[en] Hydrates of the lanthanide triiodides have been synthesized by evaporation of water from aqueous LnI₃ solutions. The highest hydrated states are nonahydrates of the iodides of the larger lanthanides, (La to Dy) and octahydrates of the iodides of the smaller ones, (Tb to Lu) whereas Tb and Dy form nonahydrates as well as octahydrates. Dehydration of the nona- or octahydrates at 10^-1 torr and room temperature results in the formation of hexahydrates of all rate earth iodides. Heating of the hexahydrates of the larger lanthanides La, Ce, Pr and Nd at 50degreeC (10^-1 torr) leads to the formation of trihydrates and anhydrous salts. With the other hexahydrates decomposition was observed. (author)

No abstract available

[en] The rare-earth diiodides RI₂ may be divided into two classes. At ambient conditions, the rare-earth cation R²⁺ may have the electronic configuration [Xe]6s⁰5d⁰4fⁿ (R = Nd, Sm, Eu, Dy, Tm, Yb). The respective diiodides, also classified as (R²⁺)(I^-)₂, are structurally reminiscent of alkaline-earth iodides. Diiodides with R = La, Ce, Pr, and Gd have one excess electron according to [Xe]6s⁰5d¹4f^n-1, chemically: (R³⁺)(e^-)(I^-)₂, and exhibit mostly CuTi₂ or MoS₂ type structures. The configuration crossover 5d⁰4fⁿ ↔ 5d¹4f^n-1 is observed with praseodymium (and neodymium) and is dependent upon the conditions (temperature, pressure) and the crystal structure adopted. 'ScI₂' is a special case as it stabilizes its electronic structure through an under-occupation of the scandium sites. Further stabilization of 'reduced iodides' is possible by encapsulation of mono- or di-carbon units in tetrahedral or octahedral clusters. Examples are Pr{Pr₆C}I₁₂, Cs₂{Pr₆(C₂)}I₁₂ and Sc₂₄C₁₀I₃₀

[en] Addition compounds of lanthanide salts and the ligands: N,N,N',N'-tetramethylmalonamide (TMMA) and N,N,N',N'-tetramethylapipamide (TMAA) have been described. This note reports the preparation of the adducts of anhydrous lanthanide iodides and TMMA. The compounds with compositions: LnI₃.5TMMA (Ln = La, Ce) and LnI₃.4TMMA (Ln = Pr-Lu, Y), were characterized by analytical procedures, X-ray powder patterns, IR spectra, absorption spectrum of the neodymium compound, emission spectrum of the europium compound and conductance measurements in nitromethane, acetonitrile and methanol. (author)

[en] Results are described of the examination of anhydrous tri-iodides of neodymium and samarium and the oxy-iodide of neodymium, by x-ray powder diffraction and spectrophotometry. Lattice parameters are given LaI₃, PrI₃, NdI₃, SmI₃, GdI₃, TbI₃, and NdOI

[en] The diffuse reflectance and photoluminescence (PL) spectra of NdI₂, SmI₂, EuI₂, DyI₂, TmI₂ and YbI₂ were measured between 225 and 12 500 nm in order to determine their 4fⁿ → 4f^n-15d¹ optical bandgaps. The results were compared with those obtained using an empirical model of the electronic structure of LnI₂. The results can be used to explain the lanthanide valency and crystalline structure changes of other lanthanide diiodides such as PrI₂. (paper)

[en] The heterogeneous exchange processes of mixed AgI+PbI₂ ppts. with I^- from KI soln. were studied at 293 K using sup(131)I in the systems in statu nascendi. Radiometrically detd. soly., DTA and X-ray diffraction data were compared with the radioanalytical results on the heterogeneous exchange process. The results show a strong mutual dependence of the metal halides AgI particles during the Ostwald's ripening process

[en] The hyperfine interaction parameters at the iodine site in various metal diiodides (M=V, Cr, Mn, Fe, Co, Ni, and Cd) were measured using the 27.8 keV Moessbauer transition in ¹²⁹I. Charge densities in the valence orbitals are deduced from an interpretation of isomer shift and quadrupole coupling constant values. Magnetic hyperfine interactions transferred at the originally diamagnetic iodine ion in the magnetically ordered phases of the compounds allow one to determine the unpaired spin densities in the valence orbitals. Information relative to the magnetic structures is obtained from the number and intensities of magnetically nonequivalent sites and from the relative orientation between the transferred field and the electric field gradient axes. The Moessbauer spectra of ¹²⁹Xe impurities created by β^- decay of ¹²⁹I in the NiI₂ lattice reveal the absence of bonding of xenon atoms in this matrix

[en] The isotopic exchange reactions between methyl iodide and sodium, potassium, rubidium, and cesium iodides in absolute methanol at 25 deg C have been studied. Individual rate constants were determined for the free iodide ions as well as for Na⁺I^-, K⁺I^-, Rb⁺I^-, and Cs⁺I^-ion pairs. The data obtained prove that the free iodide ion rate constant is independent of the cation as might be theoretically expected. The value of the overall reaction rate constant, ksub(m) indicate that in contradiction to the foregoing supposition ion-pairs do take part in exchange reactions in addition to free ions. The previous conception, namely that the rate constant of free iodide ion, ksub(i)>ksub(m)>O, was correct. Since activity coefficients have been directly determined it has been believed that these values and hence the rate constants are more accurate than previously given values. The data obtained show that ksub(m) is of the same magnitude as ksub(i). This indicates that the exchange reaction between the organic reactant and alkali iodide ion-pairs is by no means negligible. The decreasing trend of ksub(m), i.e. the decreasing reactivity of paired iodide ion, when going from sodium iodide to cesium iodide, indicates that the solvent separation of the ions in the ion-pair decreases. In other words, the character as contact ion-pair increases in the order Na⁺I^-< K⁺I^-< Rb⁺I^-< Cs⁺I^-. (T.I.)

No abstract available