Complexation of monovalent metal ions by lariat ethers in non-aqueous solvents

Abstract

The stability constants (K) of 1 : 1 complexes of the lariat ethers 7,13-bis(2-hydroxyethyl)-1,4,10-trioxa-7,13-diazacyclopentadecane (L¹) and 7,16-bis(2-hydroxyethyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (L²) with monovalent metal ions have been determined by potentiometric titration in acetonitrile, methanol and dimethylformamide. Thus the complexes of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺ and Ag⁺ of L¹ and L² are characterized by log(K/dm³ mol^–1)= 2.36 and 2.29, 3.93, and 3.65, 3.08 and 4.66, 2.50 and 3.56, 2.11 and 3.36, and 9.34 and 9.13, respectively, in dimethylformamide at 298.2 K. In some cases the rates of exchange of Li⁺ and Na⁺ in these complexes fall within the ⁷Li and ²³Na NMR time-scale. This is exemplified by [LiL¹]⁺ in dimethylformamide and methanol where the decomplexation of Li⁺ is characterized by k_d(298.2 K)= 1.5 × 10⁶ and 6.07 × 10³ s^–1, ΔH_d^‡= 65.4 and 27.1 kJ mol^–1, and ΔS_d^‡= 92.9 and –81.5 J K^–1 mol^–1, respectively, and by [NaL¹]⁺ in acetonitrile and [NaL²]⁺ in methanol where the decomplexation of Na⁺ is characterized by k_d(298.2 K)= 2.07 × 10² and 4.13 × 10³ s^–1, ΔH_d^‡= 52.6 and 42.8 kJ mol^–1, and ΔS_d^‡=–24.1 and –32.0 J K^–1 mol^–1, respectively. These data are compared with those for related systems.