Inorg. Chem. 1986, 25, 3706-3707
3706
Contribution from t h e Department of Chemistry, University of Delaware, Newark, Delaware 197 16
Crystal and Molecular Structure of Rhenium Manganese Decacarbonyl, ReMn(CO),, Containing an Unexpectedly Short Re-Mn Bond Arnold L. Rheingold,* Wilma K. Meckstroth,t and Douglas P. Ridge Received March 25, 1986
Heterobimetallic complexes have been prepared in increasing profusion in t h e last decade in a search for new catalytic properties.l In many instances these preparative studies include t h e first crystallographic characterization of a new metal-metal bond. Only four structures containing a Mn-Re bond have been reported (see Results and Discussion). The earliest is t h a t of t h e decacarbonyl MnRe(CO)10,2which could reasonably serve as the reference s t r u c t u r e for o t h e r Mn-Re bonded systems. This structure, reported in 1967, was apparently carried o u t in the wrong space group (Iu, instead of I2/a) with unit cell esd's 1 order of m a g n i t u d e greater t h a n commonly available today. Additionally, no crystallographic methodology was reported and t h e M n - R e bond distance, 2.96 A, is given without an e s t i m a t e of error. Churchill et al. recently accurately redetermined t h e homoatomic structures of M I - I ~ ( C Oand ) ~ ~Re2(CO)lo,3and Martin et al. reported a low-temperature structure for Mn2(CO)10.4We now report t h e redetermination of t h e MnRe(CO)lo structure. Experimental Section MnRe(CO),o was prepared by published procedures' and purified by sublimation. Mass spectral characterization of the sample used for crystallographic work showed no peaks corresponding to Mn2 or Rez fragments. A well-formed brick-shaped specimen was selected for data collection and found to diffract strongly. Crystal mounting and the measurement of unit cell parameters were accomplished by procedures previously employed.6 Table I provides crystal data as well as details of the data collection and refinement. Corrections were applied to the intensity data for Lp effects and absorption (empirical, $-scan, fitted to six-parameter ellipsoidal model, seven reflections, 252 data, 9' S 28 < 36'; R(int,before) = 4.2%, R(int,after) = 1.7%). An initial phasing of the data was obtained by using the metal atom coordinates from the Re2(CO)loi ~ o m o r p h . ~ As required, the structure is disordered in metal atom identity, and the asymmetric unit consists of an M*(CO)' fragment, M* = an Mn/Re composite, with the fragments related by a crystallographic twofold rotational axis. Four strategies for dealing with the metal atom disorder were refined to convergence with all atoms anisotropic: (1) half-occupancy Mn and Re atoms without positional or temperature factor constraint; (2) one Re atom with a refined occupancy of 0.657 (compared to a theoretical [(Z,, + ZMn/2)/ZR, = 0.6671 "occupancy"); (3) one "rhenganese" atom with linearly interpolated composite scattering factors at full-occupancy; (4) half-occupancy Mn and Re atoms with all positional and thermal parameters refined as single, linked variables. Some comparative results of the four strategies are given in Table 11, which reveal that, with the exception of strategy 1, there are only insignificant differences in the final parameters and no differences in the chemical information obtained from the results. Electron density plots, Figure 2, show a tightly and essentially spherically contoured metal atom, invalidating strategy 1 at the available "resolution", d = X/2 sin 8 = 0.8 A. Although strategies 2, 3, and 4 yielded chemically identical results, we report the detailed results of strategy 4 because of the lower residuals and the use of unapproximated atomic form factors. Atomic coordinates and temperature factors are given in Table 111 and bond distances and angles in Table IV.
Results and Discussion Figure 1 shows the expected a p p r o x i m a t e D4ds y m m e t r y of MnRe(CO)],,. MnRe(CO)lois isomorphous with the three group 7 homometallic decacarbonyls. A crystallographic twofold rotational axis is perpendicular to t h e midpoint of the M-M' vector. The crystallographic results appear indistinguishable from those expected for a homometallic decacarbonyl with m e t a l a t o m
'The Ohio State University-Newark, Newark, OH 43055.
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Table I. Crystal, Data Collection, and Refinement Parameters for MnRe(CO),, (a) Crystal Parameters MnReCloOlo 2 521.2 v,A' monoclinic D(calcd), g I2/a p(Mo Ka), cm-I 14.390 (4) temp, K 7.112 (2) cryst dim., mm 14.736 (3) cryst color 105.54 (2)
formula fw cryst syst space group a, A b, A c, A P, deg diffractometer radiation (A,
A)
X
0.39
(b) Data Collection Nicolet R3 octants collcd *h,+k,+l Mo Ka no. of rflns collcd 1637 (0.71073) graphite no. of unique rflcns 1427
monochromator 28 range, deg 4 5 28 5 53 scan range, [1.8 + (Ka, K4l deg 8-28 scan type scan speed deg var, 4-10 min-'
a
4 1454.9 (7) 2.379 97.7 295 0.30 X 0.35 pale yellow
RF.%'
3.26
R,F, Yc GOF AI0 data/param
3.67 1.06 0.004 11.8
R(int), % 1.84 no. of unique rflns, 1203 F, 2 20(F0) T max, T min 0.059, 0.033 stds/reflns 3/97 (
