IRON(IV) IN LAYERED COBALT-IRON OXIDE FORMED BY ELECTROCHEMICAL OXIDATION

Layered double metal hydroxides belonging to the pyroaurite group (pyr oaurite-type compounds, abbreviated PTCs) consist of positively charge d trioctahedral metal hydroxide layers, [M(a 1-x)(II)M(b x)(III)(OH)(2 )](x+), with interlayers of charge-compensating anions and water molec ules,(1,2) [A(x/n).yH(2)O](x-), with 0.15 < x < 0.70. Compounds with h ydroxide layers of mono- and trivalent metal cations are also known,(3 ) and the possible existence of PTCs containing tetravalent cations (S i, Ti(IV), V(IV)) has been indicated.(4) Recently we described the syn thesis of a (CoFeIII)-Fe-II-PTC with the composition Fe0.309III)-Fe-II (OH)(2)][(CO3)(0.140).yH(2)O].(5) The blue variety of Co(OH)2 also has a layered structure which on anodic oxidation transforms topotactical ly to the layered CoOOH.(6) Hence it is likely that the Co(II)-dominat ed Co-II-Fe-III-PTC also can be oxidized electrochemically and still r etain its layered structure. The oxyhydroxide formed by the electroche mical reaction will. be described here with emphasis on the oxidation state of the cations.