Biguanides metal complexes

A discussion of metal complexes of biguanides has recently formed part of m extensive review (532) on co-ordination compounds, so that this subject need not be considered here in detail. As in the past, Indian laboratories continue to be the main source of publications on this aspect of biguanide chemistry (38, 193, 195, 281, 282, 300, 435, 527, 528, 529, 533, 586, 649, 650). 

The numerous highly coloured metal complexes obtainable from biguanides and elements of the transition series have posed yet another interesting structural problem. The accumulated evidence suggests that the structures agreeing most satisfactorily with the observations are of type (I o M = divalent metal). This aspect of the subject has been discussed fully by Ray [532). 

The bivalent metals, as usual, combine with two molecules of biguanide to form 4-coordinated planar complexes, while the trivalent cobalt and chromium combine with three molecules of the ligand to produce a 6-coordinated octahedral configuration. The only exception is the trivalent silver which yields, however, a 4-coordinated planar complex. The preparation of the free tris(biguanidato) chromium, Cr(C2N5H6)s, in the anhydrous state,6 as well as of the corresponding anhydrous cobalt(III),8 copper(II), cobalt(II), palladium(II), and nickel(II) compounds, provides indisputable evidence for the structure proposed. Similar anhydrous metallic complexes with numerous substituted biguanides also have been included in the above-mentioned studies. 

Doornbos DA. Stabihty constants of metal complexes of L-cysteine, D-penicillamine, N-acetyl-D-peniciUamine and some biguanides. Determination of stoichiometric stabihty constants by an accurate method for pH measurement. Pharm Weekbl 1968 103(45) 1213-27. 

Complex compounds of biguanides and guanylureas with metallic elements. P. Ray, Chem. Rev., 1961,61,313-359(188). 

In view of the presence of active functional groups at suitable sites in the above ligands and their substituted derivatives, these tend to form coordination compormds/chelates with a large number of metals. Excellent reviews have been published on the complex compounds of biguanides and guanylureas, and biuret. 

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