1104 and can be explained in a similar way39f the m4

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Unformatted text preview: he case of the trinuclear carbonyls of Fe, Ru and Os (p. 1104) and can be explained in a similar way.(39f The M4 tetrahedra of Co and Rh are small enough to be accommodated in an icosahedral array of CO ligands whereas the larger Ir4 tetrahedron forces the adoption of the less dense cube octahedral array of ligands. Of the [&(C0)16] carbonyls the very darkbrown Rh compound prepared simultaneously with and separated from [Rh4(C0)12] is the best known. In the solid its structure consists of an octahedral array of Rh(C0)2 units with the remaining 4 CO’s bridging 4 faces of the octahedron (Fig. 26.8e). A black isomorphous, and presumably isostructural, Co analogue and an isostructural red Ir analogue are known. A second, black Ir isomer occurs which differs only in that it has 4 edge-bridging rather than face-bridging CO groups. Again rationalization is possible on the basis of the ligand polyhedral 39 B. F. G. JOHNSON nd a 977-90 (1993). Y.V. ROBERTS, olyhedron, 12, P $635 2.. Organometallic compounds 1747 Figure 26.8 Molecular structures of some binary carbonyls of Co, Rh, and Ir. (a) Co2(CO)8 in solid state, showing the formation of a “bent” Co-Co bond. (b) Co2(CO)s i n solution. (c) Ir4(CO)12. (d) M4(C0)12, M = Co, Rh. (e) M6(CO)16M = Co, Rh and Ir (for its red isomer). (f) black isomer of Ir6(CO)16. model. In both structures the ligands occupy the 16 vertices of a tetracapped truncated tetrahedron. In one case the 4 caps are the face-bridging ligands, i n the other the edge-bridging ligands. The two structures are related by a simple rotation of the M6 octahedron about a c axis.(39) 4 Carbonyl hydrides and carbonylate anions are obtained by reducing neutral carbonyls, as mentioned above, and in addition to mononuclear metal anions, anionic species of...
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This note was uploaded on 10/12/2012 for the course CHEMISTRY CHM1040 taught by Professor Jhon during the Spring '12 term at Florida A&M.

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