SELECTIVE RECOGNITION OF METAL-COMPLEXES BY MACROCYCLIC ETHERS - FURTHER OBSERVATIONS ON THE MACROCYCLE SIZE DEPENDENCE AND THE FIRST-SPHERE LIGAND COMPOSITION DEPENDENCE OF RECOGNITION THERMODYNAMICS

Additional studies of solution phase recognition of Ru(NH3)(x)(pyridin e-x)(y)(2+), Ru(NH3),(2,2'-bipyridine)y(2+) and Ru(NH3)(4)(1,10-phenan throline)(2+) species by dibenzo crown ethers are reported. The factor s most closely examined were crown size, ammine ligand content and anc illary ligand composition. The overall study confirms that recognition or association derives primarily from H-bond formation (ammine hydrog en/ether oxygen). Evidently opposing these interactions, however, are crown conformational rearrangements. Consequently, straightforward cor relations between association strength and potential number of H-bond interactions are found only in selected cases. Based on comparisons of association constants for (bis)pyridine, bipyridine and phenanthrolin e ligand-containing species with dibenzo crowns, evidence is also foun d for favorable polypyridine/benzene interactions. NMR(NOE) measuremen ts indicate that the preferred association geometries in solution are those that make each of the benzenes of the crown coplanar (or nearly coplanar) with the ligated polypyridine.