Structure rare-earth /1-diketonates

Strontium nitrate, for preparation of strontium sulfate or strontium selenite, 3 17 Strontium selenide, 3 20 phosphors, 3 11, 22 Strontium selenite, for preparation of strontium selenide, 3 20 Strontium sulfate, for preparation of strontium sulfide, 3 19 Strontium sulfide, 3 20 phosphors, 3 11, 21, 23 Structure, of 1,3-diketones, 2 10 electronic, of rare earth elements, 2 30... 

Up to about the 1960 s, elemental analysis coupled with absorption spectra and infrared spectra and X-ray crystallography were the primary methods used in the studies of complexes. Later on with the developments in nuclear magnetic resonance (NMR) spectroscopy, especially multinuclear NMR, this technique has been invariably used in the studies of structural features of lanthanide complexes. To illustrate these points some references to literature are herein pointed out. The studies on the rare earth 1,3-diketonates, where 1,3-diketones are acetyl acetone, benzoyl acetone, dibenzoyl methane and 2-thienoyl tri-fluoroacetone totally relied on elemental analysis, UV-Vis and IR spectra to establish the nature of the complexes [89]. The important role played by X-ray crystallography in the elucidation of the structures of lanthanide complexes has been extensively discussed in Chapter 5 and the use of this technique goes as far back as the 1960 s. Nevertheless it continues to play a major role in the studies of lanthanide complexes. 

The luminescence of various chelated compounds of the rare earths is very promising because their spectral and luminescent properties help to solve a number of theoretical and applied problems. Luminescence spectra of europium complexes with selenophene /3-diketones have been studied as a function of the ligand structure. Of the spectra obtained, m-picolinoyl-2-acetoselenophene and di-selenoylmethane look most promising for obtaining induced radiation.136... 

Figure 2.30 Representation of the asymmetric unit of [Nd(L )4(H20)][(TTF—CH=CH—Py+)] 2-The radical cation donors are drawn as balls and sticks the paramagnetic anionic coordination complexes of Nd(III) are drawn as capped sticks [23d], (Reprinted with permission from F. Pointillart, O. Maury, Y. Fe Gal, S. Golhen, O. Cador and F. Ouahab, 4-(2-Tetrathiafulvalenyl-ethenyl)pyridine (TTF—CH=CH—py) radical cation salts containing poly(P-diketonate) rare earth complexes synthesis, crystal structure, photoluminescent and magnetic properties, Inorganic Chemistry, 48, 7421-7429, 2009. 2009 American Chemical Society.)...

The structural information of the rare-earth /1-diketonates is of crucial importance in the evaluation of their luminescence properties. More than two hundred crystal structures of RE + S-diketonates determined by single crystal X-ray diffraction (XRD) have been reported in the literature and deposited in the database of the Cambridge Crystallographic Data Center. In addition, theoretical methods have been used to predict the structures of diketonate compounds. Among them, the SMLC/AMl method " has been successfully used in the determination of coordination geometries from calculations on the isolated single RE diketonate complex. ... 

The most common coordination numbers shown by RE + /3-diketonate complexes is eight, where the two most frequent chemical formulae are [RE(/3-diketonate)4] and [RE(/3-diketonate)3(unidentate)2] corresponding to dodecahedron and square antiprism polyhedra, respectively. It is noted that the number of crystal structures presented for the tetrakis complexes is very low compared with the tris complexes. The majority of the tetrakis complexes have square antiprism polyhedron structure [Ce(acac)4]. On the other hand, a number of rare earth /3-diketonate complexes has the dodecahedral coordination polyhedron. 

Finally, consider the crystal structure of the rubidium salt of 5,5-dimethyl-l,3-cyclohexanedione-2-sulfonic acid. This species exists as the ketoenol wherein the rubidium ion is surrounded by seven oxygen atoms in pentagonal bipyramidal coordination. We know of no ketoenolate (and hence dianionic) salt of this sulfo-dione with any cation. Perhaps some more highly charged cation would allow for this—note the significantly enhanced stability of rare earth complexes of 2-acetyl-5,5-dimethyl-l,3-cyclohexanedione over the parent diketone . 

Incorporating fluorocarbon moieties increases the volatility of / -diketonate complexes 18). To retain the steric effect of the bulky thd ligands and to take advantage of the volatility effect of fluorocarbon substituents, the ligand, l,l,l,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octane-dione, [H(fod)] ( see Figure 5 for structure of anion), was synthesized. Fifteen tris complexes of tervalent rare earth metal ions with this bulky fluorinated ligand have been prepared and studied. Their properties are compared with other rare earth complexes, principally those of thd. 

Selection of rare-earth tris / -diketonate complexes for which crystal structures have been determined by single crystal X-ray diffraction... 

Sc(acac)3] crystallizes in the orthorhombic space group Pbca (Andersen et al., 1973). The stmcture consists of discrete Sc(acac)3 molecules. The scandium(III) ion is six-coordinate, and the coordination polyhedron can be described as a slightly distorted octahedron (fig. 7). The site symmetry is close to D3. Another example of a six-coordinate scandium(III) )3-diketonate complex is [Sc(dbm)3] (Zaitseva et al., 1990). Two different crystal structures are described, one with a triclinic and one with a monochnic cell. So far, no scandium(lll) )3-diketonates with coordination number higher than six have been described. Because of the small ion size of Sc +, coordination number six is the general rule fortius rare-earth ion. Also in the trinuclear scandium(III) disiloxanediolate complex [(Ph2Si0)20]2Sc3(acac)5], the coordination number of Sc + is six as well (Lorenz et al., 2001) (fig. 8). 

Recently, Pikramenou and coworkers (Bassett et al., 2004) studied rare-earth complexes of the bis(jS-diketone) ligands l,3-bis(3-phertyl-3-oxopropanoyl)benzene and l,3-bis(3-phenyl-3-oxopropanoyl)-5-ethoxy-benzene. These complexes have a helical structure. Both triple-stranded neutral complexes of the type [R2L3], and quadruple-stranded anionic complexes of the type [R2L4] are formed, where L is the deprotonated form of the bis08-diketone) ligands. The solution structure of these complexes was studied in detail by NMR spectroscopy. 

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