Oxalato metal coordination compounds

A number of metal ions of variable valence, for example FeK, Ti111 and V11, can reduce silver. Among the more significant coordination compounds are those of iron and titanium. Iron(II) ion, in the presence of fluoride or pyrophosphate to sequester the Fem formed, is a developer. The bis(oxalato)ferrate(II) ion, [Fe(C204)2p, is also a developer in the presence of excess oxalate. 

This thinking applies, in particular, when planning the design of a chiral three-dimensional supramolecular host-guest system, since the mutual interaction of the two distinct complementary molecular units or coordination entities is necessary. Examples of this methodology include the above-described anionic, tris-chelated transition metal oxalato complexes [Mzl(ox)3/6 which form the host system together with the cationic, tris-chelated transition metal diimino complexes, e.g. [M(bpy)3]21/31, bpy = 2,2 -bipyridine, which play the role of the guest compounds. 

As has been seen, inert complexes of the transition metals may be inter-converted by substitution reactions, but such methods cannot generally be relied upon and it is preferable to prepare inert complexes by a different method. The chosen method is to take a compound containing the metal in a different oxidation state and oxidize or reduce it, as appropriate, in the presence of the selected coordinating ligand. This technique is used extensively in the preparation of oxalato complexes of chromium(III). Other chromium-(III) complexes are prepared by the oxidation of chromium(II) salts. 

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