Trivalent lanthanide derivatives

The synthesis and spectroscopic characterization of the monopor-phyrinate trivalent lanthanide derivatives, bearing the monoanionic Tp, of general formulas [Yb(TPP)Tp] have been reported by Boncella et who also described their photophysical properties includ-... 

The structure of this unique uranium (III) derivative is of much interest. Unfortunately we have been unable to obtain crystals satisfactory for an X-ray analysis. The compound is most likely similar to that of the binary, trivalent lanthanide derivatives, e.g., pyramidal rather than planar, on the basis of infrared spectroscopy. Planar M[N(SiMe3)2]3 show bands due to vas MNSi2 at 900 cm 1 whereas pyramidal ones absorb at 990 cm l. Since U[N(SiMe3)213 has its vas UNSi2 absorption band at 990 cm - - it is most likely pyramidal in the solid state. Not surprisingly the analogous thorium (III) derivative cannot be prepared in a similar fashion. 

Lanthanide metals are interesting as starting materials to prepare various divalent or trivalent lanthanide derivatives by reaction with or-ganic compounds, this point will not be detailed here and information can be found in ref. (10). It is well known that lanthanide metals can give intermetallic compounds with various metals (Co, Ni, Mg,..) which are able to absorb large quantities of hydrogen. Recently some of these hydride alloys were found to be able to reduce alkynes, mono and di-sub-stituted alkenes to saturated hydrocarbons (12). Some reactions performed with LaNi H at 0 C and then room temperature in THF-MeOH (2 3) are listed below ... 

Harrowfield et al. [37-39] have described the structures of several dimethyl sulfoxide adducts of homo bimetallic complexes of rare earth metal cations with p-/e rt-butyl calix[8]arene and i /i-ferrocene derivatives of bridged calix[4]arenes. Ludwing et al. [40] described the solvent extraction behavior of three calixarene-type cyclophanes toward trivalent lanthanides La (Ln = La, Nd, Eu, Er, and Yb). By using p-tert-huty ca-lix[6Jarene hexacarboxylic acid, the lanthanides were extracted from the aqueous phase at pH 2-3.5. The ex-tractability is Nb, Eu > La > Er > Yb. 

In contrast to the situation observed in the trivalent lanthanide and actinide sulfates, the enthalpies and entropies of complexation for the 1 1 complexes are not constant across this series of tetravalent actinide sulfates. In order to compare these results, the thermodynamic parameters for the reaction between the tetravalent actinide ions and HSOIJ were corrected for the ionization of HSOi as was done above in the discussion of the trivalent complexes. The corrected results are tabulated in Table V. The enthalpies are found to vary from +9.8 to+41.7 kj/m and the entropies from +101 to +213 J/m°K. Both the enthalpy and entropy increase from ll1 "1" to Pu1 with the ThSOfj parameters being similar to those of NpS0 +. Complex stability is derived from a very favorable entropy contribution implying (not surprisingly) that these complexes are inner sphere in nature. 

Several excellent reviews are available covering different scientific purposes and technological applications of phthalocyanines [46-51]. Here, we focus on synthetic aspects of one particular type of Pc-derivative, namely bis(phthalocyaninato) complexes of trivalent lanthanides, as well as analogous heteroleptic complexes containing porphyrin and porphyrin-like ligands. 

Neutral N-derivatized octadentate ligands based on cyclen (1,4,7,10-tetraazacy-clododecane) form tripositive cationic complexes with the trivalent lanthanides [116-124]. The N-substituted tetraamide derivatives have proven useful in understanding the relationship between the solution structure of the Ln3+ complex and its water exchange rate, a critical issue in attaining optimal relaxation efficiency of CA s [125-131]. 

The investigation of fluorinated alcohols as suitable ligands for low molecular lanthanide complexes was initiated in the early 1970s [76]. Recently, more detailed syntheses and characterization of derivatives of trivalent lanthanide... 

The most thermodynamically stable and kinetically inert complexes of the trivalent lanthanides are those of the ligand DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate) (42, 43). Our search for lanthanide macrocyclic complexes that would remain intact for longer time periods led us to examine derivatives of DOTA. There are two potential difficulties with the use of DOTA complexes of the trivalent lanthanides for RNA cleavage. First, the overall negative charge on the complex is not conducive to anion binding for example, Gd(DOTA)-does not bind hydroxide well (44). Second, DOTA complexes of the middle lanthanides Eu(III) and Gd(III) have only one available coordination site for catalysis. The previous lanthanide complexes that we used, e.g., Eu(L1)3+, were good catalysts and had at least two available coordination sites. 

Since tropolones and 3-hydroxy-4-pyrones are taken in this chapter to be enols, we now cite their binding as enolato ligands to lanthanum and all the other trivalent lanthanides (save the radioactive promethium) " " . Likewise, we note such studies for complexes with enolato ligands derived from 3-acetyl-4-hydroxycoumarin, dehydroacetic acid and their oximes, and with the aromatic enediolates, squarate and croconate. Periodic trends in thermodynamic parameters were reported and analyzed in these studies. 

On the other hand, there are 8 electrons for intra-cluster covalent bonding when one counts as (4x2)-i-(l x6)- (6xl) = 8. Sulfide-chloride derivatives, [R4N]S3Cl3 of this structure type may be obtained with the trivalent lanthanides R=La-Nd, Gd (Lissner and Schleid 1994). Again, these may be understood with the ionic or the covalent view, according to, for example, [(La3+)4(N3-)](S2-)3(Cr)3 vs. (4x3)-f(1 x5)-(3x2)-(3x 1) = 8. 

The Lewis acid and coordinating properties of trivalent lanthanides were used very early. In 1922, lanthanide trichlorides were compared to other metal halides as catalysts for acetalization (38). The first detailed study of the application of lanthanide derivatives to problems of organic synthesis seems to be the report of Pratt in 1962 (39) who showed that CeCl is a superior catalysts for the regioselective addition of p-toluidine on 5,8-quinoline-quinone (followed by reoxidation) (eq.j 26j). 

The metaUothermic reduction with sodium appears to be special, as Na+ has an ionic radius very similar to that of the large trivalent lanthanides, R +. Therefore, the reduction of all of the trichlorides RCI3 that crystallize with the UCI3 type of structure with sodiiun produces stuffed derivatives of this structure, Nao.sRCls or NaR2Cl6. These have been crystallographicaUy characterized for R = Ce, Pr, Nd, Sm, Eu (seeFigure 8). Two classes need to be considered Those with R = Ce, Pr are one-dimensional metals, in accord with the formulation (Na+)(R +)2(e )(C1 )6. The others with R = Nd, Sm, Eu are mixed-valent chlorides, (Na )(R ) (R +)(C1 )6. 

Frdchet and coworkers [314] have recently described a similar self-assembly of benzyl ether dendrons, possessing carboxylic acid substituents at their focal points by metal-ligand coordination around a core of trivalent lanthanide metals (e.g., Er+, Eu", or Tb+ ). These self-assembled dendrimers were isolated by using ligand exchange reactions to produce structures derived from metal-ligand ionic interactions as shown in Figure 12. As a consequence,... 

The CMPO derivatives have been designed as efficient extractants for the trivalent lanthanide/ actinide group separation in the TRUEX process studied in the United States and Russia, see, for example, the review by Paiva and Malik (2004). Danonstration tests on the use of synergic mixtures of CMPO (Af,A-di-isopropyl carbamoyl methyl alkyl phenyl phosphine oxide) and chloroderivative CCD" for lanthanide/actinide extraction have been carried out in the development of the UNEX process, see Section 19.2.2 of this review. 

In Table 20.7 are listed radii of trivalent actinide ions (coordination number CN 6) derived from measurements on trichlorides by the method of Bums, Peterson, and Baybarz [288]. Determinations of M-Cl distances have been made for M = U, Pu, Am, Cm, and Cf the other values were estimated by use of unitcell data and curve fitting. All these radii are relative to the trivalent lanthanide radii of Templeton and Dauben [396], who employed data from cubic sesquioxides and assumed atomic positions to establish M-O distances. Also included in Table 20.7 are radii of tetravalent actinide ions obtained from the M-O distances calculated from unit-cell parameters of the dioxides [1] by subtracting 1.38 A for oxygen (the value used [396] for the sesquioxides). For comparison. Shannon s ionic radii, derived from oxides and fluorides, and Peterson s tetravalent radii, derived from dioxides, are shown [537,538]. As... 

The solvent extraction of trivalent lanthanides (La, Nd, Eu, Er, and Yb) in three calixarene-type cyclophanes was described by Ludwig et al. (1993). Calixarenes are (1, w)-cyclophanes with a cavity formed by bridged phenyl units and various derivatives are formed with the introduction of substituents onto the skeleton. The three calixarenes studied are /7-tert-butylcalix/6/arene hexacarboxylic acid (LI), /i-tert-butylcalix/4/arene tetracarboxylic acid (L2) and [3,1,3, l]-cyclophane (L3). LI, L2 and L3 have different cavity sizes and contain carboxylic acid groups at the lower rim to achieve a high coordination number for Ln and to prevent the phase transfer of counter anions. 

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