Inorg. Chem. 1985, 24, 3965-3968 Table 11. Geometrical Parameters for CrC12 (Estimated Total Errors in Parentheses; Footnotes As in Table I)
rg(Cr-cIhean? A
model I b 2.207 (7)
model 2c 2.208 (8)
rg(Cr-CI), A l(Cr-CI), A K(Cr-C1), A3 r,(CI--CI), A l(Cl...CI), A L(CI-Cr-Cl), deg re1 monomer amt, %
Monomer 2.207 (10) 0.090 (3) 4.5 x 10-5 (18) 3.612 (44) 0.256 (48) 109.8 (24) 72 (5)
2.200 (1 1) 0.089 (3) 4.3 x 10-5 (16) 3.644 (44) 0.266 (50) 111.8 (25) 73 (5)
r&Cr-CIJ, A l(Cr-CI,),e A r*(Cr-CIb), A [(cr-clb)! A L(CIb-Cr-Clb), deg
Dimer 2.207 0.090 2.353 (10) 0.120 82.0 (7)
2.230 0.089 2.357 (10) 0.119 82.8 (8)
Calculated Mean Amplitudes of Vibrationf linear model bent model (exptl geom) 0.090 0.087 0.121 0.280 calculated for the linear geometry coincides with the one determined experimentally for linear FeCI2, 0.1 19 A.'O Chromium Dichloride. The experimental radial distribution (Figure 4) as well as the mass spectra indicated a large relative abundance of the dimeric species. The refinement eventually showed a 30% presence for the dimeric species. Considering the larger relative weight of the dimer vs. the monomer as regards scattering power, this situation considerably hindered the determination of an accurate structure for CrCI,. On the other hand, our early hope for a more detailed elucidation of the dimer geometry did not prove feasible because of the strong correlation among the parameters. The refinements again yielded a highly bent geometry for the monomer; the results are compiled in two parameter sets in Table 11, similarly to those for vanadium dichloride. It has been tested thoroughly whether or not the experimental data could be approximated by a model in which the monomer was linear. In fact, an earlier electron diffraction report on chromium dichloride*O communicated 2.20 ( I ) and 4.34 (5) A for the Cr-CI bonded and CI--Cl nonbonded distances which in turn yield a 161' bond angle. This, taking into account the probable shrinkage," would correspond to a linear equilibrium geometry. There is, in fact, a peak at 4.25 A on our radial distribution curve (Figure 4), which could correspond to the CI-CI interaction of a linear monomeric CrC12 molecule. Assuming the CI-CI distance to appear in this peak and constraining it at various values, we refined its amplitude to very large values (0.37 A), which is unrealistic for a linear molecule according to our earlier experience'O and to the calculated values given in Table 11. In this model the geometry of the dimer had to be taken such that its main nonbonded contribution, the CI,..CIb distance, shifts from the 4.25-A peak to the 3.4-A one (see curve b in Figure 4, where the corresponding part of the radial distribution curve of this model, together with the experimental curve, is indicated). This could only be achieved with unrealistically tilted terminal bonds for the dimer. In this model the CPCI, nonbonded distance of the dimer shifts from the 5.4-A peak to the 4.25-A one, causing marked disagreement between the experimental and theoretical distributions. Moreover, when the CI-CI distance of the monomer was allowed to vary, it shifted to the maximum at 5.4 A, rendering the model meaningless.
Discussion O u r high-temperature gas-phase electron diffraction d a t a a r e consistent with highly bent shapes of the vanadium dichloride and chromium dichloride molecules. This result represents a challenge to t h e spectroscopist t o determine t h e v 1 symmetric stretching frequency in the infrared spectrum. I t also represents a challenge to the theoretical chemist to account for the structural differences among the dichlorides of first-row transition metals. Quantumchemical calculations on manganese dichloridez1suggest that there are two orbitals with substantial d character that markedly change their energy on bending; they are the u (dZ2)and one of the K (dJ orbitals of the linear molecule. T h e energy of the first decreases (20) Kupreev, A. V., unpublished results. (21) Hargittai, M.; Rossi, A. Inorg. Chem., in press.
0020-166918511324-3965$01.50/0
3965
a n d t h a t of the second increases upon bending. Thus, the bent geometry of VClZa n d CrClz could be rationalized with a n electronic configuration in which the dyzorbital would be empty and the d,z orbital half-filled, and t h e molecules would favor a bent geometry with a lower total energy than for t h e linear configuration. Unfortunately, these systems a r e not easily amenable t o sophisticated calculations, which is especially demonstrated by t h e uncertainties in the determination of the bond lengthsz' Reliable information even merely on the bond length differences could facilitate a better utilization of the available experimental data. A more accurate determination of the bond lengths of these dihalides from the experiment is hindered by the lack of knowledge of the difference between the lengths of t h e monomer bond and the terminal bond of the dimer. Further vibrational spectroscopic information would also enhance the utility of our electron diffraction data. Acknowl&gment. W e express our gratitude to Professor Harald Schafer, University of Miinster, for t h e samples of vanadium dichloride and chromium dichloride. W e appreciate the advice and encouragement from Prof. L. V. Gurvich and Prof. I. Hargittai and some auxiliary computations by Dr. B. Rozsondai. Registry No. VCI2, 10580-52-6; CrCI2, 10049-05-5. Supplementary Material Available: Listings of total electron diffraction intensities for two camera distances (50 and 19 cm) for both compounds (2 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
Replacement of Acetate Ions in Dimolybdenum Tetraacetate by Acetonitrile Molecules: Crystal Structures of Two Compounds Containing the cis -[MO~(O,CCH~)~(CH~CN)~]~' Cation F. Albert Cotton,* Austin H. Reid, Jr., and Willi Schwotzer
Received August 6, 1984 Over a number of years the reactions of dimolybdenum(I1) carboxylates, especially the acetate, MoZ(OzCCH3),,with strong acids have provided synthetic routes t o many other compounds having the Moj' binuclear cation a t the center.' Doubtless the most important of such reactions is the one2 used t o obtain t h e [MozCl8I4-ion, from which scores of other Mo?' compounds are then prepared. There have also been several efforts, with varying degrees of success, to replace carboxylate groups with weakly coordinating anions (e.g., C F 3 S 0 3 - ) or with neutral ligands so as to obtain highly reactive complexes t h a t might be of use synthetically. Bowen and Taube3 were able to obtain the Mo:'(aq) ion and to form the [ M ~ ~ ( e n ) ~ ]complex, ,' but neither of these cationic species has been obtained in a crystalline compound suitable for X-ray crystallographic characterization. Abbott and co-workers have studied reactions of M o ~ ( O ~ C C H with ~ ) CF3S03H4 ~ and later of Mo2(0,CH), with CF3S03H.5 T h e former yielded, ( 1 ) Cotton, F. A,; Walton, R. A. "Multiple Bonds Between Metal Atoms"; Wiley: New York, 1982. (2) Brencic, J. V.; Cotton, F. A. Inorg. Chem. 1969, 8, 7, 2698; 1970, 9, 346. (3) Bowen, A. R.; Taube, H. J . A m . Chem. SOC.1971, 93, 3287; Inorg. Chem. 1974, 13, 2245. (4) Abbott, E. H.; Schoenewolf, F., Jr.; Backstrom, T. J . Coord. Chem. 1974, 3, 255. (5) Mayer, J. M.; Abbott, E. H. Inorg. Chem. 1983, 22, 2774.
0 1985 American Chemical Society
3966 Inorganic Chemistry, Vol. 24, No. 23, 1985 apparently, impure forms of M O ~ ( O ~ S C while F ~ ) ~the latter led to [Mo~(H~O)~(O~SCF~)~](CF~SO~)~ from which [Mo2(CH3CN),] (CF3S03), ws reportedly obtained. Again, no crystallographic characterizations were accomplished. A very recent report6 deals with some reactions of Mo2(02CCH3),with the acids C F 3 S 0 3 H and HBF, and describes products to which the following formulas were assigned: [ M O ~ ( O ~ C C H ~ ) ~ ( C H ~ (CCNF )3,S]0 3 ) 2 and [Mo~(O,CCH,)~(CH~CN)~](BF,OH)~. Again, no crystallographic support for these formulations was given. W e are prompted by these reports, especially the most recent one,6 to communicate work carried out some time ago in this laboratory. W e have prepared compounds containing the title cation by two routes, one of which is different from any previously reported in this field, and we have characterized two of these compounds by X-ray crystallography.
Experimental Section
Notes
Table I. Crystallographic Parameters M0204C16H24B2-
Mo2017N4S4F12C20-
FSN6
fw space group systematic absences
613.75 P21fm OkO, k = 2n
a, A b, A
7.129 (4) 10.647 (4) 19.364 (4) 99.17 (4) 1451.1 (8) 2 1.405 0.35 X 0.35 X 0.20 10.715 Enraf-Nonius CAD-4F Mo K a
c, '4 A deg
v,A3
Z dcaldrg/cm3
cryst size, mm
26
1142.56 Pnma
Okl, k + I = 2n; hkO, h = 2n
25.140 (2) 9.652 (5) 13.686 (3) 3320 (3) 4 2.246 0.40 X 0.40 X 0.30 11.256 Nicolet P3/F
~ ( M oKa), cm-I data collection instrument All manipulations were carried out under an argon or nitrogen atmosphere with use of standard Schlenk techniques. All solvents were radiation (monochromated Mo KLY dried by conventional methods and were distilled under argon immediin incident beam) was prepared by the method of Cotton ately prior to use. Mo2(02CCH3).+ orientation reflcns no., 25, 20 < 28 < 30 25, 20.0 < 28 < 35.0 and B r i g n ~ l e . ~Et30BF4(Aldrich) and CF3S03H(3M) were used as range (28), deg received. Infrared spectra were obtained on an IBM IRf85 Fourier temp, OC 22 f 1 22 f 1 transform spectrophotometer. Electronic spectra of acetonitrile solutions scan method 8-28 8-28 of 1 and 2 were recorded on a Cary 17 spectrophotometer. data collecn range, 28, deg 5.0 < 28 < 45.0 5.0 < 26' < 50.0 Preparation of C~~-[MO~(O~CCH~)~(CH~CN)~(~X-CH~CN)~](BF~)~ no. of unique data, total 1404 783 (1). To a stirred suspension of 428 mg (1 mmol) of M o ~ ( O ~ C C Hin ,)~ with F: > 34F:) 30 mL of CH2C12and 1 mL of CH3CN was added 5.0 mL of a 1.0 M no. of parameters refined 197 188 solution of (CIH5),OBF4 in CHZC12.The liquid phase of the yellowish trans factors, max, min 1.000, 0.861 1,000, 0.752 suspension immediately developed a bright red color, and all of the (exptl) suspended Mo2(O2CCH,), went into solution in less than 1 h to give a R" 0.067 0.067 clear, bright red solution. Stirring was stopped at this point, and the 0.085 0.082 Rwb solution was left undisturbed at room temperature overnight. In this way quality-of-fit indicator 1.581 1.569 an essentially quantitative yield of bright red, highly crystalline material largest shiftfesd, final 0.1 1 0.46 was obtained. Electronic spectrum (CH3CN solution): A, at 529 and cycle 372 nm. Infrared spectrum (CH3CN solution): uCN 2293 (m), 2255 (vs) largest peak, e/A3 0.982 0.952 cm-I; vBF4- 1063 (vs) cm-I. Preparation of ~ ~ ~ - [ M O ~ ( O ~ C C H ~ ) ~ ( C H ~ C N ) ~ ( ~ X - O ~ S C F ~ ) ~ ] 5 R = CllFOl - I~cll/CI~ol. * R W = [Cw(lFol - I ~ c l ) 2 / C w l ~ 0 1 2 1 ' / 2w ; (H03SCF3),(THF) (2). To a stirred suspension of 428 mg (1 mmol) of = l/a2(IFoI). cQuality of fit = [Cw(lFol - IFc12)/(Nobscrvns Mo2(O2CCH3),in 25 mL of CH3CN was added 1.5 mL of CF3S03H Npe.ram)I 'I2. by syringe. A bright purple-red solution, which resulted almost immediately, was stirred for 3 h. The volume was then reduced by half under What relationship, if any, there may be between our compound vacuum, and 20 mL of a 1:l mixture of tetrahydrofuran and benzene was 1, [Mo~(O~CCH~)~(CH,CN),I(BF,),, the cation of which has added. The resulting solution was allowed to stand at room temperature been characterized unequivocally by X-ray crystallography, and for 3 days when compound 2 was deposited on large, blocky red-purple the substance formulated by Telser and Drago as [ M o 2 ( 0 2 C C crystals in greater than 90% yield. Electronic spectrum (CH,CN soluH , ) 2 ( C H 3 C N ) 5 ] ( B F 3 0 H ) is 2 hard to say. tion): A,, at 535 and 390 nm. Infrared spectrum (CH3CN solution): It has been our experience that elemental analyses do not afford uCN 2293 (m), 2278 (s) cm-I. Infrared spectrum (CF,S03- solution): u,,(so3) 1155 cm+; Yj(S0j) 1040 cm-I; b ( S 0 , ) 638 cm-l. a satisfactory basis for characterizing precisely the compounds X-ray Details of the crystallographic procedures we have dealt with. Over a dozen attempts, using three different are given as supplementary material. Table I contains information analytical laboratories, gave unreproducible results, none of which pertinent to the data collection and structure refinements. agreed satisfactorily with the formulas established crystalloResults and Discussion graphically or with any other, related formulas. The compounds are extremely sensitive to conditions of handling, tending to dePreparation of Compounds. The method by which compound compose in various ways. 1 was prepared (eq 1) is efficient and leads readily to a pure, The electronic spectra of both of our compounds 1 and 2 are homogeneous, and highly crystalline product. The crystallographic very similar to each other and closely resemble the electronic results, to be discussed in detail below, show that the composition spectra reported by Telser and Drago. For acetonitrile solutions, is [Mo~(O~CCH,)~(CH,CN)~](BF,)~; there are six coordinated 1 has bands at 529 and 372 nm and 2 has bands at 535 and 390 acetonitrile molecules. nm. The infrared spectrum of our compound 1 gave no indication CH2C12 of the B F 3 0 H - ion proposed for one of the Telser and Drago Mo2(02CCH3)4 + 2(C2H5)30BF4 2CH3C02C2H5 + compounds; this is as we would expect since the use of (C22(C,H,)O + [MO~(O~CCH,)~CH~CN)~I(BF~)~ (1 1 H,),OBF, in a nonaqueous medium should unambiguously give CH,CN a BF,-containing product. M02(02CCH3)4 + 4CF3S03H 2CH3C02H The use of ( C 2 H 5 ) 3 0 B F 4as a reagent for removal of acetate [Mo2(02CCH,)2(CH3CN)4(ax-03SCF3)21(CF3SOH)2(2) groups from Mo2(O2CCH3), has further synthetic potential, as we shall report in the future. It can be used, for example, to Our compound 2 was prepared according to reaction 2, whereby prepare [ M O ~ ( C H ~ C N ) ~ ] ( in B Fcrystalline ~)~ form. It seems to a cation containing four C H 3 C N groups was obtained. The afford a more convenient route to the [ M o ~ ( C H , C N ) , ] ~cation + preparation of compound 2 is quite similar to the procedure rethan the reported two-step route,5 in which the formate groups cently reported6 for preparing [ M o , ( O , C C H , ) ~ ( C H , C N ) ~(C] of M o 2 ( 0 2 C H ) , are destroyed by heating with C F 3 S 0 , H . F,SO3)*. Structural Results. The [Mo,(O,CCH,)~(CH,CN)~(~XC H 3 C N ) 2 ] Z ion + in 1 resides on a crystallographic mirror plane, (6) Telser, J.; Drago, R. S . Inorg. Chem. 1984, 23, 1798. which contains both metal atoms and the axial acetonitrile (7) Brignole, A. B.; Cotton, F. A. Inorg. Synth. 1972, 13, 81. molecules. The structure is shown in Figure 1. Positional pa(8) All computing was carried out on a PDP 11/60 computer using the Enraf-Nonius SDP Structure Determination Package. rameters are given in Table 11. The distances and angles are listed
+
Inorganic Chemistry, Vol. 24, No. 23, 1985 3961
Notes
Table IV. Selected Bond Angles (deg) for cis-[Mo,(O,CCH,), (CH,CN),(ax-CH,CN), ] 2 + 0
Mo(l)-M0(2)-0(1) -N(2) -N(4) M0(2)-M0(1)-0(2) -N(1) -N(3) M0(1)-0(2)-C(l) M0(2)-0(1)-C(l) Mo(l)-N(l)-C(3)
90.6 (2) 104.6 (3) 178.2 (2) 91.1 (2) 100.8 (2) 175.0 (6) 118.8 (7) 119.7 (8) 174.7 (9)
Mo(l)-N(3)-C(7) Mo(2)-N(2)-C(5) -N(4)-C(9) 0(1)4(1)-0(2) -C(2) 0(2)C(l)-C(2) N(l)-C(3)-C(4) N(2)-C(5)
