The cluster species [Os₁₀C(CO)₂₄]^2–(1) and [Os₅C(CO)₁₄H(NC₅H₄)](2) have been obtained for the first time by pyrolysis of [Os₃(CO)₁₁(py)]. X-Ray analysis of the [N(PPh₃)₂]⁺ salt of (1) shows a tetracapped octahedral metal arrangement of the Os₁₀C unit which is the first example of a carbide-atom encapsulated in an octahedral Os₆ cavity. In the formation of [Os₅(CO)₁₄H(NC₅H₄)] orthometallation of the pyridine ligand occurs which bridges two equatorially located osmium atoms of an arachno-bipyramidal Os₅ arrangement which surrounds a semi-interstitial carbide-atom. Crystals of [N(PPh₃)₂]₂[Os₁₀C(CO)₂₄] are triclinic, space group P, a= 27.157(5), b= 17.535(4), c= 10.470(2)Å, α= 96.37(2), β= 100.71(2), γ= 85.92(2)°, Z= 2. Refinement of atomic parameters using 8 942 absorption corrected data converged at R 0.0553. Crystals of [Os₅C(CO)₁₄H(NC₅H₄)] are monoclinic, space group P2₁/c, a= 8.869(2), b= 17.870(3), c= 17.208(3)Å, β= 95.30(2)°, and Z= 4. Refinement of atomic parameters using 3 518 absorption corrected data converged at R 0.0604.