The synthesis of 1,4,7-trimethyl-1,7-bis(4-carboxybenzyl)-1,4,7-triazaheptane (LH(2)) and 1,4,7,16,19,22-hexamethyl-1,4,7,16, 19,22-hexaaza[9.9]paracyclophane (L1) is described. The interaction of both ligands with Cu2+, Zn2+ Cd2+, and Pd2+ ions has been studied by potentiometric titrations and microcalorimetry (LH(2)/Cu2+,Cd2+) in 0.15 mol dm(-3) NaCl solution at 298.10.1 K. The stability of LH(2) complexes with these cations is rather low. Thermodynamic data suggest the N-3 moiety is the binding site for Cu2+, and Pd2+, while in the case of Zn2+ and Cd2+ the carboxylate groups seem to be preferred. X-ray data confirm the coordination site for Pd2+. Crystals of [PdLH(2)Cl](NO3).2.6H(2)O are triclinic, space group P (1) over bar (Z = 2), with a 8.472(3) Angstrom, b = 12.178(2) Angstrom, c = 14.498(4) Angstrom, a = 78.26(2)degrees, beta = 87.20(3)degrees, gamma = 77.72(2)degrees, R = 0.0727, and WR(2) = 0.2294. The Pd2+ ion, is coordinated by the three amino groups of LH(2) and a Cl- anion in a square coordination environment; the two protons are located on the carboxylic groups. L1 forms both mono- and binuclear complexes with Cu2+ in aqueous solution but does not interact with Zn2+ and Cd2+. Pd2+ complexes are also formed. Crystals of [Cu(2)L1Cl(2)](ClO4)(BPh(4)).CH3CN are monoclinic, space group P2(1)/m (Z = 2), with a = 11.526(2) Angstrom, b = 13.552(2) Angstrom, c = 18.078(6) Angstrom, beta = 96.47(2)degrees, R = 0.0823, and WR(2) = 0.2366. The two Cu2+ ions are coordinated by three nitrogen atoms of L1 and a Cl- anion in a square coordination environment, the ligand behaving as a ditopic receptor. Selectivity in metal ion binding is discussed.