Praseodymium complex

Praseodymium, tris(2,2,6,6-tetramethyl-3,5-heptancdione)-photosubstitution, 1,408 Praseodymium complexes edta, 3,1089... 

The basis for applying the LIS quantitatively to problems in stereochemistry depends upon expressions including the term (3 cos2 — l)r-3, where r is the distance from the carbon to the lanthanide ion and the angle d is defined by the symmetry axis of the complex and the vector from the lanthanide ion to the carbon in question. This application depends on a LIS imposed entirely by the pseudocontact mechanism. It has been shown that the contact mechanism is important for europium and praseodymium complexes in 13C NMR for distances up to four bonds from the site of complexation, and that ytterbium complexes interact with 13C nuclei largely, if not entirely, by the pseudocontact process. (12, 13)... 

Diphosphazane dioxide complexes of lanthanides have potential application in the solvent extraction separation of lanthanides. Reaction of lanthanide nitrate with X2P(0)NPr )-P(0)X2(L-L) yields the bis chelate complexes Ln(NC>3)(L-L)2. The structure of the praseodymium complex has been determined by X-ray diffraction and the space group is P32- There are two independent molecules in the unit cell which differ in orientation of the phenyl group. The metal ion is ten-coordinated [264]. 

The chemical composition of rare earth complexes cannot by itself reveal the coordination number of the central metal ion. There are many complexes containing hydrated water molecules and coordinated water molecules. The nitrilotriacetic acid (NTA) complexes of Pr and Dy have the formulae PrNTA 3H2O and DyNTA 4H2O, respectively. The praseodymium complex is a nine-coordinate system with one molecule of water in the hydrated form [12] and the dysprosium complex is eight-coordinate with two molecules of water of hydration [13]. These structures cannot be predicted from the composition of the complexes. The complex Nd(N03>3 4DMSO is ten-coordinate [14] since the nitrate... 

The chelates can be purified, and mixtures of the complexes can be separated by fractional sublimation and distillation. In the gas phase, in solution, and in the solid state, Tb(thd)3 emits a brilliant green fluorescence when irradiated at 3660 A. with an ultraviolet lamp. Fluorescence is also exhibited by Eu(thd)3, Dy(thd)3, and Sm(thd)3. The praseodymium complex is thermally stable in the gas phase when heated for prolonged periods of time. Vapor pressure measurements on this complex showed no increase in pressure when the sample was heated at 250° for 6 hours. Thermogravimetric analyses and discussions of trends in volatility of the rare-earth-thd chelates have been published. 

Xie D., Jiang Y, Pan W., Jiang J., Wu Z., and Li Y, Study on bis [phthalocyaninato] praseodymium complex/silicon hybrid chemical field-effect transistor gas sensor. Thin Solid Films, 406, 262-267, 2002. 

Triscyclopentadienyl praseodymium complexes, magnetic susceptibility Zeeman measurements... 

Structure and the proton NMR spectrum of a new dimeric praseodymium complex [Pr2(2.2.1)2(011)2]4[0104]-2[CH3CN] whose structure is quite unusual because of the two p-hydroxo bridges that link the two metal ions. The formation of this dimeric species could account for the unexpected affinity of the lanthanide (2.2.1) cryptates for the hydroxyl ion [4]. 

Traces of water in our solutions of monomeric praseodymium cryptate are most probably responsible for the formation of the dimeric complex reported here. Partial hydrolysis of this complex takes place because the excess of (2.2.1) cryptand brings about a pH increase. Incomplete hydrolysis of a lanthanide macrocyclic complex has also been noted by Biinzli et al. [14] who prepared a dimeric praseodymium complex with 1,4,7,10,13-pentaoxacyclododecane (15-crown-5) by dehydrating in vacuo a monomeric species. The metal ions in this dimer are bridged by only one hydroxyl group and by three trifluoroacetate anions. The distance between the two praseodymium ions in the (2.2.1) cryptate reported here is 3.927(1) A this value compares very well with the values reported for the two other dinuclear lanthanide complexes mentioned above [13-14]. 

When conditions of slow exchange are approached the chemical shift between the signals corresponding to the free and coordinated states becomes a function of the mean life-time of the complex. Thus the kinetics can be evaluated from shift measurements at different temperatures provided the temperature dependence of 4b, the shift in the absence of chemical exchange is known. This approach has been used by Bidzilya et al. (1975) to study the kinetics of exchange of the Pr(fod)3 and Eu(fod)3 adducts with hexamethylphosphoramide chloroform. For the analysis of the results a T temperature dependence was assumed for 4b of the praseodymium complex and a T dependence for the europium one. The enthalpies of activation thus obtained are much lower than those reported by Evans and Wyatt (1974) for the same adducts. It is not clear whether this discrepancy is due to a solvent effect or stems from some of the approximations involved in the data treatment. 

The benzoyl peroxide, as a rule, easily splits off all metal-metal bonds in polynuclear organometallics [32]. In contrast, the tin-praseodymium complex in the reaction with (PhCOO)2 retains one Sn-Pr group. The formed heteroleptic product (Me3SiCH2)3SnPr-(OCOPh)2 belongs to the group of rare air-stable organoelement derivatives of lanthanoids. 

In general, the closer the proton is to the OH or NR 2 group interacting with the europium complex, the greater will be the downfield shift. With praseodymium complexes, shifts in the opposite direction are observed. Occasionally the nuclei may lie at an angle 0 > 55° so that the sign of the factor 1 — 3 cos 0 changes, and shifts in the opposite direction are observed. 

Extensive H NMR studies have been done with the cyclohexyl isocyanide adducts of CpsLn. In the case of the praseodymium complex, while at room temperature rapid inversion of the cyclohexyl ring gives rise to 7 discrete cyclohexyl proton resonances, by lowering the temperature ( 70 C) it has been possible to detect all 13 possible signals for the two slowly inverting conformers (AG for the ring inversion=282 15 cal/mole) (Von Ammon et al. 1971). The electronic structure of CpsLn adducts has been studied by Amberger and Schultze (1987). 

AdditioD of dipheDylphosphiDe oxide was carried out in high yields of 50-96% with high e.e. values of 75-93% (Scheme 8.80) [198]. Praseodymium complex PrPB was reported as the best catalyst for the studied conditions. 

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