There are many parallels between the coordination chemistries of the bidentate ligands 2,2-bipyridine (bpy) and 1,10-phenanthroline (phen). Both ligands form five-membered chelate rings comprising a pair of pyridyl N-donors, and they stabilize the trivalent forms of their Co complexes relative to the unknown [Co(py)6]3+ analog. This can be attributed to the chelate effect but also to the elimination of H ⋯ H repulsion in the pyridyl complex through the formation of covalent CC bonds in their place. Both [Co(bpy)3]3+ and [Co(phen)3]3+ are well-characterized, stable low-spin complexes. The crystal structures of both [Co(phen)3](ClO4)3 and [Co(bpy)3](ClO4)3 have been reported.763 The [Co(bpy)3]3+ ion has been crystallized with a number of paramagnetic complex anions and the magnetic and spectroscopic properties of these systems have been studied.764,765 Furthermore, it is found that the inert chiral CoIII complex induces the crystallization of chiral, anionic three-dimensional coordination polymers of oxalate-bridged metal complexes of the form [MII2(ox)3]n2n− or [MIMIII(ox)3]n2n−.
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