Alkoxides heterometallic

Metal AlkoxidesandDiketonates, and Double-Metal Alkoxides/ Heterometallic Alkoxides, sections in Gelest Inc. Handbook, Milwaukee, WI (1995)... 

Huhert-Pfalzgraf LG (1998) Some aspects of home and heterometallic alkoxides based on fimctional alcohols. Coordination Chemistry Reviews 180, 967-997 Huhert-Pfalzgraf LG (2003) Some trends in the design of homo- and heterometallic molecular precimsors of high-tech oxides. Inorganic Chemistry Communications 6(1), 102-120... 

This compound represents an example of an inverse crown ether stmcture (Lewis acidic host-Lewis basic guest macrocyclic heterometallic alkoxides or amides/ . 

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],... 

The intensive development of the chemistry of homo- and heterometallic alkoxides of copper started more than 10 years ago in connection with the prospects of their application in the preparation of materials and initially in high temperature superconductors. In the search for the appropriate precursors in sol-gel and MOCVD techniques, attention was focused on the alkoxides of copper (I) and the fluorinated alkoxides of copper (II) — oligomeric derivatives soluble in non-polar solvents and existing not only in condensed but also in the gas phase. The derivatives of copper (II) and aliphatic alcohols, even rather branched or functional ones (such as alkoxyalkoxides) turned out to be polymeric substances uninteresting for further application. 

The other octanuclear manganese cage known forms part of a study of heterometallic alkoxides. 103). [Mn8Sb404(OEt)2ol is made from... 

The sol gel chemistry of sihcon alkoxides is much simpler (see Silicon Inorganic Chemistry)P Si is fourfold coordinated (N = z = 4,) in the precursor as well as in the oxide so that coordination expansion does not occur. The electronegativity of Si is rather high compared to transition metals. Silicon alkoxides are therefore not very sensitive toward hydrolysis. Their reactivity decreases when the size of the alkoxy groups increases. This is mainly due to steric hindrance, which prevents the formation of hypervalent sihcon intermediates (see Hypervalent Compounds). Silicon alkoxides, Si(OR)4, are always monomeric. Heterometallic alkoxides have never been obtained via the reaction of a sihcon alkoxide with another alkoxide. Silicon alkoxides have to be prehydrolyzed before Si T M bonds can be formed. 

The reaction of metal halides with an alkoxide or aryloxide (most commonly an alkali metal alkoxide), can resnlt in metathetic exchange to give the required complex (equation 6). Such reactions can also result in the formation of heterometallic species (such as NaZr2(OR)4) this can be a problem when homometallic aUcoxides are desired, but it is an important route to heterometallic alkoxides and aryloxides. The nature of the product can be influenced by the alkali metal, the alkoxide ligand, and the relative amounts of the reactantsd ... 

Figure 6.23 The molecular (left) and crystal (right) structures of [Pr(mmp)3LiCl]2. For clarity, the ligand methyl groups are omitted from the molecular structure [49]. (Redrawn from J.M. Gaskell et al., Deposition of Pr- and Nd-almninate by liquid injection MOCVD and ALD using single-som-ce heterometallic alkoxide precursors, Chemistry of Materials, 19, 4796 803, 2007.)...

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

Heterometallic alkoxides of calcium, strontium, and barium with transition or posttransition metals have been formed by reactions with the preformed alkoxides (e.g., Table 8, Equations (8a) and (8b)). A variation on this approach generates the Group 2 alkoxides in situ by reaction of the metal with an alcohol and/or another alkoxide (e.g.. Table 8, Equations (9a) and (9b)). " " ... 

Heterometallic alkoxides and oxoalkoxides as intermediates in chemical routes to mixed-metal oxides (23). 

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-... 

In the following periodic table (Table I), the elements for which the homo-metallic and heterometallic alkoxide chemistry have been explored in detail are circled and put within a square, respectively. The metals of later Ad and 5d groups are underlined by a semicircle to indicate that not much is known about their alkoxide chemistry (40, 41) due to their instability, which is brought about by facile decomposition pathways (e.g., /3-hydrogen elimination). The elements whose alkoxides have been utilized as synthons for ceramic and other materials are marked with an asterisk ( ). 

In an excellent comprehensive review (34) on alkoxides, and aryloxides which was published in 1987, the description of heterometallic alkoxides, called... 

Elements for Which Homo- and Heterometallic Alkoxides Are Known... 

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. 

A distinctive feature, unprecedented in heterometallic alkoxide chemistry, is the exchange of the central metal atoms between two chelating ligands this rearrangement is possibly favored by the greater oxophilicity of barium and its tendency to attain higher coordination states (39a). 

Since the preparation of RBeOR from the reaction of BeR2 with R OH by Coates et al. (6), it was shown that reactions of metal alkoxides with organo-lithium or other main group metal alkyls, such as Grignard reagents or aluminium alkyls, can yield (4a) either substitution (Eq. 59) or addition products (Eqs. 60 and 61) the latter often results in formation of heterometallic alkoxides, for example,... 

Preparation of heterometallic alkoxides between pairs of metals as similar to each other as aluminum and gallium (137) or even niobium and tantalum (138) were described. However, the formation constants of the latter derivative were found to be rather low, precluding its isolation in view of the dynamism of the equilibrium. 

The close relationships in the structural features of homo- and heterometallic alkoxides can be exemplified by those of Al Al(0-i-Pr)4 3 (150) and Ln Al(0-/-Pr)4 3 (18). The molecular weights of the latter in benzene correspond to their empirical formulas. All of these compounds can be distilled in the range of 200-180°C/0.1 mm, with a lowering of the boiling point as was expected from increasing the covalent character which results from lanthanide contraction in the series. The tetrameric aluminum isopropoxide A1 A1(0-/-Pr)4 3 or A1(0-/-Pr)3 4, however, disproportionates and distills as a dimeric vapor around... 

A description of the various physicochemical properties (e.g., volatility, dipole moments, refractivity, density, viscosity, magnetic susceptibilities, IR, ESR spectra, mass spectra, and NMR spectra) for elucidation of the structural features of homo- and heterometallic alkoxides was already presented in a number of publications [e.g., (3, 4, 6, 19, 34)]. 

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