Mixed ligand precursors

FIGURE 27.3 Examples of metallo-organic precursors commonly used in the fabrication of ferroelectric perovskite thin fihns (a) zirconium butoxide butanol (b) schematic of the 2-methoxyethoxy ligand bonded to a metal center (c) barium acetate (d) the acac ligand and (e) the mixed-ligand precursor titanium bis-acac diisopropoxide. After Schwartz et ah ... 

Mixed-ligand precursors are also frequently employed in CSD processing. For example, titanium tetraisopropoxide, which is too reactive to be directly employed in most CSD routes, may be converted into a more suitable precursor by a reaction with either acetic acid or acetylacetone (Hacac). Such reactions are critical in dictating precursor characteristics and have been studied extensively. - Using these reactions, crystalline compounds of known stoichiometry and structure have been synthesized that may subsequently be used as known precursors for film fabrication.Mixed-hgand molecules (carboxylate-alkoxide and diketonate-alkoxide ) represent complexes that are not easily hydrolyzed. A typical structure for one of these compounds is shown in Figure 27.3e. 

Mohammad Jafar Soltanian Fard-Jahromi and Ali Morsali (2010) Sonochemical synthesis of nanoscale mixed-ligands lead(II) coordination polymers as precursors for preparation of Pb2(S04)0 and PbO nanoparticles thermal, structural and X-ray powder diffraction studies. Ultrason Sonochem 17(2) 435-440... 

Fe(CO)s], [Fe2(CO)g], [Co2(CO)8] and [Os3(CO)i2]) have been reacted with dicyanobenzene to form intrazeolite [M(Pc)] complexes [140]. Another class of materials prepared by the intrazeolite template synthesis method has been mixed ligand metal carbonyls and metal carbonyl clusters, frequently by reductive car-bonylation of metal ions in zeolite cages [175]. However, because these are frequently decomposed in situ to form, for example, nanoparticles, they are outside the scope of this chapter, and will be considered here only when they are used as precursors for metal complexes. 

The complex mer-[RuCl3(6)(dmf)] has been prepared and structurally characterized it is a useful precursor to a range of mixed ligand complexes of Ru. " ... 

Reynolds et al. (1985, 1987) examined petroleum porphyrin and nonporphyrin metals independently with EPR after methanol extraction of porphyrins from the petroleum. Table IV shows the EPR-derived coordination spheres of vanadyl nonporphyrin fractions of various crudes. The Ni and V coordinated to four nitrogens (N4 type) could be petropor-phyrin precursors and derivatives as previously discussed or tetradentate-mixed ligands in which N does not necessarily come from a pyrrole group. Considerable variability in the vanadyl coordination among different crude oils is evident. Figure 4 illustrates some proposed metal complexes that may exist in petroleum (Yen, 1975). 

The interaction of the metal alkoxides with the salts of carboxylic acids or with p-diketonates of other metals is especially attractive for the synthesis of bimetallic molecular precursors in the cases, when the preparation of the alkoxide of the other metal is somehow hindered or it is insoluble or irreactive under the conditions applied. This method has been widely used for the sol-gel preparation of HTSC materials (because of low solubility and reactivity of Cu(OR)2) and lead-containing ferroelectrics (in the view of difficult synthesis and low stability of Pb(OR)2). It should be mentioned that the reaction between a metal alkoxide and a functional derivative does far not always lead to the formation of a mixed-ligand bimetallic complex ... 

Not all vanadium chelates have antidiabetic properties in animals. For instance, four mixed 0,S binding bidentate ligand precursors were derived from maltol to yield four new complexes, two pyranthiones and two pyridinethiones. These complexes are hydrolytically stable and had no observable insulin-enhancing properties [147], The ultimate effectiveness of a vanadium-complex as an antidiabetic drug... 

Evans et al. sequentially reacted the Nd carboxylate precursor Nd[C>2CC (CH3)2CH2CH3]3 % first with DEAC and then with TIBA. By this reaction catalytically active systems are obtained which polymerize IP. In the first reaction step in which Nd carboxylate is reacted with DEAC mixed ligand complexes are formed which contain neodymium and aluminum as well as halide and ethyl groups. Upon crystallization NdC -based compounds are obtained in which solvent is coordinated. These compounds exhibit a more complex... 

The divalent lanthanide monohalides, which are suitable precursors for mixed-ligand divalent lanthanide complexes, can also be synthesized via metathesis reaction. For example, the divalent samarium and ytterbium monohalides stabilized by a triazacyclononane-functionalized tetramethylcyclopentadienyl group have been prepared (Equation 8.31) [97]. 

Equation 9 requires dicationic and dianionic complexes. Several stable dianionic complexes are available, while among the less common dicationic complexes, [Ni(l,4-R2pipdt)2] + have proved to be valuable precursors in the synthesis of stable mixed-hgand complexes. This reaction is very effective, with almost quantitative yields of several mixed-ligand derivatives . 

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