Macrocyclic ligands ring expansion

Like their phosphorus(III) analogues, cycloarsoxanes (RAsO) undergo metal-mediated ring expansion to produce flexible macrocyclic ligands n = 5, 6, 8) that... 

As far as quadridentate ligands are concerned, the easiest attainment of the Ni state, denoted by the less positive redox potential, is observed with the 14-membered macrocycle, 5, known as cyclam. Both contraction and expansion of tetramine ring atomicity, to 12 and to 16, respectively, makes the potential more positive, thus destabilizing Ni with respect to Ni Moreover, the isomeric 14-membered macrocycle, 6 (isocyclam) stabilizes the Ni state to a much lesser extent than cyclam. Notice that the two macrocyclic complexes simply differ in the sequence of the five-... 

---