Complexation of Alkali Metal Ions by the Cryptand 4,7,13,16-Tetraoxa-1,10-diazabicyclo[8.8.5]tricosane in Several Solvents

Abstract

A potentiometric titration study of the complexation of metal ions (M+) by 4,7,13,16- tetraoxa-1,10-diazabicyclo[8.8.5] tricosane (C22C₅) at 298.2 K and I = 0.05 (NEt₄ClO₄) yields log(K/dm³ mol-¹) =6.07 and 5.36, 7.55 and 5.95, 6.26 and 7.56, 5.5 and 6.66, 4.57 and 5.16, and 8.14 and 14.51 when M⁺ = Li⁺, Na⁺, K⁺, Rb ⁺, Cs⁺ and Ag⁺, respectively, where the first and second magnitudes of each pair refer to the stability constant (K) for [M(C22C₅)]⁺ in acetonitrile and ropylene carbonate solvent, respectively. A ⁷Li n.m.r. tudy yields kd (298.2 K) = 428 s-¹, ∆ Hd ^‡ = 24.7 kJ mol-¹ and ∆ Sd ^‡ = -111 J K-¹ mol-¹ for the monomolecular decomplexation of Li⁺ from [Li(C22C₅)]⁺, and k_c(298.2 K) = 9.83×10⁷ dm³ mol-¹ s-¹ for the complexation process in propylene carbonate. These data are compared with those for related systems and are discussed in terms of the factors affecting cryptate stability and lability.