Lanthanide complexes acetylacetone

After our report, many other examples of SIMs based on mononuclear lanthanide complexes have appeared. As relevant examples, we should mention the erbium-organometallic double-decker complexes [11] and the dysprosium-acetylacetonate complexes [12], and the dysprosium-DOTA (H4DOTA, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) complexes reported by Sessoli etal. [13]. 

ATdc values for the lanthanide acetylacetonates are the reverse from that expected for the size effect. The explanation is hkely that the neutral complex with the formula LnAs is coordinatively unsaturated, which means that a hydrated complex exists in the aqueous phase (possibly also in the organic phase). The more coordinatively unsaturated lanthanide complexes (of the larger ions) can accommodate more water and thus are more hydrophilic. The result is a A dc several orders of magnimde lower for the lightest. La, than for the heaviest, Lu. 

Fig. 5. Sublimation behavior of various lanthanide complexes at 10 3 mbar (OEP = 2, 3, 7, 8,12, 13, 17, 18-octa(ethyl) porphyrin acac = acetylacetonate)...

In the process of lanthanide complex formation with the porphyrins, the ligand loses two protons and yields lanthanide hydroxy porphyrin or lanthanide porphyrin X, where X = C1, Br, NOJ, etc. Many lanthanide complexes with substituted porphyrins have been prepared by heating a mixture of porphyrin and the lanthanide salt in imidazole melt in the range 210-240°C. When the complex formation is complete the solvent (i.e.) imidazole is eliminated by either sublimation [81] or by dissolution of the mixture in benzene, followed by washing with water [82]. Further purification requires column chromatography. The starting material can be anhydrous lanthanide chloride or hydrated lanthanide acetylacetonate. After purification the final product tends to be a monohydroxy lanthanide porphyrin complex. 

Complexes of lanthanide nitrates with Schiff derivatives of acetylacetone, 2,4-pentan-edioneanil, and 2,4-pentanedionebenzylamine of the formula [Ln(L-LH)3(N03)](N03)2, where Ln = lighter lanthanides and [Ln(L-LH)2(N03)](N03)2, where Ln = Yb have been isolated from acetone and characterized [256]. In these complexes the ligand does not lose a proton and is in neutral form. In the case of the ligand bisalicylaldehydeethylenediamine, lanthanide complexes are formed with the loss of a phenolic proton [249]. 

Apart from the compounds already mentioned, vanadium, manganese, and cobalt chlorides, tetra-alkoxy derivatives of titanium, acetylacetonates of V, Cr, Mo, Mn, and Ni, Cp derivatives of Zr and Nb, and triphenyl phosphine complexes of Ti and Fe were found to be active. Later lanthanide complexes were included in the list of dinitrogen-reducing systems, the most effective being compounds of samarium and yttrium. 

First works on synthesis of porphyrin lanthanide complexes, both hydrophobic tetraaiylporphyrins [2, 3] and water-soluble [4], appeared at the end of the XX century. Classical techniques are based on boihng of porphyrin with lanthanide metal acetylacetonate in 1,2,4-trichlorobenzene in the inert atmosphere throughout 2.5 3 h. In case of hydrophilic derivatives a short alloying in an imidazole was applied, then the imidazole subhmation was carried out and metallocomplexes were isolated by various chromatography methods. 

The above mentioned impregnated layers suffer from the limitations such as (a) the impregnants are eluted to some extent by the mobile phases used and (b) the stripping of liquid stationary phase from the support by incompatible mobile phases. To overcome these problems, chemically bonded layer materials of similar properties were developed for safer use as stationary phase. Lipophilic Cjg bonded silica gel phases with polar aqueous mobile phases were used for reversed-phase TLC of rare earth elements (52,54,56) and organometallics (180). Lanthanide complexes of tetraphenyl porphine are resolved on layers made of aminopropyl silica gel (NH2) and octadecyl silica gel (Cjg) using methanol-water-acetylacetone-diethylamine in different proportions from the mobile phase (162). 

Mn(II) > Mg(II).270 It should be underlined that titanium and zirconium alkoxides are efficient catalysts for both stages of reaction. Lanthanide compounds such as 2,2/-bipyridyl, acetylacetonate, and o-formyl phenolate complexes of Eu(III), La(III), Sm(III), Er(III), and Tb(III) appear to be even more efficient than titanium alkoxides, Ca or Mn acetates, Sb203, and their mixtures.273 Moreover, PET produced with lanthanides has been reported to exhibit better thermal and hydrolytic stability as compared to PET synthesized with the conventional Ca acetate -Sb203 catalytic system.273... 

Qi M-H, Liu G-F (2004) Synthesis and photoelectronic properties on a series of lanthanide dysprosium(III) complexes with acetylacetonate and meso-tetraalkyltetrabenzoporphyrin. Solid State Sci 6(3) 287-294... 

A broad range of metal centers have been used for the complexation of functional ligands, including beryllium [37], zinc, transition metals such as iridium [38], and the lanthanide metals introduced by Kido [39], especially europium and terbium. Common ligands are phenanthroline (phen), bathophenanthrolin (bath), 2-phenylpyridine (ppy), acetylacetonate (acac), dibenzoylmethanate (dbm), and 11 thenoyltrifluoroacetonate (TTFA). A frequently used complex is the volatile Eu(TTFA)3(phen), 66 [40]. 

Fig. 4.15 The system La(III) acetylacetone (HA) - IM NaC104/benzene at 25°C as a function of lanthanide atomic number Z. (a) The distribution ratio Hl (stars, right axis) at [A ] = 10 and [HA] rg = 0.1 M, and extraction constants (crosses, left axis) for the reaction Ln + 4HA(org) LnA3HA(org) + 3FE. (b) The formation constants, K , for formation of LnA " lanthanide acetylacetonate complexes (a break at 64Gd is indicated) circles n = 1 crosses n = 2 triangles w = 3 squares w = 4. (c) The self-adduct formation constants, for the reaction of LnA3(org) + HA(org) LnA3HA(org) for org = benzene. (A second adduct, LnA3(HA)2, also seems to form for the lightest Ln ions.) (d) The distribution constant Ajc for hydrated lanthanum triacetylacetonates, LnAs (H20)2 3, between benzene and IM NaC104. (From Ref. 28.)...

However, even this simplified formula does not justify the use of the ratio of stability constants of the extracted complexes as the only measure of selectivity of extractive separations. Such a widely used approach is obviously based on an implicit assumption that the partition constants of neutral complexes ML of similar metal ions are similar, so that their ratio should be close to unity. This is, however, an oversimplification because we have shown that the ifoM values significantly differ even in a series of coordi-natively saturated complexes of similar metals [92,93]. Still stronger differences in the values have been observed in the series of lanthanide acetylacetonates, due to different inner-sphere hydration of the complexes (shown earlier), but in this case, self-adduct formation acts in the opposite direction [100,101] and partly compensates the effect of the differences in. Tdm on S T(see also Fig. 4.15). Such compensation should also be observed in extraction systems containing coordinatively unsaturated complexes and a neutral lipophilic coextractant (synergist). 

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