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The time-differential perturbed-angular-correlation (TDPAC) technique has been used to study the temperature dependences of the electric field gradient (EFG) at /sup 181/Ta impurities in the heavy-rare-earth (RE) metals Gd, Dy, Ho, and Er. At room temperature the ratio ..cap alpha.. equivalent vertical-bar V/sub z/z/ (1-..gamma../sub infinity/) V/sup 1at//sub z/z vertical-bar of the measured EFG V/sub z/z and the calculated ionic EFG (1-..gamma../sub infinity/) V/sup 1at//sub z/z decreases linearly with increasing rare-earth atomic number. A linear but much stronger decrease of ..cap alpha.. has previously been reported for the impurity /sup 111/Cd. A simple model is proposed which explains the linear decrease of ..cap alpha.. and the different slopes for /sup 181/Ta and /sup 111/Cd in terms of the lanthanide contraction. This model assumes the conduction-electron contribution to the EFG to be mainly determined by the number of electrons in the Wigner-Seitz cell of the impurity. In all rare-earth hosts the EFG decreases with increasing temperature. This decrease, which is slightly stronger for Gd than for Er, is better described by a linear function of temperature than by a T/sup 3/2/ behavior, observed in many other impurity-host systems. The temperature dependence of the EFG is much stronger than expected from themore » lattice expansion. The difference between the temperature dependence of the measured EFG and of the calculated lattice EFG decreases across the rare-earth series. This can be attributed to a decrease of the amplitudes of the lattice vibrations between Gd and Er.« less

The effects of the lanthanide contraction on lanthanide-induced shifts are estimated using simulated structures for a set of lanthanide chelates. The variations of the Ln-donor distances cause small conformational changes in the coordination polyhedron of the Ln(III) cation, and the induced pseudocontact shifts for a series of Ln complexes vary gradually going from La(III) to Lu(III). As a result of data manipulation these gradual variations may sometimes show up as an abrupt break in the middle of the lanthanide series.

Nuclear magnetic resonance measurements of metallic nuclei (δ 207Pb, δ 95Mo, and 1J(W–Pb)) have been carried out on dimetallic Cp(CO)3MPbR3 (M = Mo, W; R = Me, Et, Ph) and trimetallic [Cp(CO)3M]2PbPh2 (M = Mo, W) complexes. 207Pb chemical shifts increase in the sequence PbEt3 3 3 and are observed at higher fields in the tungsten compounds than in the molybdenum ones. It is suggested that both paramagnetic and diamagnetic contributions determine the overall shielding of lead, and that the higher field resonances of 207Pb in the case of W–Pb compounds are due to an efficacious operation of the Z/r dependent diamagnetic term (higher atomic number Z of tungsten and roughly the same Mo–Pb and W–Pb distances resulting from the 4f level induced lanthanide contraction). 95Mo chemical shifts (−1838 to −2007 ppm) lie in the region typical of the molybdenum – main group metal bonded complexes but at lower fields than in the corresponding Mo–Sn compounds. It is concluded from this observation that the Z/r dependent diamagnetic contribution does not operate efficaciously for 95Mo shieldings, which are hence primarily dominated by the paramagnetic term. The nature of metal–metal interactions is discussed.

Solid complexes of two new derivatives of 1,5-diaryl-3-acetylformazan with lanthanide metal ions were prepared and characterized by elemental and thermogravimetric analyses. The suggested formula of the complexes is ML 2 (H 2 O) x · y H 2 O where L = formazan, x = 0–2, y = 1–4 and M = trivalent lanthanide ion. Information about the water of hydration, the coordination chemistry and the thermal stability of these complexes was obtained. A general mechanism for the thermal decomposition of the complexes is suggested. A coordination number of ten is proposed for the lanthanide ions in these complexes which decreases from La to Lu due to the lanthanide contraction.

Molecular emission has been observed in high‐pressure electrodeless microwave arc discharges from the monochloride, monobromide, and monoiodide of ytterbium. The vibrational analyses of the electronic transitions in YbBr and YbI represent the first spectroscopic data for these molecules. Emission from the A (2Σ1/2) →X (2Π+) and A (2Π+) and R (2Π3/2) →X (2Σ+) transitions in YbCl have been observed. By analogy with YbF and YbCl, the blue degraded emission in YbBr and YbI has been assigned to the A (2Π1/2) →X (2Σ+) and A (2Π3/2) →X (2Σ+) transitions. The term values for YbBr and YbI are shifted to the red with respect to YbCl by

Sc2(WO4)3, diamagnetic above 30°K, crystallizes in the orthorhombic system, Space Group Pnca, with lattice constants a=9.596±0.004, b=13.330±0.003, and c=9.512±0.004 A at 298°K. The complete x‐ray scattering pattern within a reciprocal lattice hemisphere of radius (sinθ)/λ=1.02 A−1 was measured with PEXRAD. The crystal structure was solved by use of three‐dimen sional Patterson and Fourier series and refined by the method of least squares, using 1731 independent structure factors. The final agreement factor R is 0.0622. Scandium atoms occupy slightly distorted octahedra, with average Sc–O=2.063 A and Sc–O distances ranging from 2.026±0.015 to 2.124±0.010 A. Two crystallographically independent W atoms are surrounded by somewhat distorted tetrahedra: the W–O distances vary from 1.695±0.009 to 1.829±0.016 A, the average being 1.761 A. The thermal vibrations are significantly anisotropic. Sc2(WO4)3 forms the structure type for 23 trivalent metal tungstates and molybdates, including the nine smaller rare‐earth tungstates. The larger rare‐earth tungstates, crystallizing in the Eu2(WO4)3 structure type, have 8 coordination about the rare‐earth ion; the smaller have 6 coordination. A simple correlation is found between the variation in radius ratio due to the lanthanide contraction and the change in coordination.

The heats of formation at 20°C of the 1:1 complexes of the rare earths with NTA (nitrilotriacetic acid) have been measured with high relative precision. The method used consists in simultaneously reacting the magnesium-NTA complex with lanthanum ions in one compartment of a differential calorimeter, and the same amount of the magnesium complex with the same amount of the ions of another rare earth in the other compartment. ΔH for the formation of the NTA complexes varies quite smoothly with the atomic number of the rare earth, passing first through a minimum and then through a maximum. It is considered that this trend is not connected with ligand field splittings but derives from two opposing effects brought about by the lanthanide contraction, in that on proceeding from lanthanum to lutecium there is general tendency towards an increasingly exothermic interaction of the rare earth ions with the ligands, which in the middle of the series is offset by a change in the state of hydration of the ions. The following ancillary measurements at 20°C have also been made: the heat of formation of the magnesium-NTA complex; the heat content change for the ionization of the last proton from NTA; and the heat of ionization of water (at ionic strengths of 0·1 and 0·01).

Crystallographic and preparative data are given for high‐purity rare‐earth iron garnets (R3Fe2Fe3O12 and {R3—xRx′}Fe2Fe3O12, where R and R′ are rare earths). Lattice constants are obtained for hypothetical La, Pr, and Nd iron garnets. Maxima have been found for amounts of Pr substitution in Sm, Gd, Y, and Lu iron garnets which in turn lead to a principal maximum lattice constant of 12.540 A for any rare‐earth iron garnet, in good agreement with 12.538 A obtained by Geller, Williams, and Sherwood. The maximum for La substitution in YIG is also given. A plot of lattice constant vs atomic number shows some influence of crystal field on the trivalent rare‐earth ions with nonspherical electron configuration superposed on the lanthanide contraction. The importance of the size difference of the dodecahedral rare‐earth ions in the praseodymium‐substituted rare‐earth iron garnets with respect to the maximum attainable lattice constants is shown corroborating observations on the neodymium substituted rare earth iro...

The electronegativities of sixty-nine elements have been calculated from the most recent thermochemical data. The mean deviation of the calculated electronegativity difference, 0·208 √ †, from the difference of the average electronegativities is 0·046 units. The trends of electronegativity values within the periodic system are summarized. The transition metal contraction, the lanthanide contraction, and crystal field stabilization are observed to contribute to the relative values of electronegativity.

In der Abfolge der LnPt5-Phasen (Ln = La bis Tm) werden mehrere Strukturtypen beobachtet. Die Volumeninkrementkurye fur die Ln-Atome zeigt an den Stellen eines Strukturumbaues jeweils eine der Lanthanoidenkontraktion entsprechende Unstetigkeit. Messungen der magnetischen Momente ergeben, das bei den in den relativ grosen Lucken der Platinteilgitter eingebauten Ln-Teilchen niedere Oxydationsstufen wie Ce3+, Nd2+ und Eu2+ stabilisiert werden. Relations between Structure and Magnetic Properties of LnPt5 Phases In the series of the LnPt5 phases from lanthanium to thulium different structure types were observed. The change of the atomic arrangement in the structure types is related to steps in the diagram of the atomic volumes of the Ln atoms according to the Lanthanide contraction. Measurements of the magnetic moments show the stabilisation of lower oxidation states like Ce3+, Nd2+ and Eu2+ according to the large holes in the platinum lattice.

A series of previously unreported rare-earth tellurates with the general formula R2TeO6 has been prepared by solid-state reaction at elevated temperatures. The X-ray diffraction patterns of these compounds were indexed on the basis of a hexagonal unit cell and the unit cell dimensions were calculated. The Y, La and Pr through Tm compounds form an isomorphous series, while the Sc, In and Lu tellurates are of different structure. A linear relationship exists between the lattice constants and the ionic radius of the trivalent cations which demonstrates the lanthanide contraction in these compounds.

Changes in the atomic number of the metallic and ionic radii of lanthanides, and in the unit cell volumes of intermetallics, monopnictides, mono- chalcogenides and typically ionic compounds of lanthanides have been compared. It was found that ionic radii and unit cell volumcs of ionic compounds decrease almost monotonically with increasing atomic number. However, in the case of metallic radii contraction in the Pm-Gd interval is much smaller than in any other intcrval consisting of four lanthanides. The difference between the contraction of metals and ionic compounds was explained by delocalization of 4f orbitals in lanthanide metals due to direct f-f overlap.

Shakedown effects, due to final-state screening of a core level by a (localized) $4f$ electron, have frequently been reported in x-ray photoemission spectroscopy core-level spectra of metallic systems based on the lighter rare-earth elements. Such effects appear to correlate with the hybridization between the $4f$ electrons and the conduction electrons, which decreases monotonically with increasing $Z$ in the rare-earth series because of the lanthanide contraction of the $4f$ subshell. This picture has been clouded by the recent report of a large shakedown satellite in the $3d$ emission from Eu${\mathrm{Pd}}_{3}$, such an effect being absent in Sm${\mathrm{Pd}}_{3}$ and negligibily small in Nd${\mathrm{Pd}}_{3}$. We have observed a similar effect in Sm${\mathrm{Al}}_{2}$, where the required hybridization is expected to be small, and argue that in both cases the anomalous satellite is the emission from a divalent surface layer rather than a shakedown effect in the trivalent bulk.

Powder X-ray diffraction patterns were obtained for the series of synthesized compounds RCo2Ge2 with R = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y. The compounds have been indexed on the basis of a tetragonal unit cell with two formula units per cell. Except for YbCo2Ge2 the series shows the expected lanthanide contraction.

Atomic and ionic radii are presented for the elements E104–E120 and E156–E172. It is shown that a number of effects correlated with the large relativistic contraction of orbitals with low angular momentum leads to smaller atoms for higher atomic numbers. It is expected that Cs is the largest atom in nature.

The perovskite type structures of selected lanthanonmixed oxides (LnBO/ sub 3/) were investigated to determine the factors which influence their distortion. Lanthanum, neodymium, gadolinium, and dysprosium, which have a suitable range of ionic radii, were chosen for the tripositive Ln ions. Aluminum, iron, and gallium, which have tripositive ions with an inert gas, half- filled d-shell, and 18-electron configuration, respectively, were chosen as B ions that would demonstrate the influence of partial covalent character of B-O linkages on the distortion. Complete reactions to perovskite type oxides were obtained in all cases except Gd/sub 2/O/sub 3/ + Ga/sub 2//sup O/ub 3/, and Dy/ sub 2/O/sub 3/ + Ga/sub 2/O/sub 3/. The data sho wed that>s distortion increased with the lanthanide contraction in each of the series LnAlO/sub 3/, LnFeO/sub 3/, and LnGaO/sub 3/. The orthorhombic structures of DyAlO/sub 3/ and DyFeO/sub 3/ are described. (B.O.G.)

A series of eight rare earth stannates and yttrium stannate isostructural with pyrochlore was prepared by solid state reaction at elevated temperatures. The general formula for these compounds is A2Sn2O7 where A is Nd, Sm, Pr, La, Gd, Er, Eu, Yb, or Y. Lattice constants calculated from x-ray-powder-diffraction data are given. The lanthanide contraction is demonstrated. A linear relationship is developed between lattice constant and ionic radius.

Publisher Summary This chapter discusses recent progress in means of isolating individual lanthanides and yttrium. The chapter discusses well-developed processes for the preliminary treatment of rare earth mixtures. The lanthanides comprise a series of inner-transition elements in which the number of 4-f electrons increases from 1 to 14. The main effect of increasing the number of electrons in this internal energy sublevel, as the nuclear charge increases, is to gradually decrease the cationic radius of consecutive Ln3+ ions, so that they range in size from that of La3+ to that of Sc3+. Because of the remarkable similarities in their cationic charge and their radii, lanthanons form many isomorphic series of compounds, and are always found as complex mixtures (not always of exactly the same composition) in rocks and minerals that comprise the earth's crust. The problem of separating them by reactions in aqueous media is aggravated further by the fact that increased charge density, which accompanies lanthanide contraction, promotes a greater overall degree of aquation and renders individual hydrated cationic radii even more similar.

A new ternary equiatomic compound, CeRhIn, has been synthesized which is found to crystallize in the hexagonal ${\mathrm{Fe}}_{2}$P structure. The unit-cell volume of this compound deviates from that expected on the basis of lanthanide contraction, indicating the nontrivalent state of the Ce ions in this compound. The magnetic susceptibility of CeRhIn shows a broad maximum at about 150 K. Such a maximum is a characteristic feature of the mixed-valent cerium compounds. The resistivity of CeRhIn due to magnetic scattering also shows a broad maximum at about 140 K. Thus from lattice volume, susceptibility, and resistivity measurements, it is concluded that cerium ions are in a mixed-valent state in CeRhIn.

Among the various classes of rare-earth t (RE) compounds, the fcc (NaCl-type) RE monochalcogenides (REX, with X denoting the chalcogen) are the simplest from a structural and magnetic-exchange point of view. Some of these compounds, e.g., EuS and SINS, have received much attention during the past decade because of their many unique properties owed to the presence of partially filled inner 4 f shells of the RE within the forbidden gap and close to the conduction band. Moreover, their structure affords conceptual simplicity. Although closely related in their chemical aspects, the REX show strongly differing electronic, magnetic and optical properties along with the filling of the 4.)" shell: REX can be ferromagnetic semiconductors (e.g., EuS), metallic antiferromagnets (e.g., GdS), superconductors (e.g., LaS) or exhibit valence fluctuations after senaiconductor-metal transformation (e. g., SINS). The occurrence of two different atomic configurations for the RE (4['" 5d 1 6S 2 and 4ff+~6s2), together with the nonbonding character of the 4./" shell, are responsible for this seemingly irregular pattern most of the properties of the REX appear to follow. These dissimilar features of the 4fstates are a product of the lanthanide contraction (i.e., the small, but regular decrease of the 4 f radii from Ce towards Yb), of an increasing 4fbinding energy fi'om Ce towards the heavier rare earths and of the strong Hund's rule correlation effects near the hall'filled (4 f 7) and filled ( 4 f 14) 4fshell, favoring the 4 f ''+ * 6s 2 configuration [5.1-2]. The sudden changes in the properties of the 4fwave functions result in the near equality of the 4J; 5d and 6s binding energies, despite the localization of the 4./' states inside the filled 5s and 5p orbitals of the Xe core [5.1] ; the latter being the reason why the 4fstates largely retain their highly COl-related, atomic nature after compound formation. These particular properties of the 4./ shell, apart from being the cause of the most interesting aspects of RE research, are also the source of the problems posed by the determination of the electronic structure of these materials. These problems arise because of the inadequacy of the conventional methods of band calculation to handle correlated many-electron states. The combination of Raman scattering with the great diversity of properties displayed by the REX has resulted in a very prolific area of research as judged, for instance, by the large number of publications in the field. These studies have

Complexes of the complete series of lanthanide nitrates and Perchlorates with various macrocycles have been synthesized under anhydrous conditions. Spectroscopic studies indicate that the complexation by cyclic ligands depends on the dimension of the internal cavity, on the rigidity of the macrocycle, on the nature of its donor atoms and on the complexing properties of the counter ion. These factors lead to some selectivity in the complexation of the rare earths. The structure of the complexes was deduced by nuclear magnetic resonance spectroscopy of paramagnetic compounds. It was established that a non-substitued diaaza tetraoxa cycle adopts a non-planar conformation of reduced cavity size. The influence of the lanthanide contraction was demonstrated in the study of sandwich-type complexes with a small tetraoxa macrocycle. The electrochemical behaviour of the systems Yb(III)-Yb(II) and Sm(III)-Sm(II) in the presence of macrocycles was investigated by polarography. A hexaoxa macrocycle was found to have the unique property of stabilizing the II oxydation state by complexation. Stability constants were deduced from an analysis of partially irreversible Polarographie waves. A tetraaza tetraacetic macrocycle was used to complex the lanthanides in aqueous solution. This ligand forms the most stable rare earth complexes known so far and can act as a masking agent in the separation of rare earths from transition metal ions and alkalis., Desreux J. F. La complexation des lanthanides par les macrocycles. In: Bulletin de la Classe des sciences, tome 64, 1978. pp. 814-839.

A review on the studies of solvent extraction of zirconium and hafnium, either individually or together from other associated elements, using various solvents has been presented. In the Periodic Table, one can trace some element pairs, which have very closely similar chemical properties. Of these, zirconium and hafnium, due to lanthanide contraction form one such typical pairs, which generally occur together in nature and hence are termed congeneric. Segregation of these elements and separation of the individual metals from the complex matrix is of considerable importance in geochemistry and reactor technology. Of the various methods employed in separation chemistry, liquid-liquid extraction procedure is widely used for its high degree of selectivity under specific conditions. In order to develop a simple selective separation procedure of zirconium and hafnium it is necessary to study the extraction of the individual elements with different types of solvents. The following discussion has been cla...

Nb belongs to the fifth group of the periodic table of the elements. Its atomic number is 41, its atomic weight is 92.9046 and its electronegativity is 1.6. In a six-fold coordination its ionic radius is 0.64, 0.68 and 0.62 A for the valencies of 5, 4 and 3 respectively. Niobium is virtually identical in size with tantalum as a consequence of lanthanide contraction. Nb and Ta are therefore usually found together in minerals. The chief mineral containing both elements is FeMn(NbTa)2O6. This mineral is known as columbite or tantalite, depending on which metal predominates. For Nb the most important mineral is pyrochlore (Na, Ca)2(Nb, Ta, Ti)2O6(OH, F). The crustal abundances of Nb and Ta are 20 and 1.7 ppm respectively. These abundances make them comparable with nitrogen (19 ppm), gallium (19 ppm) and lithium (18 ppm), on the one hand, and to arsenic (1.8 ppm) and germanium (1.5 ppm), on the other hand.

The high platinum loadings required to compensate for the slow kinetics of the oxygen reduction reaction (ORR) impede the widespread uptake of polymer electrolyte membrane fuel cells. In order to improve the ORR kinetics and reduce the Pt loading, we can tailor the electronic properties of the Pt surface atoms by means of alloying Pt with other metals. Researchers have intensively studied alloys of Pt with late transition metals such as Ni and Co during the last decades. However, these compounds typically degrade under fuel cell reaction conditions, due to dealloying. In contrast, alloys of Pt and lanthanides present very negative enthalpy of formation [1,2], which should increase their resistance to degradation. Herein we present eight novel Pt-lanthanide and Pt-alkaline earth ORR electrocatalysts: Pt5La, Pt5Ce, Pt5Sm, Pt5Gd, Pt5Tb, Pt5Dy, Pt5Tm and Pt5Ca [3]. All the materials are highly active, presenting a 3 to 6-fold activity enhancement over Pt. Pt5Tb is the most active polycrystalline Pt-based catalyst reported in the literature. A Pt overlayer with a thickness of few Pt layers is formed onto the bulk alloys by acid leaching [1-3]. Notably, the experimental ORR activity as a function of the bulk lattice parameter and the Pt-Pt distance follows a “volcano” relation [3], with Pt5Tb presenting the highest initial activity while Pt5Gd is the most active after 10 000 cycles stability test between 0.6 and 1.0 V versus the reversible hydrogen electrode. We use the lanthanide contraction to control strain effects and tune the electrocatalytic activity, stability and reactivity of Pt [3]. References [1] M. Escudero-Escribano, A. Verdaguer-Casadevall, P. Malacrida, U. Grønbjerg, B.P. Knudsen, A.K. Jepsen, J. Rossmeisl, I.E.L. Stephens, I. Chorkendorff, J. Am. Chem. Soc. 2012, 130, 16476. [2] P. Malacrida, M. Escudero-Escribano, A. Verdaguer-Casadevall, I.E.L. Stephens, I. Chorkendorff, J. Mater. Chem. A 2014, 2, 4234. [3] M. Escudero-Escribano, P. Malacrida, M.H. Hansen, U.G. Vej-Hansen, A. Velázquez-Palenzuela, V. Tripkovic, J. Schiøtz, J. Rossmeisl, I.E.L. Stephens, I. Chorkendorff, Science 2016, 352, 73.

The synthesis at high pressures ( ∼60 Kbar) and high temperatures (∼1100 °C) of the title new ruthenates has been achieved and the materials compared to the gadolinium analogue. The structure remains tetragonal (S.G. P4/mmm) and the cell parameters linearly decrease following the lanthanide contraction. Preliminary results concerning the complex magnetic properties of these materials, where superconductivity, antiferromagnetism and a superimposed ferromagnetic ordering coexist, are presented.

The existing range of the centrosymmetric, triclinic RE(OAc)3 · 2AcOH structure type has been extended for RE = Eu and Gd while the structure data of the Nd- and Sm-compounds have been revised and corrected, respectively, using low temperature (T = 100 K), well resolved (2θmax = 56°), highly redundant SCXRD data in order to evaluate the structural evolution within this class of acetic acid solvates by statistical methods. Within the nine-fold mono-capped square-antiprismatic coordination spheres of the RE3+ ions, RE-O distances decrease as a result of lanthanide contraction; some with different rates depending on the coordination modes (2.11/2.21) of the acetate ions. The experimental data show that the internal structural parameters of the acetate ions also correlate with their coordination modes. Both acetic acid molecules act as hydrogen bond donors but only one as monodentate ligand. The geometries of the hydrogen bonds reveal that they are strongly influenced by the size of the rare earth atom. The non-linear, one-dimensional coordination polymer propagates with unequal RE···RE distances along the a-axis. Rods of the coordination polymer are arranged in layers congruently stacked above each other with the hydrogen bonded acetic acid molecules as filler in between. In most cases, data fitting is best described in terms of a quadratic rather than a linear regression analysis.

The 10K crystal structures of high-T c RBa2Cu3O7 (R=Y and rare earths) ceramic materials investigated by neutron diffraction were consistently analysed concerning systematic trends. Several interionic distances exhibit the well known lanthanide contraction behaviour, i.e., a linear relationship with the ionic radii of trivalent rare-earth ions. The only exceptions are associated with the apex oxygen O(1) ions: the chain copper Cu(1)−O(1) distances are constant, and the plane copper Cu(2)−O(1) distances are increasing across the rare-earth series. For R=Pr the 4f−CuO2 valence band hybridization effects are found to be highly anisotropic, since exclusively the interionic distances involving the b-direction (i.e, the chain direction) indicate that the Pr ions have an intermediate valence of about+3.4.

The lanthanide-alkaline and lanthanide-alkaline-earth perrhenates LnM(ReO4)4, LnM′3(ReO4)9 and LnM′(ReO4)5 (M = Li, Na, K, Rb; M′ = Ca, Sr, Ba) and some related compounds (M = Ag; M′ = Pb) are disclosed by the study of some phase diagrams. The synthesis of a large number of these compounds (most frequently carried out in solid state by heating Ln(ReO4)3 and M(ReO4) or M ( ReO4)2 together) shows that they crystallize preferently with a cubic structure (a≅ A) and particularly with an hexagonal structure (P63/m, a ≅ 10 A; c ≅ 6 A). This last structure was determined by the X-ray diffraction study of a monocrystal of the isotypic compound ThCd(MoO4)3. It is somewhat related to the apatite structure. Other structures are possible but whatever the system is (cubic, orthorhombic, hexagonal), the different unit cells are connected by simple geometrical relations, so it is more than likely that all these compounds have closely related structures. A tetrahydrate LnM(ReO4)4·4H2O (Ln≅ EuLu and M = Na, K, Rb, Ag) is disclosed for the LnM(ReO4)4 compounds. They are all isotypic and their structure (tetragonal P 4n2) is described for GdNa(ReO 4 ) 4 ·4H 2 O. The lanthanide contraction is well observed for each series and in some cases the tetrad effect is also observed. A large number of related compounds, for example simple perrhenates as Ln(ReO4)3 and Am(ReO4)3 or complex perrhenates as Ln(MoO4)(ReO4) are structurally linked up with these series, so they are mentioned with their relationships by isomorphous substitution.

The RRh 3 B 2 (R=La to Gd) compounds crystallize in the hexagonal CeCo 3 B 3 type structure. The unit cell volume of EuRh 3 B 2 follows the usual lanthanide contraction, indicating that Eu is in a trivalent state (electronic configuration 4f 6 ; 7 F 0 ) and hence is nonmagnetic. Magnetization studies on EuRh 3 B 2 , however, reveal that this compound orders magnetically with Curie temperature of 40 K and a moment of 0.55 μ B per formula unit at 4.2 K and 20 kOe applied field. The magnetism is presumed to be of the itinerant type arising from the Rhd band. Possibly the Eu 4f electrons also play a sugnificant role.

Dicyclopentadienyl lanthanide chlorides, (C 5 H 5 ) 2 LnCl, are key intermediates for the synthesis of the compounds containing LNC σ bonds, LnN and LnO bonds. However, probably due to lanthanide contraction effect, the early lanthanocene chloride complexes, particularly for La, Ce, Pr and Nd, have not yet been synthesized [1-3]. Recently, some organometallic chemists have made their efforts to study how to stabilize the dicyclopentadienyl early lanthanide chloride. Using the di(trimethylsilyl)-lanthanide chlorides. By using a bulky pentamethylcyclopentadienyl as a ligand, Evans [4] and Andersen [5] had succeeded in stabilizing dicyclopentadienyl cyclopentadienyl as a ligand, Lappert [6] succeeded in stabilizing early (f 0 –f 3 ) lanthanocene chlorides by generating an anionic complex. We now wish to report here two methods for the stabilization of early lanthanocene chlorides by using a chelate ligand. 1. By using ring-bridged dicyclopentadiene instead of two separated cyclopentadienes as a ligand we have succeeded in synthesizing the stabilized early lanthanocene chlorides tetrahydrofuran coordinated neutral complexes [7]. Because our results are different from Tsutsui's [8], we further synthesized six 1,1′-trimethylenedicyclopentadienyl lanthanide chlorides. All the products so far obtained were found to be tetrahydrofuran coordinated neutral complexes without exception. Anhydrous lanthanide chlorides reacted with disodium salt 1,3-dicyclopentadienyl-propane in THF at −50 °C to give tetrahydrofuran coordinated 1,1′-trimethylenedicyclopentadienyl lanthanide chlorides (eqn. 1). Furthermore, we found that the coordinated tetrahydrofuran could be replaced by 2,2′-bipyridyl to afford 2,2′-bipyridyl complexes which exhibit better stability to air and moisture (eqn. 2). It should be noted that even when the molar ratios of chlorides to 2,2′-bipyridyl in starting material were changed from 1:1 to 1:2, the atomic ratios of lanthanide metal to nitrogen in products remained 1:1. The infrared spectra of 2,2′-bipyridyl complexes indicate that four characteristics absorption peaks of pyridine ring at 408, 621, 994 and 1580 cm −1 all shift to higher frequencies as compared with that in [C 5 H 4 (CH 2 ) 3 C 5 H 4 ]LnCl·2,2′-bpy) 0.5 . It implies that a pair of electrons on nitrogen is coordinated to the metal to form a coordinated covalent bond. However, the dicyclopentadienyl lanthanide chlorides reacted with 2,2′-bipyridyl giving 2,2′-bipyridyl complexes, the atomic ratios of metal to nitrogen in products always were 1:2 and the coordination number is nine (eqn. 3). The infrared spectra of these complexes indicate that four characteristics absorption peaks of pyridine ring all shift to higher frequencies too, in agreement with that of [C 5 H 4 (CH 2 ) 3 C 5 H 4 ]LnCl·(2,2′-bpy) 0.5 . The X-ray photoelectron spectra of five dicyclopentadienyl lanthanide chlorides and their corresponding bipyridyl complexes (Cp 2 LnCl·2,2′-bpy) were measured. The binding energies of both Ln 4d and Cl 2p decrease as Cp 2 LnCl forms Cp 2 LnCl·2,2′-bpy complexes. This fact also demonstrated that the lone pair of electrons on nitrogen is coordinated to the metal to form a coordinated covalent bond. It was unexpectedly found that the binding energies of Cl 2p also decrease. It seems that the electron also shifts toward chlorine. The binding energies of N 1s increase at the same time. 2. The second method of stabilizing early (f 0 –f 3 ) lanthanocene chlorides we adopted is to use other types of chelate ligand, 2,2′-bipyridyl or o -phenanthroline to satisfy the coordination saturation, and thus improve the stabilization. We succeeded for the first time in synthesizing the dicyclopentadienyl early lanthanide chloride 2,2′-bipyridyl or o -phenanthroline coordination compounds (eqns. 4,5). They were allowed to react with sodium trifluoroacetate to afford the corresponding derivatives Cp 2 LnOCOCF 3 ·nB (eqn. 6). The 1 H NMR spectrum of Cp 2 LaOCOCF 3 ·2phen was determined. It indicates that the δ values of coordinated o -phenanthroline shift to lower field as compared with that in o -phenanthroline. B = 2,2′-bpy; Ln = La, Nd B = o -phen; Ln = La, Ce; N = 2; Ln = Pr, Nd; N = 1 or 2 By using ring-bridged dicyclopentadiene, 2,2′-bipyridyl or o -phenanthroline as a ligand the disproportionation of early lanthanocene chloride is thus prevented, the stabilization of early lanthanocene chlorides achieved, and the early lanthanocene chlorides can be isolated.

VALUES are now available for ΔH1, the heat content change in the reaction where Ln represents a lanthanide element and Y a complexing agent such as the ethylenediaminetetraacetate (EDTA) or nitrilo-triacetate (NTA) ion. The measurements usually refer to dilute solutions of molar concentrations of ∼ 0.01 or less. The dependence of ΔH1 on the atomic number of the lanthanide is often rather complicated, a plot of one quantity against the other showing both a maximum and a minimum. This is true, for example, of the EDTA1 and 1:1 NTA complexes2,3 and the 1:1 and 1:2 diglycollate and dipicolinate complexes4. There are, however, grounds for believing that a complicating factor may be a change somewhere in the middle of the series in the effective hydration number of the uncomplexed lanthanide ion, consequent on the lanthanide contraction. This factor can be eliminated by measuring the integral heats of solution of a series of isomorphous lanthanide salts to give suitably dilute solutions. Such series of salts covering all the lanthanides are not numerous, but two well known ones are the bromates and the ethylsulphates, both of which crystallize as enneahydrates. If, for example, ΔH2 is measured for the process then ΔH1 + ΔH2 = ΔH3, where ΔH3, is the heat content increase for the process from which the simple hydrated lanthanide ion has been eliminated.

X-ray isochromats show, that the densities of states in the conduction band of transition metals are very similar in the sense of a rigid band model. With respect to this general scheme only lutetium, but not lanthanum, may be considered as a transition metal.

Formation of aluminosilicate glasses containing oxides of rare-earth elements, e.g. Sc, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, and Yb, was studied by melting at 1550°C and air quenching. The upper limit of the amount of rare-earth oxide which can be incorporated into the aluminosilicate glasses decreases according to the lanthanide contraction.

Ln1Ba2Cu3O y thin films with nine different lanthanide ions were prepared by a laser ablation method. Systematic changes in the structure and superconducting properties were observed in regard to the difference of the lanthanide ion radii. Smaller lanthanide ions were found to be suitable for the formation of a superconducting film with orthorhombic structure.

The discussions of the nature and magnitude of the lanthanide contraction and its relationship to size changes in the periodic table as a whole are usually misleading to the student.

FOR a given oxidation level the oxy-acids in a given sub-group of the periodic table are normally found to exhibit a regular variation in acid strengths. In group VII, for example, Cobble1 lists the logical pK values as −2.25, (−1.5) and −1.25 for HMnO4, HTcO4 (estimated, with due regard for the lanthanide contraction) and HReO4. The general behaviour of pertechnic acid in aqueous neutralimetry certainly is consistent with that of a monoprotic and ‘relatively’ strong acid.

The infrared lattice spectra from 700 to 50 cm−1 of eight cubic rare earth oxides are reported. It is evident from these data that the crystal structure determines the frequency position, and clearly shows the effect of the lanthanide contraction in this series of compounds.

This paper presents a modified form of the atomic volume curve that illustrates graphically the lanthanide contraction; a number of chemical consequences of this effect are also discussed.