Abstract. Three compounds including a proton transfer ion pair LH2 and its PdII and TlIII complexes were synthesized and characterized using 1H NMR, 13C NMR, IR spectroscopy and single crystal X-ray diffraction method. The chemical formulae are (pipzH2)2(pydc)2 for ion pair 1, (pipzH2)[Pd(pydc)2]·2H2O for PdII complex 2, and (pipzH2)[Tl2(pydc)2Cl4(H2O)2]·4H2O for TlIII complex 3, respectively (pipz: piperazine, pydc: pyridine-2,6-dicarboxylate). The space group and crystal system of all three compounds are P1¯ and triclinic. The proton transfer ion pair 1 was prepared by a reaction between piperazine and pyridine-2,6-dicarboxylic acid, and the complexes 2 and 3 were synthesized by reac-tion of 1 with palladium(II) chloride and thallium(III) nitrate, respectively. In complex 2, two water molecules present in the crystal packing are joined by hydrogen bonds and form a water dimer and similarly in complex 3, six water molecules apart from the complex and individually form an interesting water hexamer developed in the whole crystal. Hydrogen bonding and ion pairing play an important role in stabilizing the crystals. Keywords: Palladium; Thallium; Pyridine-2,6-dicarboxylic acid; Piperazine; Proton transfer; Crystal structures; Hydrogen bonds; Ion pairs
