X-ray structures and complete NMR assignment by DFT calculations of [Os(bpy)₂(CO)Cl]PF₆ and [Os(bpy)₂(CO)H]PF₆ complexes

The X-ray structures of [Os(bpy)₂(CO)(Cl)][(PF₆)] (1) and [Os(bpy)₂(CO)(H)][(PF₆)] (2) (where bpy = 2,2′-bipyridine) have been solved. In complex 1, belonging to the C2/c space group, the Cl^- and CO ligands are statically disordered along two almost orthogonal directions, and this disorder may be explained by the steric similarity of the CO and Cl^-2 groups. Conversely, in complex 2, the CO and hydride ligands are rather different and the [Os(bpy)₂(CO)(H)] moiety does not show any disorder. A more accurate model of the disordered structure of complex 1 and the hydride position in complex 2 were obtained by DFT calculations. Complete ¹H NMR chemical shift assignments were made, using 1D and 2D NMR experiments combined with theoretical calculations. The experimental ¹H NMR data have been fully interpreted with the aid of magnetic shielding constant calculations, by means of the GIAO (gauge-including atomic orbitals) method, carried out at the B3LYP level. Proton nuclear shielding constants have been calculated with the 6-311G++(2d) basis set, and geometry optimizations have been carried out employing the LanL2Dz basis set for osmium and the 3-21G or 6-31G(d) basis sets for the other atoms. Calculated and experimental results have been compared with a satisfactory level of agreement. The complete assignment of the proton spectrum of 2, in good agreement with the theoretical data, was confirmed by the ¹H-¹ NOESY results. By using this mixed experimental and theoretical approach it was also possible to obtain a calculated structure and the ¹H NMR assignment of [Os(bpy)₂(CO) (CF₃SO₃)][(CF₃SO₃)] (3), for which no suitable crystal could be obtained.