(4)(2-) + TI(CN)(2)(+) z = 1 and Pt(CN)(4)(2-) + [(CN)(5)Pt-TI(CN)](-) = 2. The corresponding expressions for the pseudo-first-order rate constants are k(obs) = (k(1)[TI(CN)(2)(+)] + k(-1))[TI(CN)(2)(+)] (at TI(CN)(2)(+) excess) and k(obs) = (k(2b)[Pt(CN)(4)(2-)] + k(-2b))[HCN] (at Pt(CN)(4)(2-) excess), and the computed parameters are k(1) 1.04 +/-0.02 M-2 s(-1), k(-1) = k(1)/K-1 = 7 x 10(-5) M-1 s(-1) and k(2b) = 0.45 +/- 0.04 M-2 s(-1), K-2b = 26 +/- 6 M-1, k(-2b) = k(2b)/K-2b = 0.017 M-1 s(-1), respectively. Detailed kinetic models are proposed to rationalize the rate laws. Two important steps need to occur during the complex formation in both cases: (i) metal-metal bond formation and (ii) the coordination of the fifth cyanide to the platinum site in a nucleophilic addition. The main difference in the formation kinetics of the complexes is the nature of the cyanide donor in step ii. In the formation of [(CN)5Pt-TI(CN)]-, TI(CN)2+ is the source of the cyanide ligand, while HCN is the cyanide donating agent in the formation of the trinuclear species. The combination of the results with previous data predict the following reactivity order for the nucleophilic agents: CN- > TI(CN)(2)(+) > HCN.
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| 7. |
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| 8. |
- Ma, G. B., et al.
(författare)
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Equilibrium and structure of thallium(III)-ethylenediamine complexes in pyridine solution and in solid
- 2001
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Ingår i: Inorganica Chimica Acta. - 0020-1693 .- 1873-3255. ; 320:02-jan, s. 92-100
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Tidskriftsartikel (refereegranskat)abstract
- The formation of three [TI(en)(n)](3+) complexes (n = 1-3) in a pyridine solvent has been established by means of Tl-205 and H-1 NMR. Their stepwise stability constants based on concentrations, K-n = [Tl(en)(n)(3+)]/{[Tl(en)(n-1)(3+)](.)[en]}, at 298 K in 0.5 M NaClO4 ionic medium in pyridine, were calculated from Tl-205 NMR integrals: log K-1 = 7.6 +/- 0.7; log K-2 = 5.2 +/- 0.5 and log K-3 = 2.64 +/- 0.05. Linear correlation between both the Tl-205 NMR shifts and spin-spin coupling Tl-205-H-1 versus the stability constants has been found and discussed. A single crystal with the composition [Tl(en)(3)](ClO4)(3) was synthesized and its structure determined by X-ray diffraction. The Tl3+ ion is coordinated by three ethylenediamine ligands via six N-donor atoms in a distorted octahedral fashion.
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| 9. |
- Pettersson, Lage, et al.
(författare)
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17O NMR study of aqueous peroxoisopolymolybdate equilibria at lower peroxide/Mo ratios
- 2003
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; , s. 146-52
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Tidskriftsartikel (refereegranskat)abstract
- Aqueous peroxomolybdates have been studied using 17O NMR together with equilibrium measurements and calculations, over a wide range of conditions. Ten peroxo species are identified, mostly in more than one state of protonation. Some are already known in the solid state, or from equilibrium analysis, but structural information is also obtained for MoO3(HO2)– and the new or previously tentative species Mo2O5(O2)22–, HpMo7O23(O2)2p–6 and HpMo7O23(O2)p–6(p= 0–2). Sites of protonation are identified, as are 17O resonances from both bidentate and monodentate peroxide. Several oxygen exchange processes are also seen, including a probable dimer–tetramer exchange.
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| 10. |
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