Crystal and molecular structures of [Os₃(CO)₁₁(NCMe)] and [Os₃(CO)₁₀(NCMe)₂]

Both the complexes [Os₃(CO)₁₁(NCMe)] (1) and [Os₃(CO)₁₀(NCMe)₂] (2) crystallise in the monoclinic space group P2₁/n with Z = 4. The cell parameters for (1) are a = 8.284(3), b = 14.787(5), c = 15.944(6) Å, and β = 102.50(2)°, and those for (2) are a = 8.520(3), b = 20.096(6), c = 12.747(4) Å, and β = 108.77(2)°. The structures have been solved by a combination of direct methods and Fourier-difference techniques, and refined by blocked-cascade least squares to R values of 0.039 for 1 459 diffractomer data, for (1), and 0.046 for 2 397 diffractometer data, for (2). The three Os atoms in (1) define an isosceles triangle. Two of the metal atoms are co-ordinated to two axial and two equatorial terminal carbonyl groups. The third Os atom is co-ordinated to one axial and two equatorial carbonyls and the second axial site is occupied by a linear nitrile ligand. The structure of (2) resembles that of (1) except that an axial carbonyl on an adjacent Os atom to and on the opposite side of the Os₃ plane from the co-ordinated nitrile has been replaced by the second NCMe ligand.