1877
Metal Ion-Aromatic Complexes. 111. The Crystal and Molecular Structure of C,H; CuAlC1, R. W. Turnerla and E. L. Ammalb Contribution f r o m the Department of Chemistry, University of South Carolina, Columbia, South Carolina 29208. Received January 10, 1966 Abstract: A new benzene complex, C6H6.CuALCI4, has been synthesized and its structure determined by threedimensional, single-crystal X-ray diffraction techniques. Cu(1) is in a distorted tetrahedral environment with three metal-to-chlorine bonds and one n-type metal ion-aromstic interaction. The three Cu-Cl(2.365, 2.398, and 2.555 A, all =t0.006 A) interactions are made with different AlC1,- tetrahedra in such a way that a pleated sheet of CuA1C14is formed with Cu-C6H6 linkages protruding from the sheet. The sheets are separated by nxmal van der Waals distances. The Cu(1) is located almost directly above a C-C bond of the benzene ring with Cu-C distances of 2.15 and 2.30 A, both h 0 . 0 3 A. It appears that the anions play an important role in the stability of this complex.
T
he existence of complexes between silver ions and olefins or aromatic donors has been known for some time.2 Mulliken3 and Dewar4 have formulated theoretical models for the bonding in these complexes. Single-crystal X-ray structure investigations of silver (I)-~lefin”~complexes and CBHs.AgC104* have been carried out and the geometry and bond distances established. However, a thorough understanding of the factors involved in metal ion-olefin or aromatic complexes can be obtained only from a systematic study of complexes with various metal ions, anions, and a number of donors. Baenziger and his co-workersg have examined a number of olefin complexes, and we are examining a number of metal-ion aromatic complexes. A preliminary communication has been published on CsH6.CuA1C1410and we now present synthetic and structure details. Experimental Section C6Hs.CuA1C14 was prepared by treating a slight excess of resublimed CuCl with 0.03 mole of resublimed AlC13 contained in easily broken Pyrex ampoules with an excess of dried benzene (20 ml) in one side of a dry evacuated H tube (Figure 1). Upon breaking the tubes, the closed system was heated for 2 hr at 40“ by immersing the two legs in dewars filled with warm water. Any HCl formed from residual water adsorbed on the vessel walls was pumped out; then the stopcock was sealed off. Since CuCl is insoluble in benzene, the solution of CsH6.CuA1Cl4in the left leg was filtered into the right leg. Single crystals were grown from the ( I ) (a) Submitted in partial fulfillment of requirements for the Ph.D. degree, University of Pittsburgh, 1965. (b) Research performed at the University of Pittsburgh. All correspondence should be addressed to this author. (2) (a) S. Winstein and H. J. Lucas,J. A m . Chem. Soc., 60, 836 (1938); (b) L. J. Andrews and R. M. Keefer, ibid., 71, 3644(1949); (c) L. J. Andrews, Chem. Rev., 54, 713 (1954). (3) R. S. Mulliken,J. A m . Chem. Soc., 74, 811 (1952). (4) M. J. S. Dewar, Bull. SOC.Chim. France, C79, 18 (1951). ( 5 ) J. A. Wunderlich and D . P. Mellor, Acta Cryst., 7, 130 (1954); 8, 57 (1955). (6) S . C. Nyburg and J. Hilton, ibid., 12, 116 (1959). (7) F. S. Mathews and W. N. Lipscomb, J . Phys. Chem., 63, 845 (1959). (8) H. G. Smith and R. E. Rundle, J. A m . Chem. Sor., 80, 5075 (1958). (9) (a) J. N. Dampsey and N. C. Baenziger, ibid., 77, 4984 (1955); (b) J. R. Holden and N. C. Baenziger, ibid., 77, 4987 (1955); (c) N. C. Baenziger, J. R. Doyle, and C. L. Carpenter, Acta Cryst., 14, 303 (1961); (d) N. C. Baenziger, J. R. Doyle, and G. F. Richards, ibid., 18, 924 (1965); (e) N. C. Baezinger, G. F. Richards, and J. R. Doyle, Inorg. Cheni., 3, 1529 (1964): (f) N. C. Baenziger, H. L. Haight, and J. R. Doyle, ibid., 3, 1535 (1964). (10) R. W. Turner and E. L. Amma, J . A m . C h e m Soc., 85, 4046 (1963).
concentrated solution in the right leg by immersing the left leg in a Dry Ice-acetone bath. After excess benzene had been removed, the lower part of the right leg was cut off; this segment was transferred to a small drybox wherein single crysta!s were transferred to thinwalled (0.01 mm) glass capillaries. The glass capillaries were sealed off with a torch. The crystals were found to be very sensitive to air and moisture, and it was difficult to avoid some decomposition. Chemical analyses were performed, but they were only sufficiently accurate to confirm the above stoichiometry. The crystal of approximately 0.3 X 0.3 X 0.6 mm was used for collecting the intensity data. Multiple film equiinclination Weissenberg techniques were used to collect 1200 independent hki observed intensities with Zr-filtered Mo Kcr radiation from /zkO, h k l , . . ., hk6 levels. In addition, /zO1 and Okl precession-timed exposure intensity data were collected with Zr-filtered M o K a radiation and used for preliminary scaling purposes. All intensities were visually estimated with a calibrated strip. The linear absorption coefficient ( f i ) for this compound is 32 cm-I with Mo K a radiation. Since no adsorption correction could be made for unavoidable surface decomposition, no absorption corrections were made. Calculations were made with an IBM 7094 computer at New York University. 11 Lorentz polarization corrections were made and intensities reduced to squared structure factors. Fourier calculations were made with the Sly-Shoemaker-Van den Hende program. The full-matrix least-squares refinement was carried out using the Busing and Levy OR FLS program with the Hughes12 weighting scheme with 4F,i, = 10. We minimized the function Zw(F, Fc)2. Atomic scattering factors were taken from the compilation of IbersI3 for Cui-, CI-, AlL3,and neutral C. The variables were scale factors, atomic coordinates, and individual atom temperature factors for the isotropic refinement. For the anisotropic refinement, the variables were the six P i j for each atom along with the atomic positional coordinates. The anisotropic temperature fac(333P 2fll2/zk tors were of the form exp [ - ( P 1 1 h 2 -t &k2 201Jzl 2P23k0]. The scale factors were fixed after the isotropic refinement and not allowed to vary further until the refinement was completed.
+
+
+
+
Results Unit Cell and Space Group. C6H6eCuA1Cl4 was found to crystallize with four formula units per cell in the monoclinic crystal system. With CuKal( 1.5405 A) a2-(1.5443 A), unit cell constants were found to be u = 8.59 A 0.01, b = 21.59 ==I 0.03, c = 6.07 0.01 A, and p = 93” 0’ f 15’. The systematic extinctions of (for h01) h 1 = 2n 1 and (for OkO) k = 2n 1 uniquely specify the space group as P24n. The calculated crystal density was found to be 1.85 g ~ m - ~
+
+
+
(1 1) We wish to thank the Atomic Energy Commission and the Courant Institute of Mathematical Science a t New York University for use of their computer facilities. (12) E. W. Hughes,J. Am. Chem. Soc., 63, 1737 (1941). (13) J. A. Ibers, “Intcrnational Tables for X-Ray Crystallography,” Vol. 111, Kynoch Press, Birmingham, England, 1962, pp 202, 204, 210.
1878 Table I. Observed and Calculated Structure Factors F(C) = lOF(Ca1cd) f10l Fl,CI 060 6 291
a 615 12 I50 IC 1 2 1 20 Lld LLC
5 8 Y 10 11
213
14
ZLb 241
115 151 12 lU1 13 1 1 1
n1 11
15
43 45
l h
102
90
17 IR
R7 5L
68 -37
2 0 IC5 114 21 IC - 7 3 2K2 2 L5d 113 3 300 2 9 9 4 167 - 1 4 6 5 15C 130 6 3 7 -19 7 v9 -83 8 126 112 1 Y I 72 I C 0 2 -44 11 1 s t - 1 4 3 1 2 22 37
13 I5 16 18
19
10
WO 9
2 5 9 10 - 4 4 c 16 159 I5 14.2 16 -111 1 256 2 -1H1 4 -311 5 I20 6 15.3 1 - 1 9 2 11 V 4 12 30 13 -44 1 4
75 4'1 39 52 01 C5
VI
LO5 (10
a10 118 54 26
3KI
I t 113 7 5 -134 I b -122 I06 119 104 - 1 1 6 YO 91
-6K
-R7 90
960
-
3K1 0 3 3 1 -394 1 2rO - 7 6 2 354 2 L9L 105 3 200 46 4 132 6 3 1 1 -3C7 7 134 -101
2
96
-89
R 123
92
3 4
7') 86
73
222
720
67
1'16 - 1 7 9
8
>v OK
-62
I
6 274 7 Zqd
L
73 5 1 Lb4 108 1 Y l 2 .)J 19 6 R 1 6 1 -135 111 3 - 2 1 4 - 2 1 9 7 -9'4 10 1 2 8 181 4 2 0 5 - 2 1 3 8 5 6 11 185 $5 7n 1 0 5 1 2 1C6 - I C O 5 9 9 IC 11 7 1 J O 14 7C - 1 0 2 I7 8 2 - 8 9 P 1 4 3 144 1 2 14 -5613 4 6 18. 71, -115 9 6 0 2 1 7 5 -115 10 1 1 2 -144 1 4 15
IC8
759 343
1 2 5 -116 79 -45 1 3 0 102 a7 70
21Q 2 3 1 230 11 111 -185'14 184 - 2 1 4 16 102 186 11 98 -73 i n 1 7 4 -155 H l 74 2 I b b -207 6 124 127 7
1 2 192
2 0 5 1 5 176 13 Y O 73 -2h2 15 1 0 3 - 1 0 4 1 1 6 8 16 I G L - I C 0 4 1 4 1 lkl h 49 0 106 - 9 4 7 >L 1 95 70 H 121 2 lud 98 9 1 7 6 5 4 - 3 5 I C 111 7 0 11 1 5 0 5 85 6 93 -67 I 2 L R 2 1 1 7 1 7 106 8 126 1C 1 3 0 - 1 2 3 1 R 1 2 0 >?. 20 1 5 5 1 2 51 1 3 102 - 1 0 5
1
I78
H 9
-154 10 100 1 7 -25 13 28 LJ3 -123
-5K2
76 166 - 1 6 7
105
Hl
94
12
60
64
13
-2U3 2 111 3 181 4 LlV 5 268 1 92
H 231
6S2
9 132 121 -107 l b c 10 2 7 1 162
'10
- / L 11 1 2 H
79 v9 87 70
-I8
12
H4 1 3 5 7 14
11 63 21
6 1 15 1 5 5 Y l - 6 0 I 6 111 1 1 7 - 1 4 ) 18 n o 19 70 -6SL 229 3K3 1 202 4 8 2 -41 0 1 4 7 7 V2 13 1 222
14
104 129 9 L4h -126 -1vo - 1 1 4 11 8 L -80 75 - 1 1 2 1 8 106 145 1 4 8 19 6 9 IKL'
2 b..Y . 4 129 5 1ov
6 110 7 144
-64 44 44
-43 64
49
3UO 1 184 -lhR 2 Id5 3 215 4 32
5 118
172 272 1H -96
P 222
228 9 190 1 9 3 10 2 5 9 - 2 1 3 11 165 - 1 6 2 1 3 34 14 112 LO 8 4 11 92 i n 81
19 20
59
21
44 4KO
56
0 181 1 2Y9 3 49 4 68 5 213 .6 155 1 244 8 170 9 102 10 100 11 1SO 12 I25 13 140 16 '44 11 14 19 95 20 5 1
-22 99 -75
-8d 76 46 48 31 -164 365
-46 100 -255 -140 250 154 -1s
77 -136
-110 130 -85 -79
103 -22 5uc 1 l1C - 1 0 0 2 177 165 3 ni 47
4 2 6 6 -312
6 1 8 10 11
YH 93 9) 55
87 83
In -47
31
25
12 13 14 15
62 59 46 76
-65 50
16
74
17
57
45
-54 -76
55
6UO 0 1
75 44
4
46
-53 -35 -32
5
50
-25
6
40
7
45
LO
53 70 LL
24 -25 36
11
I2 14 16
in IY
57
12
88
-18
62 63
62 -50
nz
-92
110
2 1 6 5 -162 3 52 45 4 135 115 7 134 -117 8 73 - 6 3
in good agreement with the observed value of 1.86 g cm- 3. Journal of the American Chemical Society
/
88:9
/ May 5, 1966
Determination of the Structure. After two false starts with the three-dimensional Patterson function,
1879 Table IIa Positional and Temperature Parameters and Errors Atom
cu
0.1790 0.2319 0.3810 0.4200 0.1381 0.4145 0.4732 0.4833 0.3789 0.2789 0.2605 0.3606
Cl(1) c1 (2) Cl(3) c1 (4) A1 C(1) C(2) C(3) C(4) C(5) (26)
Atoma
Bll
Cu Cl(1) Cl(2) Cl(3) Cl(4)
0.0090 0.0085 0.0131 0.0027
Al
0.0014 0.0075 0.0071 0.0165 0.0052 0.0056 0.0167
C(1) C(2) C(3) C(4) C(5) C(6)
+)la O.OOO4
x/a
exp[-(LJ11h2 822
U'
6 7 13 7 7 8 43 40 63 46 45 61
0.0044
0.0020 0.0005 0.0002 0.0029 0.0015 0.0001 0.0023 0.0014 0.0027 0.0025 0.0038 0.0012
0.0007
O.ooo9 0.0006 0.0006 0.0006 0.0037 0,0032 0.0047 0.0035 0.0035 0.0038
+
ylb
4Y)lb
ZIC
0.1703 0.2838 0.4318 0,3270 0.1921 0.3398 0.0896 0.1255 0.1229 0.0796 0.0403 0.0442
0.0001 0.0002 0.0003 0,0003 0.0002 0.0002 0.0016 0.0014 0.0019 0.0017 0.0019 0.0013
0.0043 0.1031 0.0692 0.6351 0.6237 0.9839 0.8261 0.9892 0.1602 0.1541 0.9699 0.8187
O.OOO4 0.0007 0.0012 0.0006 0.0006 0.0007 0.0053 0.0046 0.0066 0.0051 0.0059 0.0038
Thermal Parameters and Standard Deviations (Anisotropic temperature factors of the form Pnk2 Baal2 2P12hk 2Piahl 2Pzakr)l; U' = u X lo')
+
+
+
U'
833
1 1 1 2 1 1 9 10 11 9 9 7
0.0140 0.0119 0.0353 0.0007 0.0017 0.0016 0.0358 0.0272 0.0437 0.0323 0.0443 0.0131
U'
11 12 23 11 10 13 94 89 121 106 96 64
+
412
U'
613
U'
S*a
U'
0,0024 -0.0013 0.0003 -0.0003 -0.0015 -0.0001 0.0013 0.0000 0.0026 0.0017 -0.0005 0.0033
2 2 3 3 2 2 18 13 20 17 15 16
-0.0004 0,0067 0.0070 0.0000 -0.0008 o.Ooo1 0.0141 -0.0067 -0.0205 0.0003 -0,0024 -0.0032
5 8 12 5 5 7 38 40 50 47 46 43
0.0015 -0.0014 -0.0003 o.oo00
2 3 4 3 2 2 21 16 29 24 17 15
o.oo00 0.0001 0.0008 0.0042 -0,0007 -0.0012 0.0122 -0.0005
Layer
Scale factor
U
hkO hkl hk2 hk3 hk4 hk5 hk6
0.2321 0.3130 0.3616 0.2923 0.4801 0.3589 0.5427
0.0043 0.0036 0.0042 0,0038 0,0063 0.0059 0.0085
To put structure factors on an absolute scale, F(C)should be multiplied by l/(scale factors). Numbers in parentheses refer to subscripted numbers in other tables and drawings.
the correct solution was found. The Cu, 4C1, and A1 atoms were all located in the general positions of P21/n: ~ ( xy , z; ' 1 2 x , '/2 - y , ' 1 2 4. The disagreement index R ( R = ZllFol - lFcll/ ZIFol)with the coordinates of the heavy atoms from the three-dimensional Patterson function was found to be 0.28. A three-dimensional electron density calculation with phases based on only Cu, C1, and A1 positions located the carbon atoms of the aromatic ring. After six cycles of full-matrix least squares with individual atom isotropic temperature factors of the form exp[-(sin2 R was found to be 0.19. After eight cycles of full-matrix least squares with individual atom anisotropic temperature factors, R converged to 0.139. The maximum shift of positional coordinates for the last cycle was 0.00002 of the cell edges. A three-dimensional difference map did not indicate any unusual features. The final calculated and observed structure factors are listed in Table I. Final atomic parameters and standard deviations are tabulated in Table 11. Interatomic distances, angles, and errors l 4 are listed in Table 111. The equation for the best least-squares plane through the benzene ring carbons and the deviations of each atom from this plane are also given in Table 111. l6
+
+
R.Busing, K. 0. Martin, and H. A. Levy, OR FFE program. (15) Program courtesy of L. Dahl. (14) W.
Since the intensity data were only taken about one axis and no corrections were made for absorption, anomalous dispersion, or extinction, no physical interpretation should be made of the anisotropic temperature factors. For these same reasons our estimates of error may be somewhat optimistic. io w c w m system
Figure 1. H tube for preparation of metal ion-benzene complexes.
Description of the Structure. The structure is made up of sheets pleated about y = 1/4, 3/4, or infinite extent in the a and c directions. These sheets are composed of distorted tetrahedral Cu(1) bonded to chlorine atoms of three different A1C14- species. For example (Figure 2), Cu*, z '/2c is bonded to C11* and C13*
-
Turner, Amma
I
C&S. CuAlC14
1880 Table 111. Distances and Angles for C6H6.CuA1CI4 AI-CIi AI-CI, AI-CI3 AI-CI, CIi-AI-Cl2 CIi-AI-Cl3 CIi-AI-Cl4 CI?---AI-C13 CIZ-AI-CI 4 Cla-AI-CI 1 CU-CIi-A1 Cu-Cl3-AI Cu-Clr- A1 CI1-Cu-Cla C11-Cu-Cl4 c13-cu-c1,
2.136 f 0.007A 2.078 f 0.008 A 2.1411 O.CO7A 2.153 i 0.007A 109.9 1 0.3" 109.0 f 0.2" 109.41 0 . 3 " 112.4f 0.3" 109.9 i 0.3" 107.7f 0.3" 125.8f 0 . 2 " 113.8 f 0.2" 113.1 i.0.2" 92.9 i 0 . 2 " 92.9 f 0.2' 101.7 f 0.2"
CII-CI,
3.639i0.006 3.571 f 0.006 4.113 f 0.009 3.776 f 0.008
c11-c1, c12-cI3
CI,-C14 All others >4.5
Bonded Distances and Angles cu-CI1 2.555f 0.066A cu-c13 2.398 f 0.006A Cu-Clr 2.365i 0.004A
cu-c3 cu-Cr Cu-midpoint (C3-C4)
2.15f 0.03A 2.30 f 0.03A 2.13f 0.03A
1.25f 0.04A c1-c,-c, 123 i 3" 1.41 f 0.05A Cz-C3-Ca 119 =k 3" 1 26 i 0.05A c3-c4-cs 121 i 3" 1.40f 0.05 A Ca-Ca-Cg 119 f 3" Cj-CB 1.29 f 0.04A cs-C6-c1 121 i 3" CSCl 1.37 f 0 . 0 4 A cg-ci-c* 119 =k 3" Midpoint of C3-C4-Cu-C11 1 1 8.1 1 0.5 Midpoint of C3-C4-Cu-CI3 114.3i 0.5" Midpoint of C3-C4-Cu-CI4 127.6f 0.5" c3-cu-c4 33 f 1' ci-c3-cu 97 f 1" C&-Cu 94 1 1 " Nonbonded Intermolecular Distances (A) CI-CII 3.81 1 0 . 0 3 c1-c, 4.13f 0.05 c?-CI! 3.80 i 0.02 c1-c4 4.31 f 0.04 C4-CI3 3.66f 0.02 c3-c6 4.36 f 0.05 Ci-Cla 3.74f 0.03 c4-C 6 4.12f 0.03 C3-CI1 3.70f 0.03 All others >4.5 C4-Cl3 3.66f 0.02 C1-CI1 3.81 f 0.03 C2-CI1 3.85 f 0.02 All others > 3 . 8 5 Dihedral Angle between Planes Each Defined by Three Atoms for Benzene Ring C4-cI- c6 5 f 3" c6-cI-c4 1 rt3" C6-Cj-Ca C3-C4-C6 c1-CI-cS 2 f 3" C6-Cl-C4 1 f 3" CrC4-C3 cL-c3-c6 C6-C1-C4 1 f 3" Ring is planar within c1-c2-c3 experimental error Equation of Best Least-Squares Plane through Benzene Ring -0.6019~ 0.6338~ - 0.48594.= 1 Deviations from This Plane (A) Cq -0.030 Ci +0.006 c, -0.004 Cj $0.035 Cg -0.013 C3 +0,029 C1-Ca
c,-c, C3-Ca cr-cj
Nonbonded Intramolecular Distances (A) and Angles on AlCl43.451 i 0.008 CII-CI, CI,-CI3 3.596 i 0.006 CI,-C14 3.501 i 0.008 cl?-Cla 3.465 f 0.008 Cl?--CI3 3.508& 0.008 c13-CI.4 3.427 f 0.006
+
-
-
both at z 2/3cand also to Clr* at z 'il0c which is on the AlC1,- tetrahedron below the one containing Cia*. The Cld on the tetrahedron with CI3* is then bonded to the Cu atom in the unit cell above. Extension of the sheet in the [loo] direction is generated by the glide plane at y = 1/4. The coordination number of 4 for Cu(1) is completed by a a-type aromatic ring interaction (Figure 3). The Cu-C1 interactions with a particular A I C k ion is shown in Figure 4. Inasmuch as the sum of the tetrahedral single bond covalent radius of Cu16 and C1 is 2.34 A, Cu-C1 distances of 2.365, 2.398, and 2.555 A (all f0.006 A) indicate a substantial Cu-C1 covalent interaction. These distances are also in good agreement with tabulated l7 Cu(I)-CI distances of 2.31-2.48 found in fourfold coordinated Cu(1) compounds. It is to be noted that the "free" AI-Cl distance is significantly shorter (0.07 A) than the A1-C1 distances, wherein the C1 is also bonded to a Cu atom. This value of 2.07 A is in good agreement with the terminal A1-C1 distance found in AlzCl6l8(2.07 A) vapor and the non-Co-bonded A1-Cl distance in C O ( A I C ~ , )(2.10 ~ ' ~ A). On the other hand, the remaining A1-C1 distances are the values expected (16) L. Pauling, "Nature of the Chemical Bond," 3rd ed, Cornell University h e s s , Ithaca, N. Y.,1960, p 246. (17) H. Ondik and D. Smith, ref 13, p 260. (18) K. J. Palmer and N. Elliott, J . A m . Chem. Soc., 60, 1852 (1938). (19) J. A. Ibers, Acta Crys., 15, 967 (1962).
Journal of the American Chemical Society
1 88:9 1 May
5, 1966
for externally C1-coordinated AI-C1 distances, e.g., in Co(AICl&, -2.15 A. All CI-Cl, C1-C, and C-C distances between sheets are at least 3.6 A ; hence, only van der Waals interactions exist between sheets. The aromatic ring is bound to only one Cu(1) atom, and the rings are back-to-back. The neighborhood of a particular Cu(1) species with bond distances, angles, and errors is shown in Figure 5. Since a value of 2.12 A is expected for a Cu-C "single" bond, the Cu-C closest distances of 2.15 and 2.30 A are indicative of a strong interaction. The distance of Cu to the center of the nearest C-C bond was found to be 2.13 A.
Discussion Mulliken3 considered the use of the empty 5s orbital of silver as the electron acceptor and the el filled molecular orbital of benzene as the donor. In addition, he considered the use of excited states of Ag(1) of the proper symmetry to give a possible Cc complex but rejected them on energetic grounds. Dewar4 maintained that not only is the el + 5s interaction important but the use of a filled d orbital donating electrons to the empty ez molecular orbital is also important to the binding. This latter interaction, back bonding, is generally accepted as being important in platinum(I1)olefin complexes. Either or both of these interactions led t o the correct gross geometry for the crystalline
1881
Figure 4. Bond lengths and bonding about a particular AIClaspecies. Dotted lines indicate Cu-CI interactions.
bo
Figure 2. View of the C6He.CuA1CI4 sheet structure down the c axis. Dotted lines represent nearest neighbor Cu-X interactions. l/zc; Dot-dash line represents n glide at y = 1/4. Cu* at z CI1* at z 2/3c: CI3* at z 2/?c; Clr* at z l/loc; and c = 6.07 A. CI3 and CI3* are in reality superposed, but they are displaced here for clarity.
-
-
N
N
Figure 5 . Bond lengths, angles, and errors about a particular Cu(1) atom.
Figure 3. Local geometry around &(I) nature of the complex.
indicating the
“n”
C6Hs.AgC104 complex,s and they also correctly predict the gross features of the Cu(I).CsH6 bonding in C6H6.CuAICl4,Le., the metal ion above and approximately between two C-C bonds of the benzene ring. Although the C6H6.AgC104complex is not a 1:l metal-aromatic complex as predicted by the theory but rather m : m and each Ag(1) is bonded to two benzene rings, the Ag-0 distances are sufficiently long (2.70 A) that the neglect of cation-anion interactions seems reasonable and the theoretical framework is justified. However, in our present investigation the Cu-C1 interactions are far from negligible and must contribute substantially to the stability of the complex. The excited states of Ag(1) that could be used as acceptors for complex formation are -4 ev above the ground state, but in Cu(1) the lowest-energy excited state is only 1.5 ev20 above the ground state. Whether
this excited state plays a significant role in complex formation is difficult to decide since the true symmetry of the Cu(1) environment is low. We prefer to describe the Cu(1) as a distorted tetrahedron with an sp3hybrid orbital acting as an acceptor for the aromatic electrons (see C1-Cu-C1 and midpoint C3-C4-Cu-Cl angles). Since some of the angles are sum of covalent radii), in C6H6.AgC104 and C6H6.AgA1C14. This is in accord with gross observations that it is more difficult to remove benzene from CF,H~.CUAIC~~ than from CsH6.AgC104 or C6H6.AgA1Cl4.* l Unfortunately, the error of ~ 0 . 0 3 A makes the difference of 0.15-A Cu-C distances only five standard deviations. We believe this is a real difference in bond lengths, because not only is it greater than three standard deviations, but also it is consistent with similar results found in C6H6.AgC104and in (20) C. E. Moore, “Atomic Energy Levels,” Vol. 11, No. 467,National Bureau of Standards, Washington 25, D. C., 1952, p 112. (21) R. W. Turner and E. L. Amma, to be published.
Turner, Amma J C a 6 .CuAfCf4
1882
C6H6.A$1A1,. In the former, this asymmetry mani'"est,d itself in statis!ically disordered Ag positions, but it is unambiguous in the latter. It is not likely that molecular packing would be the cause of this asymmeti y in metal-carbon distances, because the the packing is quile different in C,H6.AgC104, C6146' CuA.CI4 and C6H6.AgA1C14. A similar asymmetry in Cu-C distances has been observed in a coFper(1)olefin c ~ m p l e x . ~ ' We suggest that this asymmetry between the closest carbon-to-metal distances is a fundamental property of metal ion-aromatic complexes. Further, we suggest that the reason for this asymmetry is a compromise between the acceptor properties of the metal ion, or coordinated metal ion, and the donor properties of this same ion. That is, if the acceptor orbital were a 4sor an sp3-hybrid orbital, the most advantageous position would be at the point of greatest electron density of the ring, directly above one of the carbon atoms. On the otiiir hand, using inner d orbitals for the metal ion as donor, the most likely position would be above and symmetrically between two carbon atoms of the aromatic system. Hence, a compromise between these
two effects is reached and unequal metal-carbon distances result. However, in platinum- and palladiumolefin complexes, there has been no evidence for different metal-to-carbon distances, but it is quite likely that details of the bonding may be quite different for olefin complexes. Although the bond distances alternate in lengths around the ring and suggest a cyclohexatriene system, the errors are sufficiently large that this variation of bond distances may not be real and caution should be applied to any interpretations based on C-C distances in this complex. It is, in fact, an interesting question as to why the complex forms at all. In the presence of chlorine donors it is surprising tht the metal-aromatic bond is preferred to M-C1 interactions. The answer may be that in the packing of anhydrous CuAIC14 large voids remain, and it becomes energetically favorable to form metal ion-aromatic bonds over metal ion-chlorine bonds. We plan to investigate the crystal structure of anhydrous CuA1C14 in the near future. Acknow edgment. We wish to acknowledge the financial support of NSF Grant GP-1575.
Cage Compounds Containing the Trirhenium( 111) Cluster: Re,Br, ( AsO, ) (DMSO)31 F. Albert Cotton and Stephen J. Lippard2 Contribution f r o m the Department of Chemistry, Massachusetts Institute 03 Technology, Cambridge, Massachusetts 02139. Received January 12, 1966 Abstract: The preparaticm and molecular structure of Re3Br,(As04)2(DMS0)3, a representative member of the new class of compounds Re3X3(M03 &Ln,are discussed. From the visible spectrum, it is apparent that the trirhenium(111) metal atom cluster occurs in this compound. Further insights into its structure are obtained from a detailed analysis of the infrared spectrum. Apparently, two tridentate arsenate ions have replaced the six axial halide ions in the Re3Brsmolecule to form a cage which in-orporates the cluster. The solvent (DMSO) molecules are thought to occupy nmbridging equatorial sites in the cluster.
T
he existence of the trirhenium(II1) metal atom cluster in complexes prepared from rhenium(II1) chloride and rhenium(II1) bromide has been well Studies by Robinson and Fergusson" established. 3-1 have shown that, of the twelve halogen atoms (six (1) Supported by the U. S . Atomic Energy Commission. (2) National Science Foundation Postdoctoral Fellow, 1965-1966. (3) J. A. Bertrand, F. A. Cotton, and W. A. Dollase, J . Am. Chem. Soc., 85, 1349 (1963); Inorg. Chem., 2 , 1106 (1963). (4) W. T. Robinson, J. E. Fergusson, and B. R. Penfold, Proc. Chem. Soc., 116 (1963). (5) J. E. Fergusson, B. R. Penfold, and W . T. Robinson, Nature, 201, 181, (1964). (6) F . A. Cotton and J. T. Mague, Inorg. Chem., 3, 1094 (1964). (7) F. A. Cotton and J . T. Mague, ibid., 3, 1402 (1964). (8) F. A. Cotton and S . J. Lippard, ibid., 4, 59 (1965). (9) F. A. Cotton and S . J. Lippard, J . Am. Chem. Soc., 86, 4497 (1964). (10) F. A. Cotton, S. J. Lippard, and J. T. Mague, Inorg. Chem., 4, 508 (1965). (11) B. H. Robinson and J. E. Fergusson, J . Chem. Soc., 5683 (1964).
Journal of the American Chemical Society
88:9
1 May
5, 1966
axial, three equatorial bridging, and three equatorial nonbridging) in the Re3X123-ion, only three, presumably the equatorial bridging ones, are not subject to exchange with thiocyanate or radioactively labeled halide ions. Apparently, then, the stable smctural unit in the trirhenium(II1) metal atom cluster compounds is the Re3X3group (I).
I From the known geometry (cf. ref 3-8) and net charge ( + 6 ) of I, it seemed likely to us that anions such
