| 1. |
- Jalilehvand, F., et al.
(author)
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Hydration of the calcium ion. An EXAFS, large-angle X-ray scattering, and molecular dynamics simulation study
- 2001
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 123:3, s. 431-441
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Journal article (peer-reviewed)abstract
- The structure of the hydrated calcium(II) ion in aqueous solution has been studied by means of extended X-ray absorption fine structure spectroscopy (EXAFS), large-angle X-ray scattering (LAXS), and molecular dynamics (MD) methods. The EXAFS data displayed a broad and asymmetric distribution of the Ca-O bond distances with the centroid at 2.46(2) Angstrom. LAXS studies on four aqueous calcium halide solutions (1.5-2 mol dm(-3)) gave a mean Ca-O bond distance of 2.46(1) Angstrom. This is consistent with a hydration number of 8 determined from correlations between mean distances and coordination numbers from crystal structures. The LAXS studies showed a second coordination sphere with a mean Ca . . .O-II distance of 4.58(5) Angstrom, and for the hydrated halide ions the distances Cl . . .O 3.25(1) Angstrom. Br . . .O 3.36(1) Angstrom, and I . .O 3.61(1) Angstrom were obtained. Molecular dynamics simulations of CaCl2(aq) were performed using three different Ca2+-OH2 pair potentials. The potential from the GROMOS program gave results in agreement with experiments, i.e., a coordination number of 8 and an average Ca-O distance of 2.46 Angstrom, and was used for further comparisons. Theoretical EXAFS oscillations were computed far individual Mn snapshots and showed very large variations, though the simulated average spectrum from 2000 snapshots gave satisfactory agreement with the experimental EXAFS spectra. The effect of thermal motions of the coordinated atoms is inherent in the MD simulation method. Thermal disorder parameters evaluated from simulated spatial atom distribution functions of the oxygen atoms coordinated to the calcium ion were in close agreement with those from the current LAXS and EXAFS analyses. The combined results are consistent with a root-mean-square displacement from the mean Ca-O distance of 0.09(2) Angstrom in aqueous solution at 300 K.
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| 2. |
- Jalilehvand, F., et al.
(author)
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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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In: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 40:16, s. 3889-3899
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Journal article (peer-reviewed)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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| 3. |
- Jalilehvand, F., et al.
(author)
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Structure studies of dimeric Pt-2(CN)(10) (4-) pentacyanoplatinum(III) and monomeric pentacyanoplatinum(IV) complexes by EXAFS, vibrational spectroscopy, and X-ray crystallography
- 2002
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In: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 106:14, s. 3501-3516
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Journal article (peer-reviewed)abstract
- The Structures of the dimeric bispentacyanoplatinate (III) (Pt-Pt) complex [Pt-2(CN)(10)](4-) and the pentacyanoplatinuni(IV) species [Pt(CN)(5)(OH)](2-), [Pt(CN)(5)(H2O)](-), and [Pt(CN)(5)I](2-) have been studied in aqueous solution by the EXAFS technique. A nonsupported Pt-Pt bond, 2.73(l) Angstrom, connects two Pt(CN)(5) entities in the dimer. Normal coordinate analyses have been made on the basis of the Raman spectra, and the force constants have been used for discussions of the bonding. The metal-metal stretching force constants for the [Pt-2(CN)(10)](4-) Complex, the [(NC)(5)Pt-TI(CN)(n)](n-) (n = 1, 2, and 3) complexes, and some other dimetallic complexes have been correlated with the metal-metal bond distances. In the [Pt(CN)(5)X](n-) complexes, the mean Pt-C bond distance of the pentacyanoplatinum group was found to increase, and the corresponding Pt-C force constants were found to decrease, with increasing donor ability of the ligand X in the order X = H2O, OH, I, and Pt(CN)(5). The crystal structures of the compounds Tl-2[Pt(CN)(5)(OH)] and K-2[Pt(CN)(5)I].0.6H(2)O were determined by single-crystal X-ray diffraction techniques and used for comparisons with the EXAFS models. The Pt-I bond distance of the [Pt(CN)(5)I](2)- complex is 2.676(2) Angstrom in the crystal structure and 2.66(1) Angstrom in solution by EXAFS. A method is described for estimating the force constant for the metal-metal bond stretch in dimetallic complexes with heavy metal atoms, based on the use of an effective spectroscopic mass of the metal atoms in a diatomic model. The 18-electron rule is found to be useful for rationalizing the structures of the metal-metal bonded cyano complexes and a guideline in searching for metal cyano complexes analogous to those currently described.
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| 4. |
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| 5. |
- Jalilehvand, F., et al.
(author)
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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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In: Chemistry - A European Journal. - 0947-6539 .- 1521-3765. ; 7:10, s. 2167-2177
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Journal article (peer-reviewed)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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| 6. |
- Kocsis, L., et al.
(author)
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Vibrational spectroscopic study of the hydrated platinum(II), palladium(II) and cis-diammineplatinum(II) ions in acidic aqueous solutions
- 2009
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In: Journal of Raman Spectroscopy. - : Wiley. - 0377-0486 .- 1097-4555. ; 40:5, s. 481-490
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Journal article (peer-reviewed)abstract
- Mid infrared, far-infrared and Raman spectroscopic studies, combined with force field analyses, were performed for the 1 hydrated platinum(II) and palladium(II) ions and cis-diammineplatinum(II) complex in acidic aqueous solutions. Simplified Density Functional Theory (DFT) calculations were made for the equatorial plane of the platinum complexes. Careful subtraction of solvent spectra allowed a number of 'internal' modes of coordinated H2O and NH3 to be determined as weak residual bands. The [Pt(OH2)(6)](2+) and [cis-Pt(NH3)(2)(OH2)(4)](2+) complexes were found to be six-coordinated with four ligands strongly bound in an equatorial plane. The assignments of the vibrational modes in the equatorial plane could be performed on the basis of the experimental observations and by comparison with metal-ligand vibrations of square-planar complexes, aided by normal coordinate calculations. For the weakly coordinated axial aqua ligands, the low wavenumber range and the polarizibility properties allowed the assignments of the bands at about 365 and 325 cm(-1) to the stretching modes of one short and one longer Pt - O* bound to axial aqua ligands, respectively. A similar picture with even less strongly bound axial water molecules emerges from Raman spectroscopy data for the hydrated palladium(II) ion, [Pd(OH2)(6)](2+). The results are consistent with a description of the [Pt(OH2)(6)](2+) and [Pd(OH2)(6)](2+) aqua ions in C-4v symmetry, and with the [cis-Pt(NH3)(2)(OH2)(4)](2+) complex in the Cs point group, and also in qualitative agreement with the structures devised from previous extended X-ray absorption fine structure (EXAFS) measurements.
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| 7. |
- Ma, G. B., et al.
(author)
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Structure of the dimethyl sulfoxide solvated thallium(III) ion in solution and in the solid state
- 2001
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In: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 40:25, s. 6432-6438
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Journal article (peer-reviewed)abstract
- The structure and vibrational spectra of the dimethyl sulfoxide solvated thallium(III) ion have been studied in a dimethyl sulfoxide solution and in the solid state. X-ray crystallography shows a trigonal unit cell, space group R (3) over bar (No. 148), for the [TI(dmso)(6)](ClO4)(3) Compound with Z = 3, a = b = 11.9764(13) [11.8995(9)] Angstrom, c = 20.802(2) [20.467(2)] Angstrom, and V = 2584.0(5) [2509.9(4)] Angstrom (3) at 295 [150] K. The crystal structure comprises a highly symmetric hexakis(dimethyl sulfoxide)thallium(III) ion, with thallium in a 3 symmetry site and a TI-O bond distance of 2.224(3) Angstrom at 295 K. The octahedral TlO6 kernel is compressed along the threefold axis with an O-Tl-O bond angle of 96.20(11)degrees. The Tl-O-S bond angle of 120.7(2)degrees corresponds to a Tl . . .S distance of 3.292(2) Angstrom. One perchlorate ion centered on the (3) over bar axis was described by a statistically disordered model. A low-temperature EXAFS study (10 K) resulted in the TI-O and Tl . . .S distances of 2.221(4) and 3.282(6) Angstrom, respectively, consistent with a Tl-O-S bond angle of 120(1)degrees. The low Debye-Waller factors confirm a regular coordination without the disorder of the dimethyl sulfoxide ligands, which would have resulted from the alternative choice of space group R3 for the crystal structure. Raman and infrared spectra have been recorded and assigned, with the bands at 435 and 447 cm(-1) corresponding to the vibrational frequency of the symmetric and asymmetric TI-O stretching modes, respectively. EXAFS data of a 0.5 mol dm(-3) thallium(III) trifluoromethanesulfonate in a dimethyl sulfoxide solution were consistent with that of a hexasolvated ion with mean Tl-O and Tl . . .S distances of 2.22(1) and 3.33(2) Angstrom, respectively, which correspond to a mean Tl-O-S bond angle of 124(2)degrees. The anomalously large disorder parameter for the TI-O distances is consistent with a weal, pseudo-Jahn-Teller effect. The Tl-205, C-13, and H-1 NMR spectra of the complex in solution show single signals at 1886, 39.5, and 2.3 ppm, respectively.
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| 8. |
- Sandstrom, M., et al.
(author)
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Hydration of some large and highly charged metal ions
- 2001
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In: Journal of Synchrotron Radiation. - 0909-0495 .- 1600-5775. ; 8, s. 657-659
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Journal article (peer-reviewed)abstract
- EXAFS studies of metal ions with hydration numbers higher than six in aqueous solution, often show asymmetric distribution of the metal-oxygen bond distances. The hydration number can be determined from a correlation with the bond distance. The mean Ca-O distance 2.46(1) Angstrom shows the calcium( II) ion to be eight-hydrated in a wide asymmetric distribution. Theoretically calculated EXAFS oscillations for individual snapshots from an MD simulation show large variations. The scandium( III) ion is surrounded by two groups of about eight water molecules, with the mean Sc-O distance 2.185(6) Angstrom. The yttrium( III) ion coordinates eight waters in an asymmetric distribution at 2.368(5) Angstrom, and the lanthanum( III) ion 6 + 3 water molecules at 2.52(2) and 2.65(3) Angstrom, respectively. For the the uranium( IV) and thorium(IV) ions, the M-O distances 2.42(1) and 2.45(1) Angstrom, respectively, indicate hydration numbers close to 10.
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| 9. |
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| 10. |
- Spangberg, D., et al.
(author)
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Model extended X-ray absorption fine structure (EXAFS) spectra from molecular dynamics data for Ca2+ and Al3+ aqueous solutions
- 2000
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 104:45, s. 10467-10472
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Journal article (peer-reviewed)abstract
- Theoretical extended X-ray absorption fine structure (EXAFS) spectra have been computed from molecular dynamics (MD) simulation data. Based on MD-generated molecular geometries, EXAFS spectra were generated with the FEFF6 program, commonly used in the analysis of experimental EXAFS spectra. The effects of multiple scattering and second-shell neighbors on the theoretical spectra were evaluated for CaCl2(aq) and AlCl3(aq), i.e., for two solutions with very different cation hydration structures. The effects are significantly larger for the more structured Al3+ solution, The theoretical Ca2+(aq) spectra are compared with new experimental EXAFS data.
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