Dibenzenechromium structure

Bailey, M. F. Dahl, L. F. (1965) "Three-dimensional crystal structure of benzenechromium tricarbonyl with further comments on the dibenzenechromium structure, Inorg. Chem. 4, 1314-1319. 

The correct identification of the sandwich structure of ferrocene led Fischer to consider the possibility of arenes acting as hexahapto 6VE ligands. By simple arithmetic, a neutral bis(arene) sandwich complex of a zerovalent Group 6 element, e.g. chromium (Figure 6.71), was anticipated, a line of reasoning which led Fischer to develop the synthesis of dibenzenechromium. His approach resulted in the comparatively general Fischer-Hafner synthesis (1955), which is applicable to many metals and arenes (devoid of Lewis-basic substituents, Figure 7.34). 

Dibenzenechromium, which forms dark brown crystals, is much more sensitive to air than is ferrocene, with which it is isoelectronic it does not survive the reaction conditions of aromatic substitution. Structural studies on arene complexes show that the C—C bond lengths are usually equivalent, or nearly so. Many other transition metals, including some lanthanides and uranium form arene complexes, and... 

Efforts were made to determine the structure of the oxygenated dibenzenechromium. Based on analysis, ultraviolet and infrared spectra, the following composition was assigned to the catalyst ... 

Preparation of ferrocene was reported at about the same time by two research groups, and a sandwich structure was proposed, based on ferrocene s physical properties (Kauffman, pp. 185-186). The sandwich structnre was confirmed by x-ray diffraction studies. Since then, other metallocenes composed of other metals and other carbon ring molecules, such as dibenzenechromium (see Figure 3) and uranocene (see Figure 4), have been prepared. 

Some crystalline compounds of the type MjPjSg (e.g. M = Mn, Zn, Fe, Ni, Cd and their selenium analogues) are lamellar semiconductors with interesting electric and magnetic properties which are consequent upon the structural arrangement (MPS3 structure-type) (Figure 9.19). These properties are profoundly modified on the formation of intercalation compounds with small quantities of amines, Li+ cations, dibenzenechromium and so forth [24-27]. 

The use of IR in the interpretation of structural problems has been well demonstrated for the compound dibenzenechromium. From a comparison of its IR spectrum and the theoretical number of bands for various possible structures, as calculated by the methods of group theory, a sandwich-type structure symmetry) was proposed. This was subsequently confirmed by an x-ray study. It was also found from a study of the far IR that the M-ring interaction force constant of this compound is slightly lower than that of ferrocene (2.39 10 dynes/cm vs 2.7 10 dynes/km). 

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