The a-MO OH structure

Metal Hydroxides, Oxyhydroxides and Hydroxy-Salts The a-MO. OH structure 

In our survey of octahedral structures in Chapter 5 we saw that double chains of the rutile type could be further linked by sharing vertices to form either 3-dimensional framework structures, of which the simplest is the diaspore structure, or a puckered layer as in lepidocrocite. These two structures are shown in perspective in Fig. 14.12. In Fig. 14.13(a) the double chains are seen end-on, as also are the c.p. 

It will be seen that OH has 3 A1 neighbours arranged pyramidally to one side, opposite to that of the H atom (Al-3 OH, 1-98 A), while 0 is bonded to three more nearly coplanar Al neighbours (Al—3 O, 1 -86 A), the 0—H—O bond being directed along the fourth tetrahedral bond direction. In the a-MO. OH structure each OH is hydrogen-bonded to an 0 atom contrast the 7-MO. OH structure. 

Bond lengths in the a structures are given in Table 14.2, which also includes 7-MnO. OH for comparison with a-MnO. OH. In groutite the length of the O-H-0 bond is 2-63 A. These Mn compounds are of special interest because of the expected Jahn-Teller distortion of the octahedral coordination group. This 

Compounds with this structure include 7-AIO. OH (boehmite), 7-FeO. OH (lepldocrocite), 7-MnO. OH (manganite), and 7-ScO. OH.  

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