Near infrared study of aqueous rare-earth ethylsulfates

The near infrared spectra of aqueous solutions of the ethylsulfates of La, Nd, Gd, Tb, Er, Yb, Lu, Y, and Na have been determined from about 0.2 mol-dm^–3 to nearly saturation. The extinction coefficients of water have been calculated taking into account the absorption of ethylslfate anions determined in separate experiments. Their values appeared to be nearly the same as that of pure water. The relative contents of free OH groups in 0.5 and 0.7M solutions have been estimated from the absorbances at 1160 nm. They were lower in solutions of the heavy rare-earth ethylsulfates (Tb, Er, Yb, Lu) than in equimolar solutions of the lighter ones (La, Nd), confirming our previous view that secondary hydration of the heavy trivalent rare-earth cations is distinctly stronger than that of the lighter ones. A comparison of the spectra of these aqueous ethylsulfates with those of perchlorates shows that the structure-breaking ability of the C₂H₅SO ₄ ^– ion is much smaller than that of perchlorate anion.     

Near infrared study of aqueous lanthanide perchlorates

The near infrared spectra of water in aqueous solutions of La(ClO₄)₃, Pr(ClO₄)₃, Nd(ClO₄)₃, Gd(ClO₄)₃, Er(ClO₄)₃, Yb(ClO₄)₃, Lu(ClO₄)₃, and NaClO₄ have been measured in the concentration range from 0.3 to 2.5 mol-dm^–3, at 25°C. The relative contents of free OH groups in the 1.0, 1.6, and 2.2M solutions have been calculated from extinction coefficients for water at 1160 nm. They increase with increasing salt concentration and are greater in solutions of the lighter lanthanide perchlorates at any fixed molarity. The results are discussed in terms of the stoichiometry and structure of hydrated cations of trivalent lanthanides.     

Correlation between thermodynamic properties and coordination states of aqueous bivalent transition metal sulfates

The osmotic coefficients for CoSO₄, NiSO₄, CuSO₄, MnSO₄, and ZnSO₄ have been found to be approximately the same up to very highest concentrations, while they are significantly higher for MgSO₄. Negligible changes in the visible spectra of CoSO₄ and NiSO₄ induced by increasing concentration indicate little, if any, coordination of the sulfate anion, while the UV spectral effects indicate outer-sphere association. More distinct spectral effects are observed for CuSO₄. However, the free sulfate anion concentration is found to be the same in equimolal solutions of CoSO₄, NiSO₄, and ZnSO₄, and probably also in CuSO₄, while it is higher in the solutions of MgSO₄. The conclusion is drawn that the four isopiestic transition metal sulfates at any given molality are in corresponding coordination states. The general problem of correlation between thermodynamic properties of solutions and the coordination states of the dissolved salts is discussed.     

Electrical conductance and ionic association of the bivalent transition metal tetrafluoroborates in acetonitrile solution

Visible absorption spectra of Co(BF₄)₂ and Ni(BF₄)² in acetonitrile (AN) indicate the existence of complex electrolytes solely of the type [M(AN)₆]²⁺·2BF ₄ ^– . Close agreement of the molar conductance curves for Mn(BF₄)₂, Co(BF₄)₂, Ni(BF₄)₂, Cu(BF₄)₂, and Zn(BF₄)₂ indicates that the same is true for the other tetrafluoroborates as well. Small specific differences in properties of the [M(AN)₆]²⁺ complex cations are reflected in the limiting molar conductances, while the first-step association constants to a good approximation are the same for the different metal cations. Penetration of the tetrafluoroborate anion in between the coordinated acetonitrile molecules is suggested as a possible explanation for the apparent independence of ionic association on the crystallographic radius of the cation.     

Solute-solvent interaction involving MX2Ln type complexes in mixed solvent media. I. Outer-sphere interactions of the NiCl2py4 complex in pyridine + diluent solutions

The standard enthalpies and entropies of transfer from pyridine to pyridine+diluent mixtures of varying composition have been determined for the NiCl₂py₄ complex at 25°C using chloroform, 1,1,2,2-tetrachloroethane, aniline, benzene, and chlorobenzene as the diluents. Large negative enthalpies of transfer to solvent mixtures involving the protic diluents contrast with the small effects observed for the aprotic diluents. For the latter, the negative entropies of transfer agree with the assumption that pyridine molecules remain attached to the complex when the diluent is added to pyridine, indicating outer-sphere interaction of the amine with the complex. Solvent effects observed in the near infrared ligand-field spectrum of NiCl₂py₄ support the assumption of specific outer-sphere interactions with protic diluents. Additional information about these interactions is provided by the CTCT(t _2g^*) metal-to-ligand band in the UV.Deceased.     

Thermodynamic and structural features of chloro-complex formation of bivalent transition metals in dimethylsulfoxide

Heats of formation of complexes of the type MCl⁺ have been determined calorimetrically for M=Mn, Co, Ni, and Cu in dimethylsulfoxide (DMSO), at 25°C. Combined with the stability constants of the complexes they complete the thermodynamic characteristics of these systems. It appears that the complexes are formed in markedly endothermic reactions and owe their considerable stabilities to the large positive reaction entropies. The exceptionally large entropy of formation of the CuCl⁺ complex indicates its essentially pentacoordinate structure, CuCl(DMSO) ₄ ⁺ , while the other complexes are octahedral, MCl(DMSO) ₅ ⁺ , with a probable contribution of the outer-sphere ion-pair for CuCl⁺. The characteristic features of complex formation in dimethylsulfoxide, as compared with water, are discussed and ascribed to the relatively large molar entropy of this liquid.Deceased.     

Mobilities of complex forming cations in non-aqueous donor solvents

Conductance measurements are reported for Al(ClO₄)₃ in acetonitrile Co(ClO₄)₂, Zn(ClO₄)₂, and Al(ClO₄)₃ in dimethylformamide, and Al(ClO₄)₃, Fe(ClO₄)₃, and FeCl₃ in dimethylsulfoxide (DMSO), at 25°C. From uv spectral effects the FeCl (DMSO) ₅ ²⁺ complex cation is shown, to predominate in DMSO, while hexasolvated cations occur in the metal perchlorate solutions. The limiting conductances of the cations, including earlier data, indicate non-Stokesian dependences of mobility on the ionic charge, a unique property of the structurally related complex ions ML ₆ ^z+ and MXL ₅ ^(z–1)+ . The observed regularities are discussed in terms of both their possible applications and the migration mechanism.     

Osmotic coefficients of aqueous rare-earth perchlorates and nitrates

Osmotic coefficients of aqueous solutions of La(ClO₄)₃, Pr(ClO₄)₃, Nd(ClO₄)₃, Sm(ClO₄)₃, Gd(ClO₄)₃, Dy(ClO₄)₃, Ho(ClO₄)₃, Er(ClO₄)₃, Tm(ClO₄)₃, Yb(ClO₄)₃, Lu(ClO₄)₃, Nd(NO₃)₃, Sm(NO₃)₃, and Gd(NO₃)₃ in the molality range from 0.1 mol kg^?1 nearly to saturation at 298.15 K have been determined by the isopiestic method. The results obtained agree very well with those of Rard et al. published recently. A distinct two-series effect has been observed for the constant-molality values of rare-earth perchlorates. The results are discussed in terms of hydration of the cations and ionic association.