Hydrogen storage capacities of some new Hg(II) complexes containing 2-acetylethiophene

Abstract

Novel mercury divalent ion complexes with 2-acetylethiophene (AcT) were synthesized. The treatment of HgCl2 with AcT in ethanol at room temperature in 1:1 and 1:2 mercury to AcT ratios affords [Hg(AcT)Cl-2] (1) and [Hg(AcT)(2)]Cl-2 (2) respectively. Both complexes (1) and (2) were used as synthone for preparation the complexes of the type [Hg(AcT)(L-L)]Cl-2 where the bidentate ligands were either aliphatic amines L-L; ethylenediamine (en) (3), N-methylethylenediamine (Men) (4), N-ethylethylene-diamine (Een) (5) and 1,3-diaminopropane (Dap) (6) or heterocyclic amines L-L; 2,2'-bipyridine (bipy) (7) and 1,10-phenanathroline (phen) (8). When complex (1) was used, the resulted complexes of the type [Hg(AcT)(L-L)]Cl-2 were pure. Column chromatography packed with silica was used to separate the resulted complexes in pure form when complex (2) was used as a starting material. Furthermore, the treatment of complex (1) with two moles of triphenylephosphine (PPh3) results in the mixture of [Hg(AcT)(PPh3)(2)]Cl-2 (9) and [Hg(AcT)(O = PPh3)(2)]Cl-2 (10). These two complexes were separated using sephadex column depending on their molecular weight. The prepared complexes were characterized by molar conductivity, FT-IR, H-1-, DEPT C-13-{H-1}, P-31-{H-1}NMR and elemental analyses. The characterization results show that AcT behaves as a chelate bi-dentate ligand through sulfur and oxygen atoms in all complexes. The prepared complexes were characterized to be tetrahedral complexes. In order to take benefit of the prepared complexes, (1), (8) and (9) were selected to test their surface areas and hydrogen storage abilities. In addition, the thermodynamic properties of H-2 adsorption (enthalpy and entropy) were determined at four different temperatures using the Clausius Clapeyron equation. The results prove that the prepared complexes were capable of storing the hydrogen.