Inorg. Chem. 1983, 22, 1301-1306 ligand molecule. Under these conditions' and
A first-order or a second-order kinetic law for ligand exchange may be obtained as limiting forms of eq 19, depending on the complex investigated.' A second-order kinetic law kNMR = k,Cf is observed in the present case, requiring k2 5o(I): 4668 no. of parameters varied: 443 cryst dec: negligible R = 0.044 largest peak, e/A3: 2 (1 A from osmium atom) temp: 23 "C 0.13 X 0.13 mm). Intensities were collected to 20 = 50° by using the w-scan method. Standard data collection procedures have been summarized el~ewhere.~A total of 7774 intensities were measured; Lorentz and polarization corrections, but not absorption corrections, were applied. The value of A* varied from 1.85 to 2.40. Of the 7774 unique intensities measured, 4668 had I > 540 and were, therefore, considered observed. The structure was solved by Patterson and Fourier methods and refined1° by full-matrix least squares. A three-dimensional Patterson synthesis provided the two osmium atom positions. Following three cycles of isotropic least-squares refinement, the remaining non-hydrogen atoms were located from difference Fourier syntheses. The ether molecule was seen to be disordered into two positions, both of which exhibited a common terminal carbon atom (C(54)). Convergence of refinement (with equal weights) of an anisotropic model with rigid phenyl rings for the dinuclear osmium molecule and isotropic temperature factors and constrained bond distances for the disordered ether molecule (C-C = 1.54 f 0.01 A, C-0 = 1.43 i 0.01 A) produced an R value of 0.044. The disorder of the ether molecule between the two sites was not statistically different from 1:l. The largest shift:error ratio in the final cycle was 0.05 in the dinuclear osmium molecule and 0.7 in a disordered ether molecule. Although a difference peak with a magnitude of about 2 e/A3 was seen at about 1 8, from the osmium atoms, no significant electron density was observed at chemically reasonable distances from the other atoms. Final positional parameters are given in Table 11. Values of F,, vs. F, for the 4668 observed data are available as supplementary material. Physical Measurements. Infrared spectra of Nujol mulls were recorded in the region 4000-200 cm-' with a Beckman IR- 12 spectrophotometer. A Perkin-Elmer R32 90-MHz spectrometer was used to obtain the 'H N M R spectra. Samples were dissolved in deuterated solvents, and resonances were usually referenced internally to tetramethylsilane (Me4Si). X-ray photoelectron spectra (XPS) were recorded with a Hewlett-Packard 5950A spectrometer. Binding energies were internally referenced to a C Is binding energy of 285.0 eV for the carbon atoms of the coordinated tertiary phosphine ligands. Magnetic susceptibility measurements were determined at 22 O C by the Gouy method. Electronic absorption spectra were recorded on dichloromethane solutions with a Varian series 634 spectrophotometer in conjunction with a Varian Model 9176 recorder. Electrochemical measurements were made on dichloromethane and acetonitrile solutions containing 0.2 M tetra-n-butylammonium hexafluorophosphate (TBAH) as supporting electrolyte. Ell*values (taken as (Ep,a+ Ep,,)/2) were referenced to the saturated potassium chloride calomel electrode (SCE) at 22 i 2 OC and were uncorrected for junction
C(171
Figure 1. ORTEP representation of the O S ~ ( ~ - O ) ( ~ - ~ ~ C C H ~ ) ~ C ~ (PPh,)* molecule with the phenyl rings of the PPh3 ligands omitted. A representation of the full structure with the appropriate numbering scheme is available as supplementary material. potentials. Cyclic voltammetry experiments were performed by using a BioAnalytical Systems Inc. Model CV-1A instrument in conjunction with a Hewlett-Packard Model 7035 X-Y recorder. Potential control for coulometric experiments was maintained with a potentiostat purchased from BioAnalytical Systems Inc. Values of n, where n is the total number of equivalents of electrons transferred in exhaustive electrolysis at constant potentials, were calculated after measuring the total area under current vs. time curves for the complete reaction. The reactions were judged to be complete when the current had fallen below 1% of the initial value. All voltammetric measurements were made at a platinum-bead electrode in solutions deaerated with a stream of dry nitrogen. Elemental microanalyses were performed by Dr. C. S. Yeh of the Purdue University microanalytical laboratory, by Chemalytics, Inc., Tempe, AZ, and by Galbraith Laboratories, Inc., Knoxville, TN. The molecular weight measurements were determined by osmometry using dichloromethane as the solvent at 37 O C .
Results and Discussion Synthesis and Spectroscopic Characterizations. The reactions between osmium(V1) complexes of the type transO S O ~ X ~ ( P R ' ,and ) ~ refluxing carboxylic acid-anhydride mixtures provide a high-yield route to a new class of diosmium(1V) complexes of stoichiometry 0 s 2 ( p - 0 ) ( p 02CR)2X4(PR'3)2for X = C1 or Br, R = CH3 or C2H5,and PR'3 = PPh3 or PEt2Ph. These brown crystalline complexes are air stable and show little tendency to undergo simple ligand-exchange reactions with either carboxylic acids or tertiary phosphines." This group of complexes is diamagnetic as judged by magnetic susceptibility measurements on Osz(p-O)(p-02CCH3)2C14(PPh3)z and the sharp resonances in the 'H N M R spectra of all the complexes (details are given in the Experimental Section). Dichloromethane solutions of the complexes exhibit an intense absorption band in their electronic absorption spectra (440-450 nm for X = C1 and 480-490 nm for X = Br), which is charge transfer in origin (log t 4.3). The infrared spectra of Nujol mulls show bands characteristic of carboxylate (e.g., v,,(COO) in the region 1540-1525 (s) cm-') and osmium-halogen bonds ( ~ ( 0 s - X )at 350-340 (s) cm-I for X = C1 and 240-225 cm-' for X = Br) but no absorption that could be assigned to ~(OS-O-OS).~~ An additional property of note, concerns the X-ray photoelectron spectra (XPS or ESCA) of these complexes. The pertinent core electron binding energies of four of these complexes are listed i n T a b l e 111. The measured Os 4f binding
-
(1 1) The reaction between Os2(p-O)(p-02CCH,)2C14(PPh,)2 and tri-n-
(9) Jaecker, J. A.; Robinson, W. R.; Walton, R. A. J . Chem. Soc., Dalton Trans. 1975, 698. (10) All crystallographic computing was performed at the Purdue University Computing Center with use of the program 'SHELX-76 Program for Crystal Structure Determination" by George Sheldrick, University Chemical Laboratory, Cambridge, England, 1977.
propylphosphine in hot toluene led to reduction of the neutral complex to its purple monoanion [OS~(~-O)(~-O~CCH,)~CI~(PP~~)~](as demonstrated by cyclic voltammetry). Workup of this solution afforded a purple solid whose IR spectrum was consistent with the formulation [n-Pr,PHI [Os2(r-O)(p-02CCH,)2C1,(PPh,)21. (12) Full details of the spectroscopic properties of these complexes, can be obtained from R.A.W. upon request.
1304 Inorganic Chemistry, Vol. 22, No. 9, 1983
Armstrong, Robinson, and Walton
Table 11. Positional Parameters and Their Estimated Standard Deviations for Os,(u-0)01-0,CCH,),C14(PPh,),~(C,H j),P)b Y
1'
z
0.14016 (4) 0.24537 (5) 0.2250 (3) 0.3454 (3) -0.0081 (3) 0.2185 (4) 0.3928 (3) 0.2200 (3) 0.2386 (7) 0.0559 (8) 0.1483 (8) 0.0736 (1 I ) -0.0050 (1 3) 0.1013 (7) 0.0502 (9) 0.0391 (12) -0.0567 (13) 0.1 866 (8) 0.1671 (8) 0.1457 (8) 0.1440 (8) 0.1636 (8) 0.1849 (8) 0.1912 (8) 0.0827 (8) 0.0510 (8) 0 1277 (8) 0.2361 (8) 0.2679 (8) 0.3716 (6) 0.4258 (6)
-0.00739 (3) -0.02073 (3) 0.0886 (2) -0.1320 (2) 0.0053 ( 2 ) -0.0982 (2) 0.0571 (2) -0.0249 (2) -0.0166 (4) 0.0646 (5) 0.0759 (5) 0.0919 (7) 0.1506 (9) -0.0783 (5) -0.0896 ( 5 ) -0.1001 (7) -0.1445 (9) 0.0975 (5) 0.0356 (5) 0.0441 (5) 0.1 144 (5) 0.1 763 (5) 0.1678 (5) 0.1790 (4) 0.1972 (4) 0.2663 (4) 0.3172 (4) 0.2990 (4) 0.2299 (4) U.0846 (5) 0.0878 (5)
0.26649 (3) 0.12550 (3) 0.3452 (2) 0.1376 (2) 0.3066 (2) 0.3497 (2) 0.1441 (2) 0.0041 (2) 0.21 72 (4) 0.1 869 (5) 0.1071 (6) 0.1325 (7) 0.0928 (9) 0.0984 (5) 0.1979 (5) 0.1316 (8) 0.0909 (8) 0.4272 (4) 0.4639 (4) 0.5290 (4) 0.5576 (4) 0.5210 (4) 0.4558 (4) 0.3027 (6) 0.2790 (6) 0.2489 (6) 0.2425 (6) 0.2662 (6) 0.2963 (6) 0.3742 (5) 0.3226 (5)
d t on1
atom
X
Y
Z
0.5374 (6) 0.5949 (6) 0.5408 (6) 0.4291 (6) 0.4398 (8) 0.4590 (8) 0.5370 (8) 0.5958 (8) 0.5765 (8) 0.4985 (8) 0.2541 (8) 0.2230 (8) 0.1526 (8) 0.1 133 (8) 0.1444 (8) 0.2148 (8) 0.4303 (8) 0.4606 (8) 0.5292 (8) 0.5676 (8) 0.5373 (8) 0.4686 (8) 0.7025 (15) 0.7474 (36) 0.6908 (32) 0.7568 (22) 0.6989 (22) 0.7318 (24) 0.6374 (39) 0.6264 (20) 0.7339 (17)
0.0903 (5) 0.0896 (5) 0.0863 (5) 0.0838 (5) -0.1414 (6) -0.2104 (6) -0.2183 (6) --0.1571 (6) -0.0880 (6) -0.0802 (6) -0.2106 (5) -0.2491 (5) -0.3086 ( 5 ) -0.3295 (5) -0.2910 (5) -0.2316 (5) 4 . 1 5 1 3 (5) -0.0952 (5) -0.1108 (5) -0.1823 ( 5 ) -0.2384 (5) -0.2228 (5) 0.0085 (10) 0.0359 (15) 0.1008 (15) 0.1643 (14) 0.2312 (12) 0.0642 (17) 0.0889 (22) 0.1671 (23) 0.2038 (12)
0.3433 (5) 0.4156 ( 5 ) 0.4671 (5) 0.4464 (5) 0.0850 (6) 0.0598 (6) 0.0247 (6) 0.0147 (6) 0.0399 (6) 0.0750 (6) 0.1 139 ( 5 ) 0.1661 ( 5 ) 0.1469 (5) 0.0755 (5) 0.0233 (5) 0.0425 (5) 0.2276 (4) 0.2783 (4) 0.3459 (4) 0.3629 (4) 0.31 22 (4) 0.2445 (4) 0.2383 (9) 0.1787 (20) 0.1477 (15) 0.1659 (18) 0.1264 (14) 0.1883 (15) 0.1363 (21) 0.1372 (44) 0.1419 (11)
' Estimated standaid deviations in the least significant digits are shown in parentheses. The ether solvate molecule is disordered in the crystal lattice and can take up either of t\vo positions with a common terminal carbon atom of C(54): (1) C(54)C(55)-0(56)-C(57)-C(58) or (2) C(54)-C(59)-0(60)-C(61 FC(62) Table 111. Core Electron Binding Energies (eV) of Diosmiurn(1V) Complexes'
os CI Br 4f7,,b 2p3,, 3d Os,(p-O)~-O,CCH,),Cl,(PPh,), 53.0 (1.6) 198.8 Os,(p-O)(~-0,CC,H,),C14(PPh,), 52.8 (2.0) 198.5 Os,(~L-O)(p-0,CCH,),Br4(PPh,), 52.5 (2.4) 69.1 69.1 5 3 .O (2 .O) Os, (p-O)(p-O,CC,H 5 ) 2 Br, (PPh,), ' Binding energies referenced to a C 1s value of 285.0 eV for the tertiary phosphine ligands. Full-width at half-maximum (fwhm) values are given in parentheses. complex
Table IV. Important Bond Lengths and Bond Angles with Their Estimated Standard Deviations for OS, ~~-O)(IJ-O,CCH,),CI,(PP~,),.(C,Hj)z@-c Bond Lengths, A Os(l)-C:1(12) 2.332 (4) 0 ~ ( 1 ) - 0 ~ ( 2 ) 3.440 (2) Os(l)-P(l) 2.374 (3) 1.830 (10) Os(l)-O(l) 0~(2)-0(11) 2.131 (10) 1.828 (9) 0~(2)-0(1) 0(10)C(12) 1.260 (19) 0~(1)-0(10) 2.083 (9) 0(11)-C(12) 1.252 (20) 0~(1)-0(15) 2.118 (9) C(12)
