Structures of metal carbonyls

The structures of the dinuclear metal carbonyls (containing two metal atoms) involve either metal-metal bonds or bridging CO groups, or both. For example, the structure of Fe2(CO)9, diiron nonacar-bonyl, contains three CO ligands that form bridges between the iron atoms, and each iron atom also has three other CO groups attached only to that atom. 

Carbonyl groups that are attached to two metal atoms simultaneously are called bridging carbonyls, whereas those attached to only one metal atom are referred to as terminal carbonyl groups. The structures of Mn2(CO)10, Tc2(CO)10, and Re2(CO)10 actually involve only a metal-metal bond, so the formulas are more correctly written as (CO)5M-M(CO)5. Two isomers are known for Co2(CO)8. One has 

The structure for Mn2(CO)10 is sometimes drawn to appear as if four CO ligands form a square plane around the Mn atom. In fact, the four CO groups do not lie in the same plane as the Mn atom. Rather, they lie about 12 pm from the plane containing the Mn on the side opposite the metal-metal bond. 

The nature of the bonds between metals and carbon monoxide is interesting and deserves some discussion. Carbon monoxide has the valence bond structure shown as 

The overlap of a d orbital on a metal with the 7T orbital on CO leading to back donation. 

Clearly, the CO bond is weakened to a greater extent as the degree of back donation increases. 

A similar reduction in C-0 bond order occurs for an isoelectronic series of metal carbonyls as the oxidation states of the metals are reduced. Consider the positions of the C-0 stretching bands in the following carbonyls  

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Hydrogen forms an extensive series of compounds with the metal carbonyls, and the nature of the H bonding within these complexes has been a point of debate for a considerable period. Both the chemistry and structure of metal carbonyl hydride compounds have been exten-... 

Comparing these results for CO bonded to Ni(lOO) and Pd(lOO) to the structure of metal carbonyl clusters, one finds that the multiply-coordinated CO on palladium has... 

HOs6(CO)18] and H2Os6(CO)18 marks one of the highlights of the early period of osmium carbonyl cluster chemistry [162]. While both the dianionic cluster and the monoanionic system have the expected octahedral metal core, a capped square based pyramidal structure was found for H2Os6(CO)18. This turned out to be the archetypal example for the capping rule , a concept which proved to be very successful in the analysis of the structures of metal carbonyl clusters of the iron and cobalt triads [166],... 

Figure 17 Structures of metal carbonyl compounds discussed In Section 12.04.1.3.4.

Since polynuclear carbonyls take a variety of structures, elucidation of their structures by vibrational spectroscopy has been a subject of considerable interest in the past. The principles involved in these structure determinations were described in Sec. 1-10. However, the structures of some polynuclear complexes are too complicated to allow elucidation by simple application of selection rules based on symmetry. Thus the results are often ambiguous. In these cases, one must resort to X-ray analysis to obtain definitive and accurate structural information. However, vibrational spectroscopy is still useful in elucidating the structures of metal carbonyls in solution. 

CRYSTAL STRUCTURES OF METAL CARBONYLS AND ORGANOMETALLIC COMPOUNDS... 

Braga and Grepioni have undertaken a series of analyses of the crystal structures of metal carbonyl clusters, 7t-arene complexes, mixed carbonyl n-arene complexes and some substituted derivatives [170]. Their analyses are based on examination of the packing details and motifs in the crystal structures, recognition of specific interactions, calculation of the packing potential energy for the crystal and consideration of contributions to the lattice volume. Their objective, to investigate the interplay between molecular structure and crystal structure, is very similar to the perspective in this article. 

Various examples of bi- and trifurcated-acceptor interactions have been found in supramolecular structures of metal carbonyl complexes. In (/<-CO)(jU-CHCH3)-[(C5H5)Fe(CO)]2, 91, the bridging carbonyl ligand participates in two C-H- -O hydrogen-bonding interactions with C-H units of the cyclopentadienyl ligands. As a result the dinuclear molecules are self-assembled into polymeric chains [152]. 

Sidgwick NV, Bailey RM (1934) Structures of metallic carbonyls and nitrosyls. Proc Roy Soc A144 521-537... 

A more precise description of electronic structures of metal carbonyls is achieved by employing molecular orbital theory for specific cases. For octahedral metal carbonyls, the molecular orbital scheme is represented in Figure 2.6. ... 

IR metal carbonyl clusters structures of metal carbonyl clusters interaction of metal carbonyl clusters with the zeolite framework Identifications of metal carbonyl dusters in cages are inferred from comparisons of their spectra with those of analogous molecular dusters in solution or in solid state most reliable for very small cluster shifts of carbonyl bands identify the interaction of carbonyl dusters with the zeolite framework. 

Electrochemical measurement as a probe for the investigation of the structure of metal carbonyls J.Organomet.Chem./ (1975)/ 102 327... 

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