Lanthanide complexes solvation

The complexes may also be prepared by the addition of a solution of carboxylic ligand to an equivalent amount of (i) a lanthanide carbonate [28], (ii) hydroxide [29] or (iii) oxide [30] with a slight excess of the latter. The insoluble part is filtered and the filtrate evaporated to obtain crystalline complex. Anhydrous lanthanide complexes of small chain carboxylic acids may be prepared by (i) the dissolution of lanthanide carbonate in excess of the carboxylic acid, followed by heating to obtain complete dissolution of the suspension and partial evaporation of the solution to obtain the crystals [31], (ii) anhydrous lanthanide is converted into the corresponding monochloroacetate by the addition of an excess of monochloroacetic acid, followed by heating under reflux at reduced pressure for 2 h. Then ether is added to precipitate the salt [32], (iii) the addition of dimethyl formamide and benzene to lanthanide acetates and distillation of the water azeotropes to obtain anhydrous complexes. The last procedure yielded lighter lanthanide complexes solvated with dimethyl formamide [33], The DMF may be removed by heating in a vacuum at 120°C. 

Ln-Halides. The complexation/solvation criteria is just one reason why lanthanide halides are the most common precursors in organolanthanide chemistry. In this evaluation, lanthanide iodides are often preferred to bromides and chlorides, however the former are more difficult to synthesize and are much more expensive [96f. Waterfree, solid Ln-halides are ionic substances with high melting points which immediately absorb water when exposed to air, forming hydrates (I > Br > Cl ). Therefore, they have to be handled under an inert gas atmosphere. The main use of the halides is for the production of pure metals [96]. Some methods of preparing Ln(III)-chlorides are summarized in Scheme IV [96],... 

The potential use of non-solvated lanthanide cyclopentadienyl hydride complexes as catalysts in alkene C-H bond activation, hydrogenation of alkynes led to synthesis of aluminum hydride organo lanthanide complexes. Examples of such complexes with polymeric structure and chain structure have been characterized [251]. 

Direct reactions of anhydrous triflic acid with lanthanide chlorides or oxides often resulted in complexes solvated by the acid, which are viscous liquids with a very low vapor pressure. Thus it is advisable to perform reactions with diluted trific acid in an aqueous solution. If anhydrous lanthanide chlorides are used, they are to be hydrated with care in water before use in order to avoid contamination by side products. For instance, anhydrous ScCl reacts violently with water, the sample is first cooled at -180 °C and water is added slowly. The mixture is then warmed in 12 h to room temperature. The anhydrous compound, ScCl -nH O (n= 3.7) is obtained as a white solid after boiling the solution to dryness. 

Note the distinction between the terms shift reagent and solvating agent. Because of the differences in the mechanism of binding and induced anisochrony, the former is reserved for lanthanide complexes and the latter for diamagnetic compounds. 

Z10 Electronic Spectra of Lanthanide Complexes 39.Z11 Lanthanides in the Dipositive Oxidation State 39.Z11.1 Hydrated species 39. Z 11.2 Other solvated species 39. Z 11.3 Complexes with nitrogen donors... 

A qualitative assessment of the relative ligand strengths of interaction between nitrate ion, water and four organic solvents and a number of 4-3 lanthanide ions was made from changes in f-f transitions. The affinity series of the lanthanides for the nitrate ion and the solvents was DMF > tributylphosphate > NO3 H2O > EtOH > dioxan. In DMF, hexadimethylformamide-lanthanides were the only complexes present, although conductivity measurements showed a major portion of the nitrate ion to be ion-paired, while in anhydrous dioxan the solvent-solute interaction is so weak that the rubidium-lanthanide nitrate double salts employed were not soluble. In water, in the absence of excess nitrate ion, hexaquo-lanthanide complexes predominate with little nitrate ion-association, in line with better nitrate solvation in protic solvents. 

Electrostatic bonding ows for a wide variety of coordination numbers (CN = 6-12) for lanthanide complexes. Steric, electrostatic, and solvation effects are the dominating criteria in determining the geometry of lanthanide complexes. The primary sphere hydration is not constant across the series hydration numbers are 9.0-9.3 for the larger, lighter lanthanides and 7.5-8.0 for the heavier, smaller lanthanides (2). 

Regarding the choice of the lanthanide salt, the nature of the counteranion (trifiate, nitrate, perchorate, etc.) is not innocent, depending on the solvent in which the complex will be studied. Indeed, the solvation process is total in water, and the aqua anion will not interact, whereas, in an organic solvent, there are possibilities of coordination of the counteranion. As an example, trifiate is more coordinating than a nitrate ion, and the choice of the counterions—with relatively weak or strong coordination abilities—may allow predicting the final structure of the lanthanide complexes. 

The coordination chemistry of other n ligands has also been explored (Chart 1 Bombieri and Paolucci, 1998 Edelmaim et al., 2002). The cyclooc-tatetraene dianion, (ri -CgHg) , commonly referred to as COT, also famous for the isolation of uranocene (Avdeef et al., 1972 Streitwieser and Mueller-Westerhoff, 1968), is known to stabilize lanthanides in all three oxidation states (+2, +3, and +4). In fact, the first COT lanthanide complexes to be prepared were solvated Ln(COT) species with Ln = Eu, Yb (Hayes and Thomas, 1969). Most rare earth COT complexes, which feature both mono-and bis-COT, are, however, of the trivalent lanthanides (Bombieri and Paolucci, 1998). Cerocene, Ce(COT)2, merits a special mention since its electronic structure is still being actively investigated (Ferraro et al., 2012 Kerridge, 2013 Kumari et al., 2013 Walter et al., 2009). 

The rate of water exchange between the inner coordination sphere of rare earth ions and bulk water has been extensively studied by ultrasonic absorption and NMR spectroscopy. It is very fast and ranges between lO and 10 s (Cossy and Merbach 1988, Rizkalla and Choppin 1991). Ligand substitution processes and the kinetics of lanthanide complexation in water, especially with polyaminocarboxylates, have also been the subject of several studies (Lincoln 1986, Nash and Sullivan 1991). As for the determination of solvation numbers, investigations in anhydrous organic solvents are more sporadic. 

Borrowing from the tools of crystal engineering [25], here we use the crystal structures of lanthanide complexes to study interactions whose effects on solution chemistry, including extraction, may be important but are not easily measured. The examples discussed here will include crystal structores of a lanthanide cation complexed to an extractant-functionahzed EL anion, a co-crystal of an ionic lanthanide complex with neutral ligands, and a salt composed of solvated metal complexes as both cations and anions. Each of these crystalline compounds is ultimately a pure salt, and in examining their crystal structures, we will pay particular attention to how high ionic strength affects both the inner- and outer-sphere interactions observed in these stmctures. 

The first is observed when the chiral solvating agent has a high association with the achiral lanthanide complex. Bonding of the CSA to the lanthanide (Ln) effectively creates a chiral lanthanide shift reagent (Ln-CSA) (Eqn [4]). This species then interacts... 

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