Bis ( tert-butyl isocyanide )-1 κ 2 Cdi-μ-carbonyl-2 : 3 κ 4 C-octa-carbonyl-1 κ 2 C , 2 κ 3 C , 3 κ 3 C-triangulo-diironosmium

# 2006 International Union of Crystallography All rights reserved The preparation of the mixed-metal cluster, [Fe2Os(C5H9N)2(CO)10], and its crystal structure at 100 K are reported. This complex, along with the cluster in the preceding paper, are the first structurally characterized substitution derivatives of Fe2Os(CO)12. The isonitrile ligands adopt axial positions on the osmium centre and the cluster is isostructural with the Fe2Ru analogue.

The preparation of the mixed-metal cluster, [Fe 2 Os(C 5 H 9 N) 2 -(CO) 10 ], and its crystal structure at 100 K are reported. This complex, along with the cluster in the preceding paper, are the first structurally characterized substitution derivatives of Fe 2 Os(CO) 12 . The isonitrile ligands adopt axial positions on the osmium centre and the cluster is isostructural with the Fe 2 Ru analogue.

Comment
The background to this study has been set out in the preceding paper (Evans et al., 2006). We report here and in that paper the synthesis and structures of Fe 2 Os(CO) 12Àn (CNBu t ) n (n = 1 and 2).
Fe 2 Os(CO) 10 (CNBu t ) 2 , (II), was prepared by carbonyl substitution of the parent Fe 2 Os(CO) 12 cluster using standard methods (Farrugia & Mertes, 2002). The compound was characterized spectroscopically, by FAB mass spectrometry, and by single-crystal X-ray structure determination. The structure was determined at room temperature and 100 K with no discernible metal atom disorder at either temperature. As the structures at different temperatures are essentially identical, only the more precise low-temperature structure will be discussed here.
The structure of (II) at 100 K is shown in Fig. 1. Both isonitrile ligands adopt axial positions on the Os atom, identical to that reported for the Fe 2 Ru analogue but contrasting with Fe 3 (CO) 10 (CNBu t ) 2 [where one isonitrile is axial and the other equatorial (Murray et al., 1990)] and M 3 (CO) 10 (CNR) 2 [M = Ru and Os; R = Bu t and Me] (Dawson et al., 1982;Bruce et al., 1983;Farrugia et al., 1998)

Figure 1
A view of Fe 2 Os(CO) 10 (CNBu t ) 2 , showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level, with H atoms represented by circles of arbitrary size.

Data collection
KappaCCD diffractometer Graphite monochromator CCD rotation images, thick slices scans Absorption correction: multi-scan (Blessing, 1995) T min = 0.197, T max = 0.294 64585 measured reflections 10967 independent reflections 9945 reflections with I > 2σ(I) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.