Rare earth triiodide

Tml2, Dyh and Ndh have also been used in an acetonitrile/amine coupling reaction, which produced amidines of general formula MeC (=NH)NR R R R2 = H, Me H, iPr H, fBu Et2). The reaction is sub-stoichiometric in rare-earth diiodide but not really catalytic since part of the produced amidine remained tightly held aroimd the rare-earth metal it could be liberated by heating a trivalent intermediate formulated as Rl2(amidine)4(amidinate) (R = Nd, Dy, Tm) imder vacuum, and the residue could be recycled to produce more amidine. This reaction is not specific of the divalent iodides since many rare-earth triiodides were also effective. In the case of dysprosium and diethylamine, an intermediate trivalent amidine complex has been isolated and structurally characterised in the form of the zwitterionic [Dy MeC(=NH)NEt2 4][(I)3] (Bochkarev et al., 2007) (Figure 9). 

Special efforts need to be taken for the preparation of rare-earth triiodides, RI3. Apparently due to the special stability of the oxyiodides ROI, the above outlined procedures do not work well. It turned out that the best route to pure triiodides is the synthesis from the elements in sealed Pyrex containers. Small amounts of hydrogen (often present in rare-earth metals, especially powder samples) seem to catalyse the reaction. The reaction of rare-earth metals with Hgli also leads to pure triiodides (Corbett 1983). The formation of elemental mercury is the major drawback of this procedure and it is, therefore, not favorable especially for large batches. 

Vibrational frequencies (in cm ) of pyramidal (Cj,) rare-earth triiodide vapors - ... 

Acetic acid-acetic anhydride, 85 Alkali azides, 79 Alkaline earth azides, 79 Alumino-oxalates, 36 Amalgams, 5 concentration of, 17 preparation of, 6 rare earth metal, 15 Ammonium nitrourethane, 69 Ammonium perrhenate, 177 Antimony oxyiodide, 105 Antimony triiodide, 104 Aquopentammino cobalti bromide, 187, 188... 

As a condenser or container for sublimation or fusion of some halides, the rare earth metal triiodides, for example (these undergo serious metathetical reactions with glass at elevatedtemperatures to yield SiX4 and the corresponding oxide or silicate). This pertains especially to the liquid and gaseous halides.6... 

LANTHANUM TRIIODIDE (AND OTHER RARE EARTH METAL TRIIODIDES)... 

The reactions described below have been applied to the syntheses of the triiodides of the rare earth elements as well as those of yttrium and scandium. 

The thermochemistry of rare-earth trifluorides was summarized in Gmelin Hand-buch (1976) and the thermochemistry of rare-earth tribromides and triiodides was summarized in Gmelin Handbuch (1978). The thermochemistry of trivalent rare-earth trichlorides was critically assessed by Morss (1976). Enthalpies of formation of most of the lanthanide tribromides were determined by Hurtgen et al. (1980). Thermodynamic properties for europium halides were assessed by Rard (1985). Only enthalpies of formation of Sc, Y, Dy and Tm triiodides have been redetermined since the classical work of Hohmann and Bommer (Morss and Spence 1992). A recent set of literature values of enthalpies of formation of rare-earth solid and gaseous trihalides has been published, accompanied by Born-Haber cycle estimated values for all trihalides (Struck and Baglio 1992). 

Containment of this particular combination of metal, trichloride, and HO at reaction temperatures presents a problem of the same character as occurs in the preparation of the triiodides of these elements (this volume. Chapter 1, Sec. 6). These metals all dissolve in (reduce) the liquid trichlorides to some d ee, and this process greatly accelerates the spontaneous reduction of SiO by the metal to form silicide and oxide. The same problem pertains to all known ceramic materials. Container metals which are the most inert to both the rare earth elements and HQ are limited to tungsten and molybdenum and then only if reactions such as Mo(s) + 4HCl(g) -> MoCl4(g) + 2H2(g) are suppressed by the addition of H2. The last is not a serious problem for example, with Phj/Pho > 10 the pressures of all gaseous molybdenum chlorides are estimated to be <10 atm at 800°. Molybdenum is the material of choice because of its greater ease of fabrication." ... 

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