Heterometallic alkoxides synthesis

As has been mentioned above, the special interest in these derivatives is connected with their application in the synthesis of the complex oxide materials (see Chapter 10 for details). The heterometallic alkoxides have been discussed in a number of reviews, the most complete of those (at different moments in time) being the corresponding chapter in the book by Bradley et al. [223] and articles of Mehrotra [1138] and also of Caulton and Hubert-Pfalz-graf [306],... 

Caulton, K.G and Hubert-Pfalzgraf, L.G. (1990) Synthesis structural principles and reactivity of heterometallic alkoxides. Chemical Reviews, 90, 969-995. 

Interestingly, the synthesis of the heterotrimetallic alkoxides of beryllium, which began in 1985 (8), was extended in 1988 to include heterotri- and tetra-metallic alkoxides of copper (25) as well as other 3d metals (26). These last two pioneering publications were included as invited papers in two reputed international journals, leading to almost universal acceptance of the formation of the stable species called heterometallic alkoxides (3, 4, 27-33). These al-... 

As the methods of synthesis employed for homo- and heterometallic alkoxides are quite similar, they are all grouped together. The procedures already covered in detail in early literature are generally indicated by representative equations with details given only for more recently illustrative examples. 

In addition, incorporation of unexpected ions such as Li+, Cl-, and O2-during the synthesis of homo- and heterometallic alkoxides by conventional methods was observed in some cases (4a, 28, 38, 39, 42). 

The bond Ms+—06+—R in homo- as well as heterometallic alkoxides is highly reactive. This reactivity is due to the positive charge induced on the metal atoms rendering them highly prone to nucleophilic attack. Almost all of the alkoxides are, therefore, extremely susceptible to hydrolysis by even traces of moisture (including the atmosphere, reaction vessels, etc.) and hence, their synthesis and handling require extraordinarily anhydrous conditions or environment. The facile hydrolyzability of homo- and heterometal alkoxides is now... 

Because of the extremely high susceptibility of metal alkoxides to even traces of moisture, stringent precautions for maintenance of anhydrous conditions (solvents, reagents, equipment, etc.) as well as careful protection from atmospheric moisture were generally regarded as essential conditions for the synthesis of simple binary or heterometallic alkoxides in a pure state. 

A new dimension has been opened during the last decade in the field of heterometal coordination chemistry because of the synthesis of a variety of thermally stable ter and higher heterometallic alkoxides. This area is expected to receive increasing attention because of the first X-ray structural elucidation done in 1996 (39a) of a termetallic isopropoxide of Ba, Zr, and Cd. This derivative also revealed an even more fascinating behavior of the shifting of the alkoxo-metallate ligands to suit the nature of the three metals involved in the species. 

This chapter deals with the synthesis and general properties of homo- and heterometallic alkoxides that are or might be used in chemical routes to electrooptical ceramic materials. Some considerations concerning structure, reactivity, and tailoring of their properties are also given. Emphasis is given to the most recent results. 

M = Li, Na, K, TI(I)3 Although they allow control of the stoichiometry between the M and M, metals, they have not been much developed so far for species-associating metals involved in electrooptical ceramics. They are mostly limited to the use of the complex alkoxide anion Zr2(OiPr)9, and La-Zr species were recently built up by this route [87]. In contrast with the preceding synthetic routes based on mixing simple compounds, Eq. (19) implies the prior synthesis of a heterometallic alkoxide based on an alkali metal and further removal of the salt. 

Heterometallic Alkoxides Are Used as a Potential Precursor for the Synthesis of Mixed Metal Oxide Nanoparticles... 

E. Hemmer, V. Huch, M. Adlung, C. Wickeder and S. Mathur, Homo- and heterometallic terbium alkoxides - Synthesis, characterization and conversion to luminescent oxide nanostructures, Eur. J. Inorg. Chem., vol. 2011, no. 13, pp. 2148-2157, 2011. 

The products C, D, E, and F have been shown (Chapter 3, Section 2.5) to be useful precursors for the synthesis of interesting types of heterometallic alkoxide systems. 

Synthesis of Higher Heterometallic Alkoxides and Allied Derivatives... 

In spite of considerable initial scepticism, the synthesis of an increasing number of well-characterized heterometallic alkoxides is now well established and attempts are being directed towards the synthesis of single-source precursors for preparation of mixed metal-oxide ceramic materials by the sol-gel or MOCVD processes. " " Before proceeding to a brief account of some novel types of heterometal glycolate and aminoalkoxide derivatives, it is appropriate to mention four review articles" summarizing the state of knowledge about the conventional heterometallic alkoxide systems at the end of the twentieth century. 

The chemical properties of heterometallic alkoxides are in general similar to their homometal counterparts (i) hydrolysis, (ii) alcoholysis, (iii) trans-esterification reactions, (iv) reactivity with carboxylic acids and enolic forms of chelating ligands such as /3-diketones/j6-ketoesters. The hydrolytic reactions are now widely employed for the preparation of homogeneous mixed metal-oxide ceramic materials and the rest have found wide applications for the synthesis of a variety of novel metallo-organic derivatives (sometimes unique), which are not often available through any other synthetic route. ... 

The synthesis of volatile and soluble (in organic solvents) covalent d83-i85 jjona-alkoxodizirconates of alkali metals such as KZr2(OR)9 (R = Et, Pr ), by Bartley and Wardlaw in 1958 initiated an entirely new dimension in the chemistry of heterometallic alkoxides. Historically, a nona-alkoxostannate derivative, NaSn2(OEt>9 had been described by Bradley et in 1957 as an intermediate during their efforts to synthesize tin tetra-alkoxides by the reactions of SnCLj with NaOEt. 

Caulton K.G., Hubert-Pfalzgraf L.G. Synthesis, Structural principles, and reactivity of heterometallic alkoxides. Chem. Rev. 1990 90 969... 

---