(1)H NMR spectroscopic identification of binding modes of 2,2'-bipyridine ligands in complexes of square-planar d(8) metal ions.

The reaction of [M(bpy)](2+) (M = Pd(II) and/or Pt(II); bpy = 2,2'-bipyridine) moieties with model nucleobases leads to a variety of products, viz. 1 : 1, 1 : 2 and 2 : 2 (head-tail, ht, or head-head, hh) complexes. By carefully analysing the H5 (H5') resonances of the bpy ligands, which in all cases occur furthest upfield, and with additional indicators (concentration dependence of H6, H6' resonances; (195)Pt-(1)H coupling constants, if observable; absolute shifts of H5, H5'), it is possible to assign binding situations of bpy ligands, even in multinuclear complexes with several [M(bpy)](2+) entities in different environments present. The analysis presented here is carried out on X-ray structurally established cases of [M(bpy)](2+) complexes, including three new ones, [Pt(1-MeC-N3)(2)(bpy)](NO(3))(2).2.5H(2)O (), ht-[(bpy)Pd(N3-1-MeC(-)-N4)(2)Pd(bpy)](ClO(4))(2).3H(2)O () and ht-[(bpy)Pd(N1-ampy(-)-N2)(2)Pd(bpy)](NO(3))(2).3H(2)O (). The data provide a consistent picture, useful for the future assignment of similar bpy complexes in the absence of X-ray structural evidence.