Lanthanide perchlorate complexes

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. 

A number of methyl substituted PyO have been tried as ligands for coordination with the lanthanides. Depending on the position of the substituent, these ligands impart different degrees of steric strain for the formation of complexes. Since substituents in the 4 or 3 position do not introduce substantial steric hindrance to coordination, Harrison and Watson (160) could synthesize octakis-4-MePyO complexes. Subsequently, Koppikar and Soundararajan (161) could also synthesize octakis-3-MePyO complexes with lanthanide perchlorates. Complexes of 4-MePyO (162, 163) and 3-MePyO (164, 165) with lanthanide iodides and bromides also have a L M of 8 1. 

It has been shown by FT-IR measurements that perchlorate which is normally thought to be innocent , forms inner-sphere complexes with lanthanides. Most of the bound perchlorate is a monodentate. In the case of Eu3+ and Tb3+ bidentate disposition of perchlorate was also observed. The value of association constants of perchlorate with lanthanides are given in Table 7.10. 

Phenomenological data for the thermal decomposition of lanthanide perchlorate complexes of A A [88]. 

Electronic spectral data (cm ) and related bonding parameters of lanthanide(IH) perchlorate complexes of CAAP. Ref. [302]. 

Tridentate N-donor ligands are efficient in separating actinides from lanthanides selectively by solvent extraction, an area of potential great importance in treatment of used nuclear fuel rods. The tridentate ligand 2,2 6 ,2 -terpyridyl (terpy) forms a range of complexes. The perchlorate complexes [Ln(terpy)3] ( 104)3 contain nine-coordinate cations with near- )3 symmetry, a structure initially deduced from the fluorescence spectrum of the europium compound (Section 5.4) and subsequently confirmed by X-ray diffraction smdies (Figure 4.7)... 

Another bidentate ligand whose complexes have been studied in some detail is 1,8-naphthyridine (naph) which, like nitrate, has a small bite angle and is similarly capable of affording high coordination numbers two types of perchlorate complexes have been made, M(naph)6(C104)3 (M = La-Pr) and M(naph)5 (0104)3 (M = Nd-Eu). The former complexes have 12-coordinate lanthanides, confirmed by diffraction methods for the praesodymium complex. The change in stoichiometry is doubtless a manifestation of the lanthanide contraction. 

From the diacetate chloride complexes, compounds containing other counterions, e.g. SCN (Bombieri et al. 1989a), Cl, Br (Bombieri et al. 1989b), or C104 (Bombieri et al. 1986) have been obtained by metathesis in methanol solution. Trinitrate or dinitrate perchlorate complexes of all lanthanide(III) ions except the three smallest ones, Tm(III), Yb(III) and Lu(lII), have also been obtained by trans-metallation from the barium perchlorate complex Ba(I)(C104)2 and the lanthanide nitrate in aqueous solution at room temperature (Arif et al. 1987). Structures have been determined for several of these compounds. 

As a continuation of our work with amides, we have now prepared lanthanide perchlorate and nitrate complexes of BuL and perchlorate complexes of NMBuL, and have examined the effects of unsubstituted and substituted lactams on the coordination number. Lanthanide perchlorate complexes of BuL were found to be eight-coordinated, [Ln(BuL)s] ( 104)3 (Ln = La, Pr, Nd, Sm, Gd Dy, Er, Yb, Y), whereas two different types of... 

The results of three ultrasonic investigations on lanthanide salts have been reported. The studies on erbium(iii) perchlorate in aqueous methanol suggest that inner-sphere perchlorate complexes occur at water mole fractions of less than 0.9. On that basis, the rate constant for the formation of the inner-sphere complex from the outer-sphere complex at 25 °C is 1.2 x 10 s. The case of erbium(m) nitrate in aqueous methanol is more complicated and it is suggested that the mechanism involves the existence of two forms of the solvated lanthanide ion, differing in coordination number, in equilibrium with the outer- and inner-sphere complexes. The results for aqueous yttrium nitrate, on the other hand, represent a simplification over those of previous ultrasonic studies on the lanthanides. The authors reject the normal multistep mechanism in favour of a single diffusion-controlled process. Unfortunately, the computed value for the formation rate constant kt of 1.0 x 10 1 mol s is at least two orders of magnitude lower than the value calculated on the Debye-Smoluchowski approach, but the discrepancy is attributed to steric effects. 

Abstract. A dimeric lanthanide cryptate was obtained by the addition of an excess of cryptand (2.2.1) to a slightly hydrated solution of the monomeric praseodymium (2.2.1) perchlorate complex in acetonitrile. This new lanthanide compound is centrosymmetric and displays the space group P2 /n. The encryptated metal ions are nine-coordinated, they are bonded to all the heteroatoms of a (2.2.1) ligand and they are linked to each other by two p-hydroxo bridges. The hydroxyl groups are relegating the cryptands to both end of the dimer and the praseodymium ions are less effectively accomodated in the macrocylic internal cavities than in the case of the monomeric Pr(2.2.1) complex. The formation of both the monomeric and the dimeric lanthanide complexes is readily observed by proton NMR. 

Moeller and Vicentini (48) have reported the complexes of DMA with lanthanide perchlorates in which the number of DMA molecules per metal ion decreases from eight for La(III)—Nd(III) to six for Tm(III)—Lu(III).apparently due to the decrease in the cationic size. The complexes of the intermediate metal ions have seven molecules of DMA in their composition. Complexes of lanthanide chlorides with DMA (49, 50) exhibit a decrease in L M from 4 1 to 3 1 through 3.5 1. These complexes probably have bridging DMA molecules. The corresponding complexes with lanthanide iodides (51), isothiocyanates (52), hexafluorophosphates (57), nitrates (54, 55), and perrhenates (49, 56) also show decreasing L M with decreasing size of the lanthanide ion. However, complexes of DMA with lanthanide bromides (55) do not show such a trend. Krishnamurthy and Soundararajan (41) have reported the complexes of DPF with lanthanide perchlorates of the composition [Ln(DPF)6]... 

Complexes of the lanthanides with a few cyclic amides are known. Miller and Madan have reported the complexes of 7-butyrolactam with lanthanide nitrates (60) and perchlorates (61). Complexes of lanthanide perchlorates and lighter lanthanide nitrates with BuL have a L M of 8 1. However, complexes of heavier lanthanide nitrates have a L M of only 3 1. By changing the solvent used for the crystallization of the abovementioned complexes, complexes of the formula [La(BuL)4(N03)3] and [Gd(BuL)3(N03)3] could be prepared (60). Complexes of NMBuL (61, 62) and CLM (63-66) have also been reported. 

Probably, the first series of lanthanide complexes with neutral oxygen donor ligands is that of AP with the lanthanide nitrates. In 1913, Kolb (79) reported tris-AP complexes with lighter lanthanide nitrates and tetrakis-AP complexes with heavier lanthanide nitrates. Subsequently, complexes of lanthanide nitrates with AP which have a L M of 6 1 and 3 1 have also been prepared (80-82). Bhandary et al. (83) have recently shown through an X-ray crystal and molecular structure study of Nd(AP)3(N03)3 that all the nitrates are bidentate and hence the coordination number for Nd(III) is nine in this complex. Complexes of AP with lanthanide perchlorates (81, 84), iodides (81, 85), and isothiocyanates (66, 86, 87) are known. While the perchlorates and iodides in the respective complexes remain ionic, two of the isothiocyanates are coordinated in the corresponding complexes of AP with lanthanide isothiocyanates. 

Castellani Bisi (98) has synthesized complexes of lanthanide perchlorates with DMP which have a L M of 8 1 for the lighter lanthanide and 7 1 for the heavier lanthanide complexes. These complexes were prepared by reacting the respective metal salts with an excess of the ligand. When the complexes were prepared under conditions of lower concentrations of the ligand, complexes of DMP with a L M of 6 1 were obtained. The perchlorate groups in all three groups of complexes are ionic. 

Substitution at the 2-position of the pyridine ring in PyO introduces steric hindrance to coordination as is evident from the formation of Heptakis-2-MePyO complexes with lanthanide perchlorates (167) and pentakis-2-MePyO complexes with the corresponding bromides (168), iodides (162) and chlorides (169). The lanthanide nitrate complexes prepared by Ramakrishnan and Soundararajan (170) have the formula Ln(2-MePy0)3(N03)3 -xH20in which all the nitrate groups are bidentate. 

Complexes of PyzO with lanthanide perchlorates (2 79) and hexafluorophosphates 180) are eight coordinate. However, La(III) perchlorate gives the complex La(Pyz0)7(C104)3 2 H20 in which both the water molecules are coordinated to La(III). In the case of complexes of PyzO with lanthanide chlorides 180), the number of coordinated ligands increases as the ionic radius of the lanthanide ion decreases. These complexes probably contain bridging ligands. 

The reactions of lanthanide thiocyanates, nitrates, and chlorides with TPPO have been studied by Cousins and Hart (202, 203, 205). The reactions of lanthanide nitrates with TPPO in ethanol, acetone, ethylacetate and tetrahydrofuran are given in Fig. 1. The nature of the complexes isolated depends on the concentrations of the ligand and the metal ion, temperature of mixing, presence or absence of the seed of the desired complex, size of the cation, and the nature of the solvent. Tetrakis-TPPO complexes of Ce(III) and Nd(III) perchlorates have been reported (206, 207). Two of the perchlorates are coordinated to the metal ion in these complexes. 

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. 

Sylvanovich and Madan (234) have isolated the complexes of OMPA with lanthanide nitrates. With the lighter lanthanide nitrates, bis-OMPA complexes were obtained and the heavier lanthanide nitrates yielded complexes of the type Ln2(OMPA)3-(N03)6. In the latter complexes both bridging and chelating ligands are present. Complexes of OMPA with lanthanide perchlorates are also known (235). Airoldi et al. 

Since 1972, complexes of lanthanides with cyclic sulfoxides have received considerable attention. Zinner and Vicentini (261) have reported the complexes of lanthanide perchlorates with TMSO. The L M in these complexes decreases along the lanthanide series. But in the case of complexes of lanthanide chlorides with TMSO, the L M increases from 2 1 for the lighter lanthanides to 3 1 for the heavier lanthanides (262). It has been suggested that these complexes, especially the bis-TMSO complexes, contain bridging chloride ions. Tetrakis-TMSO complexes with lanthanide isothiocyanates have also been reported (263). 

---