Rare tetrakis complexes

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. 

The rare earth tetrakis P-diketonate complex functionalized silica spheres are conveniently prepared by a one-pot synthesis method which is based on the modified Stober process [56]. The resulted luminescent nanoparticles are shown schematically in Fig. 8.9 (top). Because the introduction of siloxy-bearing rare earth complex precursor can result in coagulation, a step-by-step approach is adopted to implement the synthesis of uniform silica sphere. The rare earth complex precursors added into the reaction system in the second step can ensure the size uniformity of the nanoparticles furthest. As a result, the rare earth chelate mainly lies in the outer layer of the silica sphere, which has been shown schematically in Fig. 8.9 [55]. As shown in Fig. 8.9 (bottom), the nanoparticles obtained are uniform spheres, approximately 61 5 nm in diameter. And there is no obviously change in the particle size or morphology. All nanoparticles show relatively high luminescent lifetimes. Among the quantum efficiencies, the experiment values of Eu-TTA-SS (34.8 %)... 

Rare-earth jS-diketonate complexes can be synthesized by extraction methods. Halverson et al. (1964a, 1964b) obtained Lewis base adducts of europium(III) j8-diketonates by equih-bration of an aqueous solution of europium(lll) nitrate with a solution of the -diketone (or its ammonium salt) and of the Lewis base in diethyl ether. As the Lewis base, trioctylphosphine oxide (topo), tributylphosphate (tbp) or dihexylsulfoxide (dhso) were used. The molar ratios Eu + diketone Lewisbase were 1 3 2. The complexes are formed in the ether layer, and could be obtained as viscous oils from the ether solution. Richardson and Sievers (1971) prepared tris complexes of 1,1, l,5,5,6,6,7,7,7-decafluoro-2,4-heptanedione by extraction of an aqueous solution of the decafluoroheptanedione in diethyl ether. The rare-earth chlorides were used in 10 to 50% excess in order to prevent the formation of the corresponding tetrakis complexes. [Eu(tla)3(phen)] was prepared by extraction of an aqueous solution of europium(III) chloride, 2-thenoyltrifluoroacetone and 1,10-phenanthroline with benzene (Melent eva et al., 1966). After separation of the benzene layer from the aqueous layer, the [Eu(tta)3(phen)] complex was precipitated by addition of petroleum ether to the benzene layer. 

Tetrakis complexes of rare-earth /3-diketonates with amphiphilic quaternary ammonittm iorts or A-allgrlpyridinittm ions as counter iorts were often the material of choice to... 

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. 

There are three main types of rare earth -diketonates the tris complexes, the Lewis base adducts of the tris complexes, and tetrakis complexes. The tris complexes have three fi-diketonate Ugands for each rare earth ion, i.e. R( -diketonate)3. The Lewis base addircts are formed by reaction with water or other organic Lewis bases. The tetrakis complexes have forrr j8-diketonate hgands aroimd rare earth ion and have the general formula [R( -diketonate)4] . 

Tetrakis-Cp uranium complexes are readily prepared via metathesis of UCl and KCp in refluxing benzene. These complexes are a relatively rare example of a pseudotetrahedral complex with four Tj -Cp rings, (rj-ring) (25). The Cp derivative has been shown to react with CO and CO2 to give acyl and carboxylato complexes. This complex also reacts with alkyl haUdes to afford the U(IV) complex, Cp UX (X = halide). 

At the time of our investigation the only known coordination compounds of chlorophosphines (aside from phosphorus trichloride complexes) were the nickel-(0) compounds, tetrakis(methyldichlorophosphine)nickel-(0) (20) and tetrakis-phenyldichlorophosphine) nickel- (0) (17). Tetrakis (methyldichlorophosphine) -nickel-(0) is noteworthy in that it represents a still rare example of the direct reaction of a ligand with an elemental transition metal to give a complex, while tetrakis (phenyldichlorophosphine) nickel- (0), like tetrakis (trichlorophosphine) -nickel-(0), was obtained readily via the carbonyl. AD chlorophosphine-nickel-(O) complexes, including the phosphorus trichloride complex, Ni(PCl3)4, are compounds relatively stable in the atmosphere, but show poor stability in almost any organic solvent, even under strictly anaerobic conditions. 

Risse and S. Breunig, S. Transition metal catalyzed vinyl addition polymerizations of norbor nene derivatives with ester groups, Makromol. Chem. 193, 2915 (1992) C. Mehler and M. Risse, Addition polymerization of norbornene catalyzed by paUadium(2+) compounds. A pol3mierization reaction with rare chain transfer and chain termination, Macromol. 25, 4226 4228 (1992) R.G. Schulz, The chemistry of palladium complexes. III. The polymerization of norbornene systems cat alyzed by palladium chloride (1), Polym. Lett. 4, 541 (1966) C. Tanielian, A. Kiennemann, and T. Osparpucu, Influence de differents catalyseurs a base d elements de transition du groupe VIII sur la polymerisation du norbornene, Can. J. Chem. 57, 2022 (1979) A. Sen and T. W. Lai, Cat alytic polymerization of acetylenes and olefins by tetrakis(acetonitrile)paUadium(II) ditetrafluorobo rate, Organometallics 1, 415 (1982) C. Mehler and W. Risse, Pd(II) catalyzed polymerization of norbornene derivatives, Makromol. Chem. Rapid Commun, 12, 255 (1991). 

Because A is small, low-spin tetrahedral complexes are rare. The first such complex of a first row transition metal, tetrakis(l-norbomyl)cobalt (1-norbomyl is an organic ligand, C7H11), containing a low-spin Co(IV) center, was reported in 1986 (Figure 10.27). The corresponding anionic Co(III) ([Co(l-nor)4] ) and cationic d Co(V) ([Co(l-nor)4] ) low-spin tetrahedral complexes were also prepared. Another organometallic complex, lr(Mes)4 (Mes = 2,4,6-trimethylphenyl), is approximately tetrahedral and features a low spin d Ir(lV) center. " ... 

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