4847 1 week at 5 O producing three crops (410 mg) of (-)-cis-dichloro(rruns-cyclooctene)-(S)-(a-phenethylamine)platinum(II). When the
olefin was recovered from the recrystallized levorotatory diasteroisomer, (+)-COT was obtained, with an optical purity of more than 95 %. Chemical Properties of the Complexes I. From all the complexes I, the olefin can be removed by reaction with cyanide aqueous solutions, or triphenylphosphine, or a,a'-bipyridine. By reduction with Hf of the complexes I and 11, either in solution or in the absence of solvents we obtained platinum metal and the saturated hydrocarbon corresponding to the olefin witliin a short period of time. Treatment of the (-) diastereoisomer of the ethyl a-chloroacrylate in acetone solution with Hzat 50 psi led to the formation
of racemic ethyl a-chloropropionate. This behavior supports the observation that the hydrogenation,'3 even if occurring with a stereospecific mechanism, is followed by a rapid racemization process with a rate of the same order as that of the hydrogenation reaction. With regard to this argument other experiments are in progress. Acknowledgment, We wish to acknowledge many fruitful discussions with and the continuous support of Professor P. Corradini and the assistance of Dr. B. Pispisa in the gas chromatographic analyses. (13) J. H. Flynn and H. M. Hulburt, J . A m . Chem. Soc., (1954).
76, 3393
Structure of the Hexapyridineiron(11) Salt of the Tetranuclear Iron Carbonyl Anion, [Fe, (CO) 13]-2, with Comments Concerning the Nonisolation of the Corresponding Neutral Tetranuclear Iron Carbonyl, Fe, (CO ) 1 4 Robert J. Doedens' and Lawrence F. Dah1 Contribution f r o m the Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706. Received June 17, 1966 Abstract: A three-dimensional single-crystal X-ray examination of the salt [F~(C~H~N)C]~+[F~~(CO)I~]*not only has shown a new type of molecular configuration for the diamagnetic tetrameric anion, [Fe4(CO)1312-, but also has produced definite stereochemical information concerning the nonexistence of the corresponding neutral iron carbonyl, Fe4(C0)14. The triclinic crystals of [Fe(CsHsN)6][Fe4(CO)13] contain two formula species in a unit cell of symmetry P i and of reduced-cell parameters a = 10.09, b = 14.86, c = 15.61 A, CY = 90" 00', /3 = 90" 00', y = 103" 12'. Isotropic least-squares refinement carried out with a specially written full-matrix rigid-body program, in which the six pyridine rings were constrained to a fixed geometry, yielded final discrepancy factors of RI = 10.9 and RS= 12.7%. The [Fe4(C0)13]2-anion of pseudo-threefold symmetry consists of four tetrahedrally oriented iron atoms in which an apical Fe(C0)3group is symmetrically coordinated by only iron-iron bonds to a basal Fe3(CO)Qfragment containing three identical Fe(C0)3groups located at the corners of an equilateral triangle and bonded to one another by iron-iron bonds. The thirteenth carbonyl group triply bridges the three basal iron atoms. As a result of weak interactions with neighboring basal iron atoms, three of the essentially terminal basal iron carbonyl groups are slightly deformed toward a doubly bridging carbonyl configuration. The chemical significance of these highly unsymmetrical doubly bridging groups is indicated. To a first approximation the carbonyl carbon atoms lie at the vertices of a polyhedral fragment which is related to an icosahedron. The criteria necessary for the possible formation of the polynuclear metal carbonyls and their derivatives are discussed, and the little appreciated importance of the stereochemical compatibility requirements of the ligands about the metal cluster in determining the compound's stoichiometry is stressed. The hexapyridineiron(I1) cation, which has a regular octahedral array of six nitrogen atoms about the central iron(l1) with the pyridine molecules oriented in three mutually perpendicular planes such that each pair of trans pyridine rings is coplanar, is one of the few known species belonging to the centosymmetric cubic point group Th.
W
hile n o neutral tetranuclear carbonyl of iron has been prepared, the anion [Fe4(CO)13]2- is well known, having first been synthesized by Hieber and c o - w o r k e r ~in~ ~1930. ~ Initially, the products of the reactions of Fe(CO)5 and Fe3(C0)12with pyridine were formulated as Fe2(C0)4(C5HjN)32 and Fe(C0)3( C B H ~ N ) , respectively; Hieber and Werner4 later recognized that only one product of stoichiometry Fej(C0),3(C5HjN)6 is formed from either of these two reactions. Their formulation of this complex as (1) National Science Foundation Predoctoral Fellow, 1961-1964; this article is based in part on a dissertation by R . J. Doedens in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the University of Wisconsin, 1965. (2) W. Hieber, F. Sonnekalb, and E. Becker, Chem. Ber., 63,973 ( 19 30).
(3) W. Hieber and E. Becker, ibid., 63, 1405 (1930).
[Fe(C5HjN)6]2+[Fe4(CO)18]2was based on conductance measurements which established its ionic character and on identification of one of the five iron atoms per formula unit as a n iron(I1) by its precipitation as Fe(OH)2. The magnetic moment of 5.47 BM for this salt was of the magnitude expected for a single high-spin iron(II), thereby indicating that the anion is diamagneticU4 Reactions of the iron carbonyls with other bases have yielded a large number of additional salts containing the tetrameric anion. &-8 All of the salts containing this anion are air sensitive, and many are (4) (5) (6) (7) (8)
W. Hieber and R. Werner, ibid., 90, 286, 1116 (1957). W. Hieber and J. G. Floss, ibid., 90, 1617 (1957). W. Hieber and N. Kahlen, ibid., 91, 2223 (1958). W. Hieber and A. Lipp, ibid., 92, 2075 (1959). W. Hieber and A. Lipp, ibid., 92, 2085 (1959).
Doedens, Dah1 / Sfructure of Hexapyridineiron(Zl) Salt of [Fe4(CO)131~-
4848
which are a = 15.95 f. 0.04, b = 15.61 f 0.04, c = 10.09 f 0.025 A, = 90” 00’ f lo’, j3 = 114” 50’ IO’, y = 90” 00’ f 10’. The calculated density of 1.58 g/ml agrees with the observed density, which because of the instability of the crystals was only determined to lie in the range 1.58-1.66 g/ml. The centrosymmetric space group P i was inferred from the vector distribution of the Patterson function and later confirmed by the satisfactory refinement of the structure. The crystallographically independent unit thus contains one formula species composed of 5 iron, 13 oxygen, 6 nitrogen, 43 carbon, and 30 hydrogen atoms. All atoms were found from the structural analysis to occupy the general twofold set of positions (2i): +(x,J’,z). l 4 Determination of the Structure. Although the expected tetrahedral arrangement of the four iron atoms of the anion and the relative orientation of this tetrahedron in the unit cell were apparent from the threedimensional Patterson function, initial attempts to locate this tetrahedron in the unit cell were unsuccessful. Experimental Section No self-consistent set of atomic coordinates based on Large, black, air-sensitive crystals of [Fe(C,H,N)6][Fe4(CO),3] the tetrahedral iron-iron vectors was found from the were generously supplied by Professor Dr. Dr. W. Hieber and Dr. W. presumed single-weight Patterson vectors. In this Beck of the Aiiorganisch-Chemisches Laboratorium der Technisconnection the 20 strongest Patterson peaks were aschen Hochschule, Munich, Germany. Considerable difficulty was encountered in obtaining a good single crystal, and a number of sumed to correspond to the 20 centrosymmetric crystals (selected initially by optical inspection) were examined by double-weight, nonorigin vectors required for the five X-ray photographs before a suitable one was found. A crystal of independent iron atoms in the space group Pc. A trial approximate dimensions 0.35 X 0.25 X 0.25 mm was used for set of coordinates for three atoms was chosen and used gathering intensity data. This crystal was mounted about the 0.35-mm direction in a thin-walled glass capillary which was subtogether with an estimated isotropic thermal parameter sequently evacuated, filled with argon, and then sealed. of 1.5 A? as a model for calculation of structure factors, Multiple-film equiinclination Weissenberg data were taken with from which the discrepancy factors R1 = [Z./ F,/ Zr-filtered Mo K a radiation for reciprocal levels Okl through Fcj ~ / Z ~ F ‘ X , ~ 100and ] Rz = [Z wl lF,l - IFc I */Zw. 12kl. In order to eliminate errors due to spot compaction on the lower half of the film,l0a full 360” rotation range consisting F,, 1 2]1/2 X 100 yielded values of 58 and 63 %, respecof two separate sets of film data was taken for all levels except tively. A Fourier synthesis based on these structure Okl. Reflections common to both sets of films were utilized in a factors revealed distinct peaks, two of which were least-squares merging program l 1 which placed the two upper interpreted as the other two independent iron atoms halves of each level on a common scale. The intensities were whose positions were consistent with the doubleestimated visually by comparison with a calibrated set of intensities taken from the same crystal. Lattice constants were determined weight vectors of the Patterson map. However, no from /ikO and /IO/ precession photographs which were calibrated single-weight Patterson vectors corresponding to these by the superposition of a zero-level NaCl exposure on the same positions were present. Attempts to determine the film. Corrections for Lorentz polarization effects and spot exlight-atom positions by means of Fourier synthesis tension12 were made, but absorption corrections were neglected due phased on these five tentative iron positions failed, and to the small absorption coefficient (pR,,, = 0.4). Atomic scattering factors here taken from the International Tables.I3 The the discrepancy factors did not fall below 50 2,thereby standard deviations of the individual structure factor amplitudes indicating that the model being used was incorrect. were estimated as follows. If I(hkOo < dEmIa, u(F(hk00) = The key to the solution of the structure was found [ j F(/1kC)~’/20] [ ~ ~ O I , i , / Z ( h k l ) 0 ] 2ifZ(hk()o ; 2 V%Z,,,in,@(hk[)o) when it was noted that the five strongest peaks (other = F(/lkl)o /20. than those for the five input iron atoms) on one of these Fourier maps formed an image which was related Results to the five trial iron positions by a nonimposed center Crystal Data. Crystals of [Fe(C5H6N)~][Fe,(CO)1~] of symmetry at x = -0.125, y = 0.340, and z = 0.320. are triclinic with reduced cell parameters a’ = 10.09 f. The new atomic parameters obtained by a shift of the 0.025, b’ = 14.86 f 0.04, C’ = 15.61 f 0.04 A, origin of the centrosymmetric unit cell to this point a’ = 90” 00’ f IO’, 0’= 90” 00’ zk lo’, y‘ = 103” were observed to be in excellent agreement with the 12’ i 10’. The intensity data were taken with respect vectors of the Patterson map. These coordinates to a nonreduced primitive triclinic cell related to the had not been found initially because of the coincidence above cell by the following transformation: a’ = of one of the single-weight vectors with a double-weight - c ; b’ = a c ; c ’ = b. All results are reported in vector and because of the peak-height enhancement of terms of this nonreduced cell, the lattice constants of another single-weight vector at u = w = l / z , which (9) W. F. Edgell, M. T. Yang, B. J. Bulkin, R. Bayer, and N. Koizumi, thereby originally was assigned as a double-weight J . A m . Chem. Soc., 87, 3080 (1965). vector. (IO) C‘f. M. J . Buerger, “X-Ray Crystallography,” John Wiley and Based on the new coordinates of the five iron atoms Sons, Inc., New York, N. Y . , 1942, pp 227-229. (11) P. W. Sutton and M. D. Glick, “A Crystallographic Data Coras a starting point, the light-atom positions were relation Program for the CDC 1604,” University of Wisconsin, Madison, obtained by means of successive Fourier syntheses. Wis., 1964.
pyrophoric. The reported infrared spectra of several ionic substances containing the [Fe4(C0)13]2- anion show considerable variation in the absorption band frequencies in the carbonyl stretching region.’ For only one salt was an absorption band detected below 1900 cm-I (uiz., at 1875 cm-9;’ however, a very weak absorption band at 1829 cm-l has recently been listedg for the anion in D M F solution. Without the use of bridging carbonyls it is impossible to devise a probable structure in which each iron atom of the tetranuclear iron anion attains a closed-shell electronic configuration. Because of the lack of structural information on the [Fe4(CO),,]*- anion, a single crystal X-ray structural determination of [Fe(C jHjN)6][Fel(C0)13]has been carried out. The salt of the hexapyridineiron(I1) cation was chosen because of its relative stability (in the absence of air), its availability in crystalline form, and its amenability to a rigid-body least-squares refinement.
~
*
~
+
(12) D. C. Phillips, Actn Crj,st., 7, 746 (1954). (13) “International Tables for X-Ray Crystallography,” Vol. 111, The I
