Formation of Lanthanide and Actinide Oxonium Ion Complexes with Crown Ethers from a Liquid Clathrate Medium^†

Reaction of MCl3·nH2O (M = La, Eu) with 18-crown-6 in HCl/toluene affords the crystalline oxonium complexes (H9O4)[LaCl2(H2O)(18-crown-6)]Cl2 (1) and (H3O)[EuCl(H2O)2(18-crown-6)]Cl2 (2). In complex 1 the H9O4+ cation is of the unusual linear chain type with O···O contacts of 2.560(9), 2.430(9), and 2.483(9) Å. The analogous reaction with YbCl3·6H2O results in the isolation of the known species (H5O2)[H3O·(18-crown-6)]Cl2. Analogous reaction of YbCl3·6H2O with 15-crown-5 gives [Yb(H2O)8]Cl3·(15-crown-5) (5). Reaction of uranyl acetate with 15-crown-5 within a toluene/HCl mixture results in the formation of a yellow liquid clathrate layer from which crystals of (H5O2)[UO2(H2O)2Cl3]·2(15-crown-5) (6) are deposited. The H5O2+ ion in this material exhibits a particularly short O···O separation of 2.371(8) Å. On standing, loss of HCl results in the transformation of 6 into a species of empirical formula [UO2(H2O)3Cl2]·(15-crown-5) (7) which has been shown by X-ray crystallography to contain 16 unique uranium complexes, arranged in infinite hydrogen-bonded chains in the solid state. Crystal data for 1: monoclinic, P21/c, a = 7.6950(2) Å, b = 21.2160(16) Å, c = 15.8650(10) Å, β = 92.866(2)°, V = 2586.8(3) Å3, Z = 4. 2: orthorhombic, Pbn21, a = 10.2267(6) Å, b = 14.7231(9) Å, c = 29.8565(18) Å, V = 4495.5(5) Å3, Z = 4. 5: monoclinic, P21/n, a = 9.1740(3) Å, b = 17.1900(3) Å, c = 15.2450(5) Å, β = 92.643(2)°, V = 2401.60(12) Å3, Z = 4. 6: orthorhombic, Pmcn, a = 12.1740(5) Å, b = 14.7740(7) Å, c = 18.4920(11) Å, V = 3325.9(3) Å3, Z = 4. 7: trigonal, P32, a = 35.3500(2) Å, c = 21.3755(2) Å, V = 23 132.7(3) Å3, Z = 48.