Lanthanide trifluoroacetates

The ratio of the size of the metal ion and the radius of the internal cavity of the macrocyclic polyether determines the stoichiometry of these complexes. The stoichiometry of these complexes also depends on the coordinating ability of the anion associated with the lanthanide. For example, 12-crown-4 ether forms a bis complex with lanthanide perchlorate in acetonitrile while a 1 1 complex is formed when lanthanide nitrate is used in the synthesis [66]. Unusual stoichiometries of M L are observed when L = 12 crown-4 ether and M is lanthanide trifluoroacetate [67]. In the case of 18-crown-6 ligand and neodymium nitrate a 4 3 stoichiometry has been observed for M L. The composition of the complex [68] has been found to be two units of [Nd(18-crown-6)(N03)]2+ and [Nd(NCh)<--)]3. A similar situation is encountered [69] when L = 2.2.2 cryptand and one has [Eu(N03)5-H20]2- anions and [Eu(2.2.2)N03]+ cations. It is important to note that traces of moisture can lead to polynuclear macrocyclic complexes containing hydroxy lanthanide ions. Thus it is imperative that the synthesis of macrocyclic complexes be performed under anhydrous conditions. 

Boyer, J.C, Vetrone, F., Cuccia, LA., and Capobianco, J.A. (2006) Synthesis of colloidal upconverting NaYF4 nanocrystals doped with Er3-I-, Yb3+ and Tm3-I-, Yb3-I- via thermal decomposition of lanthanide trifluoroacetate precursors. J. Am. Chem. Soc., 128, 7444-7445. 

Entry 5 is an example of nitration in acetic anhydride. An interesting aspect of this reaction is its high selectivity for the ortho position. Entry 6 is an example of the use of trifluoroacetic anhydride. Entry 7 illustrates the use of a zeolite catalyst with improved para selectivity. With mixed sulfuric and nitric acids, this reaction gives a 1.8 1 para ortho ratio. Entry 8 involves nitration using a lanthanide catalyst, whereas Entry 9 illustrates catalysis by Sc(03SCF3)3. Entry 10 shows nitration done directly with N02+BF4, and Entry 11 is also a transfer nitration. Entry 12 is an example of the use of the N02—03 nitration method. 

Other solubilities relevant to this section include those for LaCl3 in aqueous ammonia (173), lanthanide trifluorides in aqueous hydrofluoric acid (133b, 240b, 281,315), and lanthanide trifluorides in aqueous trifluoroacetic acid (316). Trifluoroacetic acid seems to have a marked solubilizing effect on these trifluorides. 

In a study of the Hofmann-Loffler reaction, the jV-chloro-amine (8a) was irradiated in trifluoroacetic acid solution and underwent photolysis to yield the pyrrolidine (9a) together with the 205-isomer (9b) in a ratio 8 1. The starting amine (8b) was prepared by hydrogenation of (8c), followed by von Braun demethylation and hydrolysis of the JV-cyano-amine (8d) which was so formed. The n.m.r. spectrum of (8b) and of related amines in the presence of lanthanide shift reagents was discussed.10... 

The first report of a cycloaddition reaction in the presence of an optically active calalyst appeared in 1983 . The dienes 14 add to benzaldehyde in the presence of 1 mol% of the chiral lanthanide NMR shift reagent Eu (hfc)3, i.e. tris[3-(heptafluoropropyl-hydroxymethylene)-(+)-camphorato]-europium(in), to give, after treatment with trifluoroacetic acid, the dihydro-y-pyrone 15 enriched in the (/f)-enantiomer, the degree of... 

We considered various other counterions for the lanthanide salts with a view to producing more active nitration catalysts. The use of trifluoroacetate and... 

Other methods. Glass formation of the aqueous solutions of lanthanide perchlorates, chlorides, nitrates and trifluoroacetates were studied by Kanno and Akama... 

Fig. 11. Glass transition temperatures across the lanthanide series in the presence of trifluoroacetate, nitrate and...

To date, primarily alkali lanthanide tetrafluorides such as NaYp4 and related crystals have been prepared by thermal decomposition. The majority of publications in this field use a method first published by Mai et al [25]. These researchers used rare-earth trifluoroacetates as reactants. The trifluoroacetates decomposit in the heat under release of fluoride and volatile by-products. Mai et al. have focussed on the synthesis of differently sized and shaped nanocrystals but did not show any upconversion data. The first upconverting NaYp4-based nanocrystals synthesised using the Mai method have been published by Boyer et al. [27, 28]. The method has been modified by Ehlert et al. to realise four different, spectroscopically distinguishable upconverting nanocrystal species [26]. Figure 3 shows the upconversion luminescence of these nanocrystals on excitation with a 980 nm laser diode. 

Traces of water in our solutions of monomeric praseodymium cryptate are most probably responsible for the formation of the dimeric complex reported here. Partial hydrolysis of this complex takes place because the excess of (2.2.1) cryptand brings about a pH increase. Incomplete hydrolysis of a lanthanide macrocyclic complex has also been noted by Biinzli et al. [14] who prepared a dimeric praseodymium complex with 1,4,7,10,13-pentaoxacyclododecane (15-crown-5) by dehydrating in vacuo a monomeric species. The metal ions in this dimer are bridged by only one hydroxyl group and by three trifluoroacetate anions. The distance between the two praseodymium ions in the (2.2.1) cryptate reported here is 3.927(1) A this value compares very well with the values reported for the two other dinuclear lanthanide complexes mentioned above [13-14]. 

Y.P. Du, Y.W. Zhang, L.D. Sun and C.H. Yan, Luminescent monodisperse nanocrystals of lanthanide oxyfluorides synthesized from trifluoroacetate precursors in high-boiling solvents, J. Phys. Chem. C, 112,405 15 (2008). 

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