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Inorg. Chem. 1980, 19, 674-680
Figure 4. The sheet structure of U13, formed when adjacent U14 chains fuse and liberate one terminal iodine atom per octahedron.
distances are not much shorter than the sum of the ionic radii of U4+and I- = 3.16 A. The bond angles in the octahedra are consistent with the uranium repulsions. UI, is converted by gentle heating into U13. Presumably the layers of U14 chains a t x = 0 and x = l / z then become the sheets of the U13 structure shown in Figure 4. It is likely that in the conversion one of the two terminal iodine atoms in every octahedron is liberated, adjacent chains fuse, and cross-linked, linear -U-U-U- chains are formed with the same U-U separation as in UI,. The U coordination polyhedron changes from an octahedron to a bicapped trigonal prism. The structures of the actinide halides have been reviewed recently,s and UI, is the only actinide tetrahalide to show a
chain structure (U1214/J.However, the chain structure, either linear with trans terminal halide atoms or zigzag with cis terminal atoms, is common in the transition-metal tetrahalides. Although none of these are isostructural with UI,. Zigzag chains are found in ZrC1, and HfC14,9TcC14,10PtCl,, PtBr,, and a-PtI4I1and linear chains in NbC14,12CY-MOC~,,'~ OSC~,,~~ and Q - N ~ I ~ The . ~ ' zigzag chain is found where there is no metal-metal attraction, while the linear chain generally signifies a metal-metal interaction. An unusual chain (cornerlinked bioctahedra Re,Cl,) is found in ReC14.16 TeI, shows a Te4II6tetramer." U14 is thus a new variant of the infinite-chain structure MX2X4/2,previously found only in the halides of the transition metals. Registry No. U14, 13470-22-9.
(8) (9) (10) (11) (12) (13) (14) (15) (16) (17)
J. C. Taylor, Coord. Chem. Reu., 20, 197 (1976). B. Krebs, Angew. Chem., In?. Ed. Engl., 8, 146 (1969). M. Elder and B. R. Penfold, Inorg. Chem., 5, 1197 (1966). M. F. Pilbrow, J. Chem. Soc., Chem. Commun., 270 (1972). D. R. Taylor, J. C. Calabrese, and E. M. Larsen, Inorg. Chem., 16, 721 (1977). D. L. Kepert and R. Mandyczewsky, Inorg. Chem., 7, 2091 (1968). F. A. Cotton and C. E. Rice, Znorg. Chem., 16, 1865 (1977). L. F. Dah1 and D. L. Wampler, Acta Crystallogr., 15, 903 (1962). F. A. Cotton, B. G. De Boer, and Z . Mester, J . A m . Chem. SOC.,95, 1159 (1973). V. Paulat and B. Krebs, Angew. Chem., Znt. Ed. Engl., IS, 39 (1976).
Contribution from the Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712
Crystal Structure at -35 "C of (Cyclobutadiene)(1,Z-bis(dipheny1phosphino)ethane-P,P')iron Carbonyl and an Examination of Stereochemical Distortions in Cyclobutadiene-ML3 Complexes RAYMOND E. DAVIS* and PAUL E. RILEY
Received July 25, 1979 The structure of (C4H4)[ (C6HS)2PCH2CH2P(C6HS)*]Fe(CO) has been determined by single-crystal X-ray diffraction techniques with three-dimensional data gathered at -35 'C by counter methods. Yellow, platelike single crystals form in triclinic space group Pi with unit cell constants at -35 'C a = 9.608 (8) A, b = 14.694 (3) A, c = 9.473 (2) A, CY = 103.30 (l)', p = 102.54 (2)', and y = 92.73 (2)'. The calculated density of 1.414 (4) g cm-3 for two molecules per unit . least-squares refinement of the structure cell of the complex agrees with the measured value of 1.45 g ~ m - ~Full-matrix has converged with an R index (on 14)of 0.049 for the 4890 symmetry-independent reflections within the Mo K a shell defined by 4 < 26 < 55' which have Zo/u(Zo) > 2. The iron atom is bonded to the cyclobutadiene ring in a symmetric manner, to the two phosphorus atoms of the diphosphine ligand, and to the C O ligand. As a consequence of the electron-donating capacity of the diphosphine ligand, the electron-withdrawing C O group is more firmly bound to Fe than in the corresponding Fe(C0)3 complex, as indicated by the Fe-C and C-0 bond lengths (1.742 (3) and 1.165 (4) A) and by the lower frequency of the C O symmetric stretch (1880 cm-I), as compared to the values for the Fe(CO), complex. Stereochemical results for ten cyclobutadiene-transition-metalcomplexes of the form (C4R4)ML3,which have been characterized by X-ray diffraction methods, have been analyzed in terms of distortions from two idealized symmetrical structures, one in which an M-L bond eclipses a ring carbon atom and one in which an M-L bond bisects a ring C-C bond. The observation that torsion parameters for these structures are distributed over the entire range between those of the two idealized structures supports the experimental results and theoretical suggestions of a low barrier in such complexes.
Introduction As part of an investigation in our laboratory of the structural and spectroscopic consequences of the systematic substitution of phosphine ligands in metal complexes of the form [(aC,H,)Fe(PR3),(CO)3-,]J'+ ( n = 4 or 5, m = 0-2, p = 0 or I), we have determined the crystal structure of (C4H4)Fe(P(C6H5)2CHZ-)2(CO),a species obtained by photolysis of the parent tricarbonyl in the presence Of (C6H5)2P(CH2)2P(C6&)2.' This structural study ah0 affords an exam(1) Slegeir, W.; Pettit, R., unpublished results.
0020-1669/80/1319-0674$01.00/0
ination of the geometry of an unsubstituted cyclobutadiene ligand for which only a few examples have been and for which a very low b m k r of rotation about the metal
