Ionophoric Binding of Alkaline-Earth-Metal Cations (A < sup > 2+ < /sup > ) by Tris(arylazo oximato)iron(II) Anions (RL < sup > - < /sup > ): The Trinuclear A(RL) < inf > 2 < /inf > Family

Abstract

Reaction of NaRL·H2O and A(CI04)2 ·xH2O in ethanol or of HRL with ACO3in acetone affords A(RL)2, in > 90% yield (R = Me, Ph; A = Mg, Ca, Sr, Ba). Two complexes are formed as hydrates: Sr(MeL)2.4H2O and Ba(MeL)2•5H2O. These furnish the anhydrous species upon heating. The A(RL)2chelates have been characterized with the help of molecular weight, IR,1H NMR, electrochemical, and manganese(II)-doped complex EPR data. It is concluded that in A(RL)2the A2+ion is centrally held in an 06environment provided by the oximato oxygen atoms of the pair of facial RL-anions (1—3), which act as tridentate ligands. The complexes are soluble in polar organic solvents. Quantitative ionophoric transport of 1 mol of A2+from water to dichloromethane can be achieved with the help of 2 mol of PhL-. When the aqueous phase is made acidic with 2 mol of H+, A(PhL)2is decomposed into A2+and HPhL and A2+is returned to this phase. The equilibrium constants (KAMg) of reactions of type Mg(PhL)2(o) + A2+(a) ⇌ A(PhL)2(o) + Mg2+(a) are as follows: A = Ca, 5.10; A = Sr, 9.52; A = Ba, 24.72 (at 298 K; the abbreviations o and a signify dichloromethane and aqueous phases, respectively). This implies that the equilibrium constants KAMg reactions of type 2PhL-(o) + A2+(a) ⇌ A(PhL)2(o) are in the order KBa > KSr > ; KCa > KMg. The difference (ΔΔG°f) of the free energies of formation of Mg(PhL)2and A(PhL)2is found to be proportional to the difference (ΔΔG°h) in the hydration free energies of Mg2+and A2+as well as to the difference (ΔΔG°1) of the lattice energies of crystalline MgO and AO: ΔΔG°f/ΔΔG°h= 0.99; AAG°f/AAG°1= 0.82. © 1987, American Chemical Society. All rights reserved.