Cobalt, hexaammine structure

Gessner RV, Quigley GJ, Wang AH-J, van der Marel GA, van Boom JH, Rich A (1985) Structural basis for stabilization of Z-DNA by cobalt hexaammine and magnesium cations. Biochemistry 24 237 - 240... 

This chapter has been concerned with the effect of structural properties of cobalt(III) hexaamines on their other properties. Included in this review have been complexes ranging from cobalt hexaammine, to complexes composed of three secondary and three tertiary amine donors... 

LCo(H20)6] ion, and bidentate /V-donor ligands such as cn, bipy and phen form octahedral cationic complexes [Co(L-L)3] , which are much more stable to oxidation than is the hexaammine [Co(NH3)6l . Acac yields the orange [Co(acac)2(H20)2] which has the tram octahedral structure and can be dehydrated to [Co(acac)2l which attains octahedral coordination by forming the tetrameric species shown in Fig. 26.3. This is comparable with the trimeric [Ni(acac>2]3 (p. 1157), like which it shows evidence of weak ferromagnetic interactions at very low temperatures. fCo(edta)(H20)] is ostensibly analogous to the 7-coordinate Mn and complexes with the same stoichiometry, but in fact the cobalt is only 6-coordinate, 1 of the oxygen atoms of the cdta being too far away from the cobalt (272 compared to 223 pm for the other edta donor atoms) to be considered as coordinated. 

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