Preparation, crystal structures, vibrational spectra, and normal coordinate analyses of the trans-dihalogeno-tetrakis-pyridine-osmium(II) complexes trans-[OsX2Py4], X=F, Cl, Pr, I

By reaction of the hexahalogenoosmates(IV) with glycerine and pyridine trans-dihalogeno-tetrakis-pyridine-osmium(II) complexes are formed and purified by chromatography or by recrystallization. X-ray structure determinations on single crystals have been performed of trans-[OsF2Py4]. 4H(2)O (monoclinic, space group C12/c1, a=30.292(3), b=9.120(5), c=17.883(2)Angstrom, beta=107.96(7)degrees, Z=8), trans-[OsCl2Py4] (orthorhombic, space group Ibca, a=b=15.656(2), c=16.9577(8), Z=8), trans-[OsBr2Py4] (orthorhombic, space group Pna2(1), a=9.436(5), b=14.062(2), c=15.561(3)Angstrom, Z=4) and trans-[OsBr2Py4 (orthorhombic, space group Pcnb, a=9.550(2), b=16.165(3), c=13.827(Angstrom) Z=4). The pyridine rings are twisted propeller-like against the octahedron basis with mean angles of 75 degrees (X = F), 48 degrees (Cl), 46 degrees (Br), 44 degrees (I). Using the molecular parameters of the X-ray structure determinations and assuming D-4 point symmetry, the IR and Raman spectra are assigned by normal coordinate analysis. Good agreement between observed and calculated frequencies is obtained with the valence force constants f(d)(OsF)=2.07, f(d)(OsCl)=1.54, f(d)(OsBr)=1.24, f(d)(OsI)=0.95 and values of f(d)(OsN) between 2.15 und 2.23 mdyn/Angstrom. The F-19-NMR spectrum of trans-[OsF2Py4] in dichloromethane solution exhibits a singlet at -303.2 ppm with weak Os-187 satellites resulting in the coupling constant (1)J(F-19, Os-187) of 98 Hz.