2439
DI-p-CHLOROTRIS (trans-CYCLOOCTENE) DICOPPER (I)
The Crystal and Molecular Structure of Di-r-chlorotris(trans-cyclooctene) dicopper(I)
by P. Ganisl Department of Chemistry, Polytechnic Institute of Brooklyn, Brooklyn, New York
U. Lepore Istituto Chimico dell'Universith. di Napoli, Naples, Italy
and E. Martuscelli Laboratorw di Ricerche su Tecmbgia dei Polimeri e Reobgisa, Naples, Italy
(Receiued October 31, 1969)
A single crystal three-dimensional X-ray study of di-p-chlorotris(trans-cyclooctene)dicopper(I) [Cu2Clr (CBH14)3] has been cyried out. The unit cell data are: triclinic, P i ; a = 14.95 i0.03 A, b = 11.50 f 0.02 A, c = 11.20 f 0.12 A, a = 119.2 z t 0.3', P = 114.0 f 0.3') 7 = 101.5 f 0.3', 2 = 2; d, = 1.32 g em-3. The structure consists of units
c1 \ / \
olef
The coordinatioii around one of the copper atoms is of trigonal-planar type, while that of the other copper.atom may be described as a distorted pyramidal-trigonal arrangement. Thekond distances and angles of the bridged system are Cu(l)-Cl(l) 2.361 f 0.006 A, Cu(l)-C1(2) 2.928 f 0.007 A, Cu(2)-C1(1) 2.291 f 0.006 A, Cu(2) 2.265 f 0.006 A; Cu(l)Cl(l)Cu(2)87.2 f 0.lo, C1(1)Cu(2)C1(2)102.5 f 0.1', Cu(2)C1(2)Cu(l)75.1 i 0.lo, C1(2)Cu(l)C1(1)83.7 f 0.1'. Relevant is the torsion angle around the double bond, ca. 135 f 5O. Refinement has been based on visually measured intensities and has been accomplished by standard three-dimensional Fourier and least-squares methods to a final R value of 0.108.
No crystal structure of compounds containing the trans-cyclooctene ring has been reported in the literature so far. From a study of molecular models it is possible to deduce that, basically, two different conformations can be assigned to this eight-term cycle;2 either one characterized by a pseudo 2/m symmetry (a) or one with 2 symmetry (b) (Figure 1). On this basis conformation b has been proposed as the most probable one.2 Besides, many experimental data based on dipole moment and infrared measurements3 actually indicate that the angle of rotation around the double bond is considerably different from the ideal value of 180". It thus seemed useful to study the crystal structure of a compound containing molecules of trans-cyclooctene to substantiate these indications. Owing to the difficulty of studying directly such a low-melting material as the free olefin, a complex with Cu(1) was chosen. The following considerations favored this choice. The presence of heavy atoms facilitates the solution of the structure; it was possible to gain new data on the stereochemistry of Cu(1) com-
plexes which, in fact, have not received adequate atten tion up to the present time.
Experimental Section Crystals of the complex were prepared according to previously described procedure^;^ two crystals were used in collecting the intensity data. Both were grown to a prism with near equal edges (0.3 X 0.3 X 0.3 mm) and approximately with the shape of the unit cell (see below). The crystals were enclosed in Lindemann capillaries in an atmosphere of olefin to retard decomposition. One crystal was used to record h01 to h51; the other was used to record hkO to hk3. All data were collected using the multiple film equiinclination Weissenberg techniques (Cu K a radiation). The intensities of 2605 nonzero observable reflections were (1) Visiting professor.
(2) J. D. Dunitz, "Perspectives in Structural Chemistry," Vol 11, John Wiley & Sons, Inc., New York, N. Y.,1968,p 49. (3) N.L.Allinger, J. Amer. Chem. Soc., 80, 1953 (1958). (4) H. L. Haight, J. R. Doyle, N. C. Baeneiger, and G. F. Richards,
Inorg. Chem., 2 , 1301 (1963). The Journal of Physical Chemistry, Vol. 74, No. 18, 1970
2440
P. GANIS,U. LEPORE,AND E. MARTUSCELLI
t
t
A three-dimensional electron density map was evalu-
B)
ated using the amplitudes of 1150 of the 2605 nonzero observable reflections. From this map we were able to recognize the position of the carbon atoms of two cycloolefins. It was impossible to locate the third ring with certainty from the residual peaks. A second Fourier synthesis was calculated after a structure factors calculation including the C atoms of two olefins (R factors -0.32). The third olefin was now clearly recognized. At this stage the structure factors calculation using a thermal factor B = 5 bz for all the atoms yielded an R factor of -0.26. The structure was refined down to R % 0.18 with usual Fourier techniques. The programs used to compute the Patterson and the Fourier syntheses have been written by Immirzi.5
-Q-Q A)
Figure 1. The most probable conformations of trans-cyclooctene are schematically represented: A, with a pseudo 2/m symmetry; B, with a 2 symmetry.
estimated visually by comparison with calibrated intensity strips. The intensities were put on a common scale with a least-squares program using the reflections present in both sets. No correction was made for absorption ( p = 38.9 cm-l); the maximum error in the intensities due to the absorption is not greater than -12% if one assumes the crystal to be approximately cylindrical. The unit cell data are reported in Table I. The calcuTable I : Crystal Data of Di-p-chlorotris( trans-cyclooctene)dicopper(I), Cu2C12(CsH14)a Mol wt, 528.32 Triclinic, space group P i
F(000) = 556
a = 14.95 (3) b = 11.50 (2) c = 11.20 (2) (Y = 119.2' (3) p = 114.0' (3) y = 101.5° (3 ) d, = 1.32 g ern+ z= 2 p = 38.9 cm-l for X 1.5418 A
A A
Refinement of the Structure A block diagonal matrix least-square program written for an IBM computer was used.6 Variable isotropic thermal factors for each atom were applied, until the R factor dropped to 0.15. At this stage anisotropic thermal factors were introduced, also the contribution of the hydrogen atoms was included using geometrically calculated coordinates. The R factor dropped to 0.108. The weighting method of Cruickshank was employed: w = 1/(A BFo CF,') with A = 0.11111, B 1/(18Fo(rnin)), C = 2/18F0(m~n)F0(m,41 The minimized function was
+
+
il.
lated density (1.32 g ~ m - ~for ) two formula weights (CUZCIZ(C,H,JJ per cell agrees with the experimental value (1.25-1.35 g cm-3) measured by flotation. Determination of the Structure Copper and chlorine positions were determined from a three-dimensional Patterson map. These positions corresponded to a bridged system
c1 / \ cu cu \ / c1
in which three Cu-cl bond distances are nearh" eaual ._ .
t2.3-2.4 8); the fourth is considerably longer (-2.9 A). The bridged system is not planar and iS asymmetric. A structure factors ca~cu~ation using the coordinates of CU and C1 atoms alone yielded an R value of -0.48. The Journal of Physical Chemistry, Vol. 74,No. 19, 1970
The atomic scattering factors of Hansone were used. The final atomic coordinates and thermaI factors, with their standard deviations, are given in Table II.' Discussion of the Structure The most important interatomic distances, bond angles, and torsional angles of the molecule, with their standard deviations, are given in Table 111. I n Figure 2 is shown the bridged system
c1
/ \ cu cu \ / c1 The most interesting conformational parameters are indicated. Both copper atoms present sp2hybridization. (5) A. Immirzi, Ric. Sci., 377,743 (1967). (6) H. P. Hanson, J. D. Lea, and 8. Skilmann, Acta Cryst., 17, 1040
(1967). (7) A list of the observed and calculated structure factors has been deposited as Document No. 00899 with the ASIS, National Auxiliary Publication Science, c/o CCM Information Corp., 909 Third Ave., New York, N. Y. 10022. A COPY may be secured by citing the docume?t number and by remitting $1.00 for microfiche or $3.00 for photocopies; advanced payment is required. Make checks or money orders payable to CCMI-NAPS.
DI-~CHLOROTRIS (tr~ns-CYCLOOCTENE) DICOPPER(I)
2441
Table 11: Positional and Thermal Parameters of Cu, C1, and Carbon Atoms Bsa
2
2(
z
BII
Bza
0.181(1) 0.203(1) 0.323(1) 0.417(1) 0.431(1 ) 0.409( 1) 0.277(1) 0.220(1) -0.067(1) - 0.052( 1) -0,150(1) -0.271(1) -0.310(1) -0.331( 1) -0.224( 1) -0.136(1) - 0.189 (1) -0.285(2) -0.380(2) - 0.411( 1) -0.332(2) -0.269(2) -0.162(2) -0.190(1) 0.0342(2) 0.0664(2) - 0.0067(3) 0.0444(3)
O.OOl(2) -0.005(2) 0.007(2) 0.147(2) 0.134(2] 0.241(2) 0.177(2) 0.144(2) -0.218(1) -0,345(2) - 0.496(2) -0.524(2) -0.426(2) -0.309(2) -O.l52(2) -0.186(2) -0.289(2) 0.179(2) 0.221(2) 0.245(2) 0.404(2) 0.396(2) 0.395(2) 0.261(2) 0.0099(3) 0.2350(2) 0.1627(4) 0.2241(6)
-0.150(1) -0.273(2) -0.214(2) -0.027(2) 0.114(2) 0.239(2) 0.164(2) -0.003(2) - 0.434( 1) -0.466(2) -0.657(2) - 0.711(2) -0.760(2) - 0.640(2) -0.473(2) - 0.383(2) -0.146(2) -0.172(2) -0.206(2) -0.344(2) -0.285(2) -0.368(2) -0.291(2) - 0.283(2) -0.1724(2) -0.1522(2) O.OlOO(4) -0.2432(5)
4.7 (6) 4 . 4 (6) 6 . 1 (8) 3 . 4 (5) 3.8 (6) 5 . 1 (7) 5.1 (7) 4 . 0 (6) 3.1 (4) 6 . 0 (8) 6 . 5 (8) 4 . 3 (6) 3.7 (6) 4 . 5 (6) 4 . 8 (6) 5 . 3 (6) 6 . 3 (7) 8 . 7 (11) 7 . 8 (10) 5.9 (8) 9 . 5 (11) 8 . 7 (10) 8.1 (10) 3 . 7 (5) 4.42(8) 5.12(9) 5.34(14) 6.18(9)
3 . 8 (7) 8.8 (12) 8 . 5 (12) 9 . 0 (12) 10.3 (14) 9 . 0 (13) 7 . 8 (11) 10.0 (12) 2.6 (6) 5 . 7 (9) 3 . 5 (7) 2 . 1 (6) 8.3 (12) 6 . 4 (9) 4 . 7 (7) 5 . 4 (8) 3 . 5 (6) 10.2 (14) 9 . 4 (14) 6 . 7 (11) 6 . 6 (10) 6 . 3 (11) 5.2 (10) 5 . 5 (8) 6.00(13) 5.05(12) 5.50(21) 9.00(32)
-
To Cu(1) are coordinated Cl(1) and two cycloolefins with a nearly undistorted trigonal geometry. The Cu double bond midpoint distances (ranging from 1.93 to 2.09 8) agree, within the errors, with the values reported in the literature for similar compounds.* The bond length Cu(1)-Cl(l), of 2.36 8, is different from the known distances in C1 bridged systems of Cu(1) complexes (2.26-2.28 8). This lengthening is presumably due to the fact that Cu(1) is bonded to two rather strong electron donorsthe two olefin ligands-which may induce some electron repulsion on the electron pair of Cl(1). I n the apical position of the system
there can be found another chlorine atom, C1(2), almost exactly in the direction of the ps orbital of Cu(l), 2.93 apart. It can still be considered a weak bond distance.8 The coordination of Cu(1) may be considered as trigonal pyramidal. I n the apical direciion opposite to Cl(2) there is the Cl(1’) atom (3.35 A apart) belonging to a centrosymmetrical molecule. A similar situation has been observed in other Cu(1) compounds
4.4 5.3 6.4 6.5 6.5 4.6 5.3 5.1 4.1 6.2 5.7 7.8 5.1 6.8 4.9 5.2 6.5
(5) (6) (8) (7) (8) (6) (6) (6) (5) (7) (7) (8) (6) (7) (5) (5) (7) 8 . 7 (10) 9 . 1 (10) 9 . 5 (11) 6 . 1 (7) 7 . 6 (9) 7.3 (9) 4 . 9 (5) 5.01(8) 5.00(8) 4.65(12) 6.75(18)
BIZ
Bia
2 . 8 (5) 3.2 (6) 1 . 9 (7) 1.7 (6) 3.7 (7) 3 . 1 (7) 3.7 (7) 3.2 (6) 1 . 2 (4) 4 . 2 (7) 2 . 8 (6) 1.1 (5) 2.5 (6) 4 . 4 (6) 4 . 0 (5) 3 . 1 (6) 3 . 9 (6) 6.5 (10) 6 . 2 (9) 4.0 (7) 6 . 8 (9) 4.2 (9) 2 . 6 (8) 2 . 8 (5) 3.44(8) 3.32(8) 3.82(14) 5.14(19)
2 . 5 (4) 3.2 (5) 4 . 3 (7) 2.5 (5) 2.4 (6) 1 . 7 (6) 2.7 (5) 2.9 (5) 1.5 (4) 2.9 (6) 1 . 6 (6) 1 . 6 (6) 1.5 (5) 2.7 (6) 2 . 6 (5) 3 . 7 (5) 3 . 9 (6) 6 . 2 (9) 5 . 4 (9) 4 . 4 (8) 3 . 5 (8) 3 . 8 (8) 4.2 (8) 2 . 1 (5) 2.74(7) 2.93(7) 3.33(12) 4.53( 16)
Bza
2.5 3.9 1.6 4.3 4.1 3.3 4.6 4.8 1.8 2.9
(5)
(7) (7) (8) (8) (7) (7) (7) (4) (7) 1.8 (6) 3 . 4 (7) 3 . 5 (7) 4.4 (7) 2.7 (5) 3 . 8 (6) 4.2 (6) 6.7 (10) 7.7 (11) 4 . 7 (9) 3.8 (8) 6 . 3 (9) 3 . 5 (8) 2 . 9 (6) 3.19(9) 3.50(9) 3.94(15) 5.73(21)
and in the case of some Cu(I1) compounds although in these cases different geometric factors are involved. The coordination around Cu(2) is trigonal, but the apical positions are completely free. The Cu-Cl bond distances range between 2.26 and 2.29 8 and are comparable with those of the compounds quoted in ref 8. The bridged system is strongly distorted; the four bridged atoms do not lie on the same plane as shown by the torsional angles on the Cu-C1 bonds of the fourmember ring, all of the order of /-25”/. The two cycloolefins bonded to Cu(1) have the same configuration. The contact distances C( 1)----C(l’) and C(l)----C(2’), though very short (3.0 and 3.3 8, respectively), are comparable to those found in other organic compounds, and the involved repulsion energy is less than 1-2 kcal/m01.~ The third cycloolefin bonded to Cu(2) in the same molecule has the opposite configuration. For all three cycloolefins, the double bond is orthogonal within 2-3” to the line joining the copper atom with the center of the double bond. The direction of the double bond makes an angle not greater than 15(8) N.C.Baenaiger, G. F. Richards, and J. R. Doyle, Inorg. Chem., 3 , 1529 (1964); N. C. Baenaiger, H. L. Haight, and J. R. Doyle, ibid., 3,1535 (1964). (9) P.Ganis, A. Panunai, and C. Pedone, Ric. Sci., 38, 801 (1968); G. Avitabile, P. Ganis, and E. Martuscelli, Acta Cryst., in press; G. Allegra, E. Benedetti, and C. Pedone, ibid., A25, 53, 5136 (1969). The Journal of Physical Chemistry, Vol. 74, No. 18,1970
2442
P. GANIS,U. LEPORE,AND E. MARTUSCELLI
Table I11 : Molecular Parameters’ Bond lengths,
C(l)-C(2) C(2)-C(3) (31-c(41 C(4)-C (5) C(5)-C(6) C(6)-C(7) W)-C(8) C(8)-C(l) C(1’)-c (2’) C(2’)-C(3’) C(3’)-C(4’) c(47-C (5’) C(5’)-C(6’) C(6’)-C(7’) C(7’)-C(8’) C@’)-C( 1’) C(l”)-C(2”) C(2”)-C(3”) C(3”)-C(4”) C(4”)-C (5”) C(5”)-C(6”) C(6”)-C(7”) C(7”)-C(8”) C(8”)-C(l”) Cu(1)-C(1) CU(1)-C(8) Cu( 1)-C( 1’) Cu(1)-C(8’) CU(2)-C( 1”) CU(2)-C(S”) Cu( l)-C1(1) Cu(1)-C1(2) CU(2)-C1( 1) CU(2)-C1(2) Cl(l)-C1(2) Cu(1)-Cu( 2) Cu(1)-A Cu(l)-B CU(2)-C
c
A
1.51 (3) 1.59 (3) 1 . 5 3 (4) 1.59 (4) 1.56 (3) 1 . 6 1 (3) 1.49 (3) 1.40 (3) 1.42 (3) 1.59 (4) 1.56 (3) 1.60 (3) 1.56 (3) 1.56 (3) 1.56 (3) 1.39 (2) 1.52 (3) 1.58 (4) 1.60 (4) 1 . 5 8 (4) 1.56 (4) 1.49 (4) 1.58 (3) 1.40 (3) 2.14 (2) 2.19 (2) 2.24 (2) 2.17 (2) 2.08 (2) 2.03 (2) 2.361(6) 2.928(7) 2.291(6) 2.265(6) 3.553(8) 3.208(4) 2.04 (2)b 2.09 (2) 1 . 9 3 (2)
C(5‘)C(6’)C(7’) C(S’)C(7’)C(S’) C(7’)C(S’)C(1’) C@’)C(l‘)C(2’) C(l”)C(2”)C(3”) C(2”)C(3”)C(4’’) C(3”)C(4”)C(5”) C(4”)C(5”)C(6”) C(5”)C(6”)C(7”) C(6”)C(7”)C(S”) C(7’’)C(S”)C(1”) C(8”)C(l”)C(2”) CU(1)Cl(l)Cu(2) Cl(1)CU(2)C1(2) CU(2)C1(2)CU(1) C1(2)CU(1)C1(1) A Cu(1)B A Cu(l)C1(1) A Cu(l)C1(2) B Cu(l)C1(1) B Cu(l)C1(2) c CU(2)C1(1) c CU(2)C1(2)
107 113 119 117 114 105 120 119 110 113 116 115
a Standard deviations are given in parentheses. C(l’)-C(8’), C(l”)-C(8”).
C(l)C(2)C(3)C(4) C(2)C(3)C(4)C(5) C(3)C(4)C(5)C(6) C(4)C(5)C(B)C(7) C(5)C(6)C(7)C@) C(6)CU)c(S)C(l) C(7)C(8)C(l)C(2) C(8)C(l)C(2)C(3) C(l’)C(2’)C(3’)C(4’) C(2’)C(3’)C(4’)C(5’) C(3’)C(4’)C(5’)C( ’6) C(4’)C(5’)C(6’)C(7‘) C(5’)C(6’)C(7’)C(S’) C(6’)C(7’)C(S‘)C(l’) C(7’)C(8’)C(l’)C(2’) C(S’)C(l’)C(2’)C(3’) C(l”)C(2”)C(3’‘)C(4”) Cf2”)C(3”)C(4”)C(5”) C(3”)C(4”)C(5”)C(6”) C(4”)C(S”)C(6”)C(7”) C(5”)C(6”)C(7”)C(S”) C(6”)C(7”)C(S”)C(l”) C(7”)C(S”)C(lf’)C(2‘’) C (8”)C (1”)C(2”)C (3”) Cu(1)C1(1)CU(2)C1(2) C1(1)CU(2)C1(2)CU(1) au(2)cl(2)cu(l)cl(l) C1(2)CU(l)C1(1)CU(2)
(1) (1) (1) (1) (1) (1) (1) (1) (1) (1) (1) (1) 6 A,
(1) (1) (1) (1) (1) (1) (1) (1) (1) (1) (1) (1) (1) (1) (1) (1) (1) (1) (1) (1) (1) (1) (1)
- 53
+82 -115 +- 8252 +87 - 136 +-8850 +80 - 115 +-8353 +83 - 133 +87 +47 -80 +116 -83 +53 -84 +133 - 86 $31 - 25 24 23
+ -
B, and C are the middle points of the bonds between the atoms C(l)-C(8),
20” with the plane of the sp2hybrid of the copper atoms. I n this way a good overlap between the hybrid orbitals of Cu and the molecular n orbitals of the olefin is achieved The Journal of Physical Chemistry, Vol. 74, No. 1.2, 1970
116 107 118 120 108 113 118 116 117 106 119 121 87.2 102.5 75.1 83.7 123 118 92 118 103 128 129
Internal-rotation angles, deg
Bond angles, deg
C(1)c(23c(3) C(2)C(3)C(4) C(3YW)CG) C(4)C(5)C(6) C(5)C(S)C(7) C(6)C(7)C(8) C(7)C(8)C(1) C(8)C(l)C(2) C(l’)C(2’)C(3’) c(2’)C(3’)C(4‘) C(3’)C(4’)C(5’) C(4’)C(5’)C(6’)
Bond angles, deg
The corresponding conformational parameters of the three cycloolefinic rings of the structural unit do not differ from each other by values greater than the standard deviations (these being, however, rather high
2443
DI-p-CHLOROTRIS (~~UnS-CYCLOOCTENE)DICOPPER(I)
t 2.93A
n
l
n
134'
7
Figure 2 . The most relevant conformational parameters of the c1
/\
bridged systems Cu
Cu are shown. The geometrical
\d
t-
2
7
108'
1,57A
arrangement of the ligands around the copper atoms is evident; tJheCl(1') atom belongs t o a centrosymmetrical molecule.
for the carbon atoms: see Table 111). Each olefin shows a Czlpseudo-symmetry. The deviations from the exact twofold symmetry are again less than the standard deviations. Therefore we shall assume for the following discussion conformational parameters averaged over the three rings and the two pseudo-symmetrical moieties of each. The averaged conformation is shown in Figure 3. The local twofold axis passes through the midpoints of the double bond and of the single bond opposite to it. The C-C bond lengths are normal; the C=C length is 1.40 =!= 0.06 A. Owing to the error connected with this parameter it is difficult to tell whether it has lost part of the double bond character. The torsional angles about the C(l)-C(2) and C(2)C(3) bonds correspond to a nearly staggered conformation, the torsional angle about the C(4)-C(5) bond is nearly eclipsed and that one about C(3)-C(4) is intermediate between eclipsed and staggered conformation. Also, the internal rotation angle around the
156A
51'
i,
115'
Figure 3. The averaged conformational parameters of the three molecules of cyclooctene are reported.
double bond deviates considerably (40 to 45" from trans conformation, a t any rate much more than in the case of trans-cycIodecene10as foreseen by the mentioned dipolar moment and ir measurements. The contact distances between Cu and the methylenic groups adjacent t o the double bond are rather long (Cu-C > 3 . 1 0 i and Cu-H > 3.16 A). Therefore the deviation from the trans-planar conformation of the double bond does not seem due to steric interactions with the metal, but to intraannular tensions. The conformation of trans-cyclooctene, as a whole, appears rather strained, as a consequence mainly of (10) P. Ganis and J. D. Dunitz, Helu. Chim. Acta, 50, 2379 (1967)
The Journal of Physical Chemistry, Vol. 74,No. 18,1970
2444
P. GANIS,U. LEPORE,AND E. MARTUSCELLI tioned. These dimers constitute units of almost spherical encumbrance which pack according to a pseudo-hexagonal symmetry as can be seen in Figure 4. The packing is closest in the 100 planes as indicated by the greater number of short contact distances (Table IV) among adjacent molecules in these planes.
oc OC” Q CL
Table IV : Shortest Intermolecular Distances between Atoms ( a ) of the Molecule in zyz and Atoms (b) of the Molecule in the Positions (c) &
Figure 4. Projection of the structure of Cu&lz(CsHl& on 010. The intermolecular contact distances are omitted; they are givtrri in Table IV.
torsional strains, since intramolecular van der Waals H-C and H-H interactions and angle strains are negligible I n Figure 4, the projection of the structure along (010) is shown. The molecules of the complex appear to be associated in dimers around symmetry centers, through weak Cu----CI bonds as previously men-
.
The JOUTnal of Physical Chemietry, Vol. 74, No. 18, 1070
b
C(2). . . Cl(2) C(1’). . .C1(2) C(3’). . . C(20 C(2’). . . C(2’) C(41’). . , C(6’) C(7). . .C(7’) C(7). . .C(8’) C(8’). . .C1(1) Cu(1). . .C1(1) C(8). . . C(5”) C(7”). . . Cu(2) C(7”). . .C1(1)
4.0 A 3.7 A 4.0 4.0 A 4.0 A 4.0 A 3.8 A 3.7 3.34 A 4.0 A 3.7 A 3.8 A
4
4
The C-C intermolecular distances are nevertheless all larger than 3.8 A; the CI----C and Cu-C distances are both riot less than 3.7 A.
