Design of base metal extractants. Part 1. Inter-ligand hydrogen bonding in the assembly of pseudo-macrocyclic bis(aminosulfonamidato)M(II) complexes

Monosulfonyl derivatives of simple 1,2- and 1,3-diamines ((RHN)-H-2-R-NHSO2R1 = L) have been shown to be easily deprotonated to give neutral 2 : 1 complexes, [M(L-H)(2)], with Co(II), Ni(II), Cu(II) or Zn(II). The Ni(II) and Cu(II) complexes with deprotonated N-tosyl-1,2-diaminoethane have a planar N-4(2-) donor set and a 14-membered pseudo-macrocyclic structure based on head-to-tail S=(OH)-H-...-N-(amine) bonding between the two bidentate ligands. In the related tetrahedral Zn( II) complex the ends of the mutually perpendicular bidentate N-2(-) units are too far apart to form a cyclic H-bonded system. X-Ray structure determinations on five free ligands provide evidence for extensive inter-molecular H-bonding, which in the case of N-tosyl-1,3-diaminopropane and its N'-tert-butyl derivative involves formation of dimeric 16-membered pseudo-macrocycles. Despite favourable inter-ligand H-bonding in the neutral 2 : 1 complexes, these ligands are relatively weak extractants, showing > 50% loading of Cu(II) in "pH-swing" equilibria, 2 L-(org) + M2+ = [M(L-H)(2)]((org)) + 2H(+), only when the pH of the aqueous phase is raised above 4.