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The structure of a tetranuclear metal cluster with a four‐coordinate carbide carbon atom: bis(benzyltrimethylammonium) μ‐carbido‐dodeca‐carbonyl‐tetrahedro‐tetraferrate
| Content Provider | Semantic Scholar |
|---|---|
| Author | Boehme, Richard F. Coppens, P. |
| Copyright Year | 1981 |
| Abstract | [N(CH3)aCH2C6H5 ]2[Fe4(g4-C)(CO)12] , orthorhombic, P2~2a21, a = 11.184 (1), b = 17.554 (3), c = 18.373 (3)A, V = 3607/k 3, Z = 4. Data were collected on an automated four-circle diffractometer (Mo Ka, it = 0-71069 A, g = 1-64 mm -1) at 295 K using a variable 0 2 0 scan. The structure was solved by direct methods using MULTAN and refined by least squares to R(F) = 0.052 for the 5215 reflections with IFol > 5o'(Fo). The metal cluster has approximate C2v symmetry with the carbide C atom located directly on a stretched edge of an otherwise tetrahedral Fe 4 group at 1.784 (7) and 1.820 (7)/k from the two Fe atoms between which it is interposed, and at 1.941 (7) and 1.980 (7) ,~ from the other two Fe atoms. Introduction. The study was undertaken in preparation of a possible electron density study of this complex which exhibits bonding between a single C atom and a metal cluster, and serves as a model for a carbide C atom on a metal surface. Crystals were kindly supplied by M. A. Beno and J. M. Williams of Argonne National Laboratory. The nature of the counterion was unknown at the time of the analysis and was determined in the course of the structure analysis. The crystal used for data collection has approximate dimensions of 0.21 x 0.26 x 0.29 mm and showed the form {011} and the faces ( l l i ) and (ili); D x = l . 6 1 , D m = l . 5 M g m -3. Data were collected at 295 K by the 0-20 technique on a CAD-4 automated diffractometer. Background was corrected for by a modified Lehmann-Larsen technique as described elsewhere (Blessing, Coppens & Becker, 1974). The intensities of three standards were monitored at regular intervals and showed no deviations larger than 2.4%, the average deviation being 0.7%. l l 405 independent intensity measurements were made and reflections with identical indices were averaged yielding l l 123 observations. 6575 2 a(F2obs) were observations with I Fobsl >_ used in the least-squares refinement. The positions of the four Fe atoms and the carbide C atom were determined with MULTAN, while the remaining atoms were located 0567-7408/81 / 101914-03501.00 from subsequently calculated difference maps. The structure was refined using the program LINEX77, including an isotropic-extinction parameter (Becker & Coppens, 1975); the largest reduction in intensity due to extinction was 21%. Final R factors are R(F) = 8.5%, Rw(F ) = 5.9% for all reflections and R(F) = 5.2%, Rw(F ) = 5.2% for 5215 reflections with IFol > 5a(Fo) with weights w = 1/aZ(Fo), where a2(Fo) is derived from the expressions a2(F 2) = 0.01Fo 2 + a 2 (counting) and t72(Fo) = [(Fo2) 2 + t72(F2o)/2] 1/2 -IF21. Final positional and thermal parameters are given in Table 1.* The final R factors for the rejected enantiomorphic structure are R (F) = 8.9%, R w(F) = 6.3 % for all reflections and R(F) = 5-6% and Rw(F ) = 5.7% for reflections with I Fol >_ 5o'(Fo). Discussion. Fig. 1 shows the numbering scheme of the atoms, while the bond lengths in the Fe4C cluster are given in Fig. 2. Other bond lengths and angles are listed in Tables 2 and 3. Three other relevant structure determinations have been completed. The first two by Beno, Williams, Tachikawa & Muetterties (1980, 1981) are an X-ray and a neutron study of the neutral diprotonated cluster in which one H atom bridges the tetrahedron edge opposite the C atom, while the second H atom is attached to the C and one of the Fe atoms. The third structure determination of a monohydrate of the tetraammonium zinc salt of the dianion was performed at the same time as the present work was in progress (Davis, Beno, Williams, Zimmie, Tachikawa & Muetterties, 1981). The cluster in the tetraammonium zinc salt has a crystallographic mirror plane unlike the structure reported here. Comparison of the bond lengths (Table 2) shows small differences between the two dianions especially with regard to the F e F e distances which differ by about 0.03 ./k. The Fe (1 ) -C(1 ) -Fe (4 ) angle is found to be 176.3 (4) ° * Lists of structure factors and anisotropic thermal parameters have been deposited with the British Library Lending Division as Supplementary Publication No. SUP 36134 (21 pp.). Copies may be obtained through The Executive Secretary, International Union of Crystallography, 5 Abbey Square, Chester CH 1 2HU, England. © 1981 International Union of Crystallography [N(CH3)3CH2C6H5 ]2[Fe4(#4-C)(CO)12 ] 1915 Table 1. Fractional coordinates (x 104, f o r Fe x 105) and equivalent isotropic temperature parameters (A 2 x lOa,for Fe x 104) |
| Starting Page | 1914 |
| Ending Page | 1916 |
| Page Count | 3 |
| File Format | PDF HTM / HTML |
| DOI | 10.1107/S0567740881007577 |
| Volume Number | 37 |
| Alternate Webpage(s) | http://journals.iucr.org/b/issues/1981/10/00/a20342/a20342.pdf |
| Alternate Webpage(s) | https://doi.org/10.1107/S0567740881007577 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
