Extraction properties for alkali metal picrates of macrocyclic trinuclear ( p-cymene)ruthenium(II) and (pentamethylcyclopentadienyl)rhodium(III) complexes

Abstract

The solvent extraction properties of macrocyclic trinuclear organometallic complexes, [( p-cymene)Ru(pyO 2)] 3 and [Cp ∗Rh(pyO 2)] 3 ( pyO 2 2 - = 2 , 3 -dioxopyridine, Cp ∗ = pentamethylcyclopentadienyl ) , for Li +, Na +, and K + picrates have been investigated in a dichloromethane–water system at 25 °C. The extraction rates of the alkali metal picrates with these macrocyclic complex ligands are unusually slow; the shaking times required to attain equilibrium are at least 1 h for [( p-cymene)Ru(pyO 2)] 3 and 20–40 h for [Cp ∗Rh(pyO 2)] 3. From analysis of the equilibrium data, the extraction constants ( K ex = [ML +A −] o/[M +][L] o[A −]; M + = alkali metal ion, L = macrocyclic ligand, A − = picrate ion, o = organic phase) have been determined. The log K ex value varies in the sequences, Li + (5.72) > Na + (4.50) > K + (2.88) for [( p-cymene)Ru(pyO 2)] 3 and Li + (4.79) > Na + (2.70) ≈ K + (2.69) for [Cp ∗Rh(pyO 2)] 3. The K ex values of 6,6-dibenzyl-14-crown-4 (DBz14C4), which is one of the best Li +-selective crown ethers, have also been determined for comparison. It is revealed that [Cp ∗Rh(pyO 2)] 3 is much superior to DBz14C4 both in the extractability for Li + and the selectivity for Li + over Na +.