Four palladium(II) and mercury(II) complexes of the type [MCl 2 (HPAO)] or [M(PAO) 2 ](HPAO = syn-2-pyridine aldoxime) are prepared and characterized using FTIR, 1 H NMR spectra, molar conductivity, and melting point. The results demonstrated that a chelating bidentate behavior of APO through the indo and exocyclic nitrogen atoms. The applicability of the prepared complexes in hydrogen storage at a temperature of 77 K and a pressure of 100 bar is studied. The results show that the complexes are capable of storing hydrogen as follows: 1.54, 2.3, 0.53, and 0.63 wt.% of H 2 for [Hg(HAPO)Cl 2 ] (1), [Pd(HAPO)Cl 2 ] (2), [Hg(APO) 2 ] (3), and [Pd(APO) 2 ] (4), respectively.Thermodynamic calculations show that the storage type of hydrogen is the physico-absorption type. The study shows that the central metal has an effect on the ability of the complex to store hydrogen, as the palladium complexes are more capable of storing hydrogen than their mercury counterparts.