Anion lanthanide perchlorates

Complexes of picolinamide with lanthanide perchlorates, nitrates, and isothiocyanates have been isolated by Condorelli et al. (59). All these complexes show changes in the stoichiometry on going from La(III) to Lu(III). The ligand acts as bi-dentate with the oxygen of the amide group as well as the heterocyclic nitrogen coordinating to the metal (Structure I). While the anions in the perchlorate complexes are not coordinated to lanthanide ions, those in the nitrate and isothiocyanate complexes are coordinated. 

Vicentini and coworkers have reported the complexes of DPPA with lanthanide perchlorates 224), hexafluorophosphates 225), chlorides and nitrates 226). The anions in the perchlorate and hexafluorophosphate complexes are noncoordinated and hence the complexes are six coordinated. Conductance data for the nitrate complexes indicate that the coordination interaction between the lanthanide ion and the nitrate ion decreases along the lanthanide series 226). 

Vicentini and Dunstan (227) have obtained tetrakis-DDPA complexes with lanthanide perchlorates in which the perchlorate groups are shown to be coordinated to the metal ion. DDPA also yields complexes with lanthanide isothiocyanates (228) and nitrates (229). All the anions in these complexes are coordinated. DPPM behaves more or less like DDPA which is reflected in the stoichiometry of the complexes of DPPM with lanthanide perchlorates (230), nitrates, and isothiocyanates (231). Hexakis-DMMP complexes of lanthanide perchlorates were recently reported by Mikulski et al. (210). One of the perchlorate groups is coordinated to the metal ion in the lighter lanthanide complexes, and in the heavier ones all the perchlorate groups are ionic. 

Complexes of TSO with lanthanide perchlorates which have the formula Ln(TS0)9(C104)3 have been reported by Edwards et al. (266) (Ln = Ce or Y). Later, Vicentini and Perrier (267) have prepared the whole series of complexes of TSO with lanthanide perchlorates and have shown that the L M in these complexes gradually decreases from 9 1 to 7 1 as the cationic size decreases. These authors could not prepare Y(TS0)g(C104)3 reported by Edwards et al. (266). Instead, they obtained the complex of the composition Y(TS0)7(C104)3. Two series of complexes of TSO with lanthanide hexafluorophosphates are known (268, 269). While the L M in one of the series is 7.5 1, in the other series it is found to be 8 1. The change in the stoichiometry of the two series of compounds is attributed to the preparative procedures adopted. In both the series of complexes, the PFg ion remains ionic. Lanthanide nitrates (270), chlorides (270), and isothiocyanates (271) also yield complexes with TSO. In all these complexes, changes in the stoichiometry could be observed when the lanthanide series was traversed. In all these complexes the anions are coordinated to the metal ion. 

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. 

The complexes formed with cyclopropylene urea (CPU) have the formula [193] Ln(CPU)8X3, where X = CIOJ, NO. Complexes of this composition have been synthesized with all the lanthanides when the anion is perchlorate. When X = nitrate it was possible to synthesize complexes for the early lanthanides (i.e.) La to Gd. In both cases the anions are not coordinated as evidenced by IR spectra. Europium complexes, with X = CIO, NOJ, I-, PFg have been found to be of the same symmetry around Eu(III) as evidenced by their emission spectra [178]. 

Terpyridyl is a terdentate ligand and behaves like bipyridyl, and o-phenanthroline. The three terpyridyl ligands coordinate to the lanthanide when the anion is perchlorate. The emission spectrum of the Eu(III) complex points to D3 symmetry which has been confirmed by the determination of the structure [242],... 

In contrast to the alkali metals, the lanthanides do not form crown ether complexes readily in aqueous solution, due to the considerable hydration energy of the Ln + ion. These complexes are, however, readily synthesized by operating in non-aqueous solvents. Because many studies have been made with lanthanide nitrate complexes, coordination numbers are often high. Thus 12-coordination is found in La(N03)3(18-crown-6) (Eigure 4.4), 11 coordination in La(N03)3(15-crown-5), and 10 coordination is found in La(N03)3(12-crown-4). Other complexes isolated include Nd(18-crown-6)o.75(N03)3, which is in fact [ Nd(18-crown-6)(N03)2 +]3 psid(N03)6]. Other lanthanide salts complex with crown ethers small crowns like 12-crown-4 give 2 1 complexes with lanthanide perchlorates, though the 2 1 complexes are not obtained with lanthanide nitrates where the anion can... 

An additional phenomenon related to the anion in the aqueous phase is a so-called perchlorate effect (Gmelin 1983). It has been often observed that extraction of metal ions from perchlorate media is greater than that from equivalent nitrate or chloride solutions. Marcus reports (Gmelin 1983) the effect in two different systems involving acidic extractant molecules. The enhanced extraction of metal ions is also observed in systems based on neutral molecules. In the latter case, formation of aqueous complexes of stoichiometry 1 3 (R L) is required for neutrality in the extracted complex. As lanthanide perchlorate ion pairs normally do not exist in aqueous solution, it is something of a dichotomy that extraction from perchlorate medium should be more readily achieved than from more strongly complexing nitrate (or even chloride) solutions. An explanation for the phenomenon, and for the relative ease of extraction of metal ions from salt solutions (relative to that from equivalent acids), may lie in the effect of the solutes on water structure. 

The two ligands that have been most extensively studied are ortho-phenanth-roline and 2,2 -bipyridyl. Both of these ligands are bidentate and are only weakly basic. With ortho-phenanthroline the maximum number of bound ligands is four when the anion is the perchlorate ion (Krishnamurthy and Soundararajan, 1966). The tris-complex with one coordinated perchlorate ion (as indicated by the infrared spectrum) has also been obtained (Grandey and Moeller, 1970). There do not appear to have been any dipyridyl complexes with the lanthanide perchlorates prepared at the present time, although there does not seem to be any reason they would not form. 

Schiff base macrocyclic complexes of lanthanides have been prepared by a metal-template condensation of a diamine and 2,6-diacetyl or 2,6-diformyl derivative of pyridine or p-cresol [74]. The yield of these complexes depends on the radius of the metal ion and the donor ability of the counterion [75]. The acetate anion gave high yields while chloride and perchlorate anions gave poor yields [76]. In general the template synthesis... 

In these complexes anion coordination must be present with the exception of perchlorate. Lanthanide contraction may also be an influencing factor. The molecular structure [ 189] of Eu(TMU)3(N03)3 shows the presence of bidentate nitrates with a coordination number of nine. The coordination polyhedron is neither the tricapped trigonal prism nor the monocapped square antiprism which may be due to the small bite of nitrate ligand. The dimethyl acetamide (DMA) complexes behave similarly as those of tetramethyl urea (TMU) with less steric requirements as evidenced by the synthesis of [180-182] La(DMA)8(C104)3, La = La-Nd La(DMA)7(C104)3, La=Sm-Er La(DMA)6(C104)3, La = Tm-Lu. 

The synthesis of lanthanide complexes [244] with multidentate diethylenetriamine (dien) gave rise to two types of complexes, Ln(dien)3(N03>3 for Ln = La-Gd, and Ln(dien)2(N03)3 for Ln = La-Yb. The tris complexes contain ionic nitrate while the bis complexes contain both ionic and coordinated nitrate ions. The coordination number is nine in the tris complexes while it is not known with certainty in the bis complexes. With triethylene triamine (tren) two types of complexes [Ln(tren)(N03)3] and Ln(tren)2(N03)3 have been isolated. In the bis complexes both ionic and coordinated nitrate groups are present for larger lanthanides (La-Nd) but only ionic nitrate for smaller lanthanides (Sm-Yb). When perchlorate is the anion [245] Ln(tren)(C104)3 (Ln = Pr, Gd, Er) and Ln(tren)2(C104)3 for Ln = La, Pr, Nd, Gd, Er complexes were obtained. The monocomplexes contain coordinated perchlorate ions while the bis complexes contain ionic perchlorate ions. 

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