Structural versatility in hydrated rare earth(iii) 1,2-benzenedisulfonates

Abstract

The complexes Ln₂L₃·xH₂O (L = 1,2-benzenedisulfonate; Ln = Sc (1), x = 14; Ln = Y (2), x = 16; Ln = La (3), x = 7; Ln = Ce (4), x = 6; Ln = Pr (5), x = 10; Ln = Nd (6), x = 18; Ln = Sm (7), x = 18.25; Ln = Eu (8), Gd (9), Tb (10), Ho (11), Yb (12), Lu (13), all x = 16) were synthesised by treating Ln₂O₃ with an aqueous solution of 1,2-benzenedisulfonic acid. Single crystal X-ray studies revealed isomorphous structures of the type, [LnL(H₂O)₆]₂[L]·4H₂O for 2, 8–13, i.e. Ln = Eu–Lu (including Y) and, presumptively, intermediate Ln. These contain eight-coordinate Ln with the disulfonate ligand coordinating though one oxygen of each sulfonate group giving a seven-membered chelate ring. Complexes of the ‘earlier’ Ln are less systematically defined. The samarium complex, 7, is so far unique, with the structure [SmL(H₂O)₆] [SmL₂(H₂O)₄]·8¼H₂O. There is an eight-coordinate complex anion with two cisoid chelating disulfonate ligands (again seven-membered rings), and four unidentate water molecules, and an eight-coordinate cation, which is similar to those of 2, 8–13. A novel lanthanum complex [H₇O₃][LaL₂] (14) has been prepared by the treatment of La₂O₃ with an excess of aqueous 1,2-benzenedisulfonic acid and by treatment of 3 with perfluoroadipic acid in water. The complex anion forms polymeric chains with eight-coordinate lanthanum ions and μ-η²(O,O′):η²(O″,O″′)-disulfonate groups. Two oxygen atoms from each sulfonate group (O, O″ from one; O′, O″′ from the other) bridge pairs of adjacent La ions. In addition O, O′ (and O″, O″′) form seven-membered chelate rings with neighbouring lanthanum atoms. Two uncoordinated oxygen atoms of each dianion are hydrogen bonded to the H₇O₃⁺ ions. Another cationic lanthanum complex, [LaL(H₂O)₇]Cl·H₂O (15), from attempts to crystallize [La₂L₃]·7H₂O, has a nine-coordinate La ion with a chelating disulfonate ligand and seven unidentate water molecules, and may provide some insight into the possible structures of complexes 3–6. In all structures, hydrogen-bonding involving water of crystallization links the cations and the anions in a supramolecular superstructure.