7312 The known mixed halide-phosphine (or -arsine) TBP complexes of nickel(I1) are blue, green, or purple. The corresponding SPY complexes are red, brown, or purple, and if the number and kind of ligands are the same in the two geometries, as in those discussed here, the lowest energy ligand-field band occurs at lower energy in the case of the TBP. When we go to the mixed cyanidearsine, however, the result is that the lowest energy absorption maximum is found in the SPY spectrum.
The lowest energy band in the SPY complex is of relatively low intensity (for [Ni(diars)2CN]+, E is 420 in 2-methyl-TBP-methanol at 300°K). If we compare the most intense ligand-field bands for the two compounds, we find that for both cyanides and halides, the intense absorption at lower energy is found in the TBP. Acknowledgment. We thank the National Science Foundation for support of this research.
Structural Characterization of the Dinuclear Metal Carbonyl Anions [M2(CO)lo]z-(M = Cr, Mo) and [Cr,(CO),,H]-. The Marked Stereochemical Effect of a Linearly Protonated Metal-Met a1 Bond Larry B. Handy,la,*John K. Ruff,lb and Lawrence F. Dahl'"
Contribution from the Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, and The Department of Chemistry, University of Georgia, Athens, Georgia 30601. Received April 30, 1970 Abstract: Single-crystal X-ray structural determinations of the metal carbonyl anions [Cr2(CO)loH]-,[Cr2(CO)10]2-,
and [Mo~(C0)1~] 2- not only have unambiguously established their architectures but also have made possible for the first time a direct stereochemical comparison of two closely related transition metal complexes with and without a hydrogen atom as a bridging ligand. The [Cr2(C0)10]2-and [MO~(CO)~,I~anions possess the D d 2 m Mn2(CO)lo-type structure. The different metal-metal bond length changes observed between the isoelectronic [Cr2(C0)1;12--Mn2(CO)lopair (A(M-M) = 0.05 A) and the isoelectronic [MO~(CO)~~] 2--Tcz(CO)lopair (A(M-M) = 0.09 A) as well as the significant difference in metal-metal bond length changes between the former pair and the isoelectronic [Fe2(C0),l*--CO~(CO)~ (nonbridged isomer) pair of DZh-62mgeometry are analyzed. The prototype [Cr2(CO)loHl-structure, which is an unprecedented example of a linear three-center two-electron X-H-X system, may be formally derived from the protonation of the Cr-Cr electron-pair bond in the [Cr2(CO)10]2-anion. This linear protonation of a metal-metal bond produces a conformational change of the two sets of equatorial carbonyl ligands from the staggered Dedarrangement in the [Cr2(CO)10]2-anion to an exactly eclipsed arrangement (crystallographically required by symmetry) in the [CI-~(CO)~~HIanion which approximately possesses a D4h-4/m2/m2/m geometry. The conformation in the [Crz(CO)loH]-anion is ascribed to the two halves of the hydrogen-bridged anion being sufficientlyfar apart that the attractive part of van der Waals fogces dominates to give an eclipsed orientation of the equatorial carbonyl grovps. The marked shortening by 0.44 A between the two chromium atoms in tbe [Cr2(CO)10Hl-anion (3.41 f 0.01 A) due to deprotonation to give the resulting [Cr2(CO)lo]*-anion (2.97 + 0.01 A) apparently causes a sufficient increase in the repulsive part of van der Waals forces to give the staggered conformation. The three-center electron-pair bonding representation of the Cr-H-Cr framework of the [Cr2(CO)loH]anion is discussed with regard to the possibility of either a symmetric double-minimum potential well or a singleminimum potential well. It is accented that in a linear M-H-M system, which represents a maximum separation of the two metal atoms, as well as in other known "bent" M-H-M systems, where the contact distance between the two metal atoms decreases toward that of a deprotonated electron-pair metal-metal bond, there is extensive metalmetal bonding character due to the large direct overlap of the metal orbitals with each other as well as with the hydrogen 1s orbital, The X-ray analysis of the [Cr2(CO)loH]-anion was carried out on the tetraethylammonium salt, while both dianions were structurally characterized as bis(tripheny1phosphine)iminium salts, { [(CLJH&P]~N} Z[ML(CO)~~] CHzCls(M = Cr, Mo). The [(C2H5)2N][Cr2(CO)loH] salt crystallizes with oneoformula species in a triclinic unit cell of dimensions a = 6.82 f 0.01 A, b = 10.13 i. 0.01 A, c = 8.91 + 0.01 A, Q = 102.0 0.2", p = 101.6 i 0.2", y = 86.3 i 0.2'; the crystal-disordered model utilized in the least-squares refinements assumes an average unit cell of centrosymmetric P i symmetry with the one [Cr2(CO),,H]- anion located on an average center of symmetry and the one cation randomly oriented in one of two centrosymmetrically related positions. The isoCH2C12(M = Cr, Mo) sdts crystallize in the mqnoclinic system with symmetry morphous { [(CGH5)P]2}Z[M2(CO)LO]~ C2/c and with a = 13.125 i 0,009 A, b = 25.973 =k 0.016 A, c = 22.491 i:0.015 A, p = 94.11 0.02", (ohsd = 1.32 g/cm3 L'S. pc.,lc,l = 1.35 g/cm3 ( z = $) for the chromium comopund; and with a = 13.362 f 0.008 A, b = 26.243 f 0.016 A, c = 22.256 i 0.015 A, p = 94.21 f 0.02', pobqd= 1.36 g/cm3 us. pcaled = 1.40 g/Cm3( 2 = 4) for the molybdenum compound.
*
*
I
n recent years there has been considerable interest concerning the stereochemistry and bond properties Of systems a to hydrogen (1) (a) University of Wisconsin; (b) University of Georgia.
Journal of the American Chemical Society
bond.
Our previous work on several polynuclear tran-
(2) This paper is based in part on a dissertation submitted by L. €3. Handy to the Graduate School of the University of Wisconsin in partial fulfillment of the requirements for the Ph.D. degree, Aug 1968.
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7313
sition metal hydrido carbonyl complexes established3-5 the existence of bent three-center electron-pair metalhydrogen-metal bonds, which in each case account for the compounds' diamaghetism without the additional involvement of a separate electron-pair metal-metal bond. Another especially intriguing system appeared to be the series of chromium group carbonyl anions initially synthesized by Behrens and coworkers. 6-8 In particular, the two anions [Crz(CO)loH]- and [Crz(CO)lo]2- appeared to differ only in the presence or absence of the hydrogen atom. These anions were first with liquid ammonia as a solvent system, but recent studies'13 showed that they could be isolated from Cr(CO)6 by the use of other solvents (e,g., tetrahydrofuran, diglyme, or hexamethylphosphoramide) with a borohydride, an alkali metal amalgam, or NaBipy (Bipy = 2,2'-bipyridine)12 employed as a reducing agent. A comprehensive investigation of the course of this reduction has been reported recently by Kaska. '3 An X-ray crystal structural analysis of [Crz(CO)loH]-, undertaken early in this investigation and outlined in a previous communication, lo together with infrared and nmr spectral studies carried out independently by Hayter ' and by Anders and Grahamg established the chromium-hydrogen-chromium framework of the [Crz(CO)loH]- anion as an unprecedented example of a linear electron-deficient X-H-X system. After the X-ray characterization of this homobimetallic hydrido carbonyl anion, [Crz(CO)l~H]-, our next objective was to determine the structure of the related nonprotonated dianion, [Crz(CO)lo]2-. This dichromium anion and the corresponding ones of the congeners molybdenum and tungsten are of particular stereochemical interest, since the infrared spectrum of each of these [M2(C0)10]2-anions was found by Hayter to exhibit a carbonyl stretching band below 1800 cm-', and therefore it was initially presumed", 1 4 t 1 5 that this low frequency implied the existence of bridging carbonyl groups which, if present, would require a very substantial change in geometry from the Dlh architecture observed for the [Crz(CO)l~H]anion. This possible stereochemistry is in contradistinction to that of the heterodinuclear metal anions [(OC)5M-M'(CO)S]- (M = Mn, Re; M' = Cr, Mo, W) prepared by Anders and Graham, ' 5 who proposed the Mn2(CO)lo-type structure for these isoelectronic anions on the basis of their infrared spectra. Crystals of the tetraethylammonium salts of both the [Crz(CO)~o]2and [ M O ~ ( C O ) ~ ~anions ] ~ - were generously supplied by Dr. Roy G. Hayter (Shell Develop(3) R. J. Doedens and L. F. Dahl, J . Amer. Chem. SOC.,87, 2576 (1965). (4) H. D. Kaesz, W. Fellmann, G. R. Wilkes, and L. F. Dahl, ibid., 87, 2753 (1965). (5) L. F. Dahl and J. F. Blount, Inorg. Chem., 4, 1373 (1965). (6) H. Behrens and W. Haag, Chem. Ber., 94, 312 (1961); 2.Nuturorsch. B, 14, 600 (1959). (7) H. Behrens and W. Klek, Z . Anorg. Allg. Chem., 292, 151 (1957). (8) H. Behrens and J. Vogl, Chem. Ber., 96, 2220 (1963). (9) U. Anders and W. A. G. Graham, Chem. Contmun., 499 (1965). (10) L. B. Handy, P. M. Treichel, L. F. Dahl, and R. G. Hayter, J . Amer. Chem. Soc., 88, 366 (1966). (11) R. G. Hayter, ibid., 88, 4376 (1966). (12) E.Lindner, H. Behrens, and S. Birkle, J. Orgunomeful. Chem., 15, 165 (1968). (13) W. C. Kaska, J . Amer. Chem. SOC.,90, 6340 (1968); 91, 2411 (1969). (14) J. K. Ruff, Inorg. Chem., 6, 2080 (1967). (15) U. Anders and W. A. G. Graham, J . Amer. Chem. Soc., 89, 539 (1967).
Handy, Ruf, Dah[
ment Co.), but these compounds unfortunately proved too X-ray sensitive even in argon-filled capillaries to allow collection of intensity data. The tetraphenylarsonium salt of the [Crz(CO)lo]2-anion was prepared by one of us (L. B. H.), but an attempted three-dimensional photographic X-ray determination was unsuccessful, owing presumably to crystal disordering of the [Crz(CO)lo]2- anions in the lattice. In order to stabilize the reactive dianions, particularly toward oxygen and water, the chromium, molybdenum, and tungsten species were prepared (by J. K. R.) and crystallized as salts of the bis(tripheny1phosphine)iminium cation (abbreviated PPN). '6 Crystals of these compounds could be exposed to air for several hours and suffered only moderate decomposition upon prolonged exposure (2 weeks) to X-ray irradiation. The X-ray studies of both the [Crz(CO)lo]2- and [ M O ~ ( C O ) ~ Oanions ] ~ - have unambiguously established their configurations as the Ddd-82m Mnz(CO)lo-type structure, and thereby have made possible, from a comparison of molecular parameters with those of their corresponding neutral counterparts, Mnz(CO)l~17 and Tcz(CO)lo,l8 an evaluation of the change in metalmetal bond length with increased localized negative charge on the metal atom. 19-21 More importantly, these studies presented here have allowed a detailed stereochemical appraisal of the observed conformational change in the molecular [M2(C0)1~]2-species due to protonation of the metal-metal bond. The large changes in molecular parameters found for this resulting linear M-H-M system are assessed in connection with known molecular parameters in other bent M-H-M systems in order to determine structural interrelationships.
Experimental Procedure Preparation and X-Ray Data Collection of [(C2Ht)4N][Cr2(CO)loH]. The [Cr2(CO),oH]- anion was prepared (by L. B. H.) by the reduction of Cr(CO)e with (C2H5)4NBH4 in THF solution as previously reported.10711 Well-formed single crystals of [(CZHS)IN[Cr2(CO)l~H]were obtained from slowly cooled ethanol solutions. A needle-like crystal of length 0.35 mm and uniform thickness 0.18 mm was mounted about the needle axis in a thin-walled Lindemann glass capillary. The capillary was then evacuated and filled (16) J. K. Ruff and W. J. Schlientz, Inorg. Syn., in press. (17) L. F. Dahl and R. E. Rundle, Acru Crystullogr., 16, 419 (1963). (18) M. F. Bailey and L. F. Dahl, Znorg. Chem., 4, 1140 (1965). (19) Hayterll originally found five infrared carbonyl stretching bands
for the Na2[Crt(CO)lo] salt dissolved in THF. It was first pointed out by Edgell and coworkers20 for the [Co(CO)$ anion and shown independently by Lindner, Behrens, and Rirkle,12 by Kaska,13 and by Edgell and Paauwezl for the [C~Z(CO)IO]~anion that solvent effects as well as the cations may markedly affect the frequencies and shapes of the carbonyl bands; the five infrared carbonyl bands in THF for Nat[Crz(CO)~o] were demonstrated12t13721 to be due to incomplete dissociation of the solvated cations and anions (oiz., contact ion pairs), which causes a breakdown in the molecular symmetry, thereby giving rise to the observed complex spectral pattern. The above three groups12~13~21 independently showed in more polar solvents (where dissociation is essentially complete) the existence of only three fundamental carbonyl stretching frequencies (at 1912, 1883, and 1786 cm-1 for Nap[Crs(CO)lol dissolved in DMSO)*] in accord with the selection rules for the D 4 d molecular geometry of the [C~Z(CO)IO]~anion reported here. The relatively low carbonyl frequencies found for this anion are therefore a consequence of a low carbon-oxygen bond order resulting from extensive dissipation of the electron charge from the filled dT orbitals of the chromium atoms into the empty ?r* orbitals of the carbonyl groups. (20) W. F. Edgell, M. T. Yang, and N. Koizumi, J. Amer. Chem. SOC.,87,.2563 (1965); W. F. Edgell, A. T. Watts, J. Lyford, IV, and W. M. Risen, Jr., ibid., 88, 1815 (1966). (21) W. F. Edgell and N. A. Paauwe, Chem. Commun., 284 (1969); N. A. Paauwe, Ph.D. Thesis, Purdue University, 1968.
I Structural Characterization of [M2(CO)10]2and [Cr,(CO),oHl-
7314 Crystal Data of [(C2Hs~~Nl[Cr~~CO)loHl. Crystals of [(C2H& Nl[Cr2(CO)1~H] are triclinic with primitive cell parameters of a = 6.82 f.0.01 A, b = 10.13 f 0.01 A, c = 8.91 f.0.01 A, cy = 102.0 i 0.2", p 7 101.6 i 0.2", y = 86.3 f 0.2"; the unit cell volume equals 590 A3. The observed density of 1.49 g/cm3, measured by flotation in 1-bromonaphthalene, is in satisfactory agreement with the calculated value of 1.45 g/cm3 for one formula species per unit cell. The presence of one tetra_ethylammonium cation per cell suggested that P1 rather than P1 is the probable space group. Subsequent refinement !o the structure disclosed a disorder of this cation consistent with P I . This centrosymmetric space group necessitates that the average unit cell contain the one [CrS(CO)lOH]-anion located on an average center of symmetry, arbitrarily designated at l / * , 1 / ~ , ~ / 2to fix the origin of the cell, and the one [(C2H&N]+ cation Figure 1. The disordered tetraethylammonium cation in crystalline then positioned on the average center of symmetry at O,O,O. For [(C2Hd)4N][Cr2(CO)IoH].On the basis of an analysis of the Fourier the anion the solution of the structure involved the location of one peak positions of the nonhydrogen atoms, a rigid-body model emchromium, five carbon, and five oxygen atoms, with the hydrogen ployed in the final least-squares refinement assumes a random atom (if nondisordered) residing on the center of symmetry. The distribution of the cation in one of two centrosymmetrically related cation was assumed from the structural analysis to be randomly orientations in the crystal, with an ordering of the methyl carbon oriented in one of two centrosymmetrically related positions such atoms (due to presumed superimposed positioning) and disordering as to require in general the determination of 4 half-weighted methylof the tetrahedrally disposed methylene carbon atoms. The disene carbon atoms, 4 half-weighted methyl carbon atoms, and 20 ordered cation ideally conforms to D * h symmetry with the methyl half-weighted hydrogen atoms; final least-squares refinements were carbon atoms located on the horizontal mirror plane. The drawing based on an assumed superimposed positioning of pairs of halfshows for one orientation the nitrogen and carbon atoms linked by weighted methyl carbon atoms to give 2 independent whole-weighted solid lines and for the other orientation the atoms linked by dashed methyl carbon atoms. For this particular disorder observed, the lines. crystallographically independent unit contains 1 chromium, 5 oxygen, 7 whole-weighted carbon, 4 half-weighted carbon, and 20 halfweighted hydrogen atoms, all of which occupy the twofold set of with argon to prevent decomposition. Preliminary X-ray photogeneral positions (i) at i ( s , y , z ) , together with 1 nitrogen atom, graphs of this crystal revealed only triclinic Ci-T Laue symmetry. which occupies the onefold special position (a)at O,O,O and 1 hyMultiple-film equi-inclination Weissenberg photographs of reciprodrogen atom which (if nondisordered) occupies the onefold special cal layers Okl-7kl were taken with Zr-filtered Mo K a radiation. position ( h ) at '/*,1/2,1/2.27 For all nonzero levels two sets of photographs, each covering Solution of the Structure of [(C2H3,N][Cr2(CO)loH]. A threeapproximately 220", were taken at spindle settings 180" apart. dimensional Patterson function established the relative positions In this way only Weissenberg spot extension corrections22 needed of the two chromium atoms in the u@t cell. A three-dimensional to be applied as only the top half of the film was used for intensity measurements. Fourier map based on space group P1 and phased on the one indeTimed sets of precession photographs were obtained from a pendent chromium revealed the positions of the four equatorial second needle-like crystal of length 0.25 mm and uniform thickness carbonyl groups and the nitrogen atom at the cell origin. A second 0.09 mm. This crystal was grown from an acetone-water mixture Fourier map phased on the above partial structure showed the axial carbonyl group but not the cation carbon atoms. No images and was also sealed in a Lindemann capillary under argon. Sets of the carbonyl groups were qbserved, so the carbonyl groups also of 12 films were obtained for each of reciprocal levels h01, h2/, hkO, and h k l . Cell parameters were determined from h01 and conformed to space group P1. Several cycles of full-matrix isohkO precession photographs on each of which was superimposed the tropic least-squares refinement resulted in an unweighted discrephkO diffraction pattern of a sodium chloride crystal. ancy factor of Ri = 10.7% and a weighted discrepancy factor of All intensity data from the Weissenberg and precession films were R2 = 13.8 A difference map then indicated that the methylene judged by visual comparison with a timed set of standard intensities carbon atoms of the tetraethylammonium cation were disordered prepared from the same crystal and by the same camera method by inversion through the origin, while the methyl carbon atoms utilized to collect the intensity data. The data for each reciprocal were related by the center of symmetry without any obvious dislevel were averaged, and analytical corrections were made for order (Figure 1). Further isotropic refinement based on this model Lorentz-polarization effects as well as for Weissenberg spot exresulted in Rl = 9.1 % and R2 = 8.9%. Discrepancy factors based tension. 2 2 Standard deviations for each reflection were assigned on each of the possible ordered acentric models with P1 symmetry All attempts as follows:23 if Io ?-_.\/Elmin, o(FJ = 0.05/F0(;if Io < _.\/GIm;,,, were only slightly higher, with R2 = 9.1 and 9.5 a t refinement of an ordered structure based on P1 symmetry were a(F,) = O.OSlF,/( V'101m~n/I~)2. The linear absorption coefficient unsuccessful, however, owing to extremely high correlation between ( g ) for Mo K a radiation is 10.4 cm-l; since firmsx for both crystals the previously centrosymmetrically related atoms. Four cycles of was less than 0.2, no absorption corrections were applied. The refinement were carried out for each acentric model. Correlations maximum intensity variation on a given reciprocal layer due to remained high, and the attempted refinements resulted in discrepabsorption was estimated to be less than 6%. The Weissenberg ancy factors greater than 12%. For the disordered centric model, and precession data were merged2*to one relative scale factor cia the isotropic temperature factors for the disobdered methylene carleast squares to give 830 independent observations. The weighted bon atoms were all within the range of 6-8 A2, while those for the reliability index for this merge was 4.6%, based on 303 duplicate presumably ordered methyl carbon atoms were slightly higher at and 43 triplicate reflections. This low value for the reliability 9 and 11 A2. Both ordered acentric orientations failed to display index suggests that no serious systematic errors are present in the similar consistency of thermal parameters; the isotropic temperadata. ture factors ranged from -1 to 20 A2. Packing considerations Normal atomic scattering factors for all atoms were taken from also did not reveal any advantage for either possible ordered orithe Hartree-Fock-Slater calculations of Hanson, el a/. 2 5 The entation of the cation. For each orientation there is one nonreal and imaginary anomalous contributions to the chromium scatbonding (methylene carbon)-(carbonyl oxygen) distance of ol~ly tering factor were taken from the tabulation by Templeton.26 3.0 A, which might indicate weak hydrogen bonding. Hence, it is concluded that the disordered centric model is preferable. (22) D. C. Phillips, Acta Crjstallogr., 7 , 746 (1954). An examination of the atomic parameters obtained from the (23) D. L. Smith, Ph.D. Thesis, University of Wisconsin, 1962, isotropic least-squares refinement based on the disordered centric Appendix I. (24) P. W. Sutton and M. D. Glick, "A Crystallographic Data Cor(27) Reference 26, Vol. I, p 75. relation Program," University of Wisconsin, 1964. (28) All least-squares refinements reported in this work were based on (25) H. P. Hanson, F. Herman, J. D. Lea, and S. Skillman, Acta the minimization of the quantity Zw2(AFt)2; the weights here assigned Crqslallogr., 17, 1040 (1964). according to the estimated standard deviations of the structure factors. (26) D. H . Tcmplcton in "International Tables for X-ray CrystalThe discrepancy factors, RI and RZ are defined as follows: Ri = 100. lography," Vol. 111, The Kynoch Press, Birmingham, England, 1962, [ZllFo'- IFo[I/Z'FJ]; Rz = l O O [ Z w ~ ~ F oI ~ F ~ ~ ~ * / Z W ~ F ~ ~ I ~ ~ ~ . p 215.
z.28
z
Journal of the American Chemical Society
92:25
December 16, 1970
x.
7315 model showed that the thermal-parameters for the carbonyl groups For the molybdenum compound, intensity data were collected were quitemhigh,from 7 to 9 A Z for the carbon atoms and from for one asymmetric unit, octants hkl and hkl. A set of four stan10 to 12 A a for the oxygen atoms. A difference Fourier map dard reflections was measured every 100 reflections as a check on phased on this ordered-disordered centric model showed residual crystal and instrument stability. electron density characteristic of anisotropic thermal motion for the For the chromium compound, intensity were collected for chromium, carbon, and oxygen atoms of the anion. Hence, furtwo equivalent forms, octants hkl, hki and hki, hkl. A set of five ther refinement was carried out with anisotropic temperature factors standard reflections was measured every 100 reflections, and a linear for these atoms. Final discrepancy factors were R1 = 7.4 and Rz decrease in intensity of 19% was observed for the total period of = 7.0%. A difference Fourier map calculated a t this point redata collection. The derived structure factors were corrected for vqled no residual electron density greater than 0.6 or less than -0.7 this linear decay. e/A3. No indication of the hydrogen positions was obtained. In Structure factors were calculated from the intensity data by means particular, no maximum of this residual density was located within of the data reduction program D A T R E D , ~in~ which the intensities a 2-A diameter sphere centered between the chromium atoms. were corrected for background and Lorentz-polarization correcExamination of the positional parameters of the tetraethylamtions, and o(I)’s for each reflection were calculated as previously monium ion suggested that some constraint should obe applied, outlined. 3 3 , 3 4 Reflections were considered unobserved if I 5 since carbon-carbon distances were as large as 1.74 A. The dis3 4 ) for the molybdenum compound and I 5 2u(I) for the chroordered cation appeared to conform very nearly to Dph symmetry mium compound. Unobserved data were not employed in any with the methyl carbon atoms located on the idealized horisubsequent analysis. The two equivalent forms for the chromium zontal mirror plane and the methylene carbon atoms positioned compound were merged by a least-squares procedure35 to give a above and below this plane. A rigid-body mode129~~0with single set of data on one scale. A total of 822 common reflections C-N obonds of length 1.50 A and C-C bonds of length gave a weighted discrepancy factor of 5.0%. A total of 1256 inde1.54 A was therefore prepared. The HzC-N-CH~ angles were aspendent observed reflections resulted from this procedure. For the sumed to be tetrahedral, which results in N-CH2-CH3 angles molybdenum compound, only data for which 28 5 30’ were proof 113”. The origin of the rigid body was taken to be the cessed, since the data from 30” to 40” were largely unobserved or nitrogen atom a t the crystallographic origin and so could not be weak. For 28 5 30°, a total of 1090 independent observed reflecvaried. This cation model was refined with individual atomic isotions were processed. No absorption corrections were applied tropic thermal parameters for the rigid body atoms, while anisosince firrnaxfor both compounds was less than 0.15; the maximum tropic thermal parameters were again employed for the anion. The possible variation in the intensities caused by neglect of absorption final discrepancy factors were RI = 7.7 and Rz = 7.9 %. This geocorrections was estimated to be 11 7:. The atomic scattering facmetrical constraint on the cation had no significant effect on the tors used for all atoms were those based on the Hartree-Fockstructure of the anion, since none of the calculated interatomic Slater calculations as compiled by Hanson, et al.25 Crystal data distances and angles in the anion changed by more than one estifor [PPN]z[M~(CO)l~] .CHZCIZ(M = Cr, Mo) are given in Table I. mated standard deviation; in particular, the important chromiumchromium distance changed by only 0.001 A, or one-ninth of the standard deviation of this distance. Table I. Crystal Data for [PPN]Z[ML(CO)IO] * CHzClz Preparation and X-Ray Data Collection of [PPNIZ[C~Z(CO)~OI.(M = Cr, Mo) CHZC12 and [ P P N ] Z F ~ O ~ ( C .CHzCln. O ) ~ ~ ] Both compounds were prepared (by J. K.R.) according to the Hayter procedure.” The bis(tripheny1phosphine)iminium cation (PPN)16 was employed as the counterion in the crystallizations. Well-formed single crystals a, 13.125 (9) 13.362 (8) were obtained by recrystallization from methylene chloride-ethyl b, 4 25.793 (16) 26.243 (16) acetate solutions. Prismatic crystals of approximate dimensions 22.256 (15) c, A 22.491 (15) 0.4 X 0.2 X 0.2 mm were cemented to a glass fiber, with an obvious 94.21 (2) f13 deg 94.11 (2) twofold crystal axis oriented along the fiber axis. Preliminary osV , A3 7594.4 7783.3 cillation and Weissenberg photographs confirmed that both crystals Pobsd, g/cm* 1.32 1.36 were monoclinic with the unique axis b as the oscillation axis. Each 1.40 ( z = 4) 1.35 ( z = 4) Pealed, g/cm3 crystal in turn (the Mo compound first) was then transferred to a 4.9 p , cm-l 4.3 General Electric four-circle automatic diffractometer and centered by optical and X-ray techniq~es.3~The orientation of the crystal was then defined by the manual centering of 50 reflections with known indices for the molybdenum compound, and 16 reflections Systematic absences of ( h k l ) for h k odd and { h O l ) for I odd for the chromium compound. Lattice parameters and the orientaestablished the probable space groups as either c2/c-c2h6 or Cc-C.‘. tion of all reflections with 28 5 40” were derived from these manSubsequent solution and refinement of the structures verified the ually centered reflections with a local version of the Argonne Nacentrosymmetric choice, C2/c. The four formula species occupy tional Laboratory orientation and angle setting program.32 the cell in the following way: the two metal atoms, the axial carIntensity data were collected by the 8-28 scan technique at a takebonyl carbon and oxygen atoms, and the methylene chloride carbon off angle of 2”. Symmetric scans of 2” in 28 a t a rate of 4”/min atom occupy the fourfold set of special positions (e) on twofold were employed for all reflections. Stationary crystal-stationary all other atoms occupy the axes: (O,O,O; 1/2,1/z, 0) f counter background counts of 15 sec were taken a t both extremes eightfold set of general positions (f): (O,O,O; 1/z,1/2,0)f ( x , of each scan range. A counter aperture of 2-mm diameter was y , z ; X , Y , , ~ / ~- Z ) . ~ S Thus, the solution of the structure required located 31 mm from the crystal. Zirconium-filtered Mo Ka radithe location of 2 metal (Mo or Cr), 2 phosphorus, 1 chlorine, 6 ation was used with a scintillation detector followed by a pulseoxygen, 1 nitrogen, and 43 carbon atoms. The 30 phenyl hydrogen 90% of the Mo Ka height analyzer which accepted approximately atoms were included in the least-squares refinements after the locapulse distribution. tion of the carbon atoms of the 6 phenyl groups enabled each CsHs group to be treated as a rigid body. Solution of the Structures of [PPN]z[Mz(CO)IO] ’CHZCIZ(M = Cr, Mo). A three-dimensional Patterson synthesis based on (29) The rigid body rotation angles, 4, 8, and p , as used in the local the molybdenum data revealed the positions of the two independent least-squares program, are defined in the following manner: an molybdenum atoms on the crystallographic twofold axis. Sucorthonormal basis set of vectors, (x,y,z), is defined such that a is along x and b is in the x,y plane. Another orthonormal set, ( x ’ , y ’ , cessive Fourier syntheses established reasonable positions for all z’), is defined relative to the actual crystallographic positions of the remaining atoms except for those of the solvated methylene atoms which comprise the rigid body. The set (x,y,z) is then brought chloride molecule. Several cycles of full-matrix least-squares reinto coincidence with (x’,y’,z’) by the following rotations: $ , about z, 0 about the resulting x , and p about final y . (30) The orthonormal set ( x ’ , y ’ , z ’ ) for the disordered tetraethyl; (33) E. F. Epstein, Ph.D. Thesis, University of Wisconsin, 1968, Apvendix. ammonium ion has x ’ along (H2C(l)-N), y’ along (HaC(2)-N), and z along (x’ cross 9’). The origin is at the nitrogen atom position. (34) V. A. Uchtman and L. F. Dahl, J . Amer. Chem. Soc., 91, 3756 (3 1) T. C. Furnas, “Single Crystal Orienter Instruction Manual,” (1969); E. F. Epstein and L. F. Dahl, ibid., 92, 502 (1970). General Electric Co., Milwaukee, Wis., 1966. (35) J. F. Blount, “ I N T A V ~ A , A Crystallographic Data Correlation Program,” University of Wisconsin, 1967. (32) Argonne National Laboratory, “Orientation and Angle Setting (36) Reference 26, Vol. I, p 101. General Program,” Program B-101, 1965.
cats
+
Handy, Ruff,Dah1
1 Structural Characterization of [M2(CO)l~]zand [Cr2(CO),oHI-
7316 Table II. Final Parameters of [(CzH,)4N][Cr2(CO)loH],Idealized Cation Model. Atom
Y
X
0.3801 (3) 0.166 (2) 0.595 (2) 0.403 (2) 0.167 (2) 0.339 (1) 0.245 (2) 0.512 (2) 0.401 (2) 0.257 (3) 0.364 (2)
0.4742 (3) 0.425 (2) 0.336 (3) 0.905 (2) 0.608 (2) 0.041 (2) 0.443 (2) 0.391 (3) 0.740 (3) 0.556 (2) 0.202 (3)
0.6025 (3) 0.763 (2) 0.864 (2) 0.772 (1) 0.347 (2) 0.429 (2) 0.701 (2) 0.766 (3) 0.704 (2) 0.444 (2) 0.492 (2)
0 0.011 -0,225 -0.150 0.045 -0.035 -0.070
0 -0.076 -0.164 0.032 -0.150 0.076 -0.193
B
z
0
5 . 9 (4) 8.6 ( 5 ) 10.9 (6) 6 . 7 (7) 6 . 6 (7) 6 . 5 (7) 7 . 1 (7)
-0.285 -0.063 -0.042 -0.128 -0.151 -0.020
Rigid-Body Parametersb Group
X
Y
Z
$ ,
[(CzH5 ) A“
0
0
0
-28.1 (4)
Atom
Anisotropic Thermal Parameters ( X lO3)c Bzz B33 Biz
Bii
a Estimated standard deviation of the last significant figure is given in parentheses. of the form exp[-(h2Bll k2Bzz PB33 2IzkB12 2/1& 2klB~)I.
+
+
+
+
+
finement, with the phenyl groups treated as rigid b0dies,~g,37failed to reduce the value of R1below 19 %. Three of the phenyl groups failed to refine in a satisfactory manner, with group isotropi: temperature factors of about 12 A2 compared to values of 4-5 A 2 for the other three groups. The structural determination was temporarily abandoned a t this point, while the structure of the isomorphous and presumably isostructural chromium compound was determined. Owing to the unexplained difficulty encountered in the molybdenum refinement, no assumptions were made concerning the chromium structure. A three-dimensional Patterson synthesis proved nearly identical with that of the molybdenum analog and provided initial coordinates of the two chromium and two phosphorus atoms. Successive Fourier syntheses again revealed all the remaining atoms except those of the methylene chloride molecule of solvation. Refinement was somewhat more satisfactory than that for the molybdenum compound, but appeared to converge a t R1 = 15 and RP = 16 %. An electron-density difference map calculated at this point revealed a peak, nearly as intense as a typical phenyl carbon atom, near the twofold axis. Close examination of the Fourier difference map along the twofold axis revealed a very weak peak on the axis within bonding distance of the first pegk. Since the crystals were grown from a methylene chloride-ethyl acetate mixture, methylene chloride solvation was suspected, and samples of both the chromium and molybdenum compounds were recrystallized by the same procedure as for the crystals used for the X-ray structure determination. Subsequent chemical analyses38 showed the pres-
See ref 29, 30.
9
-167.6 (3) B13
P -96.5 (4) B23
Anisotropic thermal parameters are
ence of one molecule of CHzClz per formula species. The peaks observed on the difference map, however, indicated that only about half of a methylene chloride statistically occupied the position on the twofold axis. In order to estimate the occupancy factors of the methylene chloride atoms, th? chlorine and carbon temperature factors were fixed at 6 and 8 A2, respectively, and their scattering factor multipliers were varied. Both multipliers converged rapidly to a value of approximately 0.5, although the exact value would certainly change if different arbitrary temperature factors were employed. A final Fourier difference synthesis failed to reveal any significantofeatures with no peaks greater than 0.54 or less than -0.51 e/A3. In particular, no other positive electron density interpretable as solvent could be found near the axial carbonyl group attached to Cr(2), either in the final Fourier difference synthesis or in a similar Fourier synthesis in which the contribution from this carbonyl group was not included. The very high temperature factors for this axial group, the relatively high standard deviations, the moderately high discrepancy factors, and the elemental analysis all indicate the presence of additional methylene chloride of solvation, but these molecules presumably must be quite randomly disordered, as no further evidence of their atomic coordinates could be found. The final discrepancy factors for the isotropic least-squares refinement are Rl= 14.3 and RZ = 10.0%. Comparison of the corresponding final parameters from the reCH2Clzwith those of the partial refinefinement of [PPNJ2[Cr2(CO)lo]. ment of [PPNJ2[Mo2(CO)lo]. CH2C12showed essential agreement, but the three phenyl groups which had previously failed to refine were displaced by nearly 0.2 A in the Mo compound. The values of all parameters were then taken from the refinement of [ P P N I ~ C ~ Z (C0)10].CH~CIZ and used as a starting set for the Mo analog. ISO-
(37) All phenyl group refinements were based on the following model. Each ring has D a h symmetry with a C-C bond length of 1.392 A. The hydrogen atoms are located on the lines defined by diagonally opposite carbons with a C-H bond length of 1.08 A. The orthonormal set ( x ’ , y ‘ , z ’ ) has x ’ along C(4)-C(1), y’ along C(5)-C(3), and z’ along N)Z[C~P(CO),O].CHZCI~: C, 64.5; H, 4.1; N, 1.8; CI, 4.6. Found: ( x ’ cross y ’ ) , The origin is at the center of the carbon framework. C, 64.1; H, 4.2; N, 1.9; CI, 5.0, Calcd for {((CEHS)~PIZN)ZIMOZ(38) Analyses were carried out at the Rohm and Haas Co., Redstone CI, 4.3. Found: CI, 4.6. Research Laboratories, Huntsville, Ala. Anal. Calcd for [ [(CEHO)BP]P- (CO)lo]~CH~Cl2:
Journal of the American Chemical Society
92:25
December 16, I970
7317
Q
Figure 2. View of the [ { (CeH6)8P)zN]+ cation and the [Crz(C0)lol2The anion as found in the structure of [PPNl2[Crz(CO)l~]+CH~C1~. solvated methylene chloride molecule (half-weighted) lying on the Figure 3. Comparison of the geometries of the [Cr2(CO)lo]z-, same crystallographic twofold axis which passes through the [ M O ~ ( C O ) ~ O ][Cr2(CO)t~Hl-, ~-, and [Cr2(CO)loI]- anions. The [Crz(CO)lo]~anion is also shown. [ C ~ ~ ( C O ) ~ anion O ] + ~ is - isoelectronic and isostructural with Mnz(CO)lo, while the isosteric [Mo~(CO)10lz-anion is isoelectronic with Tc2(CO)lo. The [CrZ(CO)toH]- anion, containing the unprecedented example of a linear three-center two-electron metal-hydrogentropic least-squares refinement then proceeded without further metal bond, may be considered to arise from the protonation of the complications to give final discrepancy factors of R1 = 9.8 and electron-pair Cr-Cr bond in the [Cr,(CO),o] 2- anion. This proJonaRz = 11.5%. A final Fourier difference synthesis again failed to tion not only increased the Cr-Cr bonding distance by 0.44 A but to reveal any additional solvent with no peaks greater than 0.66 also results in a confor_mationalchange of the equatorial carbonyl or less than -0.51 e/A3. groups from the D4d-82m “staggered” arrangement in the [CrzBecause of the large number of parameters required to carry out (CO)lo]2- anion to an “eclipsed” D4h-4/m2/m2/m structure in the the isotropic thermal least-squares refinements of [PPN]z[Crz[Crz(CO)loH]- anion. In contrast, the monohalogen-bridged (CO)lo] CHzCIz and [PPN]z[Moz(CO)Io] .CH2C12, the resulting com[Crz(CO)l~I]-anion has a dinstinctly nonlinear Cr-I-Cr framework puting time per least-squares cycle was already sufficiently long, whose linkage may be appropriately formulated from a localized and therefore expensive, that it could not be justified by us to continue with anisotropic thermal refinement in these particular cases valence-bond representation as two electron-pair Cr-I u bonds. from the standpoint that the scientific value of obtaining more refined structures with somewhat better molecular parameters (involving mainly the nonmetal atoms) was not worth the financial sented in Tables IV and V for [PPN]2~Cr~(CO)Io]~CHzC1~ and [PPNIzcost. The relatively large estimated standard deviations of both [Mo~(C0)lo]CHzCl~;bond lengths and angles are recorded in the positional parameters of the carbonyl atoms and the bond Table IV. lengths and angles involving these atoms are attributed not only to the effect of the methylene chloride of solvation (of which only half of one molecule could be crystallographically resolved) on the Results and Discussion refinement of the entire crystal structure but also in part to the isotropic thermal model not being adequate to compensate for the The [Cr2(CO)~~]zand [M02(C0)1~]~-Anions. (a) presumed high anisotropic thermal motion of the carbonyl atoms Comparison of the [Cr2(CO)~o]z - and [MO~(CO)IO]~in the [Crz(CO)lo]2-and [ M O ~ ( C O ) ~anions; ~ ] ~ - large anisotropic Anions with Their Respective Isoelectronic Neutral thermal motion of the carbonyl atoms was previously detected in the structural determinations17’l8 of the Mnz(CO)loand Tcz(CO)lo Molecules M I I ~ ( C O ) and ~ ~ T C ~ ( C O ) ~ ~Crystals . of homologs. Both the crystallographically resolved and unresolved [PPN]2[M2(CO),o].CHzClz(M = Cr, Mo) are essentially methylene chloride molecules of solvation as well as presumed isomorphous and isostructural, as is evident from a large anisotropic thermal character probably account for the very comparison of lattice and atomic parameters for the high isotropic temperature factors (Table 11) of the axial carbonyl two compounds. The dimeric [M2(CO)l~] *- anion, atoms, C(2-1) and O(2-l), since the packing appears somewhat congested in the regions of the unit cell near these and their symlocated on a crystallographic twofold axis coincident metry-related atoms. with the metal-metal bond, approximately possesses All Patterson and Fourier calculations were carried out with the D4d-82msymmetry with nearly octahedral coordination Blount program. 39 Least-squares refinements were carried out about each metal atom such that the two sets of four with a local modification of the Busing-Martin-Levy ORFLS program.40 Interatomic distances and angles and their estimated equatorial carbonyl groups are in a staggered constandard deviations (which include the effect of estimated errors formation (Figure 2). This configuration of the [Cr2in lattice parameters) were calculated with the Busing-Martin(C0)10]~and [ M O ~ ( C O ) ~ ~anion ] ~ - is contrasted in Levy ORFFE program41 from the full inverse matrix. The atomic Figure 3 with the D4h-4/m2/m2/m configuration of are parameters from the output of the last least-squares given in Table I1 for [(CzH,)4N‘l[Cr2(CO)loH], while Table 111 gives the [Crz(CO)loH]- anion and with the configuration selected bond lengths and angles. Atomic and rigid-body paramof the [Cr2(CO)loI]- anion. 4 3 Thus, the [Cr2(CO)lo]2eters from the output of the last least-squares cycles42 are pre(39) J. F. Blount, Ph.D. Thesis, University of Wisconsin, 1965, Appendix. (40) W. R. Busing, K. 0. Martin, and H. A. Levy, “ORFLS, A Fortran Crystallographic Least-Squares Program,” ORNL-TM-305, Oak Ridge National Laboratory, 1962. (41) W. R. Busing, K. 0. Martin, and H. A. Levy, “ORFFE,A Fortran Crystallographic Function and Error Program,” ORNL-TM306, Oak Ridge National Laboratory, 1964. (42) Calculated and observed structure factors are deposited as Document No. NAPS-01148 with the ASIS National Auxiliary Pub&
and [ M O ~ ( C O ) ~ anions ~ ] ~ - have virtually the same configuration as their respective isoelectronic neutral analogs Mnz(CO)lo17and Tcz(C0)lo. l8
cation Service, c/o CCM Information Corp., 909 3rd Ave., New York, N. Y. 10022. A copy may be secured by citing the document number and by remitting $2.00 for microfiche or $5.00 for photocopies. Advance payment is required. Make checks or money orders payable to: CCMIC-NAPS. (43) L. B. Handy, J . K. Ruff, and L. F. Dahl, J . Amer. Chem. SOC., 92, 7327 (1970).
Handy, Ruff, Dahl / Structural Characterization of [Mz(CO),,J2-and [Cr2(CO),oHl-
7318 Table III. Intramolecular Distances (A) and Angles (degyfor [(C?H5)4N][Cr?(CO),oH] Cr-Cr
'
A. Bond Lengths
Cr'-Cr-Carbonyl C,, Cr'-Cr-C( 1) 176.8 (6)
3.406 (9)
Chromium to Equatorial Carbonyl Carbon Cr-C(2) 1.91 (3) Cr-C(3) 1.87 (2j Cr-C(4) 1.83 (2) Cr-C(5) 1.92(2)
Cr'-Cr.
Cr'-Cr-Carbonyl O,, O(1) 177.2 (4) C,,-Cr-Ce,
C( 2)-Cr-C( 3) C( 3)-Cr-C(4) C(4)-Cr-C( 5) C(5)-Cr-C( 2)
1.88 (av) Chromium to Equatorial Carbonyl Oxygen C r . . .0(2) 3.09 (2) C r . . aO(3) 3.02 (2) Cr . . .O(4) 3.03 (2) Cr. 'O(5) 3.06 (2)
90.3 (8) 89.4 (8) 90.1 (8) 9 0 . 2 (8) 9 0 . 0 (av) C,,-Cr-C,,
C(2)-Cr-C( C( 3)-Cr-C( C(4)-Cr-C( C(5)-Cr-C(
3.05 (av) Chromium to Axial Carbonyl Carbon Cr-C(1) 1.82(2)
1) 1) 1) 1)
91 .O (8) 9 0 . 0 (8) 90.6 (9) 90.6 (8) 91 $ 0(av)
Chromium to Axial Carbonyl Oxygen C r . . .0(1) 2.90 (2)
Cr-C-0 Cr-C( 1)-O( 1) Cr-C( 2)-O( 2) Cr-C( 3)-O( 3) Cr-C(4)-O(4) Cr-C(5)-0(5)
Carbonyl Carbon to Oxygen C(1)-0(1) 1 . 0 9 (2) C(2)-0(2) 1.18 (3) C(3)-0(3) 1.16 (2) C(4)-0(4) 1.21 (2) C(5)-0(5) 1.15 (2)
179 (2) 178 (2) 174 (2) 174 (2) 172 (2)
175 (av) C. N nbondinn Di nces within the Cr(COj5 Fragment C(1). . .C(2) 2.65 (3) C(1). . .C(3) 2 , 6 6 (4) 2.65 (3) C(1). . .C(4) 2.59 (3) C(1). . .C(5) 2.71 (4) C(2). . .C(3) 2.68 (3) C( 3) ' . ' C(4) C(4). "C(5) 2.60 (3) C(5). ' .C(1) 2.66 (3)
1.16 (av) B. Bond Angles Cr'-Cr-Carbonyl C,, Cr '-Cr-C( 2) Cr'-Cr-C(3) Cr'-Cr-C(4) Cr '-Cr-C( 5)
1
91.8 (6) 89.7 (6) 86.7 (7) 87.8 (6) 89.0 (av)
between Cr(C0)6 Fragments C(2). . .C(4') 3.32 (3) 3.36 (3) C(3). . .C(5') O(2). . .0(4') 3.54 (2) O(3). . . 0 ( 5 ' ) 3.43 (3)
0'-Cr-Carbonyl O,, Cr'-Cr. .0(2) 91.4 (4) Cr '-Cr ' .O(3) 92.0 (4) 89.1 (3) Cr'-Cr. . .O(4) Cr '-Cr . .O(5) 90.5 (4) a
within the Constrained [(C2Hs)4N]+ Cation H ~ c ( 1 ) .. .H,C(2) 3.55 HaC(1). . .H2C(4) 2.93 2.45 HzC(1). . .HzC(2)
~-
90.8 (av)
Although the crystalline [PPN]z[Mz(CO)l~].CH2CIz is largely determined by the bulky [PPN]+ cations. Acstructure is ionic, the packing depicted in Figure 4 cordingly, there are n,o interionic anion . . anion distances less than 5.0 A, while the shortest interionic carbon...carboa distances of the cations are in the range 3.5-3.8 A. The interionic (cation carton). . (anion oxygen) distances are all greater th!n 3.2 A. The Cr-Cr distance ofo2.97 f 0.01 A in the [Crz(CO)lo]2- anion is 0.05 A g5eater than the Mn-Mn distance of 2.923 i 0.003 A in Mn2(SO)lo,17while the Mo-Mo distance of 2.123 f 0.007 A in the [Moz(CO)lo]2- anion is 0.09 A, greater than the Tc-Tc distance of 3.036 i 0.006 A in T C ~ ( C O ) ~The ~ . ~equa~ torial carbonyl groups in both dianions are bent away from the axial carbonyl groups. The average C,,-MC, angles are 93 and 94" in the chromium and molybdenum compounds, respectively. This same distortion from exact octahedral coordination is observed not only in Mnz(CO)lo17and Tcz(CO)lo,l8 but also in both the s0lid~~145 and g a s - p h a ~ estructures ~~ of Mn(COhH, b (44) S. J. La Placa, W. C. Hamilton, and J. A. Ibers, Inorg. Chem., 3, e
-
-1
1'4
c
4
Figure 4. [loo] projection of the monoclinic unit cell of [PPN]JM2( C O ) , O ] . C H ~(M C~~ = Cr, Mo), showing the orientations of the four formula species per cell related to one another by the space group symmetry C2/c.
Journal of the American Chemical Society
1491 11964) , -- ~ .,.
(45) S . J. La Placa, W. C. Hamilton, J . A . Ibers, and A . Davison, ibid., 8, 1928 (1969). (46) A. G. Robiette, G . M. Sheldrick, and R. N. F. Simpson, Chem. Commun., 506 (1968),
/ 92:25 / December 16,I970
7319 Table IV. Final Parameters for [PPNl$3dCO)la]~CH2C12a Atom
Y
X
0 0 0 0 0 0 0.077 (2) 0.122(2) 0.124 (3) 0.195 (2) -0.146 (3) -0.225 (2) -0.037 (2) -0.161 (2) 0 0.076 (1) -0,0349 (6) -0.0252 (6) -0.053 (1)
Cr( 1) Cr(2) C(1-1) o(1-1) C(2-1) O(2-1) C(1-2) O(1-2) C(l-3) 0(1-3) C(2-2) O(2-2) C(2-3) 0(2-3) C-M C1 P(1) P(2) N
B
z
0.0836 (3) 0.25 4 . 3 (2) -0.0317 (4) 0.25 5.4 (2) 0.153 (2) 0.25 8 (2) 0.197 (1) 0.25 7 (1) -0.105 (4) 0.25 12 (3) -0.148 (2) 0.25 18 (2) 0.076 (1) 6 . 1 (9) 0.187 (2) 0.0659 (8) 0.143 (1) 6 . 8 (7) 0.082 (1) 0.296 (2) 7 (1) 0.329 (1) 9.6 (8) 0.079 (1) -0.028 (1) 0.264 (1) 7 (1) 0.270(1) 8.9(8) -0.023 (1) 0.171 (2) 6 . 8 (9) -0.028 (1) -0.018 (1) 0.118 (1) 8.6 (7) 8b 0.417 (3) 0.25 0.292(1) 6b 0.393 (1) 0.3695 (4) -0.0030 (4) 2 . 8 (2) 0.2700 (3) -0,0643 (4) 3 . 1 (2) 0.3095 (8) -0.0160 (9) 2.3 ( 5 )
c43H5(1) PC(1-1) PC(1-2) PC(1-3) PC(1-4) PC(1-5) PC(1-6) PH(1-2) PH(1-3) PH(1-4) PH(1-5) PH(1-6)
0.063 0.112 0.188 0.216 0.168 0.091 0.090 0.226 0.275 0.189 0.054
0.378 0.335 0.340 0.390 0.433 0.428 0.297 0.307 0.394 0.472 0.461
CsHs(2) PC(2-1) PC(2-2) PC(2-3) PC(2-4) PC(2-5) PC(2-6) PH(2-2) PH(2-3) PH(2-4) PH(2-5) PH(2-6)
0.002 0.101 0.126 0.053 -0.046 -0.071 0.158 0.203 0.072 -0.103 -0.148
0.405 0.423 0.450 0.457 0.439 0.413 0.418 0.464 0.478 0.445 0.398
0.055 0.080 0.126 0.147 0.121 0.075 0.065 0.146 0.182 0.137 0.056 -0.066 -0.070 -0.121 -0.168 -0.164 -0.113 -0.034 -0.124 -0.207 -0.200 -0.110
2 . 3 (7) 4 . 3 (8) 6 . 2 (9) 5 . 0 (8) 7 (1) 6 . 2 (9) 10” 10 10 10 10 4 . 1 (8) 6.1 (9) 7 (1) 6 . 4 (9) 8 (1) 4 . 0 (7)
X
Y
C aH 5(3) PC(3-1) PC(3-2) PC(3-3) PC(3-4) PC(3-5) PC(3-6) PH(3-2) PH( 3-3) PH(3-4) PH(3-5) PH(3-6)
-0.148 -0.198 -0.284 -0.320 -0.270 -0.184 -0.170 -0.324 -0.388 -0.298 -0.144
0.399 0.372 0.393 0.441 0.468 0.447 0.334 0.372 0.457 0.506 0,468
0.066 0.024 0.001 0.078 0.119 0.084 0.009 -0.032
CeHs(4) PC(4-1) PC(4-2) PC(4-3) PC(4-4) PC(4-5) PC(4-6) PH(4-2) PH(4-3) PH(44) PH(4-5) PH(4-6)
0.002 0.063 0.076 0.027 -0.034 -0.047 0.102 0.124 0.037 -0.073 -0.095
0.210 0.173 0.124 0.111 0.148 0.197 0.183 0.096 0.076 0.138 0.225
-0.029 -0.055 -0.030 0.021 0.046 0.021 -0.095 -0.050 0.041 0.086 0.042
4 . 3 (8) 4 . 3 (8) 5 . 9 (9) 6 (1) 6 . 4 (9) 4 . 2 (8) 1o c 10 10 10 10
CBHS(5) PC(5-1) PC(5-2) PC(5-3) PC(5-4) PC(5-5) PC( 5-6) PH(5-2) PH(5-3) PH(5-4) PH(5-5) PH(5-6)
0.084 0.078 0.165 0.259 0.266 0.178 0.005 0.160 0.366 0.339 0.184
0.287 0.302 0.317 0.317 0.303 0.288 0.301 0.328 0.329 0.304 0.277
-0.104 -0.164 -0.191 -0.158 -0.099 -0.072 -0.189 -0.237 -0.179 -0.073 -0.025
3 . 2 (7) 5.0 (9) 8 (1) 8 (1) 6 (1) 5.9 (9) lo< 10 10 10 10
0.257 0.221 0.213 0.242 0.279 0.287 0.198 0.184 0.236 0.301 0.315
-0.119 -0.164 -0.205 -0.202 -0.157 -0.116 -0.167 -0.240 -0,233 -0.154 -0.081
4 . 6 (8) 6 . 0 (9) 5 . 8 (9) 5 . 5 (9) 7 (1) 5 . 4 (9)* 1o c 10 10 10 10
CeH5(6) PC(6-1) PC(6-2) PC(6-3) PC(6-4) PC(6-5) PC(6-6) PH(6-2) PH(6-3) PH(6-4) PH(6-5) PH(6-6)
1oc 10 10 10 10
B
Atom
-0.130 -0.124 -0.207 -0.296 -0.301 -0.218 -0.055 -0.203 -0.360 -0.370 -0.222
L
0 I020 0.063
0.086
Rigid-Body Parametersd Group
X
Y
z
@
0
P
CeH5(1) CsH5(2) CRH5( 3) CeH5(4) C&5(5) C&5(6)
0.1396 (9) 0.028 (1) -0.234 (1) 0.0145 (9) 0.172 (1) -0.213 (1)
0.3841 (6) 0.4311 (4) 0.4200 (6) 0.1605 (6) 0.3023 (4) 0.2496 ( 5 )
0.1008 ( 5 ) -0.1169 (6) 0.0433 (6) -0,0042 (6) -0.1312 (7) -0.1604 (6)
- 173.8 (7)
-177.4 (8) -156.5 (8) 144.9 (7) -134.5 (7) -120.6 (8) 153.4 (8)
132.5 (5) -116.3 (7) -27.1 (9) -35.3 (9) 59 (1) -47.8 (7)
-82.7 (7) -8 (1) 69 (1) - 107 (1) -142.4 (8)
a Estimated standard deviation of last significant figure is given in parentheses. * Temperature factors were fixed and the scale factors for the scattering factors were varied. The final scale factors are: 0.56 ( 5 ) for CM (corrected for the special position) and 0.49 (1) for C1. c The isotropic thermal parameters for the hydrogen atoms of the phenyl groups were held constant throughout the refinement. d See ref 29, 30, and 37.
in the structure of each MnFe(CO)9 segment of MnzFe(CO)14,47,48 and in the structures of the ReMn(CO)9
segment of RezMn(C0)14H47s49 and of the Rez(C0)9 segment of Re3(C0)14H.47,50
(47) The MntFe(CO)14 molecule4* may be constructed in “tinkertoy” fashion by the trans-octahedral addition of two Mn(C0)a ligands to a planar Fe(CO)4 fragment to give a molecule of Dah symmetry, in which the four equatorial carbonyl groups attached to each octahedrally coordinated manganese atom are staggered relative to the four equatorial carbonyl groups of the central iron atom. On the other hand, the Fellmann-Kaesz trimetallic hydrido complexes Re2Mn(CO)14H48 and Rea(CO)laH60 have a nonlinear trinuclear metal framework which may be visualized in terms of each of the three metal atoms being in an
octahedral-like environment, with the central Re(C0)r fragment cis-disubstituted with a M(CO)s group (M = Mn or Re) and a HRe(C0)s fragment. (48) P. A. Agron, R. D. Ellison, and H. A. Levy, Acta Crystallogr., 23, 1079 (1967); E. H. Schubert and R. K. Sheline, 2. Naturforsch. E, 20,
Handy, Ruff,Dahl
1306 (1965). (49) H. D. Kaesz, R. Bau, and M. R. Churchill, J. Amer. Chem. Soc., 89, 2775 (1967); M. R. Churchill and R. Bau, Inorg. Chem., 6, 2086 (1967).
1 Structural Characterization
of [M2(CO)la]zand [Cr2(CO)loHl-
7320 Table V. Final Parameters for [PPN]2[Mo2(CO)lo]CH2C1p Atom
Mo( 1) Mo(2) C(1-1) O(1-1) C(2-1) O(2-1) (31-2) O(1-2) C(l-3) 0(1-3) C(2-2) O( 2-2) C(2-3) 0(2-3) C-M
c1
P(1) P(2) N
X
Y
0 0 0 0 0 0 0.077 (3) 0.125 (2) 0.128 (3) 0.196(2) -0.144 (3) -0.230 (2) -0.038 (3) -0,060(2) 0 0.078 (2) -0.0311 (6) -0.0214 (6) -0.049 (2)
CeHs(1) PC(1-1) PC( 1-2) PC(1-3) PC(l-4) PC(1-5) PC(1-6) PH(1-2) PH(1-3) PH(1-4) PH(1-5) PH(1-6)
L
0.0875 (2) 0.25 -0.0315 (3) 0.25 0.158 (3) 0.25 0.203 (2) 0.25 -0.106 (3) 0.25 -0.151 (3) 0.25 0.080 (1) 0.187 (2) 0.0701 (8) 0.143 (1) 0.082 (1) 0.298 (2) 0.079(1) 0.336(1) -0.027 (1) 0.265 (1) -0.021 (1) 0.272 (1) -0.026 (2) 0.168 ( 2 ) -0.018(1) 0.144(1) 0.416 (4) 0.25 0.396 (1) 0.291 (1) 0.3691 (4) -0.0017 (4) 0.2718 (4) -0.0648 (4) 0.3108 (9) -0.016 (1)
0.066 0.115 0.193 0.222 0.173 0.095 0.093 0.231 0.282 0.195 0.057
0.377 0.334 0.341 0.390 0.432 0.426 0.297 0.308 0.395 0.470 0.458
0.004 0.100 0.121 0.046 -0.051 -0.072 0.160 0.197 0.062 -0.110 -0,147
0.404 0.422 0.448 0.458 0.440 0.414 0.414 0,462 0 479 0.448 0.400
0.059 0.085 0.129 0.148 0.122 0.078 0.070 0.149 0.182 0.137 0.058
Atom
4 . 4 (1) 5 . 5 (1) 10 (2) 9 (1) 12 (3) 16 (2) 7 (1) 5 . 5 (6) 7 (1) 9.3(8) 5 . 0 (8) 7 . 3 (6) 9 (1) 8 . 1 (7)
Ce"(3) PC(3-1) PC(3-2) PC(3-3) PC(3-4) PC(3-5) PC(3-6) PH(3-2) PH(3-3) PH(3-4) PH(3-5) PH(3-6)
-0.144 -0.197 -0.282 -0.314 -0.262 -0.177 -0.172 -0,323 -0.380 -0.287 -0.136
0.396 0 367 0.386 0.435 0.464 0.445 0.328 0.363 0.450 0.503 0.468
0.024 0.063 0.087 0.072 0.033 0.009 0.075 0.117 0.091 0 021 -0.021
C6Hd4) PC(4-1) PC(4-2) pc(4-3) pc(4-4) pc(4-5) PC(4-6) PH(4-2) PH(4-3) PH(4-4) PH(4-5) PH(4-6)
0.003 0.062 0.074 o.026 -0,033 - 0.044 0.100 0.120 0.035 -0,070 - 0.090
0.211 0.175 0.127 0.114 0.149 0.198 0.186 0.099 0.076 0.139 0.226
-0.029 -0.056 -0.032 0.019 0.046 0 I022 -0.096 -0.054 0.037 0.086 0.043
C sHd 5 ) PC(5-1) PC(5-2) PC(5-3) PC(5-4) PC(5-5) PC( 5-6) PH( 5-2) PH(5-3) PH(5-4) PH(5-5) PH(5-6)
0.086 0.076 0.160 0.254 0.264 0.179 0.003 0,153 0.320 0.337 0.187
0.288 0.305 0.321 0.320 0.303 0.288 0.306 0.334 0.332 0.303 0.275
-0.106 -0.166 -0.194 -0.162 -0.103 -0.075 -0.190 -0.240 -0.184 -0.079 -0.029
0.260 0.224 0.215 0.242 0.279 0.288 0.202 0.186 0.235 0.301 0.317
-0.121 -0.165 -0.206 -0.202 -0.157 -0.117 -0.169 -0.240 -0.233 -0.154 -0.082
8b
6b 3 . 3 (2) 3 . 8 (2) 3.7 (6) 4 . 0 (8) 5.0 (9) 6 (1) 7 (1) 6 (1) 7 (1) 10' 10 10 10 10
c6H d 2)
PC(2-1) PC(2-2) PC(2-3) PC(2-4) PC(2-5) PC(2-6) PH(2-2) PH(2-3) PH(2-4) PH(2-5) PH(2-6)
I
-0.066 -0.073 -0.125 -0.169 -0.163 -0.111 -0.038 -0.130 -0.209 -0.197 -0.106
B
B
4 . 0 (8) 5 . 0 (9) 7 (1) 6 (1)
C6Hd6) PC(6-1) PC(6-2) PC(6-3) PC(6-4) PC(6-5) PC(6-6) PH(6-2) PH(6-3) PH(6-4) PH(6-5) PH(6-6)
Y
X
-0.126 -0.121 -0,204 -0.291 -0,296 -0,214 -0.053 -0.199 -0.355 -0,364 -0.218
Z
I
t
10c 10 10 10 10
Rigid-Body Parametersd Group
X
Y
z
Q
0
P
CeH5(1) C6Hk2) CeHd3) C6Hd4) C sH :( 5) CsHd6)
0.144 (1) 0.02s (1) -0,229 (1) 0.015 (1) 0.170 (1) -0.208 (1)
0.3832 (7) 0.4310 (5) 0.4155 (7) 0.1623 (7) 0.3042 (5) 0.2514 (6)
0.1034 (6) -0.1178 (7) 0.0480 (7) -0.0052 (8) -0.1344 (8) -0.1612 (7)
-173.9(8) -84.7 (9) - 10 (1) 69 (1) - 110 (2) -142.2(9)
-176.3 (8) - 159.5 (8) 150.1 (9) -133.7 (8) -123.2 (9) 153.3 (8)
134.8 (8) -118.7 (8) -26 (1) -34 ( I ) 5 5 (2) -46.1 (9)
Estimated standard deviation of last significant figure is given in parentheses. b Temperature factors were fixed and the scale factors for the scattering factors were varied. The final scale factors are: 0.44 (6) for CM (corrected for the special position) and 0.44 (2) for cl. See ref 29, The isotropic thermal parameters for the hydrogen atoms of the phenyl groups were held constant throughout the refinement. 30, and 37,
(b) Estimation of Chromium and Molybdenum Radii. One-half of >he metal-metal single-bond distanc: which is 1.48 A for the [Cr2(CO),,]2- anion and 1.56 A for the [ M O ~ ( C O ) ~ anion ~ ] ~ - may be taken as the covalent metal radius. Although there are no previous direct evaluations of a covalent chromium radius in the sense of one-half of a Cr-Cr distance, from the
Cr-N bond lengths in the compound cis-Cr(dien)(COd3 Cotton and Richardson6' estimated a value of 1.48 A, which is in excellent agreement with the value obtained in this work. However, a similar estimate of the molybdenum radius based on the isostructural coompound ci~-Mo(dien)(C0)~52 gives a value of 1.62 A which
(50) R. P. White, Jr., T. E. Block, and L. F. Dahl, submitted for publication.
(1966).
(51) F. A. Cotton and D. C . Richardson, Inorg. Chem., 5, 1851 (52) F. A . Cotton and R. M. Wing, ibid., 4, 314 (1965).
Journal of the American Chemical Society / 92.25 / December 16, 1970
7321 Table VI. Intramolecular Distances (A) and Angles (deg) for [PPN]2[M~(CO)lo].CH2C1~ ( M = Cr, M o ) ~ M = Cr A.
M( 1)-M( 2)
Bond Lengths Metal-Metal 2.97 (1)
3.123 (7)
M(l)-C(1-2) M( 1)-C( 1-3) M( 2)-C( 2-2) M( 2)-C( 2-3)
Metal-Equatorial Carbon 1.81 (4) 1.87 (4) 1.97 (4) 1.82 (4)
M(1)-C(1-1) M( 2)-C( 2-1)
Metal-Axial Carbon 1.79 ( 6 ) 1.90 (9)
1.87 (av)
.
3.02 (av)
C( 1-l)-O( 1-1) C(1-2)-0(1-2) C( 1-3)-O( 1-3) C(2-1)-0(2-1) C(2-2)-0( 2-2) C( 2-3)-O( 2-3)
Carbon-Oxygen 1.14 (6) 1.21 (3) 1.15 (3) 1.11 (8) 1.06 (4) 1.23 (3)
1
9
1.90 (av) 3.04 (2) 3.13 (3) 3.16 (3) 3.09 (3) 3.10 (av)
3.08 (av) 1.17 (7) 1 .24 (4) 1.18 (4) 1 . 1 9 (8) 1.18 (3) 1 . 2 3 (4)
1.15 (av) Phosphorus-Nitrogen 1.59 (2) 1.55 (2)
Phosphorus-Phenyl Carbon-1 P( 1 )-PC( 1-1) 1.78 P( l)-PC( 2-1) 1.78 P( l)-PC( 3-1) 1.77 P(Z)-PC(4-1) 1.77 P(2)-PC(5-1) 1.80 P(2)-PC(bl) 1.81 1.78 (av) Methylene Chloride 1.46 (3)
1 .20 (av)
1.57 (av) 1.82 1.80 1.80 1.80 1.81 1.83 1.81 (av) 1.44(4)
B. Bond Angles Metal-Metal-Equatorial Carbon M(2)-M( 1)-C( 1-2) 84 (1) 84 (1) M(2)-M( 1)-C( 1-3) 89 (1) 86 (1) M( 1)-M(2)-C( 2-2) 87 (1) 86 (1) M( l)-M(2)-C(2-3) 87 (1) 86 (1) 87 (av) ~
86 (av)
Metal-Carbon-Oxygen M(1)-C( 1-2)-O( 1-2) 173 (3) 173 (3) M(1)-C( 1-3)-0( 1-3) 175 (4) M( 2)-C(2-2)-0(2-2) 172 (3) M( 2)-C(2-3)-0( 2-3)
173 (3) 168 (4) 176 (3) 174 (4) 173 (av)
Phosphorus-Nitrogen-Phosphorus P( 1)-N-P( 2) 137 (1) 137 (2) Nitrogen-Phosphorus-Phenyl N-P(1)-PC( 1-1) 111 N-P( 1)-PC(2-1) 114 N-P( 1 )-PC( 3-1) 111 N-P( 2)-PC(4-1) 109 N-P( 2)-PC( 5-1) 115 N-P( 2)-PC(6-1) 113
Carbon-1 110 113 109 108 116 112
Phenyl Carbon-1-Phosphorus-Phenyl PC( 1-1)-P( l)-PC(2-1) 107 PC( 1-1)-P( 1 PPC(3-1) 108 PC(2-1)-P(l)-PC(3-1) 107 PC(4-1)-P( 2)-PC( 5-1) 107 PC(4-1)-P( 2)-PC(6-1) 105 PC(5-1)-P(2)-PC(6-1) 107 107 (av)
Carbon-1 109 107 109 108 105 106 107 (av)
Phosphorus-Phenyl Carbon-1-Phenyl Carbon-4 P( l)-PC( l-l)-PC( 1-4) 179 177 P( l)-PC(2-1)-PC(2-4) 177 177 P(l)-PC( 3-1)-Pc(3-4) 175 176 P( 2)-PC(4-1)-PC(4-4) 175 174 P(2)-PC(S-l)-PC(5-4) 176 175 P(2)-PC(6-1)-PC(6-4) 177 177
1.58 (2) 1.56 (2)
1.57 (av)
CM-Cl
1 . 9 0 (av)
3.03 ( 5 ) 3.14 (7)
2.97 (av)
P( 1)-N P(2W
Equatorial Carbon-Metal-Equatorial Carbon C( 1-2)-M(l)-C( 1-3) 85 (1) 84 (2) C(2-2)-M(2)-C(2-3) 88 (1) 88 (1)
173 (av)
Metal-Equatorial Oxygen M(1). . *0(1-2) 3.01 (2) M(1). *0(1-3) 3.02 (3) M(2). . .0(2-2) 3.03 (3) 3.04 (3) M(2). .0(2-3)
M( 1). O( 1-1) M(2). * .0(2-1)
M = MO
M = Cr
86 (av) 1.81 (4) 1.96 (4) 1 . 9 8 (3) 1.86 (4)
1.86 (7) 1.95 (9)
1.84 (av)
Metal-Axial Oxygen 2.93 (4) 3.01 (6)
M = MO
176 (av) Cl-CM-Cl
Chlorine-Carbon-Chlorine 129 (6)
176 (av) 137 (8)
C. Nonbonding Distances within the M(CO)s Fragment C(1-1). * .C(1-2) 2.69 ( 5 ) C(l-l)...C(1-3) 2.62 ( 5 ) 2.79 (7) C(2-1). * .C(2-2) C(2-1). * ‘C(2-3) 2.70 (7) C(1-2). . .C(1-3) 2.50 (4) C( 2-2) * . * C( 2-3) 2.63 ( 5 )
2.72 (7) 2.80 (7) 2.87 (7) 2.80 (8) 2.53 ( 5 ) 2.66 ( 5 )
between M(CO,s Fragments C(l-2). * *C(2-3) 3.06 ( 5 ) C( 1-2) . .(32-2’) 3.01 ( 5 ) C(1-3). . *C(2-2’) 3.17 ( 5 ) C(1-3). . *C(2-3’) 3.15 ( 5 ) O(1-2) * * 0(2-3) 3.26 (3) O(1-2). *.0(2-2‘) 3.24 (3) O(1-3). * .0(2-2’) 3.49 (4) 0(1-3). . .0(2-3’) 3.32 (4)
3.20 ( 6 ) 3.11 ( 5 ) 3.20 ( 5 ) 3.20 (6) 3.42 (3) 3.30 (3) 3.59 (4) 3.36 (4)
86 (av) ~~~~
Estimated standard deviation of the last significant figure is given in parentheses.
is 0.06 A larger than that derived from the [ M O ~ ( C O ) ~ ~ ] ~value of 1.61 A obtained from the molybdenum-moanion. This difference in derived molybdenum radius, lybdenum distance in [ M O ( ~ ~ - C ~ H ~ ) (isCinO good )~]~~~ which is difficult to explain in view of the agreement agreement with the value derived from cis-Mo(dien)obtained for the chromium radius from the similarly (CO),. Stevenson and Dah153 pointed out that this related chromium compounds, deserves some comment. (53) D. L. Stevenson and L. F. Dahl, J . Amer. Chem. SOC.,89, 3721 Numerous other estimates have been made of a mo(1967), and references therein. lybdenum radius for a variety of formal oxidation (54) F. C. Wilson and D. P. Shoemaker, J . Chem. Phys., 27, 809 states with values ranging from 1.44 to 1.64 A.53 The (1957). Handy, Ruff, Dahl
1 Structural Characterization of [ M ~ ( C O ) ~ Oand ] ~ - [Cr~(CO)~orrl-
7322
range of values for the molybdenum radius supports the premise that the type of substituents attached to the molybdenum atom, and in partiuclar their steric and charge acceptor properties, is a more important factor in determining the resulting bond lengths used to obtain the metal radius than the particular formal oxidation state assigned to the metal. Hence, unknown differences in nonbonding ligand-ligand interactions due to differing steric compression effects prevent ,a meaningful rationalization of the difference of 0.05 A in the molybdenum radii obtained from onehalf the Mo-Mo electron-pair bond lengths in the [MO,(CO)~~]*anion and in [Mo(h5-C5H5)(CO)&. For identical structures where steric effects can be neglected, it is qualitatively expected that ligands which reduce the negative charge localized on the metal will cause a contraction of the metal orbitals, thus reducing the internuclear separation for maximum overlap (more rigorously minimum molecular energy). The metal-metal bond length changes in the two pairs of isoelectronic dinuclear metal complexes [Fez(co)8]2--coZ(co)8 (nonbridged) and [Cr,(CO)lo]2-Mnz(CO)lo together with the essential invariance of metal-metal bond lengths in phosphine-substituted Mn2(CO)lo and CO,(CO)~complexes provide a means of assessment of the influence of the stereochemistry of each type metal carbonyl species on the degree of electron delocalization from the metal atoms of different coordination. Although the Co-Co distance for the non-carbonyl-bridged CO,(CO)~ t a ~ t o m e r , ; ' ~ - ~ which is isostructural with the [Fe2(CO)8]2-anion, has not been directly determined, X-ray diffraction studies60+? of three nonbridged phosphine-substituted cobalt carbonyl homologs CO.?(CO)~R, (where R represents P(n-C4H9)3,5Q-61 P(0C6H5)3,62 and P(C6Hj)362)showed rather unexpectedly that the cobalt--cobalt bond lengths in these three molecular complexes areo all experimentally equivalent (of range 2.66-2.67 A) despite a significant variation of 0.1 A being observed62in the ( 5 5 ) Each metal atom in the [Fez(C0)8]z- anion50 and in the noncarbonyl-bridged isomer of Co~(C0)s(i.e., the nonbridged form exists only in solution in equilibt ium with the carbonyl-bridged form)&' as well as in mono- and disubstituted cobalt carbonyl phosphine complexes (with one or both axial carbonyl groups replaced by a phosphine 1igand)bs has a localized trigonal-bipyramidal environment with the two halves of the dimeric molecule linked along their trigonal axes by a direct metal-metal bond such that the two sets of threeequatorial carbonyl groups are arranged in a staggered conformation with each other. X-Ray anaIyses56,53-62 have shown the geometries of the [Fez(CO)8Izanion and of the common Coz(C0)aPz fragment in each of the disubstituted cobalt carbonyl complexes to conform approximately to D3,3-32/m symmetry. The Co-Co distance in the carbonyl-bridged isomer (i,e., the low-temperature solution and solid-state form of Cor(CO)s) was found from an X-ray studyC3 to be 2.524 =!= 0.002 A. (56) 0. S. Mills, private communication to L. F. Dahl, 1961; the Fe-Fe bond length was originally given as 2.88 A; subsequently, a refinement of the structure of the salt [Fe(en)3l[Fe~(CO)a](F.S. Stephens, Acta Crystallogr., Sect. A , 21, 154 (1966)) was found to result in an FeFe bond length of 2.75 Afor the anion: F. S . Stephens and 0. S. Mills, private communication to L. F. Dahl, 1970. (57) (a) I
