Metal-ion selectivity by macrocyclic ligands. Part 3. The interaction of MnII and CoII with pyridinyl-derived N3O2 macrocycles; X-ray structures of endomacrocyclic complexes of MnII and CoII

Abstract

The interaction of Mn^II and Co^II with the macrocycles L¹ and L², each containing an N₃O₂-donor set, has been investigated. Conductometric titration of the 1 : 1 Mn^II complexes with chloride indicated the formation of a 2 : 1 complex presumably through bridging of a chloride ion. The stability constants of the complexes have been determined in 95% methanol. The X-ray crystal structures of the 1 : 1 complexes [MnL¹Br(EtOH)]ClO₄ and [CoL¹(NO₃)]NO₃, have been determined. The metal in [MnL¹Br(EtOH)]ClO₄ is seven-co-ordinate and lies within the macrocyclic cavity. The donor set comprises the five macrocyclic donor atoms, a bromide anion and an ethanol molecule. Overall, the co-ordination sphere corresponds to a distorted pentagonal-bipyramidal arrangement. The complex [CoL¹(NO₃)]NO₃ also has all donors of the macrocycle co-ordinated together with a nitrate anion. The cobalt is seven-co-ordinated and the co-ordination polyhedron is intermediate between a capped trigonal prism and a pentagonal bipyramid.