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

Abstract

A series of rare earth complexes with p-aminobenzoic acid (HL) have been synthesized: [RE 2L 6(H 2O) 2] n [RE=La ( 1), Ce( 2), Pr( 3), Sm( 4), Eu( 5), Tb( 6), Dy( 7), Er( 9)] and [RE 2L 6(H 2O) 4]·2H 2O [RE=Tb( 6′), Ho( 8), Yb( 10), Lu( 11), Y( 12)]. The crystal structures of 1, 2, 6, 6′, 7, 9 and 12 have been determined and the isomorphous relationships of the others have been identified. Their structures change from two-dimensional (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 6′, 8 and 10–12, as controlled by lanthanide contraction. The structural type has been found influenced by the pH value of the reaction mixtures.