Monosulfonyl derivatives of simple 1,2- and 1,3-diamines (R2HN–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 N42− donor set and a 14-membered pseudo-macrocyclic structure based on head-to-tail SO⋯H–N(amine) bonding between the two bidentate ligands. In the related tetrahedral Zn(II) complex the ends of the mutually perpendicular bidentate N2− 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)
+ 2 H+, only when the pH of the aqueous phase is raised above 4.
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