Lanthanide contraction and pH value controlled structural change in a series of rare earth complexes with p-aminobenzoic acid

A series of rare earth complexes with p-aminobenzoic acid (HL) have been synthesized: [RE2L6(H2O)2]n [RE ¼ La (1), Ce(2), Pr(3), Sm(4), Eu(5), Tb(6), Dy(7), Er(9)] and [RE2L6(H2O)4]·2H2O [RE ¼ Tb(60), Ho(8), Yb(10), Lu(11), Y(12)]. The crystal structures of 1, 2, 6, 60, 7, 9 and 12 have been determined and the isomorphous relationships of the others have been identified. Their structures change from twodimensional (2D) array (the coordination number of the metal ions is nine for 1 and eight for 2–7 and 9) to double-nuclear structure (the metal ions are eight-coordinated) for 60, 8 and 10–12, as controlled by lanthanide contraction. The structural type has been found influenced by the pH value of the reaction mixtures. q 2004 Elsevier B.V. All rights reserved.