Edge-bridging carbonyl

Q Terminal carbonyl groups Edge bridging carbonyl groups Face bridging carbonyl groups... 

Form A, as confirmed by an X-ray diffraction study (3), has structure XI (see Fig. 4) with six terminal and eight face-bridging CO groups (vco = 1640-1680 cm-1), whereas form B should have some edge-bridging carbonyl groups (rco = 1710-1760 cm-1) (37). On oxidation both... 

In the solid state, the dianion [Rh4(CO)ii]2 possesses a distorted tetrahedral geometry with four terminal and seven edge-bridging carbonyl groups, whereas in solution it is fluxional at — 70°C (18, 74). 

Two isomeric forms of hexadecacarbonylhexairidium(O), Ir6(CO)i6, are known a red isomer, isostmctural with Rli6(CO)i6, and a black isomer that has four edge-bridging carbonyl groups rather than face-bridging. The structure of the black isomer is described as Ir6(CO)i2(/u.2-CO)4. 

Z —CO— (/1, 75, 76). The two known compounds in which an edge-bridging carbonyl is fully protonated (73, 74) are thermally unstable and have been detected only by low-temperature NMR spectroscopy. 

I —CO— Stretching Frequencies for Main Group III and Lanthanide Adducts of Edge-Bridging Carbonyls... 

Fig. 15. Molecular structure of (Cp 2Yb)2[(OC)4Fe3(CO)7] showing a nearly planar array of three linear Fe atoms and four edge-bridging carbonyls forming Z —CO— interactions with two Yb(Hl) centers. [By permission from the American Chemical Society, T. D. Tilley and R. A. Andersen, J. Am. Chem. Soc. 104, 1772 (1982).]...

There appear to be no examples of transition metal acceptors attached to edge-bridging carbonyls in molecular compounds. This paucity of data undoubtedly arises from the lack of synthetic work rather than fundamental chemical reasons. There is, however, one example in surface chemistry which is likely to fit into this category. 

A distinctive feature of the Mn2(CO)5(PP)2 series of compounds (166) is their ability to reversibly add CO when heated in solution under a CO atmosphere. The IR spectrum of the product, for example, Mn2(CO)6(dppm)2, suggests the presence of two terminal carbonyls on each manganese as well as two C-bonded edge-bridging carbonyl ligands. This compound decarbonylates to the starting Mn2(CO)5(dppm)2 when it is allowed to stand in air for a few weeks. Systematic studies of the de-carbonylation of Mn2(CO)6(PP)2 complexes demonstrate that the tendency... 

The edge-bridged carbonyl cluster compound [Ru3( -H)(//-dmdab)(CO)9] (36) (Hdmdab = 3,5-dimethyl-l,2-diaminobenzene) (Fig. has proved to be an ex-... 

X-ray diffraction of the PPN salt reveals a tetrahedral cluster of iron atoms (Fig. 5.14(c)). One triangular face is capped by a triply bridging CO group around each of the sides of this same face there is an edge-bridging carbonyl. On protonation the tetrahedral cluster opens out to a butterfly framework (cf. p. 350) the protonated CO ligand is now a-bonded to the fourth iron atom. Further reduction under acid conditions affords methane it has been suggested that this... 

Three-center or edge-bridging carbonyl (/ 2-CO). The CO-group is bonded simultaneously to two neighbour atoms in a metal polyhedron. The detection of bridging carbonyl groups often indicates the presence of metal-metal bonds. 

Among tetrahedral metal clusters the carbonyl complexes are the more representative. Neutral carbonyl clusters of cobalt and rhodium have similar structures (Fig. 2.16) with nine terminal and three edge-bridging carbonyl... 

Ir (CO),3( <-CO)3] - Octahedral Irg cluster with three symmetri- 34 cal edge-bridging carbonyl groups. d(Ir-Ir) = 2.736 and 2.785 A for bridged and unbridged edges respectively. 

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