Tetrakis -diketonates

It is interesting to note that fZr(acac)3Cl] can be recrystallized unchanged from hot acetylacetone.250 An NMR study247 has shown that substitution of the chlorine atom is very slow under anhydrous conditions heating [Zr(acac)3Cl] with neat acetylacetone for 24 h at 80 °C yields a product which is only 20% [Zr(acac)4j. In the presence of water, [Zr(acac)3Cl] is readily converted to [Zr(acac)4],250,251 evidently due to preliminary hydrolysis of the Zr—Cl bond. In anhydrous media, the ease of complete substitution is dependent on the nature of the diketone certain aryl-252 and trifluoromethy 1-substituted253 diketones readily react with ZrCU to give the tetrakis(diketonates). 

Lanthanide tetrakis / -diketonates can be prepared by any of the procedures described above for the adducts [55]. Preparation of Ce(IV) tetrakis-/ -diketonate is described in the literature [56]. 

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

Many examples of hemicyanine dyes with rare-earth tetrakis -diketonate complexes incorporated into Langmuir-Blodgett films have been described in the literature. These rrraterials are discussed in section 7.7. The rare-earth complex does not only improve the qrrality of the LB-films, but better nonlinear optical properties were foimd as well. Pavier et al. (1997) investigated the photoluminescence of LB-films in which ytterbium(III) complexes of pyrazolone ligands were used as counter ions. The fluorescence of the hemicyanine ligand was observed in the visible region, and metal-centered luminescence of Yb + in the near-infrared region. 

The tetrakis- 8-diketonate complexes of the lanthanides constitute an important stereoisomer in the dodecahedral geometry. The four diketonate ligands are found to span the four g-edges of the dodecahedron (Fig. 22) (146, 147). In other do-... 

Cerium tetrakis(acetylacetonate), a venerable compound,695 exists as a and /3 modifications. Both these contain [Ce(acac)4] monomers of D2 square antiprismatic coordination but differ in the crystal packing. In the a form,696 Ce—0 = 2.36-2.43 A with the ring angle O—Ce— 0 = 72°, while in the / form697 Ce—0 = 2.32 A and O—Ce—0 = 71.3°. The tetrakis(acetyl-acetonates) of Zr, Hf, Th, U and Pu also show dimorphism. The tetrakis(dibenzoylmethanate) [Ce(dbm)4] adopts a similar square antiprismatic structure with Ce—O = 2.299-2.363 A and O—Ce—O = 70.8° or 71,2°.698 There is some tendency for Ce3+ /J-diketonates to pass into the Ce4+ tetrakis(/3-diketonate). A series of tri- and tetra-valent cerium /3-diketonates has been examined from the point of view of the effect of additional ligands such as Ph3PO on this process, and it was found that Ce3+ /J-diketonates were stabilized by adduct formation, particularly by 1,10-phenanthroline.699... 

Solvent extraction technique has been used in the synthesis of tris chelates of l,l,l,5,5,6,6,7,7,7-decafluoro-2,4-heptanedione. An aqueous solution of lanthanide chloride is equilibrated with an ether solution of ammonium diketonate, with the condition of an excess of lanthanide in the aqueous phase to prevent the formation of the tetrakis complex [46]. 

The absorption spectra of Pr(III) (3H4 -> 3Po transition), Nd(III) (4l9/2 -> 2P /2 transition) and Eu(III) (7Fo —> 5Do transition) with several /J-diketoncs having alkyl and aryl radicals were studied [241], The spectra of mono, bis, tris and tetrakis /J-diketonates were analysed by comparative absorption spectrophotometry. In the stepwise complexation... 

Absorption spectra of Pr(M) and Nd(III) complexes with alkyl, aryl, fluorine substituted P-diketones and the associated hypersensitive transitions were studied in detail. Mono, bis, tris and tetrakis complexes in benzene, DMF, DMSO and ethanol were also studied. Spectra both in solids and solution permitted the interpretation of the state of p-diketones based on the trends in the intensity and energy interaction parameters [238,244]. The various complexes were isolated and their IR, 1H NMR, stability constants were studied as well. Octacoordination in the tetrakis complex and tris complex associated with two solvent molecules was noted. 

Dielectrophilic species are 1,4-diketones, certain 1,3-dienes, a,B-unsaturated isocyanates, isothiocyanates, cyanates, and thiocyanates bearing electron-withdrawing (e.g., polyfluorinated and perfluorinated) substituents the most frequently used 1,1-dinucleophiles are water, potassium sulfide, primary amines, and ammonia. From this repertoire of building blocks many combinations are possible. Tetrakis(trifluoro-methyl)furans, thiophenes, and pyrroles have been synthesized from per-fluoro-3,4-dimethylhexa-2,4-diene on addition of water, potassium sulfide, or aniline (90CC1127) (Scheme 39). 

Diketones Tetrakis(triphenylphos-phine)palladium. Tin(ll) trifluoromethane-sulfonate. Titanium(IV) chloride. 

---