Crystal praseodymium

In pigments, 2irconium sHicate serves as the host lattice for various chromophores, such as vanadium, praseodymium, iron, etc. Zirconium sHicate crystals are usuaHy formed in situ during pigment preparation by a high temperature reaction of Zr02 and Si02 ... 

In the crystal structure of Pr2ls there are two crystallographically independent praseodymium sites, Prl and Pr2, which have coordination numbers of 7 and 8 with mean Pr-I distances of 322.0 and 335.3 pm, respectively [19]. These distances are much like the respective Pr-I distances for coordination number 7 in K2PrIs (d= 321.2 pm [20]) and are as expected for coordination number 8 in... 

Analysis of the lanthanide-induced crystalline arrays by negative staining (Fig. 5) or freeze-fracture electron microscopy reveals obliquely oriented rows of particles, corresponding to individual Ca -ATPase molecules [119]. The unit cell dimensions for the gadolinium-induced Ca -ATPase crystals are a = 6. l A, b = 54.4 A and y = 111°. Similar cell constants were obtained for the crystals induced by lanthanum, praseodymium and calcium. The unit cell dimensions of the Ei crystals are consistent with a single Ca -ATPase monomer per unit cell. The space group of the Eptype crystals is PI [119], while that of the E2 crystals is P2 [88,90]. 

Fig. 5. Image and optical diffraction pattern of praseodymium-induced crystals, (A). Crystallization was induced with 8 PrCU. Doublet tracks so prominent in vanadate-induced crystals are not evident in crystals induced with lanthanides. This results in an approximate halving of the A-axis of the unit cell. Magnification x 222000. (B) The image of the superimposed top and bottom lattices of the flattened cylinder give rise to two separate diffraction patterns. (C) Projection map of praseodymium-induced crystals. Map scale 0.55 mm per A. From Dux et al. [119].

The Sr-doped praseodymium manganites and cobaltites have been studied by several groups as potential cathodes for ITSOFC. Kostogloudis et al. [116-118] systematically investigated the crystal structure, electrical conductivity, and thermal expansion properties of (Pr, Sr)Mn03, (Pr, Sr)Co03, and (Pr, Sr)(Co, Mn)03 systems. All compounds have the orthorhombic perovskite GdFe03-type structure (Pbnm... 

Varsanyi (7/2), in an interesting paper, reported the observation of some very unusual infrared fluorescence in PrCl3 Nd3+ crystals. He observed that when praseodymium chloride containing a few tenths of a per cent neodymium is illuminated with a small-filament lamp, very intense and... 

COVER PHOTO Praseodymium 123 Single Crystal. 1995-1998 by Michael W. Davidson and The Florida State University. 

The first published work on the pressure dependence of optical spectra of solids seems to be of Paetzold (1940), who has studied the effect of pressure on absorption spectra of praseodymium nitrate, ruby, and other minerals between 1938 and 1939. To generate a maximum pressure of 0.1 GPa the samples were subjected to pressurised nitrogen. Using the same high pressure apparatus, Hellwege and Schrock-Vietor (1955) studied the pressure dependence of the absorption spectra of EuZn-nitrate. These authors, for the first time, applied the crystal-field Hamiltonian formalism for the analysis of the high pressure spectroscopic results. 

By far, the most studied quantum cutting system to date is for praseodymium, where the 4f2 1 So state lies below the lowest 5d state for many fluorides and some oxides. For most Pr3+ doped systems, the nephelauxetic effect and the 5d crystal field splitting are large enough to push the lowest 5d level below the 1 So state. However, for those systems in which the So... 

Classical methods of separation [7] are (1) fractional crystallization, (2) precipitation and (3) thermal reactions. Fractional crystallization is an effective method for lanthanides at the lower end of the series, which differ in cation radius to a large extent. The separation of lanthanum as a double nitrate, La(N03)3-2NH4N03-4H20, from praseodymium and other trivalent lanthanide with prior removal of cerium as Ce4+ is quite a rapid process and is of commercial significance. Other examples are separation of yttrium earths as bromates, RE(Br03>9H20 and use of simple nitrates, sulfates and double sulfate and alkali metal rare earth ethylenediamine tetraacetate complex salts in fractional crystallization separation. 

Recently we have reported the analysis of crystal structures of single crystals of DyMnOj [3] and LnMnOj (Ln = Nd, Sm, Eu and Gd) [4] using a four cycle X-ray diffractometer. In this study the growth of single crystals of PrMnOj and TbMnOj and the refined crystal structures are described. Since praseodymium and terbium have several valence states, some considerations about the atmospheric conditions are necessary. 

Hydrates of rare earth chlorides also have two different crystal systems a triclinic system for lanthanum, cerium, and praseodymium, as well as a monoclinic system for neodymium to lutetium and yttrium. CeCl3-7H20, as an example of the former system, is different from the above infinite polymer as two cerium atoms are connected by two [i2-bridges to form a dimer. The formula for this dimer is [(H20)7Ce([i2-Cl)2Ce(H20)7]Cl4 as shown in Figure 1.18. Therefore, the coordination number of cerium is nine and the polyhedron takes on a destroyed mono-capped square antiprism configuration. 

Figure 3.11 Structures of (a) [Sm2L6(MeOH)4] (HL = benzoic acid) and (b) [Pt2L6(H20)3] (HL = acetic acid) [RE, black O, grey C, white H, omitted]. (Redrawn from the CIF files of U.R Singh, R. Kumar and S. Upreti, Synthesis, structural, photophysical and thermal studies of benzoate bridged Sm(III) complexes, Journal of Molecular Structure, 831 (1-3), 97-105, 2007 [56] and D. Deiters and G. Meyer, Synthesis and crystal structure of praseodymium propionate trihydrate, Pr(CH3CH2C00)3(H20)3, Zeitschrift filr Anorganische und Allgemeine Chemie, 622 (2), 325-328, 1996 [57].)...

Deiters, D. and Meyer, G. (1996) Synthesis and crystal structure of praseodymium propionate trihydrate, Pr(CH3CH2C00)3(H20)3. Zeitschrift filr Anorganische und Allgemeine Chemie, 622 (2), 325-328. 

Figure 4.17 The structure of [Pr(16)6] [33]. (Reproduced with permission from A. Clearfield, R. Gopal and R.W. Olsen, Crystal structure of hexakis(l,8-naphthyridine)praseodymium(III) perchlorate, Inorganic Chemistry, 16, 911, 1977. 1977 American Chemical Society.)...

Hie precursors, cerium(TV) ammonium nitrate (NH4)2Ce(N03)3 and praseodymium(lll) nitrate Fh-(N03)3 6H20, are added in a i I weight ratio to the molten salts at 673 - 873 K, and the melt is maintained for 15 - 120 min. After the melt is quenched to room temperature, the reaction products are washed with water and then dried at 393 K. Well-crystallized Ce,.jPr,02 (x = 0 - 10) powders with very fine size (10 - 20 nm), narrow size distribution, and a clearly spherical shape are obtained. 

Compounds of divalent samarium, europium, and ytterbium are well-known. In recent years, lower halides of other lanthanides, such as neodymium 48), praseodymium 45, 49, 90), and thulium 4) have been obtained by reducing the trihalide with the metal. The corresponding reaction of thorium tetraiodide with thorium metal has led to the identification of two crystalline forms of Thl2 41, 91) it is unlikely that the Th ", or even Th ", ion is present in Thl2, but like Prl2, which is formulated as Pr " (r)2( ) (2), the compound is probably of the type Th " (r)2(2 ) 41). Certainly one crystal form is diamagnetic 41), suggesting the latter formulation. 

Praseodymium dioxide crystallizes in the fluorite-type structure (space group Fm3m) with four praseodymium atoms and eight oxygen atoms per unit cell. This structure may be visualized easily as an infinite array of coordination cubes (each consisting of a Pr atom at the center with eight O atoms at the corners) stacked so that all cube edges are shared. 

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