Heterometallic derivatives

Interesting examples of simple substituted heterometallic species are [(thf)M p-N(SiMe3)2 2M (th 2] (M/M = Li/Na, Li/K and Na/K) which were obtained from solutions of 1 1 mixtures of the metal salts.The unsolvated ( LiXtSiMe J , K- lSiXleO, ), has a polymeric, one-dimensional chain structure formed by alternating lithium and potassium centres bridged through the hexamethyldisilazides (Li—N= 1.935(1) A and K—N = 2.86(1) A) with linear coordination at K and almost linear coordination (N-Li= 176.4(3)°) atLi.  

A variety of examples of discrete and polymeric lithium-group 13 metal amides 

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The complexes [M(/i-C7H4NS2)(COD)]2 (M = Rh, Ir) and [Rh(/i-C7H4NS2)(CO)(PPh3)]2 react with silver compounds to give the heterometallic derivatives with the silver(I) atoms bonded to the thiolate sulfur atoms. The structure of [Rh2Ag2(/i3-C7H4NS2)2(C104)] shows a short Rh—Ag distance.1010... 

The first tt complexes of 1,3-diynes were reported by Greenfield. Shortly thereafter, Tilney-Bassett described the first heterometallic derivatives. This area has grown steadily since these initial reports and many complexes of this type are now known. Diyne complexes are often simply alkyne-substituted analogues of conventional jr-alkyne complexes. Indeed, transition metal compounds that form -complexes with mono-alkynes can be expected to form complexes with diynes. However, the thermal sensitivity of terminal diynes, especially 1,3-butadiyne, may limit the application of routine reaction conditions in some cases. Further coordination of the ynyl ligand by additional metal fragments is usually determined by the reagent stoichiometry and by steric effects. 

A modification of this route is a simultaneous reaction of two metals with alcohol that can be considered as the in situ reaction of the alkoxides formed. Thus the interaction of Mg and A1 with ethanol (leading to the formation of the perfectly soluble MgAl2(OEt)8) occurs very rapidly and does not need activation, in contrast with the reactions of individual metals with alcohol, leading to polymeric Mg(OEt)2 andAl(OEt)3 [1101, 887] (see Section 2.1). The preparation of the heterometallic derivatives has been achieved even via anodic oxidation of one metal in solution of the other (the complex solutions obtained have been used for the deposition of films in sol-gel technique) [1777]. 

Type M is by far the most common coordination mode for cluster-bound allenyl fragments. Several homo- and heterometallic derivatives have been crystallographically characterized, and Table IV contains a selection of the more salient structural features. Deeming et al. have described several clusters in which severe structural distortions of the p,-allenyl ligand arise from the presence of heteroatom substituents with strong IT donor character (56). These structural types are discussed further below. Both homo- and heterometallic clusters with p,-r), ri, r) -coor-dinated allenyls have been prepared. The C-C bond distances in these cluster types are similar to those found in the bimetallic /u.-t, > -bridged... 

The interest for pyrazolate complexes containing the pz group as a mono-dentate ligand arises because of their recognized usefulness in the synthesis of dinuclear and trinuclear heterometallic derivatives. The mononuclear complex... 

Pr)9] (LZr) by the chloride method, the preparation of derivatives with more than two different metals in the same molecular species was not even attempted because of the expected instability of such heterometallic derivatives. 

The general synthetic procedures for heterometallic derivatives and the chemical concepts which are involved are as follows ... 

Mass spectrometry can give valuable information on the structural details of Sn(II) heterometallic derivatives, subject to stability with respect to the disproportionation reaction in the vapor phase. The mass spectral results demonstrate that fast atom bombardment mass spectrometry (FARMS) could find immense applications in the characterization of heterometallic derivatives, particularly of non-volatile, high molecular weight compounds, such as those of tin. 

Table 1. References to solution NMR measurements on, and X-ray structures of, [Rli6(CO)i6] and related homo- and heterometallic derivatives.

In addition to the chemistry of heterometallic derivatives of alkoxometallate(iv), and tetraalkoxoaluminate ligands, the properties of hexa alkoxoniobates and -tantalates of various metals have also been extensively studied. An account of these different alkoxometallates is presented in Section 3.3, after presentation of their general properties in Section 3.2. 

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