H2 storage abilities of some novel Pd(II) complexes containing 2H[1,4]benzothiazin-3(4H)-one

Abstract

Initially, a novel series of mixed ligand Pd(II) complexes of 2H[1,4]benzothiazin-3(4H)-one (Hbto) and diamine or phosphine ligands were successfully prepared with yields of 61 to 92%. The treatment of Na2PdCl4 with Hbto in acetone with 1:2 Pd to Hbto ratio affords cis-[PdCl2(Hbto)2] (1) that delivers an appropriate entry into mixed-ligand Hbto complexes. The complex (1) was used as a precursor for preparation the complexes of the type [Pd(Hbto)2(κ2-diamine)]Cl2; (diamine = en (2a), bipy (2b), phen (2c)) and [Pd(Hbto)2(κ2-diphosphine)]Cl2; (diphosphine = dppm (3a), dppe (3b), dppp (3c), dppf (3d)). Likewise, the mono phosphine (PPh3) was used to prepare the contrast complex with complex (1), however, to dissipate the suspicion that define complex [Pd(Hbto)2(PPh3)2]Cl2 is present in the cis or trans structure, two methods were used to prepare this complex, both of which demonstrated that the cis is the preferred structure for the complex [Pd(Hbto)2(PPh3)2]Cl2 (4). For all as-prepared complexes, the characterization techniques (molar conductivity, IR, 1H-, 13C-{1H}, 31P-{1H}NMR and elemental analyses) prove that the Hbto links to Pd(II) in a mono-dentate fashion through the exocyclic oxygen atom. To benefit from the complexes prepared, some as-prepared complexes (1), (2b) and (4) have been evaluated for their H2 storage at 77 K after measuring the N2 adsorption/desorption isotherms in order to get some information about BET surface areas of the samples. The results demonstrate that the selected prepared complexes were all able of storing the H2 and among the complexes (1), (2b) and (4), (2b) was the best one and was able to store 5.4 wt% of H2 under 70 bar and 77 K.