The analysis of crystal structures of the series of ammine-nitro cobal
t(III) complexes has shown that Co-NO2 bond lengths can be successfull
y rationalized on the basis of the anisotropic pi-effect of nitro grou
ps. This effect governs both the orientation of the nitro group and th
e Co-NO2 length, and explains the irregularities in the increase of th
e latter with the increasing number of NO2 groups present in the coord
ination sphere. (C) 1997 Elsevier Science Ltd.