A new type of hexaosmium boride cluster, H3Os6(CO)(16)B, was produced in the thermolysis of H3Os3(CO)(9)- (BCO). This complex is an 86 valence electron cluster, but the O-S6 framework does not possess one of the geometries previously observed for Os-6 clusters that have 86 valence electrons. [HOs6(CO)(18)](-) and [Os-6(CO)(18)](2-) have octahedral frameworks while that of H2Os6(CO)(18) is a face-capped square pyramid. The Os-6 framework Of H3Os6(CO)(16)B can be viewed as being derived from a pentagonal bipyramid that is missing one equatorial vertex. It contains an interior boron atom. Alternatively, it can be viewed like the 84 valence cluster Os-6(CO)(18) as either a bicapped tetrahedron, with a boron atom residing on the edge of the tetrahedron that is common to the capped faces, or a face-capped trigonal bipyramid, with the boron atom on an equatorial edge of the bipyramid that is also an edge of the capped face. H3Os6(CO)(16)B was characterized by H-1, and B-11, C-13 NMR, IR, and mass spectroscopies and single-crystal X-ray diffraction analysis. The molecular structure was determined from two separate crystals. The analysis of each crystal yielded virtually identical structures, but their volumes differed by 36 Angstrom(3) due to differences in packing in the unit cell. Data for crystal I of H3Os6(CO)(16)B: monoclinic P2(1)/n, a 9.954(2) Angstrom, b = 15.780(4) Angstrom, c = 16.448(3) Angstrom, beta = 91.07(1)degrees, Z = 4. Data for crystal II of H3Os6(CO)(16)B: monoclinic P2(1)/n, a = 9.927(2) Angstrom, B = 16.623(2) Angstrom, b = 16.0233(10) Angstrom, beta = 97.78(1)degrees, Z = 4.