275 (1971). (35) The 0.016 8, difference between the two crystallographically inde endent Ni-Ni distances more than likely indicates that the esd's of 0.001 noted are underestimates. Since the two molecular units are chemically equivalent, one may independently derive the magnitude of the likely errors by direct comparison of the chemically equivalent bonds. Such a procedure suggests that the true uncertainty in the Ni-Ni distance is around 0.005 A. (36) A Bondi, (n-CSH5) [((C6HS)2PCH2)2](CH30CH,)Fe and (s-CsH5)((C6H5)3P)(CH30CH2)Fe(CO) have been synthesized and their abilities to transfer C H 2 to cyclohexene have been examined. The structure of the compound ((r-C5H5)-[((C6H5)2PCH2)2]Fe(NCCH3)}B(C6H5)4, resulting from the acid treatment of the diphosphine complex has been determined by single-crystal x-ray diffraction techniques with intensity data gathered at -35 "C. Crystals form as deep red irregular blocks in monoclinic space group Cc with a = 23.542 (8) A, b = 11.494 (3) A, c = 18.774 (4) A, p = 112.26 (2) A. The calculated density of 1.248 g cm-3 for four formula weights of ((C5H5)[((C,H5)2PCH2),IFe(NCCH3)}B(C6H5)4 per unit cell agrees with the measured value of 1.24 g cme3. Iron is bonded to the C5H5 ring in a symmetric r manner, to the two phosphorus atoms of the diphosphine ligand-thereby forming a five-membered chelate ring-and to the nitrogen atom of the CH3CN molecule. The angle at the N atom of the Fe-N-C linkage is 171.9 ( 5 ) " . Four of the atoms of the C-P-Fe-P-C ring are essentially coplanar; one carbon atom lies -0.7 8, from this plane, so that the ring has an envelope conformation. Full-matrix least-squares refinement of the structure has converged with an R index (on 14) of 0.059 for the 4963 symmetry-independent reflections within the Mo Kcu shell defined by 4 < 20 < 55" which have Io/u(I0) > 2.0. 4 CllFol -IFcll/CI~ol = 0.060 and R, = [Cw(lFoI -IFcl)2/CwIFo121i'2 M represents the appropriate transition metal.
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