ChemInform Abstract: Metal Ion Size Selectivity in Ligands with Groups Containing the Neutral Oxygen Donor Atom. A Crystallographic and Thermodynamic Study

The coordinating properties of open-chain ligands containing alcoholic or ethereal oxygen donors are examined. Addition of oxygen donors usually leads to complex stabilisation for large metal ions (Pb2+, Cd2+) and to less favourable effects on complex stability for small metal ions (Cu2+, Ni2+). The formation constants of these metal ions with the set of ligands RN(CH2CHOH·CH3)2 where R is H, CH2CHOH·CH3, CH2CH2OCH3, CH2CH2OCH2CH2OH, and CH2CHOCH2CH2CH2 are reported. The largest stabilisation for each case where R is an O-donor group relative to R = H occurs for Pb2+, the largest metal ion, while Cu2+, the smallest metal ion, shows the smallest stabilisation. The crystal structure of [Ni(HOCH2CH2NHCH2CH2NH2)2] (NO3)2 is reported. The space group is P 1 , with cell constants a = 13.098(3), b = 8.737(4), and c = 7.746(3) A, β = 112.66(3), β = 90.65(3), and γ = 85.03(2), and Z = 2. Disorder of the nitrate anions hindered refinement, with the result that a final conventional R factor of 0.0903 was achieved. The NiN bond lengths average 2.06(1) (secondary nitrogen) and 2.10(2) (primary nitrogen). The NiO bond lengths are rather long, averaging 2.15(1) A, which is used to support the idea that the steric effects are responsible for destabilising the complexes of small metal ions such as Ni(11) when neutral oxygen donors are present.