Synthesis, crystal structures, vibrational spectra, and normal coordinate analyses of the mer-trihalogeno-tris-pyridine-osmium(III) complexes mer-[OsX3Py3], X = Cl, Br, I

By reaction of the hexahalogenoosmates(TV) with pyridine and iso-amylalcohol mer-trihalogeno-tris-pyridine-osmium(III) complexes are formed and purified by chromatography. X-ray structure determinations on single crystals have been performed of mer-[OsBr3Py3] (monoclinic, space group P2(1)/n, a=9.098(5), b=12.864(5), c=15.632(5) Angstrom, beta=90.216(5)degrees Z=4) and mer-[OsI3Py3] (monoclinic, space group P2(1)/n, a=9.0952(17), b=13.461(4), c=15.891(10), beta=91.569(5)degrees, Z=4). The pyridine rings are twisted propeller-like against the Ng meridional plane with mean angles of 49 degrees (Cl), 46 degrees (Br), 44 degrees (I). Based on the molecular parameters of the X-ray structure determinations and assuming C-2 point symmetry, the IR and Raman spectra are assigned by normal coordinate analysis. Due to the stronger trans influence of pyridine as compared with the halide ligands for N'-Os-X-. axes significantly different valence force constants are observed in comparison with symmetrically coordinated octahedron axes: f(d)(OsCl)=1.74, f(d)(OsCl.)=1.49, f(d)(OsBr)=1.43, f(d)(OsBr.)=1.18, f(d)(OsI)=0.99, f(d)(OsI.)= 0.96, f(d)(OsN) between 1.96 and 2.07 and f(d)(OsN') between 2.13 and 2.32 mdyn/Angstrom.