J . Am. Chem. SOC.1980, 102, 7691-7701
7691
Isolation and Structural Characterization of the Triiron Undecacarbonyl Dianion [ Fe3(CO)l1]2-: Stereochemical Interrelationship with Triiron Dodecacarbonyl and the Triiron Undecacarbonyl Hydride Monoanion Frederick Yip-Kwai Lo,la Giuliano Longoni,IbPaolo Chini,*lcLoren D. Lower,l*and Lawrence F. Dahl*'" Contribution from the Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, and the Centro del CNR per lo studio e la, sintesi dei composti dei metalli di transizione, and Istituto di Chimica Generale dell' UniversitB, 201 33 Milano, Italy. Received September 12, 1979
Abstract An X-ray diffraction investigation of the classical [Fe3(CO)ll]2-dianion has finally ascertained its solid-state configuration which represents the heretofore missing structural link between the known triangular iron geometries of the other two closely related and stereochemically prominent triiron carbonyl clusters Fe3(C0)12and the [HFe3(CO)II]-monoanion and of the 0-methylated derivative HFe3(CO),,(COMe) of the monoanion. The [Fe3(C0)11]2dianion in the tetraethylammonium salt exemplifies an unprecedented M3(C0),(p-CO) (w3-CO)-typeconfiguration of crystallographic CS-msymmetry containing a symmetrical doubly bridging carbonyl linking two mirror-related Fe(CO)3 fragments which are connected to each other and to the third Fe(C0)3 fragment by an unsymmetrical triply bridging carbonyl as well as by electron-pair Fe-Fe bonds. A crystallographic examination was first carried out on the tetraphenylarsonium salt, which exhibited for the dianion a centrosymmetric crystal disorder analogous to that previously found for Fe3(C0)12.The resulting overall architecture, unraveled from the superposition of carbonyl peaks for the two centrosymmetrically related, half-weighted orientations, was found to be in accordance with the crystal-ordered configuration of the dianion established from a subsequent structural determination of the tetraethylammonium salt. Salient structural features obtained from the latter, relatively precise analysis include (1) an essentially equilateral iron triangle with two identical FeA-FeBbonds of 2.593 (2) A vs. an FeB-FeBbond of 2.603 (3) A between the two mirror-related Fee atoms, (2) a symmetrically coordinated doubly bridging CO(DB) ligand with two identical FeB-CO(DB) distances of 1.96 (1) A (Evidence is presented for a ossible semibridging interaction with the third iron Fe, even though the observed long Fe,-CO(DB) distance of 2.72 (1) indicates such an interaction to be minimal.), and (3) a triply bridging CO(TB) ligand which is highly unsymmetrical in being 1.85 (1) A from Fe, compared to 2.21 (1) from both FeBatoms. Besides pointing to the insensitivity of the previously reported Mossbauer spectrum of the dianion as the [Fe(en)J2+ salt in not being able to differentiate between the different environments of the two kinds of iron atoms (viz., Fe, vs. the two Fee), the determined structural parameters for the solid-state configuration of the dianion not only enable an analysis of the existing carbonyl infrared data to be made but also lead to the suggestion of a new kind of possible mechanistic pathway for carbonyl interconversion in solution (involving a synchronous movement of a terminal axial carbonyl on FeAand both bridging carbonyls over both triangular faces) in order to account for "C NMR spectral data exhibiting only one resonance even at low temperatures. This direct axial-to-(face-bridged)pathway is used to rationalize part of the previously observed stereodynamic fw = 736.15, solution behavior of the [HFe3(CO)11]-monoanion and of R U ~ ( C O ) ~ ~ ( N ~ C[NEt4],+[Fe3(CO) ~H~). orthorhombic, Pcmb [nonstandard setting of Pbcm (D1, No. 57)], a = 11.589 (4) A, b = 14.979 (4) c = 19.527 ( 5 ) A, V = 3389 (2) A', pc = 1.44 gcm-' for Z = 4. For 1452 diffractometry collected reflections with I > 2 4 4 , R,(F) = 6.9% and R2(F)= 7.8%.
1
A,
Introduction Prior to the work presented here, the correct solid-state structure of the [Fe3(C0)1L]2-dianion had not been determined. A knowledge of its static geometry is of particular interest not only in conjunction with its fluxional behavior in solution (vide infra) but also from the viewpoint that its unique geometry consisting of 1 1 ligands encapsulating a triangular metal core provides a heretofore missing link within the unsubstituted trinuclear iron carbonyl series relative to the crystallographically known geometries of two other members, viz., the neutral Fe3(C0)L2parent2 and the [HFe3(CO)II]- m ~ n o a n i o n . These ~ latter triangular iron clusters containing twelve ligands are electronically equivalent to the [Fe3(C0)Ll]2-dianion by a formal replacement of a C O or H- ligand, respectively, with two electrons. The reddish [Fe3(CO)11]2-dianionwas first isolated in a pure state by Hieber and c o - ~ o r k e r s in ~ *1957 ~ by the reaction of (1) (a) University of Wisconsin-Madison. (b) Centrol del CNR. (c) Istituto di Chimica Generale dell' UniversitP. (2) (a) Wei, C. H.; Dahl, L. F. J. Am. Chem. Soc. 1966.88, 1821-2; 1969, 91, 1351-61. (b) Cotton, F. A,; Troup, J. M. J . Am. Chem. SOC.1974, 96, 4155-9. (3) Dahl, L. F.; Blount, J. F. Inorg. Chem. 1957, 4 , 1373-5. (4) Hieber, W.; Brendel, G. Z . Anorg. Allg. Chem. 1957, 289, 324-37; 324-37; 1957, 289, 338-44. (5) Hieber, W.; Sedlmeier, J.; Werner, R. Chem. Ber. 1957, 90, 278-86.
Fe3(C0)12either with 2 M KOH methanolic solution4 or with eth~lenediamine.~Its complex behavior in solution including interconversion to other iron carbonyl anions and carbonyl hydride anions has been further explored by others."I0 The diamagnetic character of the [Fe3(CO)11]2-dianion (as well as that of the protonated [HFe3(CO)11]-monoanion) was established" from magnetic susceptibility measurements of the K2+[Fe3(C0)1L]2and [Ni(phen)3]2+[Fe3(CO)ll]2salts (Le., the observed paramagnetic moment of 3.3 pB for the latter salt was found to be in accordance with the expected moment of 3.2-3.4 wg previously reportedL2for the tris( 1,lO-phenanthroline)nickel(II) dication). On the basis of a preliminary X-ray diffraction analysis (which was presumably coupled with their structural substantiationL3of (6) cf.: Calderazzo, F.; Ercoli, R.; Natta, G. In "Organic Syntheses via Metal Carbonyls"; Wender, I., Pino, P., Eds.; Interscience: New York,1968; Vol. I, pp 1-272, and references cited therein. (7) Case, J. R.; Whiting, M. C. J . Chem. SOC.1960, 4632-7. ( 8 ) Hieber, W.; Beutner, H. Z . Naturforsch., B Anorg. Chem., Org. Chem., Biochem., Biophys., Biol. 1962, 178, 211-6. (9) Hieber, W.; Schubert, E. H. Z . Anorg. Allg. Chem. 1965,338, 32-6, 37-46. (10) Farmery, K.; Kilner, M.; Greatrex, R.; Greenwood, N. N. J . Chem. SOC.A 1969, 2339-45. (11) Hieber, W.; Floss, J. G. Z . Anorg. Allg. Chem. 1957, 291, 314-24. (12) Cf.: Nyholm, R. S. Q. Rev., Chem. SOC.1953, 7 , 377-406.
0002-7863/80/ 1502-7691 $01 .OO/O 0 1980 American Chemical Society
Lo, Longoni, Chini, Lower, and Dah1
1692 J. Am. Chem. SOC.,Vol. 102, No. 26, 1980
Laue symmetry of the crystal to be orthorhombic Dzh-mmm. Intensity triply bridging carbonyl ligands for the Fischer-Palm Ni,($data were collected via the 8-28 step scan mode with variable scan speeds C5H5)3(p3-C0)2 cluster14) Mills, Hock, and R o b i n ~ o nin ’ ~ 1959 ranging from 2.0 to 24.0°/min and with scan widths of 1.0” above K a , proposed that the [Fe3(CO)11]2-dianion is composed of a trianand 1.Oo below Kaz. A background-to-scan time ratio of 2/3 was made gular array of Fe(CO), fragments which are coordinated to one on each side of a peak. The intensities of two standard reflections were another by two triply bridging carbonyl ligands in addition to periodically measured at intervals of every 98 reflections in order to metal-metal bonds. This molecular model was later found by monitor the instrument’s stability as well as the crystal’s alignment and Greenwood and co-workers1° to be consistent with their MWbauer decay. No significant changes in the intensities of these standard reand Nujol mull infrared measurements on [ F e ( e ~ ~ ) ~ ] ~ y [ F e , -flections were observed during the entire data collection over one independent octant of the reciprocal lattice. Intensities were measured at (CO), A room-temperature Mossbauer spectrum exhibited room temperature (-23 “C) between 20 limits of 3 and 60°, but since (in addition to a doublet assigned to the cation on the basis of the scattering power of the crystal diminished sharply for reflections with its position being typical for high-spin d6 Fe(I1) complexes) an 28 > 45”, only the 2566 reflections sampled within the range 3” I 28 unbroadened quadrupole doublet which was attributed’O to the 5 45” were processed. An analytical absorption correction20Bwas applied three iron atoms being in equivalent environments. The large to the intensity data in that the calculated transmission coefficients observed quadrupole splitting of 2.1 mm/s was ascribed’O to a (based upon the crystal dimensions and a linear absorption coefficient highly distorted environment about each iron atom. An IR of 13.6 cm-’ for Mo K a radiation) varied from 0.577 to 0.862. The spectrum in Nujol mull displayed a plethora of ten carbonyl indexed faces of the utilized crystal and its perpendicular distance (in absorption bands ranging from 2089 (w) to 1592 (m) cm-I; this mm) from the crystal center to each face are as follows: (OlO), 0.055; latter frequency was tentatively assigned’O to the triply bridging (oio), 0.055; (103), 0.20; TO^), 0.24; (Toi), 0.22; (TOT), 0.28; (loo), 0.28. A data reduction20bicgave 1452 independent reflections with I > carbonyl groups. Recently, Longoni and ChiniI6 synthesized the [Fe3(CO)II]2244. The measured lattice constants for the orthorhombic unit cell at 23 dianion both by previous methods29 as well as by deprotonation1° “ C are a = 11.589 (4) A, b = 14.979 (4) A, and c = 19.527 (5) A. The of the [HFe,(CO),,]- monoanion in a 1.2 N KOH methanolic unit cell volume of 3389 (2) A3 and fw of 736.15 g/mol give rise to a solution. Salts of this dianion with various counterions including calculated density of 1.44 gecm-) based upon 2 = 4. [NEt,]’, [PPh,]’, [AsPh4]+, and [PPN]+ were obtained by The observed systematic absences of {Okd for I odd and (hM))for k odd metathesis in methanol from the potassium salt. These salts indicate the probable space group to be either PcZlb or Pcmb [nonstandissolve in THF to give dark red solutions which show infrared dard settings of PcaZl (Ck,No. 29) and Pbcm (D&, No. 57), respecabsorption bands at 1938 (s), 1910 (ms), 1890 (sh), and 1670 (w, tively]. An initial choice of the centrosymmetric space group Pcmb was later substantiated on the basis of the successful structural determination br) cm-’.17 In Nujol mull the [PPN]2+[Fes(CO)ll]2-salt exhibits and refinement. only one band in the bridging carbonyl region at 1665 cm-’. A (a) Structural Determination and Refmement. The centrosymmetric 13C N M R investigation by Heaton(* revealed that the [Fe3space group P2/c2,/m2,/b requires that the four dianions in the unit cell (CO)ll]2-dianion is a nonrigid structure in solution in that the lie on fourfold special positions such that one half dianion constitutes the I3C spectra exhibit only one sharp singlet at -23 1.6 ppm even crystallographically independent species. The crystal structure was at low temperatures. solved21s22 via the Patterson interatomic vector method (which yielded Herein are presented the results of X-ray diffraction studies initial coordinates for one iron atom) followed by repeated Fourier of both the [AsPh,] 2+[ Fe,(CO) I ,] 2- and [NEt4]*+[Fe3(CO) 2synthesesw which located 19 other independent nonhydrogen atoms. At salts. Although the structural characterization of the former salt this point it was determined that the dianion possesses crystallographic site symmetry C,-m with 16 independent atoms (of which one iron, three was impeded by a crystal disorder (of an analogous kind to that carbon, and three oxygen atoms are situated on the mirror plane). In previously found2 for Fe3(CO)12) which thereby precluded an addition, it was found that four of the eight [ N E 4 ] +cations per cell are accurate determination of the molecular parameters, a correalso positioned on mirror planes and the other four cations are located sponding structural characterization of the latter salt posed no on twofold axes such that two half cations are crystallographically insuch difficulty. The same overall solid-state configuration was dependent. Least-squares refinement2”Q3 of the determined 20 atoms observed together with reasonably precise parameters which have followed by Fourier and difference Fourier maps resolved the locations enabled a comparative analysis with other related triangular iron carbonyl complexes including HFe3(CO)lo(COMe).19 These results have provided a much better understanding of the stere(20) k) Blount, J. F. “DEAR, a FORTRAN Absorption-Correction Program , 1965, based on the method given by: Busing, W. R.; Levy, H. A. ochemistry and bonding of this unusual series of iron clusters.
,
Experimental Section [NEt4]2~Fe3(CO)ll~-. (a) Crystal Data. Crystals were grown by slow solvent diffusion from a THF-toluene mixture. A dark brown pentagonal-shaped platelike crystal of thickness of 0.1 1 mm with perpendicular distances of 0.20-0.28-mm range from the center to the five pentagonal faces was optically chosen and mounted inside a thin-walled Lindemann glass capillary which was evacuated, filled with argon, and then hermetically sealed. After optical alignment of the crystal on a Syntex P I diffractometer, 15 diffraction maxima, centered automatically with graphite-monochromatized Mo Kh radiation (X(Kal) = 0.709 26 A; X(Ka2) = 0.713 54 A), were used to determine the lattice constants and orientation matrix for data collection. Axial photographs showed the
(13) Hock, A. A.; Mills, 0. S. In “Advances in the Chemistry of the Coordination Compounds”; Kirschner, S., Ed.; MacMillan: New York, 1961; pp 640-48. (14) Fischer, E. 0.; Palm, C. Chem. Ber. 1958, 92, 1725-31. (15) Mills, 0. S.; Hock, A. A,; Robinson, G. Proc. Int. Cong. Pure Appl. Chem. 1959, 17, 143. (16) Longoni, G.; Chini, P., to be submitted for publication. (17) It is noteworthy that the three higher frequencies are in excellent agreement with those of 1941 (s), 1913 (m), and 1884 (w) cm-I reported previously for the IR spectrum of the dianion in dimethylformamide solution by Edgell et al. (Edgell, W. F.; Yang, M. T.; Bulkin, B. J.; Bayer, R.; Koimmi, N. J . Am. Chem. SOC.1965, 87, 3080-8). (18) Heaton, B. T., personal communication to P. Chini, 1977. (19) Shriver, D. F.; Lehman, D.; Strope, D. J . Am. Chem. SOC.1975,97, 1594-6.
Acta Crystallogr. 1957, 20, 18Cb2. (b) Broach, R. W. “CARESS, a FORTRAN Program for the Computer Analysis of StepScan Data”, Ph.D. Thesis, University of Wisconsin-Madison, 1977, Appendix I. (c) Broach, R. W. “QUICKSAM, a FORTRAN Program for Sorting and Merging Structure Factor Data”, Ph.D. Thesis, University of Wisconsin-Madison, 1977, A p pendix 11. (d) Calabrese, J. C. “MAP, a FORTRAN Summation and M e lecular Assemblage Program”, University of Wisconsin-Madison, 1972. (e) Calabrese, J. C. “A Crystallographic Variable Matrix Least-Squares Refinement Program”, University of Wisconsin-Madison, 1972. (f) Calabrw, J. C. “ M I R A G E , Ph.D. Thesis, University of Wisconsin-Madison, 1971, Appendix 111. (g) Busing, W. R.; Martin, K. 0.; Levy, H. A. “OR FLS, A FORTRAN Crystallographic Least-Squares Program”, Report ORNL-TM305, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 1962. (h) Busing, W. R.; Martin, K.0.;Levy, H. A. “OR FFE, A FORTRAN Crystallographic Function and Error Program”, Report ORNL-TM-306, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 1964. (i) Smith, D. L. “PLANES” Ph.D. Thesis, University of Wisconsin-Madison, 1962, A p pendix IV. 6 ) Johnson, C. K. “OR TEP-11, A FORTRAN Thermal-Ellipsoid Plot Program for Crystal Structure Illustrations”, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 1976. (k) “OR FLSR, A Local Rigid-Body Least-Squares Program”, adapted from the BusingMartin-Levy OR FLS. (21) Atomic scatteringfactors for neutral atom were ~ s e d . 2 “ ~Anomalous dispersion corrections2zcwere applied to the scattering factors of the Fe and As atoms in the structural determinations of the [AsPh,]’ and [NEt,]’ salts. (22) (a) Cromer, D. T.; Mann, J. B. Acta Crystallogr., Sect. A 1968, A24, 321-4. (b) Stewart, R. F.; Davidson, E. R.; Simpson, W. T. J. Chem. Phys. 1965, 42, 3175-87. (c) “International Tables for X-Ray Crystallography”, Kynoch Press: Birmingham, England, 1974; Vol. IV, p 149. (23) The unweighted and weighted discrepancy factors used are Ri F) 100IXllFol- l~cll/Xl~oll and &(F) = 1OO[EwillFoI- I~c112/C~il~d21i/ . All least-squares refinements were based on the minimization of 13willFol - lFJ2 with individual weights of wi = 1/u2(F,,).
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J. Am. Chem. SOC.,Vol. 102, No. 26, 1980 7693
Structural Characterization of the Triiron Undecacarbonyl Dianion Table I. Atomic Parameters for [NEt,],+[Fe,(CO),,]'-
B. Anisotropic Thermal Parameters (X 10')'
A. Positional Parametersa atom
X
Y
Z
atom
0.35673 (16; 0.18246 i i i j 0.2120 (12) 0.1636 (8) 0.2336 (11) 0.2693 (9) 0.4608 (12) 0.5333 (9) 0.4060 (10) 0.4397 (9) 0.0580 (13) -0.0271 (10) 0.2808 (12) 0.3499 (11) 0.1302 (10) 0.0980 (8) 0.2024 (9) 0.2471 (18) 0.1030 (19) 0.3044 (16) 0.1589 (23) 0.1502 (15) 0.2676 (16) 0.3305 (8) 0.2604 (IO) 0.4041 (12) 0.1784 (25) 0.4974 (16) 0.221 0.3 12 0.438 0.354 0.137 0.219 0.121 0.542 0.464 0.552
314 0;66311 (10) 3/4 3/4 314 314 314 314 0.6600 (13) 0.5996 (11) 0.6438 (9) 0.6360 (10) 0.5889 (8) 0.5395 (7) 0.5974 (8) 0.5503 (6) 114 0.1924 (15) 0.1 827 (29) 0.3101 (14) 0.3089 (25) 0.1321 (12) 0.3680 (9) 112 0.5378 (9) 0.4312 isj 0.6056 (17) 0.3920 (13) 0.489 0.560 0.455 0.381 0.625 0.658 0.581 0.347 0.364 0.442
0.48284 (9) 0.43296 (7) 0.5229 (7) 0.5779 (5) 0.3641 (7) 0.3075 (5) 0.4144 (7) 0.3750 ( 5 ) 0.5296 (6) 0.5635 (6) 0.3842 (7) 0.3535 (6) 0.3995 (7) 0.3775 (5) 0.5026 (6) 0.5467 (4) 0.4163 (6) 0.3557 (11) 0.3863 (19) 0.4416 (12) 0.4799 (13) 0.3248 (9) 0.5063 (7) 314 0.6944 (5) 0.7177 (6) 0.7112 (7) 0.7623 (8) 0.669 0.65 7 0.675 0.700 0.669 0.732 0.745 0.735 0.804 0.777
Fe(1) Fe(2)
C(1) O(1) C(2) O(2) C(3) O(3) C(4) O(4) C(5) O(5) C(6) O(6) C(7) O(7) N(1)
C(11) C(12) C(13) C(14) C(15) C(16) N(2) C(21) C(22) C(23) C(24)
PI,
022
033
61 (2) 107 (2) 20 (1) 83 (1) 50 (1) 30 (0) 91 (14) 112 (13) 16 (4) 86 (9) 108 (8) 29 (3) 91 (13) 61 (9) 23 (4) 155 (12) 96 (8) 19 (3) 73 (13) 74 (11) 31 (5) 108 (10) 93 (8) 33 (3) 87 (11) 242 (18) 33 (4) 173 (12) 309 (17) 79 (5) 185 (17) 111 (12) 52(5) 239 (16) 299 (17) 86 (5) 202 (17) 62 (8) 52 (5) 338 (18) 101 (7) 83 (5) 130 (12) 63 (8) 45 (5) 211 (12) 81 (6) 59 (3) 64 (11) 121 (11) 45 (5) 111 (21) 94 (16) 45 (8) 57 (20) 300 (50) 97 (16) 83 (18) 68 (13) 51 (9) 138 (27) 272 (48) 47 (10) 232 (22) 148 (15) 62 (6) 291 (25) 85 (10) 55 (5) 73 (9) 60 (7) 27 (3) 140 (12) 102 (10) 31 (3) 199 (17) 104 (10) 38 (4) 666 (53) 254 (24) 38 (5) 350 (27) 235 (19) 67 (6)
PI2
PI 3
013
0 0 (1) 0 1(1) 2 (1) -1 (1) 13 (6) 0 0 5 (4) 0 0 0 -12 (6) 0 7 (5) 0 0 -3 (7) 0 0 25 (5) 0 0 13 (12) 14 (6) 39 (7) 54 (11) 16 (7) 114 (8) -71 (11) -13 (8) 16 (6) -156 (14) -77 (8) 27 (8) 17 (10) 52 (8) 7 (5) 67 (10) 93 (8) 4 (5) 0 (5) 27 (8) 20 (6) 20 (7) 46 (5) 24 (4) -210 (16) 11 17 (6) (11) -350 (10)
-112 (25) -7 (13) 160 (30) -100 (15) 67 (13) 0
-7 (15) -2 (10) 33 (14) -27 (10) -1 (10) 0
14 (10) 10 (6) 43 (11) -33 (7) 298 (31) 28 (13) 223 (20) -66 (12)
61 (23) -11 (9)
12 (15) -5 (8) -23 (6) -6 (4) 18 (5) -32 (5) 36 (9) -87 (10)
(I The seven Fe(l), C(n), and O(n) atoms (n = 1-3) in the independent half dianion and the N(1) atom in one of the two independent half - z ) . Likewise, the N(2) atoms [NEt4]+cations each occupy a s e t offourfoldspecial positions (4d) o n a mirror plane: * ( x , I / 4 , z ; x , 3 / 4 , in the other independent half [NEt,]' cation occupies a set of fourfold special positions (4c) on a twofold axis: *&, 0, 1 / 4 ; x ,1 / 2 , l/,). Each of t h e other independent atoms occupies an eightfold set (8e) of general positions: +(x, y , z;x, y , + z;x, - y , z;x, + y , 1 / 2 - 2). These latter independent atoms include: (1) nine Fe(2), C(n), and O(n) atoms (n = 4-7) in half of t h e dianion; (2) four halfweighted methylene C(1n) atoms (n = 1-4) and t w o whole-weighted methyl C(15) and C(16) atoms (each due t o an assumed superposition of two half-weighted methyl carbon sites) in t h e mirrorconstrained half [NEt,]' cation; and (3) two methylene C(21) and C(22) atoms, two methyl C(23) and C(24) atoms, four methylene H(21-n) and H(22-n) atoms (n = 1,2), and six methyl H(23-n) and H(24-n) atoms (n = 1-3) in t h e twofoldconstrained half [NEt, 1' cation. No idealized hydrogen positions were obtained for the c v stal-disordered mirror-constrained [NEt,]+ cation. Idealized coordinates for t h e methylene and methyl hydrogen atoms of the ordered tetraethylammonium cation were calculated on the basis of an assumed regular staggered tetrahedral geometry with C-H distances of 1.0 A. These hydrogen positions (which were calculated after each cycle of least squares due t o their dependence upon the shifted carbon positions) together with an assumed The anisoindividual isotropic temperature factor of 6.0 A 2 were included in t h e least-squares refinement as fixedatom contributions. tropic thermal parameters are o f t h e form exp[-(h2pl, + k'p,, + 12p3, + 2hkpl, + 2hlp13+ 2klPZ3)].
of the other nonhydrogen atoms. These maps revealed that each of the four methylene carbon atoms in the mirror-constrained [NEt,]+ cation is randomly disordered between two tetrahedral sites with each of the four methyl carbon atoms being ordered (due to presumed superimposed positioning). Hence, each of the four independent methylene carbon sites was given an occupancy factor of An isotropic least-squares refinement converged at Rl(F)= 14.1% and Rz(F)= 15.6%.23 Idealized tetrahedral coordinates for the hydrogen atoms in the ordered half [NEt4]+ cation were calculatedzaf at that time. Further least-squares refinement2$ was then carried out with varying positional and anisotropic thermal parameters for the nonhydrogen atoms and with fixed positional and fixed isotropic temperature parameters for the hydrogen atoms. After each cycle of refinement, new regular tetrahedral coordinates for each hydrogen atom were calculated on the basis of the new carbon positions. The final cycle of the full-matrix least-squares refinement converged to R,(F) = 6.9% and R2(F) = 7.8% with no parameter shift-to-error ratio being greater than 0.06. The standard error-of-fit was I .79, while the data-to-parameter ratio was 6.5/ 1. A final difference map revealed no unusual features. The atomic parameters from the output of the final least-squares cycle are given in Table I. Interatomic distances and bond angleszah are
presented in Table I1 and selected least-squares planesm and interplanar angles in Table 111. Observed and calculated structure factors are tabulated as supplementary material. All figures were computer-generated and computer-drawn.zaj [AsPh&+[Fe3(CO)l,y-. (a) Crystal Data. Crystals suitable for X-ray investigation were obtained via an acetone-isopropyl alcohol solvent diffusion. A cylindrical-shaped needle-like crystal of 0.22-mm diameter and 0.42-mm length was selected by optical examination. The procedures for crystal alignment and data collection were analogous to those previously described for the tetraethylammonium salt. Axial photographs confirmed both the lattice lengths and symmetry of the chosen monoclinic unit cell. The intensities of 3863 reflections were measured for the reciprocal lattice Octants hkl and fikl over the range 3O I20 5 45". A linear decay correction of -5% (based upon the variations in intensities of two standard reflections) was applied to the intensities. A sorting and merging of the reduced data gave 3724 independent reflections, of which 1816 had diffraction maxima greater than 2a(I). An absorption correction was made (on the basis of the linear absorption coefficient of 21.7 cm-I for Mo Ka radiation). The determined monoclinic cell constants at 23 OC are a = 17.894 (3) A, b = 10.285 (2) A, c = 14.835 (2) A, 6 = 99.21 (1)O, and V = 2695
7694
J. Am. Chem. SOC.,Vol. 102, No. 26. 1980
Lo,Longoni, Chini, Lower, and Dahl Table 111. Least-Squares Planes for the [Fe,(CO), , ]” Dianion
Table 11. Interatomic Distances and Bond Angles for [NEt, I,+[Fe,(CO),, 1’Fe(l)-Fe(2) Fe (2)-Fe (2‘) Fe(l)-C(l) Fe(1). . C ( 2 ) Fe(l)-C(3) Fe(1 ) - C W Fe(21-W) Fe(2)-C(2) Fe(2)-C(5) Fe(2)-C(6) Fe(2)-C(7) C(1)-0(1) C(2)-0(2) C(3)-0(3) C(4)-0(4)
A. Intraanion Distances (A)= 2.593 (2) C(5)-0(5) 2.603 (3) C ( 6 ) 4 ( 6 ) 1.850 (13) C(7)-0(7) 2.723 (13) C(1) . C ( 4 ) 1.800 (15) C(1). . .C(7) 1.725 (17) C(2) . .C(3) 2.212 (11) C(2). . 4 3 5 ) 1.963 (11) C(2) . .C(6) 1.752 (15) C(3). . .C(4) 1.721 (13) C(3). . .C(6) 1.784 (13) C(4) . .C(4’) 1.21 2 (14) C(5). . C ( 5 ’ ) 1.180 (14) C(5). . .C(6) 1.140 (14) C(6). . .C(7) 1.186 (17)
B. Intraanion Bond Angles (Deg)‘ Fe(2)-Fe(l)-Fe(2‘) 60.27 (8) C(l)-Fe(l)-C(3) Fe(l)-Fe(2)-Fe(2’) 59.87 (4) C(l)-Fe(l)-C(4) C(3)-Fe(l)-C(4) C(l)-Fe(l)-Fe(2) 56.8 C(4)-Fe(l)-€(4’) 44.4 C(l)-Fe(2)-Fe(l) C(l)-Fe(2)4(2) 54.0 C(l)-Fe(2)-Fe(2’) C(1 )-Fe(2)-C(5) 71.9 C(2)-Fe(2)-Fe(l) C(l)-Fe(2)-C(6) 48.5 C(2)-Fe(2)-Fe(2’) C(l)-Fe(2)-C(7) 104.1 C (3)-Fe (1 )-Fe (2) C(2)-Fe(2)-C(5) 93.7 C(4)-Fe(l)-Fe(2) C (2)-Fe(2)€(6) 148.1 C(4)-Fe(l)-Fe(2’) C(2)-Fe(2)-C(7) C(S)-Fe(2)-Fe(l) 158.1 C(5)-Fe(2)4(6) 99.5 C(5)-Fe( 2)-Fe(2’) C(5)-Fe(2)-C(7) 87.2 C(6)-Fe(2)-Fe(l) C(6)-Fe(2)-C(7) 130.2 C(6)-Fe(2)-Fe(2’) C(7)-Fe(2)-Fe(l) 104.8 Fe(l)-C(l)-0(1) C(7)-Fe(2)-Fe(2’)
C. Distances (A) and Bond Angles (Deg) for Two Tetraethylammonium Cationsa C(ll)-C(15) N(l)-C(11) 1.55 (2) C(12)C(15) N(l)-C(12) 1.64 (3) C(13)-C(16) 1.57 (2) N ( l ) - C ( l 3) C(14)-C(16) N(l)-C(14) 1.60 (3) C(21)-C(23) 1.47 (1) N(2)-C(21) C(22)-C(24) 1.48 (1) N(2)4(22) C(21)-N(2)-C(22) C(ll)-N(l)C(l3) 1 0 8 (1) C(21)-N(2)C(2lf’) C(ll)-N(1)4(12’) 1 0 8 (2) C(21)-N(2)4(22”) C(ll)-N(l)-C(14‘) 1 1 3 (1) C(22)-N(2)-C(22“) C(l3)-N(l)-C(12’) 107 (2) c(13)-N(1)-c(14‘) lo8( l ) N(2)4(21)4(23) c(12’)-N(1)-C(14’) (2) N(2)-€(22)
