  A series of pentanuclear heterometallic coordination compounds of the general
formula (Bu 4 N) 5 [Ln{Os(NO)($\mu$-ox)-Cl 3 } 4 (H 2 O) n ] [Ln = Y (for 2)
and Dy (for 3) when n = 0; Ln = Dy (for 3), Tb (for 4), and Gd (for 5) when n =
1] were synthesized by the reaction of the precursor (Bu 4 N) 2 [Os(NO)(ox)-Cl
3 ] (1) with the respective lanthanide(III) (Gd, Tb, Dy) or yttrium(III)
chloride. For the five new complexes, the coordination numbers eight or nine
are found for the central metal ion. The compounds were fully characterized by
elemental analysis, IR spectroscopy, single-crystal X-ray diffraction analysis,
magnetic susceptibility measurements, and ESI mass spectrometry. In addition,
compound 1 was studied by UV/Vis spectroscopy and cyclic voltammetry. The X-ray
dif-fraction analyses revealed that the anionic complexes consist of a
lanthanide or yttrium core bridged through oxalato li-gands to four octahedral
osmium-nitrosyl moieties. This picture , in which the central ion is
eight-coordinate, holds for
