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The Crystal Structure of Fe,( CO) llP (C,H,) 31 Donald J. Dahm and Robert A. Jacobson
Contribution f r o m the Institute f o r Atomic Research and Department of Chemistry, Iowa State University, Ames, Iowa 50010. Received January 17, 1968 Abstract: The crystal structure of Fe3(CO)~1P(C&I&has been determined from three-dimensional ?-ray data. Sixteen molecules crystallize in the monoclinic space group Czi0with a = 37.14, b = 12.26, c = 26.05 A, and 0 = 93.96". The structure was refined by full-matrix least squares with iron and phosphorus atoms anisotropic to a conventional R value of 0.082 for 1800 reflections collected by counter methods. The structure is similar t o that of Fe3(C0),2. The iron atoms form a nearly isosceles triangle with the short side connected by two asymmetric
carbonyl bridges. The rest of the carbonyls are terminal. Each asymmetric unit contains two molecules which are structural isomers of one another, with the P(C&)3 group attached t o different iron atoms.
F
or several years a controversy has existed concerning the molecular structure of Fe3(C0)12. An early X-ray crystal structure investigation2 indicated a disordered structure, with the iron atoms forming an equilateral triangle. However, Mossbauer studies showed that two of the iron atoms had a different electronic environment than the third, and some workers interpreted this as being consistent only with a more linear model. 3-5 Subsequently a different arrangement of the carbonyls was proposed (Figure la) based on the crystal structure determinations of HFe3(CO)11which could explain this disparity. Mossbauer data indicated that Fe3(C0)12and HFe3(CO)11- have similar structures.' However, HFe(C0)n- is not a derivative of Fe3(C0)12and the two have somewhat different physical properties. Therefore, it is difficult to assess the degree of disparity between the two structures. A derivative of Fe3(C0)12,namely Fe3(CO)1lP(C6H& which has properties very similar to its parent,8 was prepared and came to our attention. We felt a structural study of this derivative might well give better evidence for the exact arrangement of the iron and carbonyl groups in Fe3(C0)12than studies of its own disordered crystal, and therefore we decided to undertake such a project.
Experimental Section Fe3(CO)nP(CsH5)3 was prepared by Angelici and Sieferts by the reaction of Fe3(C0)12and P(CBH&. They obtained dark green, plate-like single crystals by evaporation of a pentane solution. Because these crystals were reported to decompose in the atmosphere, they were placed in thin-walled, Lindemann glass capillaries. Preliminary precession photographs (Cu K a ) showed the unit cell to be monoclinic with systematic absences: hkl when h k # 2n, and kOl when l # 2n. These absences are consistent with either space group CS4-C,or Gh6-CZ/c.The unit cell parameters at 25" are a = 37.14 f 0.03, b = 12.26 =k 0.01, and c = 26.05 0.02 A, and p = 93.96 f 0.15". These parameters and their standard deviations were obtained by averaging several reflection positions (Mo Kcr radiation, X 0.7107 A) whose centers were determined by left-right , topbottom beam splitting on a previously aligned Gen-
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(1) Work was performed in the Ames Laboratory of the u. s. Atomic Energy Commission. Contribution No. 2243. (2) L. F. Dahl and R. E. Rundle, J . Chem. Phys., 26, 1751 (1957). (3) (a) M. Kalvius, U. Zahn, P. Kienle, and H. Eicher, Z . Narurforsch., 17a, 494 (1962); (b) R. H. Herber, W. R. Kingston, and G . I
