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)(kappa(2)-diamine)]Cl-2; (diamine = en (2a), bipy (2b), phen (2c)) and [Pd(Hbto)(2)(kappa(2)-diphosphine)]Cl-2; (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)]Cl-2 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)]Cl-2 (4). For all as-prepared complexes, the characterization techniques (molar conductivity, IR, H-1-, C-13-{H-1}, P-31-{H-1)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 H-2 storage at 77 K after measuring the N-2 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 H-2 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.