Metal-ion selectivity by macrocyclic ligands. Part 1. The interaction of Ni II and Cu II with pyridinyl-derived N3O2 macrocycles; the X-ray structures of a free macrocycle, its endomacrocyclic complexes of Ni II and Cu II and an exomacrocyclic nickel(II) complex

Abstract

The interaction of CuII and NiII with two macrocycles L1 and L2, each containing an N3O2 donor set, has been investigated. Spectrophotometric studies in dimethyl sulphoxide reveal the formation of complexes with 1 : 1 and 1 : 2 metal : ligand ratios and conductometric studies in the same solvent indicated that all of the complexes were 1 : 2 electrolytes. Conductometric titration of the 1 : 1 copper(II) complexes with chloride in each case indicated the formation of a 1 : 1 electrolyte, presumably through co-ordination of a chloride ion to the central copper of each complex. Similar titration of the nickel(II) complexes gave evidence for the formation of dinuclear species; each of these was postulated to contain a bridging chloride anion. The stability constants of the complexes together with their enthalpies of co-ordination have been determined in 95% methanol. Extraction and related transport experiments were carried out and under the conditions employed CuII was favoured over NiII. The X-ray crystal structures of the free macrocycle L1, the 1 : 1 complexes [CuL1(H2O)][ClO4]2 and [NiL1(I)]I·MeOH, and the 1 : 2 complex [NiL12(NO3)]NO3·2MeOH have been determined. The metal in [CuL1(H2O)][ClO4]2 is six-co-ordinate and lies within the folded macrocyclic cavity. The donor set comprises the five macrocyclic donor atoms and a water molecule. Overall, the co-ordination sphere corresponds to a restricted tetragonal rhombic arrangement. The complex [NiL1(I)]I·MeOH also has all donors of the macrocycle co-ordinated with an iodide anion occupying the sixth site to yield a distorted-octahedral geometry. The structure of [NiL12(NO3)]NO3·2MeOH shows that the nickel is again six-co-ordinated, to the aliphatic nitrogen atoms from two macrocycles (each showing exo co-ordination) and a bidentate nitrate anion.