The complexation of Cm(III) and Eu(III) with 4-t-butyl-6,6'-bis-(5,6-diethyl-1,2,4-triazin-3-yl)-2,2'-bipyridine (t-Bu-C2-BTBP) in water/2-propanol solution is studied. With increasing ligand concentration, 1 : 2 complexes [M(t-Bu-C2-BTBP)(2)(H(2)O)](3+) form from the solvated metal ions. The stability constants are log K(Cm(III)) = 11.1 and log K(Eu(III)) = 9.0. For both Cm(III) and Eu(III), the complexation reaction is both enthalpy and entropy driven. DeltaH(Cm(III)) is 11.7 kJ mol(-1) more negative than DeltaH(Eu(III)), whereas the entropy difference is negligible. This is in good agreement with t-Bu-C2-BTBP's selectivity in liquid-liquid extraction.

Lithium transition metal oxides are commonly used as cathode materials in modern mobile and stationary power supplies. Lithium transition metal fluorides are an interesting new class of materials for lithium ion batteries featuring a higher voltage due to substitution of oxygen by the more electronegative fluorine. A sol-gel based process with trifluoroacetic acid as fluorine source was used to synthesize LiNiFeF 6 . Ball-milling with carbon and binder was applied to obtain an electrochemical active LiNiFeF 6 /carbon/binder nano composite. In this study we report on the first electrochemical characterization of a quaternary lithium transition metal fluoride as positive electrode for lithium ion batteries, containing two different transition metals. After 20 cycles of galvanostatic cycling a reversible specific capacity of 88 mAh/g, which is 92% of the initial specific capacity, was retained. In a rate performance test with rates of up to 1C a reversible capacity of 53 mAh/g was obtained. The electrochemically active redox couple Fe 3+ /Fe 2+ was identified by Mössbauer spectroscopy and cyclic voltammetry.The search for alternative cathode materials for lithium batteries to replace common oxide materials has generated considerable research activity to provide reliable battery systems for large-scale applications such as electric vehicles and grid storage. Previous investigations have been performed on a large number of compounds that can be applied as cathode materials for secondary lithium ion batteries such as layered LiMO 2 , silicates Li 2 MSiO 4 and polyanionic olivines LiMPO 4 (M = Fe, Mn, Co). 1,2 Several hundred publications have been published on quaternary lithium metal oxides. 4,5 However, no electrochemical investigations are given about quaternary lithium transition metal fluorides as positive electrode materials. Lithium transition metal fluorides in particular are very promising materials compared to common oxide materials with corresponding electrochemically active cations because the more electronegative fluorine atoms increase the redox potential leading to a higher specific energy. 3 Regarding the theoretic capacity of quaternary lithium transition metal fluorides, they could offer multiple redox couples e.g. M 3+/2+ or M 4+/3+ (e.g. M = V, Cr, Mn, Co or Ni) (eq.

LiNiFeF 6 was used as cathode material in lithium-ion cells and studied by in situ X-ray diffraction (XRD), in operando X-ray absorption spectroscopy (XAS) and 7 Li MAS NMR spectroscopy. An optimised electrochemical in situ cell was employed for the structural and electrochemical characterisation of LiNiFeF 6 upon galvanostatic cycling. The results for the first time reveal the lithium insertion process into a quaternary lithium transition metal fluoride with a trirutil-type host structure (space group P4 2 /mnm). The in situ diffraction experiments indicate a preservation of the structure type after repeated lithium insertion and extraction. The lithium insertion reaction can be attributed to a phase separation mechanism between Li-poor Li 1+x1 NiFeF 6 and Li-rich Li 1+x2 NiFeF 6 (x1 ≲ 0.16 ≲ x2), where not only the weight fractions, but also the lattice parameters of the reacting phases change. The insertion of Li ions into [001]-channels of the trirutile structure causes an anisotropic lattice expansion along the tetragonal a-axes. An overall increase in the unit cell volume of~6% and a reduction in the c/a ratio of~4% are detected during discharge. Changes of atomic coordinates and distances suggest the accommodation of intercalated lithium in the empty six-fold coordinated 4c site. This is confirmed by 7 Li MAS NMR spectroscopy showing two Li environments with similar intensities after discharging to 2.0 V. Furthermore, in operando XAS investigations revealed that only Fe 3+ cations participate in the electrochemical process via an Fe 3+ /Fe 2+ redox reaction, while Ni 2+ cations remain electrochemically inactive. CrystEngCommThis journal is