Volatile /1-diketonate complexes

VOLATILE DIKETONATE COMPLEXES OF CALCIUM(II), STRONTIUM(H), AND BARIUM(H)... 

The volatile metal-containing precursors which satisfy the ALD criteria fall into four main categories (i) halides, (ii) y0-diketonate complexes, (iii) alkoxides, and (iv) true organometallics, viz. metal alkyls and cyclopentadienyl-type compounds (Fig. 3). Also amido complexes have recently gained attention as possible ALD precursors. Occasionally other compounds have been used as ALD precursors for thin films, for instance, metal nitrates, carboxy-lates and isocyanates [17,18]. 

For the deposition reactions carried out under an Ar atmosphere, up to 41% of the dark red tris-/3-diketonate complex Ru(hfac)3 is observed as a volatile byproduct. This finding suggests that the operation of a parallel pathway, which involves self-disproportionation of the source reagent, is necessary to account for the observed film growth ... 

The main problem here is to obtain suitable coordination compounds that can be vaporized at reasonably low temperatures at which they are thermally stable. To this end a great deal of work has been published on the gas chromatography of (3-diketone complexes such as (61 R2 = H) 93 Volatile complexes of the rare earths with dipivaloylmethane (61 R1 = R3 = CMe3 R2 = H) were first prepared in 1965 but while the separation of pairs of neighbouring metals (e.g. Eu and Sm) has been reported, the complete separation of the whole group has not been successfully achieved. Attempts to use columns longer than 70-75 cm result in peak-broadening and inefficient separation.94... 

Detailed investigations of metal complexes of monovalent CHdo-alcohols were initiated to find alternatives to the /S-diketonate complexes as precursors to ceramic materials. In particular, mononuclear and very volatile complexes of the elements Cu, Zn, Bi, Pb were pointing the way [94], Section 4 will put the main emphasis on the adaptation of this strategy to lanthanide elements. 

Judging by their appearance, monoclinching alcohols resemble j8-diketonate ligands (Fig. 13). Bulky (tBu) or fluorinated (CF3) alkyl groups in R1 and R3 position ensure volatility of /J-diketonate complexes [107]. 

Recent work by Cole-Hamilton and coworkers has demonstrated that stability and volatility are enhanced by the use of long-chain fluorinated p-diketonate ligands, that is those derived from Hdfhd (6) and Htdfhd (7). The hydrafed bis(/3-diketonate) complexes M(dfhd)2(H20) and M(tdftid)2(H20) were prepared for Cu, Ca, Sr, and Ba and were all found to sublime below 200 °C with weight loss ranging from 85 to 98% (see Table 15). In addition, the anhydrous compound Ba(tdfiid)2 was reported to melt at 196 °C and volatilize at 220 °C with essentially no decomposition (residual mass by TGA ca. 1%). 

A more dramatic change in volatility and stability of barium bis(/3-diketonate) complexes is seen when a nitrogen-containing base, such as an amine or ammonia, is added to or... 

It is important to note that in none of these examples of intermolecularily stabilized barium bis( -diketonate) complexes was found complete achievement of the criteria for CVD precursors for SMO given at the outset of this section. Therefore, other routes had to be explored in the search for the required higher volatility, higher stabihty vapor transport vehicles to be employed for the heavy group 2 elements desired for electronic materials applications. 

Cerium(III) tris(/3-diketonate) complexes are readily oxidized to the cerium(IV) compounds. They are volatile with vapor pressures high enough for MOCVD use. A number of diketonates are now better characterised, prompted by the possibility of using them as CVD materials and petrol additives, as well as a source of cerium oxide as an oxygen store for catalytic converters. [Ce Me3CCOCHCOCMe2(OMe) 4], Ce(acac)4 (Figure 32), Ce(dbm)4, [Ce(pmhd)4], and Ce(tmhd)4 all have square-antiprismatic coordination of cerium (in the [Ce(catecholate)4]" ion the coordination is dodecahedral). 

Figure 4.42. Molecular structures of commonly used CVD precursor classes. Shown are (a) metal p-diketonate (acetylacetonate, acac) complex to grow a metal oxide film (H2 as the coreactant gas yields a metal film) (b) a heteroleptic (more than one type of ligand bound to the metal) p-diketonate complex to yield a Cu film the ancillary ligand helps prevent oligomerization, enhancing volatility (c) various types of complexes to deposit metallic, oxide, nitride, or oxynitride films (depending on coreactant gas(es) used - respective ligands are p-ketoiminato, p-diketiminato, amidinato, and guanidinato (d) a metal azolato complex commonly used to deposit lanthanide metal thin films.

Terbium complexes reported for electroluminescence can be separated mainly into two classes terbium carboxylates and P-diketone complexes. Terbium carboxylates have good luminescence but they are difficult to use as efficient emission materials in OLEDs due to their multi-coordination mode and consequent formation of inorganic polymers with poor solubility or volatility. For these reasons, in this section we will focus on use of the newly developed f)-diketonate terbium complexes in OLEDs. 

Volatile tungsten(IV) 0x0 alkoxide//3-diketonate complexes of structural type W(0)(/1-diketonate)(OR)3 (R = t-Pr, f-Bu /3-diketonate = acac, 32, hfac, 33) are excellent precursors for the low-pressure CVD of electrochromic tungsten oxide films, as shown by Chisholm and coworkers. While with 32b and 33b the produced films were transparent and blue, 32a and 33a led to pale yellow layers which darkened to pale green-blue when exposed to air for several days. With the exception of 33a, all other tungsten complexes formed good-quality films with respect to adhesion and surface coverage however, no surface selectivity for quartz, pyrex or ITO was observed. 

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. 

Turning now to the more tightly bound filled orbitals we examine the evidence from photoelectron spectroscopy. By comparing the ultra-violet excited photoelectron spectrum (UPES) of volatile uranyl beta-diketonate complexes [45] with the spectrum of complexes of the same ligands with other metals, two sharp ionisations are observed, at 10.30 and 10.80 eV, which. seem to be assignable to uranyl-oxygen ionisations. The lower of these ionisations increases in relative... 

Novel lanthanide fi-diketonate complexes have been synthesized, Their properties include thermal, hydrolytic and oxidative stabilities, volatility, Lewis acidity, and unusually high solubility in nonpolar organic solvents. Various combinations of these properties make lanthanide complexes useful as NMR shift reagents and fuel antiknock additives and in other applications. NMR spectral studies revealed that the Pr(III), Yb(III), and Eu(III) complexes of 1,1,1,2,2,3,3,7,7,7- decafluoro-4,6-heptanedione have sufficient Lewis acidity to induce appreciable shifts in the proton resonances of weak Lewis bases such as anisole, acetonitrile, nitromethane, and p-nitrotoluene. Data from single-crystal structure determinations indicate that the NMR shift reagent-substrate complexes are not stereochemically rigid and that effective axial symmetry may exist by virtue of rapid intramolecular rearrangements. 

---