Cobalt(III) Metallacryptates and Their Guest Cation-Exchange in Solution Monitored by 59Co NMR.

One-pot reactions of the catechol-scaffolding aroylbis(N,N-diethylthiourea) H2Lcat with mixtures of CoCl2 and MCl (M+ = Cs+, Rb+, K+, Tl+, or NH4+) or with a Co(NO3)2/TlNO3 mixture lead to the self-assembly of a series of cationic Co(III) metallacryptates of the general formula [M ⊂ {Co2(Lcat)3}]+ (M+ = Cs+, Rb+, K+, Tl+, or NH4+). Crystalline PF6- salts were obtained after workup with (n-Bu4N)(PF6), and the single-crystal structures of all five metallacryptates have been determined. Depending on the nature of the guest cations, the directional interactions between guest cations and the metallacryptand {Co2(Lcat)3} are either weak coordination contacts or hydrogen bonds. The bonding mode and the size of the guest ions slightly influence the molecular skeleton of the host molecule. These small structural variations also exist in solution and could be detected by means of 59Co NMR spectroscopy, which is shown to be a unique tool for an easy characterization of such compounds. 59Co NMR chemical shifts are extraordinarily sensitive to the guest cation in the metallacryptates, and time-arrayed 59Co NMR experiments show that cation-exchange processes in biphasic organic/aqueous systems can be studied in detail. This leads to insights into the relative rates of cation exchange, as well as the relative conditional distribution coefficients of such Co(III) metallacryptates between the aqueous and organic phases. Thus, the extent and the relative rate of the NH4+ ion exchange in [NH4 ⊂ {Co2(Lcat)3}](PF6) by Cs+ and K+ ions across the organic/aqueous phase boundary at room temperature have been studied by in situ 59Co NMR experiments. Preliminary 59Co NMR experiments show that the K+ ion in [K ⊂ {Co2(Lcat)3}](PF6) can be removed by its competitive complexation with the highly potassium-selective [2.2.2]cryptand, to give a transient 59Co NMR signal of the relatively unstable "empty" {Co2(Lcat)3} complex, which slowly decomposes in solution.

Reversible photo-isomerization of cis-[Pd(L-κS,O)2] (HL = N,N-diethyl-N'-1-naphthoylthiourea) to trans-[Pd(L-κS,O)2] and the unprecedented formation of trans-[Pd(L-κS,N)2] in solution.

Upon ex situ UV-visible light irradiation, complex cis-bis(N,N-diethyl-N'-naphthoylthioureato)-palladium(ii), cis-[Pd(L-κS,O)2], undergoes isomerization in acetonitrile-d3 and chloroform-d to yield trans-[Pd(L-κS,O)2] which then rearranges thermally to novel trans-[Pd(L-κS,N)2] prior to reverting thermally to the cis isomer in the absence of light. The thermal isomerization rate is highly solvent dependent and harnessed to enable each of these three geometric isomers to be isolated and characterized by 1H NMR spectroscopy, X-ray crystallography, melting point and thermal analysis. The formation of the trans-[Pd(L-κS,N)2] isomer as part of this isomerization has only been observed with the sterically demanding cis-bis(N,N-diethyl-N'-(naphthoylthioureato)palladium(ii) precursor based on our knowledge to date. In situ irradiation with monochromatic laser light (λ = 355 nm) coupled to 1H NMR spectroscopy of solutions of cis-[Pd(L-κS,O)2] in acetonitrile-d3 supports the ex situ photo-induced isomerization experiments.

195Pt NMR and Molecular Dynamics Simulation Study of the Solvation of [PtCl6]2- in Water-Methanol and Water-Dimethoxyethane Binary Mixtures.

The experimental 195Pt NMR chemical shift, δ(195Pt), of the [PtCl6]2- anion dissolved in binary mixtures of water and a fully miscible organic solvent is extremely sensitive to the composition of the mixture at room temperature. Significantly nonlinear δ(195Pt) trends as a function of solvent composition are observed in mixtures of water-methanol, or ethylene glycol, 2-methoxyethanol, and 1,2-dimethoxyethane (DME). The extent of the deviation from linearity of the δ(195Pt) trend depends strongly on the nature of the organic component in these solutions, which broadly suggests preferential solvation of the [PtCl6]2- anion by the organic molecule. This simplistic interpretation is based on an accepted view pertaining to monovalent cations in similar binary solvent mixtures. To elucidate these phenomena in detail, classical molecular dynamics computer simulations were performed for [PtCl6]2- in water-methanol and water-DME mixtures using the anionic charge scaling approach to account for the effect of electronic dielectric screening. Our simulations suggest that the simplistic model of preferential solvation of [PtCl6]2- by the organic component as inferred from nonlinear δ(195Pt) trends is not entirely accurate, particularly for water-DME mixtures. The δ(195Pt) trend in these mixtures levels off for high DME mole fractions, which results from apparent preferential location of [PtCl6]2- anions at the borders of water-rich regions or clusters within these inherently micro-heterogeneous mixtures. By contrast in water-methanol mixtures, apparently less pronounced mixed solvent micro-heterogeneity is found, suggesting the experimental δ(195Pt) trend is consistent with a more moderate preferential solvation of [PtCl6]2- anions. This finding underlines the important role of solvent-solvent interactions and micro-heterogeneity in determining the solvation environment of [PtCl6]2- anions in binary solvent mixtures, probed by highly sensitive 195Pt NMR. The notion that preferential solvation of [PtCl6]2- results primarily from competing ion-solvent interactions as generally assumed for monatomic ions, may not be appropriate in general.

Intrinsic 37/35Cl and 18/16O isotope shifts in 195Pt and 103Rh NMR of purely inorganic Pt and Rh complexes as unique spectroscopic fingerprints for unambiguous assignment of structure.

Well-resolved intrinsic 1ΔM(37/35Cl) and 1ΔM(18/16O) isotope shifts (where M = 195Pt or 103Rh) are visible in the 195Pt NMR peak profiles of relatively kinetically inert [PtCln(H2O)6-n]4-n (n = 1-6) complexes, their corresponding hydroxido [PtCl6-n(OH)n]2- (n = 1-5/6) anions, and [RhCln(H2O)6-n]3-n (n = 3-6) complexes in aqueous solutions at ca. 293 K. Although some such isotope effects have been previously reported, there are very limited published data in the open literature, and the first systematic studies of such intrinsic 1ΔM(37/35Cl) and 1ΔM(18/16O) isotope effects are reviewed in this perspective. In high magnetic-field NMR spectrometers, the 195Pt and 103Rh NMR peak profiles acquired within a relatively narrow temperature range (288-300 K) constitute unique 'spectroscopic fingerprints', which allow unambiguous structural assignment in solution. Available data for Pt(iv) and Rh(iii) complexes give rise to intrinsic isotope 1Δδ195Pt/103Rh(37/35Cl) profiles, which are extraordinarily sensitive to the structure of a particular complex or its geometric isomer. The profiles of aquated Pt(iv) and Rh(iii) complexes in acidic solutions may be resolved at either an isotopologue level only or at both an isotopologue and an isotopomer level depending on the structure. By contrast, in the series of [PtCl6-n(OH)n]2- (n = 1-6) anions, 1Δδ195Pt(37/35Cl) isotope shifts are resolved only at an isotopologue level. Relatively larger 1Δ195Pt(18/16O) isotope shifts obtained by the partial 18O enrichment of both the [PtCln(H2O)6-n]4-n (n = 1-6) and [PtCl6-n(OH)n]2- (n = 1-6) series give rise to remarkable 195Pt NMR peak profiles showing both 37/35Cl and 18/16O shifts. In the [PtCl6-n(OH)n]2- (n = 1-5/6) anions a typical NMR peak profile spanning ∼2 ppm only may be resolved at both the isotopologue and isotopomer levels, depending on whether 18/16OH- ions are coordinated trans to chloride ions or not. The potential utility of such 1Δ195Pt(37/35Cl) and 1Δ195Pt(18/16O) isotope shifts in selected practical applications involving such complexes is briefly illustrated.

A DFT study to unravel the ligand exchange kinetics and thermodynamics of Os(VIII) oxo/hydroxido/aqua complexes in aqueous matrices.

The Os(VIII) oxo/hydroxido complexes that are abundant in mild to relatively concentrated basic aqueous solutions are Os(VIII)O4, [Os(VIII)O4(OH)](-) and two cis-[Os(VIII)O4(OH)2](2-) species. Os(VIII) complexes that contain water ligands are thermodynamically unfavoured w.r.t. the abovementioned species. Os(VIII)O4 reacts with hydroxide in two, consecutive, elementary coordination sphere expansion steps to form the [Os(VIII)O4(OH)](-) complex and then the cis-[Os(VIII)O4(OH)2](2-) species. The Gibbs energy of activation for both reactions, in the forward and reverse direction, are in the range of 6-12 kcal mol(-1) and are relatively close to diffusion-controlled. The thermodynamic driving force of the first reaction is the bonding energy of the Os(VIII)-OH metal-hydroxido ligand, while of the second reaction it is the relatively large hydration energy of the doubly-charged cis-[Os(VIII)O4(OH)2](2-) product compared to the singly-charged reactants. The DFT-calculated (PBE-D3 functional) in the simulated aqueous phase (COSMO) is -2.4 kcal mol(-1) for the first reaction and -0.6 kcal mol(-1) for the second reaction and agree to within 1 kcal mol(-1) with reported experimental values, at -2.7 and 0.3 kcal mol(-1) respectively. From QTAIM and EDA analyses it is deduced that the Os(VIII)[double bond, length as m-dash]O bonding interactions are ionic (closed-shell) and that Os(VIII)-OH bonding interactions are polar covalent (dative). In contrast to QTAIM, NCI analysis allowed for the identification of relatively weak intramolecular hydrogen bonding interactions between neighbouring oxo and hydroxido ligands in both [Os(VIII)O4(OH)](-) and cis-[Os(VIII)O4(OH)2](2-) complexes.

Isotope effects in (195)Pt NMR spectroscopy: unique (35/37)Cl- and (16/18)O-resolved "fingerprints" for all [PtCl6-n(OH)n](2-) (n = 1-5) anions in an alkaline solution and the implications of the trans influence.

A detailed analysis of the intrinsic (1)Δ(195)Pt((37/35)Cl) and (1)Δ(195)Pt((18/16)O) isotope 128.8 MHz (195)Pt NMR profiles of the series of kinetically inert [PtCl6-n(OH)n](2-) (n = 1-5) anions generated in strongly alkaline aqueous solutions shows that each (195)Pt NMR resonance of the [Pt(35/37)Cl6-n((16/18)OH)n](2-) (n = 1-5) anions is resolved only into [(6 - n) + 1 for n = 1-5] (35/37)Cl isotopologues at 293 K. Evidently, the greater trans influence of the hydroxido ligand in the order OH(-) > Cl(-) > H2O in [PtCl6-n(OH)n](2-) (n = 1-5) complexes results in somewhat longer Pt-Cl bond displacements trans to the hydroxido ligands, resulting in the absence of isotopomer effects in the [PtCl6-n(OH)n](2-) (n = 1-5) anions in contrast to that observed in the corresponding [PtCl6-n(H2O)n]((2-n)-) (n = 1-5) complexes. In suitably (18)O-enriched sodium hydroxide solutions, additional intrinsic (1)Δ(195)Pt((18/16)O) isotope effects are remarkably well-resolved into unique isotopologue- and isotopomer-based (195)Pt NMR profiles, ascribable to the higher trans influence of the OH(-) ligand. The consequent significantly shorter Pt-OH bonds in these anions emphasize (16/18)O isotopomer effects in the (195)Pt NMR peaks of [Pt(35/37)Cl6-n((16/18)OH)n](2-) (n = 1-5) for magnetically nonequivalent (16/18)OH isotopomers statistically possible in some isotopologues. These (195)Pt NMR profiles constitute unique NMR "fingerprints", useful for the unambiguous assignment of the series of [PtCl6-n(OH)n](2-) anions including their possible cis/trans/fac/mer stereoisomers in such solutions, without a need for accurate chemical shift measurements.

Speciation of [Pt(IV) Cl6-n Brn]2- (n = 0-6) and some of their mono-aquated [Pt(IV) Cl5-n Brn (H2O)]- (n = 0-5) anions in solution at low concentrations by means of ion-pairing reversed-phase ultra-high-performance liquid chromatography coupled to electrospray ionization quadrupole time-of-flight mass spectrometry.

RATIONALE: The speciation of the purely inorganic [PtCl6-n Brn](2-) (n = 0-6) anions and their corresponding mono-aquated [PtCl5-n Brn (H2O)](-) (n = 0-5) anions is of considerable importance to the precious metal refining and recycling industry, to ensure optimum recovery and separation efficiencies. Speciation of platinum complexes present in precursor solutions used for the preparation of precious metal nano-crystals of defined size and morphology appears also to be important. The various possible Pt(IV) complex anions in dilute aqueous can be characterized using ion-pairing reversed-phase high-performance liquid chromatography coupled to electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-Q-TOFMS). METHODS: Ion-pairing reversed-phase ultra-high-performance LC separation of the Pt(IV) complex anions present in aqueous solutions prior to detection by means of high-resolution ESI-Q-TOFMS using a low ESI source cone voltage (5 V) allows for the clear identification of all the platinum complexes from the characteristic pattern of fragment ions (m/z), presumably generated by 'reductive conversion' in the ESI source of the mass spectrometer. Sufficient chromatographic resolution for the series of Pt(IV) complexes is achieved using the (n-butyl)3 NH(+) ion generated in a formic acid/water/methanol (pH ~3.5) mobile phase. This mobile phase composition facilitates a low-background for optimal ESI-Q-TOFMS detection with enhanced sensitivity. RESULTS: Direct-infusion mass spectrometry of the inorganic platinum complexes in aqueous solution is impractical due to their low volatility, but more importantly as a result of the very extensive series of fragment ions generated in the ESI source, which leads to virtually uninterpretable mass spectra. However, with prior separation, and by using low ESI cone voltages (5 V), the mass spectra of the separated analyte ions show simpler and systematic fragmentation patterns [Pt(IV) X5](-) → [Pt(III) X4 ](-) → [Pt(II) X3](-) → [Pt(I)X2 ](-) (X = Cl(-) and Br(-)), resulting in clear assignments. This methodology facilitates the characterization of the partially aquated [PtCl5-n Brn (H2O)](-) (n = 0-5) anions derived from the homo- and heteroleptic [PtCl6-n Brn](2-) (n = 0-6) anions, in equilibrated solutions at low concentrations. CONCLUSIONS: Speciation of homo- and heteroleptic [PtCl6-n Brn](2-) (n = 0-6) anions, together with some of their partially aquated [PtCl5-n Brn (H2O)](-) (n = 0-5) species in dilute solution, can successfully be carried out by means of prior ion-pairing reversed-phase LC separation coupled to high-resolution ESI-Q-TOFMS at low ESI cone-voltage settings.

Mechanism of tetrachloroplatinate(II) oxidation by hydrogen peroxide in hydrochloric acid solution.

Oxidation of tetrachloroplatinate(II) by hydrogen peroxide in hydrochloric acid was studied by UV-Vis spectrophotometry. Oxidation takes place via two parallel reactions with hypochlorous acid and hydrogen peroxide, respectively, according to the overall rate law d[Pt(IV)]/dt = (k(0) + k(H2O2)[Pt(II)])[H2O2]. For oxidation of [PtCl4](2-) at relatively low concentrations, [PtCl4](2-) ≪ 0.5 mM, hypochlorous acid formation is fast relative to the oxidation of [PtCl4](2-) by hydrogen peroxide, as a result of the rate determining reaction H2O2 + H(+) + Cl(-) → HOCl + H2O, resulting in a rate law d[Pt(IV)]/dt = k(0)[H2O2] with a value k(0) = (8 ± 2) × 10(-7) s(-1) at 35 °C. For concentrations of [PtCl4](2-) > 0.5 mM, oxidation by hydrogen peroxide becomes dominant, resulting in the pseudo-first order rate law d[Pt(IV)]/dt = k(H2O2)[Pt(II)][H2O2] with the value k(H2O2) = (1.5 ± 0.1) × 10(-2) M(-1) s(-1) at 35 °C. The final oxidation product is a mixture of [PtCl5(H2O)](-) and [PtCl6](2-), with [PtCl6](2-) formed as a result of [PtCl4](2-) assisted chloride anation reactions.

Probing isotope shifts in 103Rh and 195Pt NMR spectra with density functional theory.

Zero-point vibrationally averaged (rg(0)) structures were computed at the PBE0/SDD/6-31G* level for the [Pt(35)Cln(37)Cl5-n(H2(18)O)](-) (n = 0-5), cis-Pt(35)Cln(37)Cl4-n(H2(18)O)(H2(16)O) (n = 0-4), fac-[Pt(35)Cln(37)Cl3-n(H2(18)O)(H2(16)O)2](+) (n = 0-3), [Pt(35)Cln(37)Cl5-n((16/18)OH)](2-) (n = 0-5), cis-[Pt(35)Cln(37)Cl4-n((16/18)OH)2](2-) (n = 0-4), fac-[Pt(35)Cln(37)Cl3-n((16/18)OH)3](2-) (n = 0-3), cis-[Pt(35)Cln(37)Cl2-n((16/18)OH)4](2-) (n = 0-2), [Pt(35)Cln(37)Cl1-n((16/18)OH)5](2-) (n = 0-1), [Rh(35)Cln(37)Cl5-n(H2O)](2-) (n = 0-5), cis-[Rh(35)Cln(37)Cl4-n(H2O)2](-) (n = 0-4), and fac-Rh(35)Cln(37)Cl3-n(H2O)3 (n = 0-3) isotopologues and isotopomers. Magnetic shielding constants, computed at the ZORA-SO/PW91/QZ4P/TZ2P level, were used to evaluate the corresponding (35/37)Cl isotope shifts on the (195)Pt and (103)Rh NMR spectra, which are known experimentally. While the observed effects are reproduced reasonably well computationally in terms of qualitative trends and the overall order of magnitude (ca. 1 ppm), quantitative agreement with experiment is not yet achieved. Only small changes in M-Cl and M-O bonds upon isotopic substitution, on the order of femtometers, are necessary to produce the observed isotope shifts.

Cation-π induced aggregation of water-soluble [Pt(II)(diimine)(L(n)-S,O)]+ complexes studied by 1H DOSY NMR and TEM: from 'dimer aggregates' in acetonitrile to nano-aggregates ('metallogels') in water.

(1)H NMR chemical shift concentration dependence as well as the diffusion coefficients from DOSY NMR of mixed ligand [Pt(II)(1,10-phenanthroline)(N-pyrrolidyl-N-(2,2-dimethylpropanoyl)thiourea)]Cl ([Pt(II)(phen)(L(1)-S,O)]Cl) dissolved in mixtures of acetonitrile-water in the range 0-30% (v/v) D(2)O-CD(3)CN shows that the complex cation (M(+) = [Pt(II)(phen)(L(1)-S,O)](+)) aggregates to form dimers, 2M(+) ⇌ {M(+)}(2), with association constants ranging from K(D)(CD(3)CN) = 17 ± 2 M(-1) to K(D)(30% (v/v) D(2)O-CD(3)CN) = 71 ± 8 M(-1) at 299.3 K, presumably via non-covalent cation-π interactions. Experimental data are consistent with an 'offset' face-to-face cation-π stacking arrangement of the planar cation. However in water-rich solvent mixtures from >30% (v/v) D(2)O-CD(3)CN to pure D(2)O, the extent of aggregation significantly increases until a critical aggregation concentration (CAC) is reached, estimated to be 9.6 and 10.3 mM from (1)H NMR chemical shift concentration dependence and DOSY NMR measurements respectively. Above the CAC the formation of nano-structures formulated as {[Pt(II)(phen)(L(1)-S,O)](+)}(n)Cl(-)(y) (n, y > 2) is indicated. DOSY studies show a significant decrease of the average diffusion coefficient D(obs) as a function of increasing concentration of [Pt(II)(phen)(L(1)-S,O)]Cl in D(2)O. The aggregation number (N) estimated from hydrodynamic volumes of the mononuclear [Pt(II)(phen)(L(1)-S,O)](+) cation (V(H)(0)), and those V(H) estimated from D(obs) (N = V(H)/V(H)(0)) as a function of total complex concentration, ranges from ~2 to ~735 in pure D(2)O. Above the CAC well defined nano-structures which may be loosely termed "metallogels" could be characterized by means of transmission electron microscopy. As expected the addition of NaCl appears to increase the extent of aggregate formation, by presumably stabilizing the formation of nano-sized {[Pt(II)(phen)(L(1)-S,O)](+)}(n)Cl(-)(y) aggregates preventing excessive positive electrostatic charge build-up.

(35/37)Cl and (16/18)O isotope resolved 195Pt NMR: unique spectroscopic 'fingerprints' for unambiguous speciation of [PtCl(n)(H2O)(6-n)](4-n) (n = 2-5) complexes in an acidic aqueous solution.

At high magnetic fields the 128.8 MHz (195)Pt NMR of all the species in the series [PtCl(n)(H(2)O)(6-n)](4-n) (n = 2-6) display unique (35/37)Cl isotope effects resulting in a unique 'fine-structure' of each individual resonance, which constitutes an unambiguous spectroscopic 'fingerprint' characteristic of the structure of the octahedral platinum(IV) complex, provided (195)Pt NMR are recorded at optimum magnetic field homogeneity and carefully controlled temperature (293 ± 0.1 K). The detailed (195)Pt resonance fine-structure observed experimentally can readily be accounted for by an isotopologue and isotopomer model for each complex, showing particularly noticeable differences between stereoisomer pairs such as the cis/trans- and fac/mer-complexes. Moreover partial isotopic (18)O enrichment of the coordinated water molecules in the series [Pt(35/37)Cl(n)(H(2)(16/18)O)(6-n)](n-2) (n = 2-6) confirms this model. This technique can thus be considered a novel, direct spectroscopic method of chemical speciation of appropriate platinum(IV) complexes in solution without reference to accurate chemical shifts of authentic members of such a series. These effects are interpreted qualitatively in terms of the high sensitivity of (195)Pt NMR shielding to very small and subtle Pt-(35/37)Cl and Pt-(16/18)OH(2) bond displacements. Preliminary work shows this also applied to the corresponding bromido-complexes.

35Cl/37Cl isotope effects in 103Rh NMR of [RhCl(n)(H2O)(6-n)](3-n) complex anions in hydrochloric acid solution as a unique 'NMR finger-print' for unambiguous speciation.

A detailed analysis of the (35)Cl/(37)Cl isotope effects observed in the 19.11 MHz (103)Rh NMR resonances of [RhCl(n)(H(2)O)(6-n)](3-n) complexes (n=3-6) in acidic solution at 292.1K, shows that the 'fine structure' of each (103)Rh resonance can be understood in terms of the unique isotopologue and in certain instances the isotopomer distribution in each complex. These (35)Cl/(37)Cl isotope effects in the (103)Rh NMR resonance of the [Rh(35/37)Cl(6)](3-) species manifest only as a result of the statistically expected (35)Cl/(37)Cl isotopologues, whereas for the aquated species such as for example [Rh(35/37)Cl(5)(H(2)O)](2-), cis-[Rh(35/37)Cl(4)(H(2)O)(2)](-) as well as the mer-[Rh(35/37)Cl(3)(H(2)O)(3)] complexes, additional fine-structure due to the various possible isotopomers within each class of isotopologues, is visible. Of interest is the possibility of the direct identification of stereoisomers cis-[RhCl(4)(H(2)O)(2)](-), trans-[RhCl(4)(H(2)O)(2)](-), fac-[RhCl(3)(H(2)O)(3)] and mer-[RhCl(3)(H(2)O)(3)] based on the (103)Rh NMR line shape, other than on the basis of their very similar δ((103)Rh) chemical shift. The (103)Rh NMR resonance structure thus serves as a novel and unique 'NMR-fingerprint' leading to the unambiguous assignment of [RhCl(n)(H(2)O)(6-n)](3-n) complexes (n=3-6), without reliance on accurate δ((103)Rh) chemical shifts.

On the Origin of (35/37)Cl Isotope Effects on (195)Pt NMR Chemical Shifts. A Density Functional Study.

Zero-point vibrationally averaged (rg(0)) structures were computed at the PBE0/SDD/6-31G* level for [Pt(35)Cl6](2-) and [Pt(37)Cl6](2-), for the [Pt(35)Cln(37)Cl5-n(H2O)](-) (n = 0-5), cis-Pt(35)Cln(37)Cl(4-n)(H2O)2 (n = 0-4), and fac-[Pt(35)Cln(37)Cl(3-n)(H2O)3](+) (n = 0-3) isotopologues and isotopomers. Magnetic (195)Pt shielding constants, computed at the ZORA-SO/PW91/QZ4P/TZ2P level, were used to evaluate the corresponding (35/37)Cl isotope shifts in the experimental (195)Pt NMR spectra. While the observed effects are reproduced reasonably well computationally in terms of qualitative trends and the overall order of magnitude (ca. 1 ppm), quantitative agreement with experiment is not yet achieved. Only small changes in Pt-Cl and Pt-O bond lengths upon isotopic substitution, on the order of femtometers, are necessary to produce the observed isotope shifts.

A robust method for speciation, separation and photometric characterization of all [PtCl(6-n)Br(n)]2- (n=0-6) and [PtCl(4-n)Br(n)]2- (n=0-4) complex anions by means of ion-pairing RP-HPLC coupled to ICP-MS/OES, validated by high resolution 195Pt NMR spectroscopy.

A robust reversed phase ion-pairing RP-HPLC method has been developed for the unambiguous speciation and quantification of all possible homoleptic and heteroleptic octahedral platinum(IV) [PtCl(6-n)Br(n)](2-) (n=0-6) as well as the corresponding platinum(II) [PtCl(4-n)Br(n)](2-) (n=0-4) complex anions using UV/Vis detection. High resolution (195)Pt NMR in more concentrated solutions of these Pt(II/IV) complexes (≥50 mM) served to validate the chromatographic peak assignments, particularly in the case of the possible stereoisomers of Pt(II/IV) complex anions. By means of IP-RP-HPLC coupled to ICP-MS or ICP-OES it is possible to accurately determine the relative concentrations of all possible Pt(II/IV) species in these solutions, which allows for the accurate determination of the photometric characteristics (λ(max) and ɛ) of all the species in this series, by recording of the UV/Vis absorption spectra of all eluted species, using photo-diode array, and quantification with ICP-MS or ICP-OES. With this method it is readily possible to separate and estimate the concentrations of the various stereoisomers which are present in these solutions at sub-millimolar concentrations, such as cis- and trans-[PtCl(4)Br(2)](2-), fac- and mer-[PtCl(3)Br(3)](2-) and cis- and trans-[PtCl(2)Br(4)](2-) for Pt(IV), and cis- and trans-[PtCl(2)Br(2)](2-) in the case of Pt(II). All mixed halide Pt(II) and Pt(IV) species can be separated and quantified in a single IP-RP-HPLC experiment, using the newly obtained photometric molar absorptivities, ɛ, determined herein at given wavelengths.

A kinetic and thermodynamic study of the unexpected comproportionation reaction between cis-[Os(VIII)O4(OH)2](2-) and trans-[Os(VI)O2(OH)4](2-) to form a postulated [Os(VII)O3(OH)3](2-) complex anion.

A kinetic study of [OsO(4)] reduction by aliphatic alcohols (MeOH and EtOH) was performed in a 2.0 M NaOH matrix at 298.1 K. The rate model that best fitted the UV-VIS data supports a one-step, two electron reduction of Os(VIII) (present as both the [Os(VIII)O(4)(OH)](-) and cis-[Os(VIII)O(4)(OH)(2)](2-) species in a ratio of 0.34:0.66) to form the trans-[Os(VI)O(2)(OH)(4)](2-) species. The formed trans-[Os(VI)O(2)(OH)(4)](2-) species subsequently reacts relatively rapidly with the cis-[Os(VIII)O(4)(OH)(2)](2-) complex anion to form a postulated [Os(VII)O(3)(OH)(3)](2-) species according to: cis-[Os(VIII)O(4)(OH)(2)](2-) + trans-[Os(VI)O(2)(OH)(4)](2-) (k+2) <−> (k-2) 2[Os(VII)O(3)(OH)(3)](2-). The calculated forward, k(+2), and reverse, k(-2), reaction rate constants of this comproportionation reaction are 620.9 ± 14.6 M(-1) s(-1) and 65.7 ± 1.2 M(-1) s(-1) respectively. Interestingly, it was found that the postulated [Os(VII)O(3)(OH)(3)](2-) complex anion does not oxidize MeOH or EtOH. Furthermore, the reduction of Os(VIII) with MeOH or EtOH is first order with respect to the aliphatic alcohol concentration. In order to corroborate the formation of the [Os(VII)O(3)(OH)(3)](2-) species predicted with the rate model simulations, several Os(VIII)/Os(VI) mole fraction and mole ratio titrations were conducted in a 2.0 M NaOH matrix at 298.1 K under equilibrium conditions. These titrations confirmed that the cis-[Os(VIII)O(4)(OH)(2)](2-) and trans-[Os(VI)O(2)(OH)(4)](2-) species react in a 1:1 ratio with a calculated equilibrium constant, K(COM), of 9.3 ± 0.4. The ratio of rate constants k(+2) and k(-2) agrees quantitatively with K(COM), satisfying the principle of detailed balance. In addition, for the first time, the molar extinction coefficient spectrum of the postulated [Os(VII)O(3)(OH)(3)](2-) complex anion is reported.

A comparison of experimental and DFT calculations of ¹95Pt NMR shielding trends for [PtX(n)Y(6-n)](2-) (X, Y = Cl, Br, F and I) anions.

A comparison between experimental and calculated gas-phase as well as the conductor-like screening model DFT (195)Pt chemical shifts of a series of octahedral [PtX(6-n)Y(n)](2-) complexes for X = Cl, Br, F, I was carried out to assess the accuracy of computed NMR shielding and to gain insight into the dominant σ(dia), σ(para) and σ(SO) shielding contributions. The discrepancies between the experimental and the DFT-calculated (195)Pt chemical shifts vary for these complexes as a function of the coordinated halide ions, the largest being obtained for the fluorido-chlorido and fluorido-bromido complexes, while negligible discrepancies are found for the [PtCl(6-n)Br(n)](2-) series; the discrepancies are somewhat larger where a significant deviation from the ideal octahedral symmetry such as for the geometric cis/trans or fac/mer isomers of [PtF(6-n)Cl(n)](2-) and [PtF(6-n)Br(n)](2-) may be expected. The discrepancies generally increase in the order [PtCl(6-n)Br(n)](2-) < [PtBr(6-n)I(n)](2-) < [PtCl(6-n)I(n)](2-) < [PtF(6-n)Br(n)](2-) ≈ [PtF(6-n)Cl(n)](2-), and show a striking correlation with the increase in electronegativity difference Δχ between the two halide ligands (X(-) and Y(-)) bound to Pt(IV) for these anions: 0.09 < 0.52 < 0.63 < 1.36 ≈ 1.27, respectively. The computed (195)Pt sensitivity to Pt-X bond displacement, ∂(δ(195)Pt)/∂(ΔPt-X), of these complexes is very large and depends on the halide ion, decreasing from 24 800, 18 300, 15 700 to 12 000 ppm/Å for [PtF(6)](2-), [PtCl(6)](2-), [PtBr(6)](2-) and [PtI(6)](2-), respectively.

Separation and quantification of [RhCln(H2O)(6-n)](3-n) (n=0-6) complexes, including stereoisomers, by means of ion-pair HPLC-ICP-MS.

A hyphenated ion-pair (tetrabutylammonium chloride-TBACl) reversed phase (C(18)) HPLC-ICP-MS method (High Performance Liquid Chromatography Inductively Coupled Plasma Mass Spectroscopy) for anionic Rh(III) aqua chlorido-complexes present in an HCl matrix has been developed. Under optimum chromatographic conditions it was possible to separate and quantify cationic Rh(III) complexes (eluted as a single band), [RhCl(3)(H(2)O)(3)], cis-[RhCl(4)(H(2)O)(2)](-), trans-[RhCl(4)(H(2)O)(2)](-) and [RhCl(n)(H(2)O)(6-n)](3-n) (n=5, 6) species. The [RhCl(n)(H(2)O)(6-n)](3-n) (n=5, 6) complex anions eluted as a single band due to the relatively fast aquation of [RhCl(6)](3-) in a 0.1 mol L(-1) TBACl ionic strength mobile phase matrix. Moreover, the calculated t(1/2) of 1.3 min for [RhCl(6)](3-) aquation at 0.1 mol kg(-1) HCl ionic strength is significantly lower than the reported t(1/2) of 6.3 min at 4.0 mol kg(-1) HClO(4) ionic strength. Ionic strength or the activity of water in this context is a key parameter that determines whether [RhCl(n)(H(2)O)(6-n)](3-n) (n=5, 6) species can be chromatographically separated. In addition, aquation/anation rate constants were determined for [RhCl(n)(H(2)O)(6-n)](3-n) (n=3-6) complexes at low ionic strength (0.1 mol kg(-1) HCl) by means of spectrophotometry and independently with the developed ion-pair HPLC-ICP-MS technique for species assignment validation. The Rh(III) samples that was equilibrated in differing HCl concentrations for 2.8 years at 298K was analyzed with the ion-pair HPLC method. This analysis yielded a partial Rh(III) aqua chlorido-complex species distribution diagram as a function of HCl concentration. For the first time the distribution of the cis- and trans-[RhCl(4)(H(2)O)(2)](-) stereoisomers have been obtained. Furthermore, it was found that relatively large amounts of 'highly' aquated [RhCl(n)(H(2)O)(6-n)](3-n) (n=0-4) species persist in up to 2.8 mol L(-1) HCl and in 1.0 mol L(-1) HCl the abundance of the [RhCl(5)(H(2)O)](2-) species is only 8-10% of the total, far from the 70-80% as previously proposed. A 95% abundance of the [RhCl(6)](3-) complex anion occurs only when the HCl concentration is above 6 mol L(-1). The detection limit for a Rh(III) species eluted from the column is below 0.147 mg L(-1).

A novel approach to the rapid assignment of (13)C NMR spectra of major components of vegetable oils such as avocado, mango kernel and macadamia nut oils.

Assignment of (13)C nuclear magnetic resonance (NMR) spectra of major fatty acid components of South African produced vegetable oils was attempted using a method in which the vegetable oil was spiked with a standard triacylglycerol. This proved to be inadequate and therefore a new rapid and potentially generic graphical linear correlation method is proposed for assignment of the (13)C NMR spectra of major fatty acid components of apricot kernel, avocado pear, grapeseed, macadamia nut, mango kernel and marula vegetable oils. In this graphical correlation method, chemical shifts of fatty acids present in a known standard triacylglycerol is plotted against the corresponding chemical shifts of fatty acids present in the vegetable oils. This new approach (under carefully defined conditions and concentrations) was found especially useful for spectrally crowded regions where significant peak overlap occurs and was validated with the well-known (13)C NMR spectrum of olive oil which has been extensively reported in the literature. In this way, a full assignment of the (13)C{1H} NMR spectra of the vegetable oils, as well as tripalmitolein was readily achieved and the resonances belonging to the palmitoleic acid component of the triacylglycerols in the case of macadamia nut and avocado pear oil resonances were also assigned for the first time in the (13)C NMR spectra of these oils.

(195)Pt NMR isotopologue and isotopomer distributions of [PtCl(n)(H(2)O)(6 - n)](4 - n) (n = 6,5,4) species as a fingerprint for unambiguous assignment of isotopic stereoisomers.

A detailed analysis of the (35)Cl/(37)Cl isotope shifts induced in the 128.8 MHz (195)Pt NMR resonances of [PtCl(n)(H(2)O)(6 - n)](4 - n) complexes (n = 6,5,4) in acidic solution at 293 K, shows that the unique isotopologue and isotopomer distribution displayed by the resolved (195)Pt resonances, serve as a fingerprint for the unambiguous identification and assignment of the isotopic stereoisomers of [PtCl(5)(H(2)O)](-) and cis/trans-[PtCl(4)(H(2)O)(2)].