[en] There appears to be a continuous demand for the synthesis of complex lanthanide(III) chlorides, bromides and iodides. This is because they do not only exhibit an interesting crystal chemistry, but they do have interesting physical properties, too. These properties arise from coordination geometries that are not known from the binary halides (like coordination number seven) and from the fact that the lanthanide ions are diluted. Therefore, such halides have been the target of many spectroscopic and magnetic investigations. In this article, the focus is on ternary halides and on one type of quaternary halides, the so-called elpasolites. Synthetic procedures developed for these may be used analogously for other types of complex halides as well. (author). 53 refs.; 3 figs.; 1 tab

[en] This chapter reviews the preparation of binary lanthanide(III) halides. The starting materials for synthesis of lanthanide chlorides and bromides is the lanthanide or the sesquioxide. There are two principle strategies for the conversion of the sesquioxide into chloride or bromide: metathesis or acid-base reactions. In case of the synthesis of lanthanide iodides there are other possible methods like: conversion of the chlorides by hydrogen iodide, the conversion of acetates with acetyl iodide or the conversion from oxides with molten aluminium iodide. (R.A.B.). 22 refs.; 5 figs

[en] Praseodymium diiodide, PrI₂, is obtained from the triiodide, PrI₃, by reduction with praseodymium metal at elevated temperatures. The two modifications, PrI₂-IV and -V, are obtained in different ratios upon fast and slow cooling, respectively. PrI₂-IV crystallizes with the CdCl₂ type of structure (trigonal, R-3m, a=426.5(1), c=2247.1(8) pm) while PrI₂-V (cubic, F-43m, a=1239.9(2) pm) represents an own structure type that may be considered as a structural variant of the CdCl₂ type with tetrahedral Pr₄ clusters. To elucidate the electronic properties of the modifications of PrI₂ first principles electronic band structure calculations have been carried out using the tight-binding linear-muffin-tin-orbital method (LMTO) as well as the full potential augmented plane wave method (FP-LAPW). The band structure and the bonding were analysed in terms of projections of the bands onto orthogonal orbitals. It was especially focussed on Pr-Pr interactions by crystal orbital Hamiltonian population (COHP) analysis. The calculations show accordingly that a configurational crossover between a [Xe]6s⁰5d⁰4fⁿ and a [Xe]6s⁰5d¹4f^n-1 configuration can be observed in the case of PrI₂, depending upon the structure adopted. A higher d orbital contribution results in stronger Pr-Pr interactions. Thus, the driving force appears to be an optimisation of bonding

[en] This chapter review the reduction of lanthanide(III) halides into lanthanide dihalides by the use of an alkali metal as a reducing agent. (R.A.B.). 44 refs.; 1 fig.; 1 tab

[en] The high resolution absorption, luminescence and excitation spectra of the orthorhombic potassium lanthanum praseodymium ternary chloride, K₂La_1-xPr_xCl₅, (0.02 ≤ x ≤ 0.15) single crystals were recorded at 4, 77 and 293 K with different excitation sources. The experimental 4f² energy level scheme of the Pr³⁺ ion in K₂LaCl₅ derived from the absorption and emission spectra consisted of 86 (out of 91) Stark components. This energy level scheme was simulated by using a phenomenological crystal field (cf) model which included eight free ion and nine cf parameters according to the C_2v symmetry. Despite the approximate C_2v point symmetry instead of the real C_s one, the simulation yielded a very satisfactory rms deviation of 17 cm^-1 between the experimental and calculated energy level schemes. The results, especially the weak cf strength, are discussed taking into account the bonding characteristics in K₂LaCl₅

[en] The new condensed double-chain cluster complex compound {Ir_2Gd_5}Br_5 was obtained from a reaction of GdBr_3 with metallic gadolinium and iridium at elevated temperatures. The thin black needles crystallize with the orthorhombic crystal system, space group Pnma(no. 62); a = 1255.4(1) pm, b = 414.05(3) pm, c = 2633.8(3) pm, Z = 4, R_1/wR_2 = 0.0504/0.0346 for all data. Monocapped trigonal prisms of gadolinium atoms with endohedral iridium atoms are connected by common rectangular faces to chains and further by edges to double chains, which form a herringbone arrangement. The double chains are coordinated by bromido ligands and are connected in accord with the formulation {Ir_2Gd_5}Br_4_/_2"iBr_2_/_3"i"("e")Br_1_/_3"i"("f")Br_2_/_2"i"-"i"("e"/"f")Br_1_/_2 "i"-"aBr_1_/_2"a"-"i. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[en] The oligomeric cluster complex {Ir_3Gd_1_1}Br_1_5 was first obtained from a reaction of Gd, GdBr_3 and Ir in a 3:4:1 molar ratio at 1123 K. The crystals belong to the hexagonal space group P6_3/m with lattice parameters a = 1276.79(14) pm and c = 1286.92(16) pm. The structure features isolated {Ir_3Gd_1_1} cluster trimers, which are built up by three face-sharing gadolinium octahedra each centered by an iridium atom. The endohedral iridium atoms form a triangle with Ir-Ir distances of 295.51(11) pm. Thus, the {Ir_3Gd_1_1} cluster is topologically equivalent to the suboxide {O_3Cs_1_1}. The {Ir_3Gd_1_1} clusters are encapsulated in a coordination sphere of 30 bromide ions, which act as bridging ligands according to the formulation {Ir_3Gd_1_1}Br"i"-"i_1_2_/_2Br"i"-"a_9_/_2Br"a"-"i_9_/_2. In {Ir_3Gd_1_1}Br_1_5 there are 45 electrons present for intracluster bonding. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

[en] The first rare-earth metal telluride chlorides, RTeCl with R = La, Ce, Pr, Nd, were obtained as single crystals and/or powder samples by the reaction of anhydrous rare-earth trichlorides, RCl_3, with the respective rare-earth metals R and elemental tellurium (Te) in sealed tantalum containers at temperatures as high as 1050 C. All four telluride-chlorides crystallize with the so-called tetragonal PbFCl type of structure but according to RTeCl = PbClF, with, for the example of LaTeCl-I, a = 451.7(1), c = 827.4(2) pm, V_E/Z = 84.5(1) Aa"3, tetragonal, P4/nnm (No. 129). LaTeCl and CeTeCl are dimorphic, the second modification crystallizes with the PbCl_2 type of structure with, for LaTeCl-II, a = 795.2(1), b = 450.8(1), c = 940.4(1) pm, V_E/Z = 84.3(1) Aa"3, orthorhombic, Pnma (No. 62). In both structures, La"3"+ is nine-coordinate, [LaTe_5Cl_4], with similar mean La-Te and La-Cl distances in both modifications, 333.2 vs. 333.1 pm and 302.9 vs. 301.8 pm, respectively. (Copyright copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[en] It takes two to tango: The ''reduced'', divalent lanthanides M"2"+ have electronic ground-state configurations of either 4f"n"+"15d"0 or 4f"n5d"1. The latter may be incorporated in the spacious anions [M(Cp')_3]"- and thus the single d"1 trapped in a z"2 like SOMO. This chemistry has now been transcribed to U"2"+ (5f"36d"1), a much sought-after species. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[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