Helical Structures Featuring Thiolato Donors - Metallofoldamers: Supramolecular Architectures from Helicates to Biomimetics - page 163

structure-determining effect similarly to the situation observed for complexes of related
tricatechoylamide ligands [36].

5.2.2 Dinuclear Double-Stranded Complexes

Bis(benzene- o -dithiol) ligands with an inflexible or short spacer unit are not capable of
forming mononuclear chelate complexes like the previously discussed derivatives H 4 - 14
and H 4 - 15 or tris(benzene- o -dithiol) H 6 - 8 . Benzene- o -dithiolato ligands mostly yield
square-planar complexes with metal ions from the first transition period [37]. The forma-
tion of square-planar complexes is also expected for bis(benzene- o -dithiolato) ligands
even if the ligand topology prevents the formation of a chelate complex. In fact, the bis
(benzene- o -dithiol) ligands H 4 - 2 and H 4 - 3 (Figure 5.3) react with Ni II to give dinuclear
double-stranded complexes containing two square-planar Ni II or Co II ions (Figure 5.7)
[25]. Both Ni II complexes undergo aerial oxidation to give the Ni III derivatives. Molecular
structure determinations (Figure 5.7) established the expected square-planar coordination
geometry for the Ni II and Ni III complexes. The Ni II and Ni III complex anions with ligand
3 4 possess very similar molecular structures. The major difference is found in the orien-
tation of the amide N

H groups which are pointing towards the sulfur atoms in the Ni II
complex. This was taken as an indication for weak intramolecular N H S hydrogen

Figure 5.7 Molecular structures of the complex anions [Ni II 2 (2) 2 ] 4 (top), [Ni II 2 (3) 2 ] 4 (bot-
tom left) and [Ni III 2 (3) 2 ] 2 (bottom right).