Lanthanide bromides

Dimethyl sulfoxide complexes of the lanthanide bromides [M(Me2SO)gBr2][Br] have been isolated (480), which are 1 1 electrolytes in acetonitrile solution, indicating a coordination number of ten. 

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]... 

In the complexes of TBPO with lanthanide perchlorates, absorptions at 400 cm-1 have been ascribed to i>Ln o (210). Absorptions due to lanthanide-perchlorate vibrations (Ln—OC103) have been identified in the region 290—360 cm-1 for the complexes of lanthanide perchlorates with 2,6-DMePyO (171), TBPO (210), DMMP (210), and for the complexes of Ce(III) perchlorate with TPPO and TBPO (206, 211). Ln-Cl vibrations occur at 230 cm-1 in the complexes of lanthanide chlorides with TBP (195) and TPPO (202). In the complexes of lanthanide bromides with TBP (295), i Ln— Br occurs in the region of 195 cm-1. 

Figure 4. Spectra of 6-month-old mixtures of EsBr3 10 mole %) in several lanthanide bromides. Absorption peaks of trivalent californium are also present.

Lanthanide bromides and iodides have found important applications in a completely different field. They are added as additives in high-pressure discharge lamps in the lighting industry to improve the arc stability and the colour quality. The latter is due to the contribution of the multiline spectrum of the doped rare earths which are added to the salt mixture. Lanthanide trihalides of dysprosium, holmium, thullium, gadolinium and lutetium are used frequently for this purpose (Hilpert and Niemann, 1997). 

The number of vapour pressure studies of the tribromides is significantly less. Gietmann et al. (1996) systematically measured the vaporization of the lanthanide bromides using mass spectrometry, showing the importance of the dimeric molecules in the vapour. For the light lanthanide tribromides (La, Ce, Nd) the fraction of dimers is around 0.01, but for TbBr3 it is 0.03,... 

Preparation of lanthanide bromides and iodides is performed under similar but aggravating conditions, according to Scheme IV [96fj. Small-scale syntheses of solvated iodides are given in Scheme V [110-112], Strongly donating solvents such as iV-methylimidazole (iV-Melm) can accomplish complete anion-cation separation, as has been shown for [Sm(lV-MeIm)8]l3 under anaerobic conditions [113],... 

As a rule, lanthanide bromides, and more especially the iodides, are more reactive because of their often higher solubility (Table 5), and also show enhanced thermodynamic lability (Scheme III). Moreover, reactivities different from those of the chloride analogues should be expected because of, for example, the softer Lewis basicity of the iodide anion and different solubility properties of the eliminated alkali salts. Table 5 gives an arbitrary sample of solubilities for lanthanide halides in various standard-laboratory donating solvents [97f]. 

Shen and co-workers reported a method for preparing lanthanide-NHC halides through protonolysis.75 Reaction of the imidazolium bromide salt with anionic LiLn(N Pr)4 affords salicylaldiminato-functionalized NHC-lanthanide bromides (Scheme 33). The complexes were all characterised by single crystal X-ray diffraction and exhibit capped octahedral geometries. The NHC-Ln MIC bond angles decrease Nd>Sm>Er> which is consistent with decreasing ionic radii, and the Ln-NHC bond lengths also... 

Scheme 33 Synthesis of salicylaldiminato-functionalized N-heterocyclic carbene lanthanide bromides.

Figure 8.19 Synthesis of aryloxo functionalized NHC lanthanide bromides.

Zhang, J.G, Yao, H.S., Zhang, Y. et al. (2008) Lanthanide carbene halides through protonolysis of Ln-N bonds by imidazolium salts synthesis and structure of salicylaldiminato-functionalized N-heterocyclic carbene lanthanide bromides. Organometallics, 27, 2672. 

Bipyridyl complexes with lanthanide bromides do not seem to have received attention, but the first lanthanide iodide complexes were reported in 1999. In a comparative study with UI3, complexation of bipy with (Ln = Ce, Nd) was investigated. UI3 and Cels both form 1 1 and 1 2 complexes in solution, with a 1 3 complex at high bipy concentrations, whereas Ndls only forms a 1 2 complex. The structure of [Cel3(bipy)2(py)].5py.bipy was reported it has eight-coordinate Ce, with Ce—(bipy) = 2.67(3) A, Ce—I = (average 3.23(3) A) and Ce—N 2.678(9) A. Reaction of [Ndl3(py)4] and bipy in attempts to make the Nd analogue resulted in dimeric [(bipy)3Nd(/i-OH)2Nd(bipy)3]l4 3Py, presumably due to inadvertent hydrolysis. ... 

G. Vicentini and C. Airoldi, J. Inorg. Nucl. Chem., 33, 1733 (1971). Addition compounds between lanthanide bromides and Y,iV-dimethyl-acetamide. 

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