For the first time the structural characterization of dimethyl selenoxide coordinated to metal complexes has been performed confirming the Me2SeO arrangement assigned by spectroscopic techniques for the molecule in solution and solid state. The structure of Me2SeO is trigonal pyramidal with Se-O and Se-C bond lengths of 1.70 and 1.92 A, respectively, and Sigma(X-Se-Y) = 301degrees. As a ligand, dimethyl selenoxide was found to bind to the rhodium centers of various Lewis acidity strengths by using only its oxo functionality in both terminal and bridging fashions. This O-directed coordination preference contrasts with an ambidentate (-S and -O) binding character revealed by dimethyl sulfoxide upon formation of analogous donor-acceptor complexes. The study of dimethyl selenoxide in the gas phase at 135-140degreesC resulted in a thermal degradation of this molecule. The major decomposition product has been entrapped by a metal complex and identified as dimethyl selenide. The isolation of the coordinated Me2Se fragment clearly demonstrates that the Me2SeO molecule is less thermally stable than Me2SO, which under similar reaction conditions shows no sign of decomposition at temperatures up to 160degreesC.