Finite hydroxy-metal complexes

One product of the hydrolysis of Al2(S04)3 by alkali is a salt with the empirical formula AI2O3. 2 SO3. 11 HjO which contains bridged hydroxy-aquo complexes (a) and should therefore be formulated as [Al2(0H)2(H20)s] (804)2 2 H2O/ A more complex example is the dimeric Th2(0H)2(N03)j(H20)j complex, formed by hydrolysis of the nitrate in solution. Three bidentate NO 3 ions and 3 H2O complete an 11-coordination group about each metal atom. 

The compounds originally formulated ZrOCl2. 8 H2O and ZrOBr2. 8 H2O also contain hydroxy-complexes. The complicated behaviour of these compounds in aqueous solution suggests polymerization, and in fact the crystals contain square complexes (c) in which there is a distorted square antiprismatic arrangement of 8 0 atoms around each Zr atom. The halide ions and remaining H2O molecules lie between the complexes, and the structural formula of these compounds is therefore [Zr4(0H)8(H20)i ft] Xg. 12 H20. We refer again to this type of complex later. 

A type of chain found in a number of hydroxy-salts with OH M = 1 consists of octahedral coordination groups sharing opposite edges which include the (OH) groups. The simplest possibility is that these chains are then joined through the oxy-ions to form a 3-dimensional structure, as illustrated by the plan and elevation 

The structure of Cu(0H)103 (a) plan, (b) elevation, in which the octahedral chains are perpendicular to the plane of the paper. 

The dioxides of Ce, Zr, Th, and U all crystallize with structures of the fluorite type, and it is interesting to note that three of the complexes we have described 

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