Anthony Fratiello

A hydrogen-1, chlorine-35, and lanthanum-139 NMR coordination study of the lanthanum(III) ion in aqueous solvent mixtures

A La(III) hydration study has been carried out for solutions of La(ClO4)3 and, in a preliminary way, La(NO3)3 in aqueous mixtures with acetone-d6 and Freon-12, using hydrogen-1, chlorine-35, and lanthanum-139 NMR spectroscopy. Low temperature, proton magnetic resonance experiments allowed the direct observation and area evaluation of separate signals for water molecules in the primary solvation shell of La(III) and in bulk medium. Measurements over a wide range of salt and solvent concentration gave a maximum La(III) hydration number of 6 and no evidence for inner-shell ion-pairing in La(ClO4)3 solutions. Chlorine-35 chemical shift and linewidth data in these solutions confirmed the absence of contact ionpairing. Hydration numbers of 3–4 for La(III) in several La(NO3)3 solutions clearly indicated inner-shell complex formation. Lanthanum-139 chemical shift and linewidth measurements for these systems revealed the presence of some process, possibly hydrolysis, in the La(ClO4)3 solutions at extremely high acetone-d6 concentrations.

A hydrogen-1, chlorine-35, and yttrium-89 NMR complex formation study of aqueous Y(ClO4)3 and Y(NO3)3 solutions

A Y (III) coordination study of Y (ClO4)3 and Y (NO3)3 solutions in aqueous solvent mixtures has been carried out by hydrogen-1, chlorine-35, and yttrium-89 NMR spectroscopy. An accurate measurement of the Y(III) hydration number by a direct hydrogen-1 NMR method was not possible in Y (ClO4)3 solutions, even at −115°C, but these experiments were successful for Y(NO3)3 solutions. The hydrogen-1 spectra for the Y(NO3)3 solutions revealed two coordinated water signals, appearing at different temperatures, and corresponding to total Y(III) hydration numbers of 2.5 to 3.5. The yttrium-89 NMR spectra showed one signal for Y(ClO4)3 solutions for all conditions of concentration and temperature, whereas the Y (NO3)3 solution spectra at low temperature consisted of two signals, which varied in intensity with solvent composition. The hydrogen-1 and yttrium-89 NMR results were interpreted in terms of combinations of (H2O)4Y (NO3)2+ and (H2O)2Y (NO3)12+ in the Y(NO3)3 solutions, but similar experiments, along with chlorine-35 NMR data, ruled out inner-shell complex formation in the Y(ClO4)3 systems.

A hydrogen-1, nitrogen-15, and chlorine-35 NMR coordination study of Lu(ClO4)3 and Lu(NO3)3 in aqueous solvent mixtures

A coordination study of Lu(III) has been carried out for the nitrate and perchlorate salts in aqueous mixtures of acetone-d6 and Freon-12 by1H,15N and35Cl NMR spectroscopy. At temperatures lower than −90°C, proton and ligand exchange are slow enough to permit the direct observation of1H resonance signals for coordinated and free water molecules, leading to an accurate measure of the Lu(III) hydration number. In perchlorate solution, in the absence of inner-shell ion-pairing, Lu(III) exhibits a maximum coordination number of six over the allowable concentration range of study, contrasting markedly with the report of values of six to nine or greater as determined by a similar NMR method. The absence of contact ion-pairing was confirmed by35Cl NMR chemical shift and linewidth measurements. Extensive ion-pairing was observed in the nitrate solutions as reflected by the lower Lu(III) hydration numbers of two to three in these systems, the observation of two coordinated water signals, and15N NMR signals for two complexes. The1H and15N NMR spectra and the hydration number could be accounted for by the presence of (H2O)4Lu(NO3)2+ and (H2O)2Lu(NO3)21+.

A direct nitrogen-15 NMR study of cerium(III)-nitrate complexes in aqueous solvent mixtures

A study of the complex formation which occurs between cerium(III) and nitrate ions in aqueous solvent mixtures has been carried out by a direct, low-temperature, nitrogen-15 (15N) NMR technique. At temperatures in the range of −95 to −110°C, ligand exchange is slow enough to permit the observation of separate15N NMR signals for bulk nitrate, and this anion in the cerium(III) principal coordination shell. In water-acetone-Freon-12 mixtures, the spectra reveal the nitrato complexes do not form consecutively. Rather, signals are observed for Ce(NO3)2+, Ce(NO3)21+, and only two other higher order complexes, even at very high NO3− to Ce(III) mole ratios. Signal area evaluations were used to identify the possible higher order complexes. At comparable salt concentrations in aqueous-methanol mixtures, only Ce(NO3)2+ and Ce(NO3)21+ are formed, reflecting a decreased tendency for complexation in media of higher dielectric constant.

A direct15N NMR study of erbium(III)-nitrate complexation in aqueous solvent mixtures

The extent of inner-shell ion-pair formation of Er3+ with nitrate ion in aqueous mixtures has been studied by nitrogen-15 (15N) NMR spectroscopy. At low temperature, exchange is slow enough to permit the direct observation of15N signals for nitrate ions in the Er3+ solvation shell and in bulk medium. In water-acetone mixtures,15N NMR signals for the mono-and bis complexes are observed at low nitrate to Er3+ mole ratios, but only the bis complex is evident at higher anion concentrations. No spectral evidence for the tris complex was seen at any nitrate concentration. In water-methanol-acetone mixtures, signals for the mono and bis complexes persist even at higher nitrate concentrations, indicating a reduced tendency to ion-pair with increasing dielectric constant. Preliminary15N NMR results are presented for the nitrate complexes of other paramagnetic lanthanide ions.

A direct nitrogen-15 NMR study of neodymium(III)-nitrate complex formation in aqueous solvent mixtures

A study of contact ion-pair formation between the neodymium (III) and nitrate ions in aqueous solvent mixtures has been carried out by a direct, low temperature, nitrogen-15 (15N) nuclear magnetic resonance (NMR) technique. At low temperatures, −90 to −120°C ligand exchange is slow enough to permit the observation of15N NMR signals for uncomplexed nitrate ion, and this anion in the primary solvation shell of Nd(III). In aqueous mixtures with inert acetone and Freon-12, resonance signals for Nd(NO3)2+, Nd(NO3)21+, and two higher complexes are observed. Signal areas indicate these additional species are possibly a combination of the tetra-, penta-, and hexanitrato complexes, but not the trinitrato. In water-methanol, a medium of higher dielectric constant, complexation is much less and signals only for the mono-and dinitrato complexes are observed. The effect of solvent on complexation is demonstrated more clearly by a series of measurements in water-methanol-acetone mixtures.

A direct hydrogen-1 and phosphorus-31 nuclear magnetic resonance cation solvation study of Al(ClO4)3, Ga(ClO4)3, In(ClO4)3, UO2(ClO4)2, and UO2(NO3)2 in water-acetone-dimethylsulfoxide and water-acetone-hexamethylphosphoramide mixtures

A competitive solvation study of Al(ClO4)3, Ga(ClO4)3, In(ClO4)3, UO2(ClO4)2, and UO2(NO3)2 in water-acetone-dimethylsulfoxide (DMSO) and water-acetone-hexamethylphosphoramide (HMPT) mixtures has been carried out by direct H1 and P31 nuclear magnetic resonance (NMR) techniques. At low temperature, proton and ligand exchange are slow enough in these systems to permit the observation of signals for bulk and coordinated molecules of water and the organic bases (DMSO and HMPT). Both DMSO and HMPT compete effectively with water for coordination sites in the Al3+, Ga3+, and In3+ systems, with steric effects dominating the HMPT results. Both Al3+ and In3+ are able to bind a maximum of two to three HMPT molecules, for example. In contrast, UO2+ is solvated selectively by the organic molecules to the allowed maximum of 4 molecules per cation. H1 and P31 NMR spectral results support the formation of only the mono-, tri-, and tetra-HMPT solvation complexes.

A direct carbon-13 and nitrogen-15 NMR study of samarium(III) complexation with nitrate and isothiocyanate in aqueous solvent mixtures

The extent of inner-shell, contact ion-pairing between samarium(III)-nitrate and in a preliminary manner, samarium(III)-isothiocyanate, has been determined by a direct, low-temperature, multinuclear magnetic resonance technique. In water-acetone mixtures containing Freon-12 or Freon-22, the slow exchange condition is achieved at −110 to −120°C, permitting the observation of15N NMR resonance signals for bulk and coordinated nitrate. In these mixtures, signals are observed for Sm(NO3)2+, Sm(NO3)2+, and two higher complexes, possibly the tetranitrato with either the penta-or hexanitrato.1H NMR signals for bound water molecules in these mixtures were observed, but accurate hydration numbers can not yed be determined. In anhydrous or aqueous methanol mixtures,15N NMR signals for only three complexes are observed, with the dinitrato clearly dominating. Using15N and35Cl NMR chemical shift and linewidth measurements, the superior complexing ability of nitrate compared to perchlorate and chloride, was demonstrated. Successful preliminary13C and15N NMR measurements of Sm3+-NCS− interactions in water-acetone-Freon-22 mixtures also have been made. The13C NMR spectra reveal signals for five complexes, presumably Sm(NCS)2+ through Sm(NCS)52−. In the15N NMR spectra, signals for only three complexes are observed (the result of insufficient spectral resolution.) displaced about +240 ppm from bulk anion.

A direct carbon-13 nuclear magnetic resonance study of boron trihalide complexes with several ethers

Abstract The preliminary results of a direct, low-temperature 13 C NMR study of BF 3 and BCl 3 complexes with a series of ethers are reported. By lowering the sample temperature to slow exchange, it is possible to observe separate 13 C signals for coordinated and free ligand molecules. The 13 C chemical shifts at the α-carbon produced by complex formation are to lower field and they decrease in the order THF > Et 2 O > Pr 2 O ≅ Bu 2 O. The 13 C signals for all other carbon atoms in these ethers are displaced to higher field in the complexes. A preliminary interpretation in terms of ligand basicity, and possible electronic changes occurring in the complexes is presented.

A direct nitrogen-15 NMR study of praseodymium(III)-nitrate complex formation in aqueous solvent mixtures

A direct, low-temperature nitrogen-15(15N) NMR technique has been applied to the study of inner-shell complex formation between praseodymium(III) and nitrate ion in aqueous solvent mixtures. In water-acetone mixtures at −95°C, ligand exchange is slow enough to permit the observation of15N NMR signals for uncomplexed and coordinated nitrate ion, but satisfactory resolution is obtained only by the addition of Freon-12 to these systems for study at −110 to −115°C. Four coordinated nitrate signals are generally observed and a very small signal for an additional complex, or an isomer of one of the others, appears at the highest nitrate concentrations. Signals for the mono-and dinitrato complexes are unambiguously identified, but with the exception of the trinitrato complex, several possibilities exist for the remaining peaks. To overcome excessive viscosity signal broadening, measurements in methanol and ethanol are possible only with praseodymium trifluoromethanesulfonate (triflate). Coordinated nitrate signals in aqueous and anhydrous methanol are observed only for the mono-and dinitrato species, and signal areas indicate a maximum of two moles of nitrate per Pr(III) are complexed. A third signal is evident in the ethanol solution spectra, and the presence of this higher complex was confirmed by area measurement of the fraction of bound nitrate. The extent of complex formation in these solvent systems is attributed to differences in the dielectric constant. A comparison of the complexing tendencies of Pr(III) to other ions studied by this NMR method suggests the possibility of a coordination number change across the lanthanide series. Preliminary15N NMR results for metal-ion complexes with the isothiocyanate ion are presented.