As a part of an ongoing project on the synthesis and spectroscopic studies of osmium compounds with interesting electrochemical and photochemical properties, we have synthesized a series of bis-(diimine)carbonylpyridineosmium(II) complexes where diimine = various substituted 2,2'-bipyridines and 1,10-phenanthrolines; pyridine = pyridine, 4-phenylpyridine and 5-pyridyl-10,15,20-triphenylporphyrin. We will discuss the synthesis and initial characterization of these compounds by ¹H NMR, and UV-visible absorbance spectroscopies. These compounds are of interest as possible models of the photosynthetic reaction center, as energy transfer agents, as photochemical electron transfer agents, and as potential DNA, molecular oxygen and anion sensors.