Inorg. Chem. zyxwvu 1986, zyxwvu 25, zyxwvut 3703-3705 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLK 3703 have an average torsional twist of Oo. The present study of the iodo derivative presents an opportunity to further compare the energy of the 6 zyxwvutsrqponm - 6* transition as a function of the halide. This comparison is believed to be particularly meaningful since the three complexes exhibit practically identical structural parameters (see previous section). These absorptions occur at 15 600, 15 300, and 14 100 cm-’ for the chloro, bromo, and iodo derivatives, respec- tively. These values are taken from spectra recorded as Nujol mulls on solid samples. An earlier comparison of the ]Al, - ‘Az,, transition energy for three other related chloro and bromo com- plexes led to an average energy difference of 600 ~ m - ’ . ~ Our work shows that the transition for Mo214(dppm), is considerably red- shifted from those of the chloro and bromo analogoues. Pre- sumably there are interactions between the halogen p“ and dn orbitals and the metal-metal 6 and 6* orbitals, and these differ on going from chloride to bromide and then to iodide. Acknowledgment. We are grateful to Prof. R. A. Walton for helpful discussions and for sending us a copy of his manuscript prior to publication. We also thank the National Science Foundation for support. Supplementary Material Available: Full tables of bond distances and angles and a listing of anisotropic displacement parameters (5 pages); a listing of observed and calculated structure factors (20 pages). Ordering information is given on any current masthead page. Contribution from the Department of Chemistry and Laboratory for Molecular Structure and Bonding, Texas A&M University, College Station, Texas 77843 Products of the Reaction between Mo214(C0)8 and zyxwvut Bis(dimethy1phosphino)methane (dmpm). X-ray Crystal Structure of MoI,(CO) (dmpm)2-C7HS F. Albert Cotton* and Rinaldo Poli Received April 7, zyxwvutsrqp I986 The molybdenum(I1) diiodide tetracarbonyl dimer, Mo214(C- 0)8,1 whose synthesis has been recently2 made possible on a large scale, has been found to react with monodentate3 and bidentate3,4 phosphines to afford quadruply bonded dimolybdenum(I1) de- rivatives. Tricarbonyl and dicarbonyl mononuclear intermediates were isolated or detected in the bis(dipheny1phosphino)methane (dppm) reaction. In order to acquire further information on the mechanism of this metal-metal bond formation, we carried out a similar reaction with bis(dimethy1phosphino)methane (dmpm), the results of which are herein reported. Experimental Section All the operations were carried out under an atmosphere of prepurified argon. Solvents were dried by conventional methods and distilled under dinitrogen. M O ~ I ~ ( C O ) ~ was prepared as described elsewhere.2 The dmpm ligand was purchased from Strem Chemicals and dissolved in toluene to give a 1.2 M solution, which was then used directly. Spec- trometers: UV-visible, Cary 17; IR, Perkin-Elmer 783. Solution IR spectra were recorded on an expanded abscissa scale and calibrated with both CO(g) and water vapor. Reaction of MO~I~(CO)~ with dmpm. MO~I~(CO)~ (0.41 g, 0.44 mmol) was dissolved in 25 mL of toluene and treated at room temperature with 0.96 mmol of dmpm. An immediate reaction took place with evident gas evolution and formation of a flocculent yellow solid suspended in an orange solution. The solution had IR bands at 2070 vw, 2016 w, 1939 s, 1920 m, 1898 ms, and 1855 m cm-I. The mixture was refluxed for 24 h and then filtered hot and cooled to room temperature. Further cooling to -20 OC gave, over a period of 24 h, a mixture of emerald green and red crystals. A red crystal from this crop was used for the X-ray dif- fraction study. The two compounds were separated by handpicking. (1) Colton, R.; Rix, C. J. Aust. J. Chem. 1969, 22, 305. (2) (a) Poli, R. “Tesi di perfezionamento”, Scuola Normale Superiore, Pisa, Italy, 1985. (b) Calderazzo, F.; Poli, R.; Zanazzi, P. F., manuscript in preparation. (3) Cotton, F. A,; Poli, R. J. Am. Chem. SOC. 1986, 108, 5628. (4) Cotton, F. A,; Dunbar, K. R.; Poli, R. Inorg. Chem. 1986, 25, 3700. Table I. Crystal Data for M01~(C0)(dmpm)~C~H~ formula fw space group systematic absences zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONM a, zyxwvut A zyxwvu b, A c, .a a, deg fl, deg Z cryst size, mm @(Mo Ka), cm-’ data collecn instrument radiation (monochromated in incident beam) orientation reflecns: no., range (20) temp, OC scan method data collecn range, 28, deg no. of unique data, total with F: > no. of parameters refiend transmission factors: max, min Ra quality-of-fit indicator‘ largest shift/esd, final cycle largest beak, e/A dcalcdr qcm3 3.V:) Rwb C18H3612M00P4 742.13 P212I 21 hOO, h # 2n; OkO, k # 2n; 10.331 (3) 11.725 (I) 22.997 (5) 90 90 90 2785 (2) 4 1.77 0.1 X 0.2 X 0.5 28.877 CAD4 Mo Ka (A, = 0.71073 A) 25, 18-33 20 4-50 001, I # 2n w 1483 20 1 99.98, 90.52 0.0406 0.0466 1.128 0.08 0.480 Green compound (1): UV-visible spectroscopic properties (CH2CI2, A , , cm-I (e)) 14400 (1610), 23 900 (7240). Red compound (2): IR (tolu- ene) 1794 cm-I. X-ray Crystallography for M OI~(CO)(~~~~)~.C~H~. Data Collection. A single crystal of approximate dimensions 0.1 X 0.2 X 0.5 mm was mounted in a capillary in the presence of a small amount of its saturated toluene solution. Data collection was carried out at room temperature with the use of an automated CAD-4 diffractometer equipped with monochromated Mo Ka radiation (li = 0.71073 A). No significant change of intensity was observed for three standard reflections monitored throughout the data collection. The data were corrected for Lorentz and polarization effects, and empirical absorption corrections5 based on az- imuthal ($) scans of nine reflections having an Eulerian angle zy x near 90” were applied. Pertinent crystallographic parameters are summarized in Table I. Structure Solution and Refmement. Axial photographs and systematic absences from the data uniquely determined the space group as the orthorhombic P212121.The structure was solved and refined by using the Enraf-Nonius Structure Determination Package. The positions of the heavy atoms were determined by direct methods, and full-matrix least- squares refinement followed by a difference Fourier map revealed the positions of all the other non-hydrogen atoms. Subsequent anisotropic refinement was carried out independently on both enantiomers. The one reported here is the one that converged to the lowest R value. The hydrogen atoms were not included in the refinement. Table I1 contains positional and thermal parameters for compound 2. Selected bond dis- tances and angles are reported in Table 111. Results and Discussion The reaction of M O ~ I ~ ( C O ) ~ with dmpm is very fast at room temperature; CO evolution occurs, and carbonyl products are formed, among which Mo12(CO),dmpm and M01~(CO)~(dmpm), have been recognized. Their identification is based on the com- parison of the CO stretching vibrations of the resulting toluene solution (see Experimental Section) with those of the corresponding dppm compounds. The bands at 2016 w, 1939 s, and 1898 ms cm-I are therefore assigned to the M01~(CO)~dmpm species (cf. (5) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr., Secr. A: Cryst. Phys., Diff, Theor. Gen. Crystallogr. 1968, A24, 351. 0020-1669/86/1325-3703$01.50/0 0 1986 American Chemical Society