CRYSTAL-STRUCTURE OF FE2OS(CO)12, A STRUCTURAL ANALOG OF FE3(CO)12 WITH NO REQUIRED SITE SYMMETRY AND ONLY A APPROXIMATELY 12-1 STAR OF DAVID DISORDER PATTERN - EXAMPLE OF AN ACENTRIC, BUT CLOSE TO CENTRIC, STRUCTURE - SOME THOUGHTS ON THE SOLID-STATE STRUCTURE OF FE3(CO)12

The heteroatomic trinuclear cluster Fe2Os(CO)12 crystallizes in the noncentrosymmetric monoclinic space group Pn (variation of Pc; Cs2; No. 7) with a = 8.377 (2) Å, b = 22.715 (8) Å, c = 8.953 (2) Å, β = 96.510 (18)°, V = 1692.6 (8) Å3, and Z = 4. The molecular packing is close to, but not exactly, that required for space group P21/n (cf. Fe3(CO)12, P21/n, a = 8.359 (2) Å, b = 11.309 (2) Å, c = 8.862 (2) Å, β = 97.00 (2)°, V = 831.5 (3) Å3, and Z = 2, i.e., similar except that, in the Fe2Os(CO)12 structure, 21 and i operations are absent and b is doubled). Diffraction data for ±h,±k,±l were collected for 2θ = 4.5-50.0° with Mo Kα radiation. The structure was solved by Patterson and difference-Fourier methods, and refinement converged with RF = 4.9%, Rw = 4.8%, and GOF = 1.772 for all 5993 point-group-unique reflections (RF = 4.0%, RwF = 4.6% for those 5220 data with |Fo| > 6σ(|Fo|)). There are two crystallographically distinct Fe2Os(CO)12 molecules in the unit cell. Each suffers an approximately 12:1 “star of David” disorder of the metal atoms. The major components are unambiguously defined and contain an Os(CO)4 system linked to two Fe(CO)3 units, which, in turn, are bridged by two asymmetrically bridging carbonyl ligands—i.e., a connectivity similar to that in Fe3(CO)12. Bond lengths of note (in Å) are as follows: molecule A, Os(A)–Fe(lA) = 2.735 (2), Os(A)–Fe(2A) = 2.740 (3), Fe(1A)–Fe(2A) = 2.589 (4), Fe(1A)–C(BR1A) = 2.245 (16), Fe(2A)–C(BR1A) = 1.939 (16), Fe(1A)–C(BR2A) = 1.918 (17), Fe(2A)–C(BR2A) = 2.224 (16); molecule B, Os(B)–Fe(1B) = 2.745 (3), Os(B)–Fe(2B) = 2.746 (3), Fe(1B)–Fe(2B) = 2.594 (4), Fe(1B)–C(BR1B) = 2.084 (20), Fe–(2B)–C(BR1B) = 2.047 (19), Fe(1B)–C(BR2B) = 1.937 (17), Fe(2B)–C(BR2B) = 2.123 (17). © 1990, American Chemical Society. All rights reserved.