SOME FACTORS INFLUENCING THE STABILITY OF COMPLEXES WITH LIGANDS CONTAINING NEUTRAL OXYGEN DONOR LIGANDS, INCLUDING CROWN ETHERS

The formation constants for triethanolamine (L) and ethanolamine (L′) are reported for a variety of metal ions at ionic strength 0.1 molar and 25°. For Cu(II), logK 1 with L is found to be 4.07, while logK values for the equilibria Cu 2+ + L + OH − °CuLOH + and CuLOH + + L°CuL 2 OH + are found to be 12.42 and 1.99 respectively. For Pb(II) with L′, logK 1 is found to be 4.10, while for L logK 1 is 3.39, and logK 2 is 2.47. The equilibria PbL 2+ + 20H − → PbL(OH) 2 and 2PbL + OH − → Pb 2 L 2 OH are found to have corresponding values of 13.05 and 8.89 respectively. For Ni(II) with L logK 1 is found to be 2.76, and logK 2 0.84, while logK 1 for Co(II) is found to be 2.25, with logK 1 and logK 2 for Zn(II) 2.05 and 1.23, respectively. The formation constants of ligands containing neutral oxygen donors (alcoholic or ethereal) are examined, and it is concluded that for some metal ions such as Pb(II), Ca(II), or La(III), the inductive effects of the ethylene bridges outweigh the adverse steric effects of increasing the number of chelate rings. For these metal ions, addition of neutral oxygen donors leads to an increase in complex stability, which effect also contributes to the stability of their complexes with crown ethers. For other metal ions, such as Cu(II), Fe(III), or Ni(II), the steric effects outweigh the inductive effects, and the stability of their complexes is not enhanced by neutral oxygen donor atoms.