The new heteronuclear iminodiacetic acid (H2L) complexes (LnCu(6)(mu(3)-OH)(3)(HL)(2)(L)(4)](ClO4)(2). 25H(2)O with Ln = La (1) and Tb (2) have been prepared in aqueous solution and characterized by single-crystal X-ray diffraction to be isomorphous (crystallographic data for 1 and 2: hexagonal, P6(3)/m; a = b = 12.6425(14) Angstrom, c = 24.541(5) Angstrom, Z = 2 (1); a = b = 12.5802(9) Angstrom, c = 24.285(4) Angstrom, Z = 2 (2)). Ln(3+) was found to be located in the center of the trigonal prismatic cage formed by six Cu2+ ions, with a tricapped trigonal prismatic coordination environment of nine O atoms. The magnetic properties of complexes 1 and 2 have been studied. The results indicate the presence of ferromagnetic couplings between Tb3+ and Cu2+ in compound 2.