At room temperature, the reaction of (mu-H)(2)Os-3(CO)(10) with BH3S(CH3)(2) produces the new borylidyne cluster (mu-H)(2)Os-3(CO)(9)(mu-H)(2)BH, a methylidyne cluster analog. At 65 degrees C the previously reported ketenylidene cluster analog (mu-H)(3)Os-3(CO)(9)(mu(3)-BCO) is formed. The complex (mu-H)(2)Os-3(CO)(9)(mu-H)(2)BH was characterized by H-1 NMR, B-11 NMR, and infrared spectroscopies as well as mass spectrometry. Its molecular structure was determined from a single-crystal X-ray analysis. The molecule is of approximate C-s symmetry. It consists of a tetrahedral Os3B core with a terminal B-H bond, two Os-H-B, hydrogen bridge bonds, and three Os(CO)(3) units. A similar structure has been proposed for one of the isomers of a ruthenium analog, (mu-H)(2)Ru-3(CO)(9)(mu-H)(2)BH, but it differs from the related iron complex (mu-H)(2)Os-3(CO)(9)(mu-H)(2)BH: triclinic space group P (1) over bar, a = 9.501(4) Angstrom, b = 9.525(4) Angstrom, c = 10.070(2) Angstrom, alpha = 87.72(3) beta = 88.32(3)degrees, gamma = 61.45(3)degrees, Z = 2.