Heterobimetallic isopropoxides

Heterobimetallic isopropoxides of two lanthanide metals (Sm and Yb) in the divalent state were prepared recently (75) by the following reaction ... 

The first clue to the formation of a heterotrimetallic alkoxide was, however, detected in 1985 in the case of beryllium. Its stability was initially ascribed to the small size of beryllium, which hindered the disproportionation of the species. The heterobimetallic isopropoxide (Pr-f-0)Be(/i-0-/-Pr)2Al(0-z-Pr)2 was found on the basis of NMR studies to dimerize on ageing (8) into a product that could be reported as [(0-f-Pr)2Al( -0-/-Pr)2Al(0-i -Pr)2]. This observation led to the feasibility of reactions of the following types, which resulted for the first time in 1985 in the synthesis and characterization of heterotrimetallic isopro-poxides. 

The currently determined X-ray structure of a tetranuclear heterobimetallic isopropoxide, ErAI3(0-/-Pr),2 (Fig. 25) (251), possesses a noncrystallographi-cally imposed C3 point symmetry, with the rotation axis perpendicular to the plane through the aluminum atoms. The coordination geometry around the erbium atom is a distorted trigonal prism, in contrast to the ideal octahedral coordination for the central aluminum atom in the structure of A1A13(0-/-Pr),2 (see Fig. 2). 

The crystal structures of two heterobimetallic isopropoxides containing lead and zirconium (148), Pb2Zr4(O-/ -Pr)20 (Fig. 32) and Pb4Zr2(0-j-Pr))6 (Fig. 33), were determined by X-ray diffraction methods. These molecules adopt rare serpentine structures. 

Although many heterobimetallic alkoxides were characterized structurally (cf. Section III. A), the crystal structure of the first homoleptic heterotrimetallic isopropoxide [Ba Zr2(0-/-Pr)9 (/i-0-(-Pr)2Cd(/t-0-/-Pr)]2 was recently elucidated (39a). 

The reactions of isopropoxides of alkahne earth metals (M = Ca, Sr, Ba) with (HOC2H4)3N(H3tea) in 1 2 molar ratio yield colourless insoluble nonvolatile solids (J) with the composition, M(H2tea)2, which on treatment with 4 moles of Al(OIV)3 afford soluble monomeric heterobimetallic triethanolaminate products (K) according to Eqs (3.106) and (3.107) ... 

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