Lanthanide Ion Complexes with 2-, 3-, or 4-Sulfobenzoate and Cucurbit[6]uril

The reaction of lanthanide nitrate, trifluoromethanesulfonate, or chloride salts with the three positional isomers of sulfobenzoic acid (SBH2) in the presence of cucurbit[6]­uril (CB6) under hydrothermal conditions yielded 13 complexes which were crystallographically characterized. The ortho isomer gave a series of one-dimensional polymeric complexes of columnar shape, {[Ln­(2-SB)­(NO3)­(H2O)2]2CB6}·xH2O [isomorphous for Ln = La (1) and Ce (2), x = 10 or 11], {[Nd­(2-SB)­(H2O)3]­[Nd­(2-SB)­(H2O)4]­CB6}·2NO3·7.5H2O (3), and {[Ln­(2-SB)­(H2O)4]2CB6}·2NO3·xH2O [isomorphous for Ln = Eu (4), Dy (5), Er (6), and Yb (7), x = 5 or 6]. These compounds all comprise carboxylate-bridged dinuclear units connecting the CB6 molecules through lanthanide–carbonyl coordination, and they differ by sulfonate bonding and formation of a chelate ring being only present in 1–3. In contrast, [Lu­(2-SB)­(H2O)7]2·CB6·2NO3·7H2O (8) does not display sulfonate and carbonyl coordination, the carboxylate group being monodentate and the complex species being held as a lid over the CB6 portal by hydrogen bonding. The complexes obtained from erbium trifluoromethanesulfonate and chloride salts, {[Er­(2-SB)­(H2O)4]2CB6}·2CF3SO3·2.5H2O (9) and [Er­(2-SB)­(H2O)7]2·CB6·2Cl·6H2O (10), present the same features as 4–7 and 8, respectively. The meta isomer is in the form of the carboxybenzosulfonate 3-SBH–, with the carboxylic acid retaining its proton, in the isomorphous complexes {[Ln­(3-SBH)­(H2O)4]2CB6}·4NO3 [Ln = Ce (11) or Nd (12)]. These complexes display the feature, unusual in this series, of coordination by the monodentate sulfonate group only. A columnar assembly is formed by coordination of each metal ion to two CB6 molecules, the 3-SBH– ligand having no role in the polymer formation. Finally, the para isomer is only coordinated by the chelating carboxylate group in [Nd1.5(4-SB)­(CB6)­(NO3)­(H2O)6.5]·4-SBH·4-SBH1.5·15H2O (13).