Lanthanide acetates

A number of complexes of urea and substituted ureas with various lanthanide salts have been isolated. The lanthanide acetates give both anhydrous and hydrated complexes with urea (67, 68). The hydrated complexes could be dehydrated by drying the complexes over CaCl2 or P4Oi0 (68). It is interesting to note that in the complexes of substituted ureas like EU (70) and CPU (71), the L M is independent of the anion. The anions in these complexes with a L M of 8 1 are apparently nonco-ordinated. Seminara et al. (72) have reported complexes of lanthanide chlorides with DMU and DEU which contain five and three molecules of the ligand respectively per... 

The spectra of the adducts of lanthanide nitrates (123) and perchlorates (124, 125) with dioxane and lanthanide acetates with DMF (44) show very little change from the corresponding ligand spectra. In these cases, it has been suggested that the ligands occupy only lattice positions and that there is no strong interaction of the ligand with the metal. 

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. 

Vadura, R. and Kvapil, J. (1971) Growth and lattice parameters of the lanthanide carboxylates 1. Tetrahydrated lanthanide acetates. Materials Research Bulletin, 6, 865-873. 

Fig. 15. Plots of the formation constants (log Kj) and the enthalpy (AHj) of formation of the lanthanide acetate complexes vs. L (25, 64).

Another source of inaccuracy for most of these nuclei is represented by the large, non-negligible contribution of the diamagnetic CS A, which may pollute the experimental measurements, yielding a combined interaction rather than the electron-nuclear dipolar anisotropy alone. Simulations where the CSAs are added to the hyperfine tensors indeed provide a better approximation to the observed spectra. However, as described in the case of lanthanide acetates by Brough et al. [23], this correction is experimentally demanding, as it requires the measurement of CS A... 

Ganapathy S, Chacko V, BryantR,EtterM (1986) Carbon CP-MASS NMR and X-ray crystal structure of paramagnetic lanthanide acetates. J Am Chem Soc 108 3159-3165... 

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