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Molecular structure of gaseous copper(I) trifluoroacetate as determined by electron diffraction
of Molecular Structure, 158 (1987) 315-322 Elsevier Science Publishers B.V., Amsterdam -Printed
Journal
in The Netherlands
MOLECULAR STRUCTURE OF GASEOUS COPPER(I) TRIFLUOROACETATE AS DETERMINED BY ELECTRON DIFFRACTION
KINYA ILBMA, JUN-ICHI OHKAWA and SHUZO SHIBATA* Department
of Chemistry,
Shizuoka
University,
Oya, Shizuoka
422
(Japan)
(Received 15 September 1986)
ABSTRACT The molecular structure of gaseous copper(I) trifluoroacetate was determined by electron diffraction. The molecule is dimeric and its skeleton is essentially planar. The molecular parameters and the uncertainties are rdCu-Cu) = 2.566 f 0.018 A, ra(Cu-0) = 1.874 + 0.002 A, rg(C-O) = 1.253 + 0.004 A, r&C-C) = 1.542 f 0.005 A, ra(C-F) = 1.333 + 0.003 A and LOCuO’ = 170.3 +_0.6”. The rotational barrier height of the CF, group is 5.9 + 2.5 kd mol’ , and the minimum of the barrier is at the position such that one of the C-F bonds lies on the plane perpendicular to the ring.
INTRODUCTION
Structural studies on dimeric copper(H) complexes of carboxylic acids have shown that the more acidic the carboxylic acid the longer is the metalmetal separation; the Cu-Cu distance of quinoline adduct of copper(I1) acetate is 2.642 A [I], a-picoline adduct of copper(I1) chloroacetate 2.747 A [2] and quinoline adduct of copper(I1) trifluoroacetate 2.886 a [3] . Copper(I) acetate is dimeric in the gas phase [ 41 and the coppercopper separation is 2.491 8, which is the shortest for copper acetates reported so far [5]. We were interested in the effect of halogen substitution on the copper-copper separation of monovalent copper acetate. The crystal structure of copper(I) trifluoroacetate has not yet been determined, but the adduct with benzene was found to be tetrameric in the solid phase [6]. For this compound the orientation of the CF3 groups could not be determined because of the disorder, but the activation energy for the CF3 reorientation has been reported as 5.5 kJ mol-’ from NMR [7] . However, mass spectroscopy has shown that copper(I) trifluoroacetate is dimeric in the gas phase [4] as well as copper(I) acetate. Thus we attempted to determine the molecular structure of copper(I) trifluoroacetate by gasphase electron diffraction and hoped to obtain the orientation and rotational barrier height of the CF3 group though the orientation of the CH3 group of acetate could not be obtained in the study on gaseous copper(I) acetate [5]. 0022-2860/87/$03.50
o 1987 Elsevier Science Publishers B.V.
316 EXPERIMENTAL
Copper(I1) butyrate was prepared from copper carbonate by addition of butyric acid [8]. After the reduction by hydrazine hydrate, copper(I) butyrate was added to trifluoroacetic acid containing a little trifluoroacetic anhydride [9]. The solution was concentrated by pumping in vacua. The white precipitate of copper(I) trifluoroacetate was filtered off and sublimed under vacuum. Electron diffraction photographs were taken by using an r3-sector on Kodak electron-image plates at camera distances of 293.78 and 143.84 mm. The sample was sublimed at 416 K using a high-temperature nozzle. The accelerating voltage was 40 kV and the wavelength was determined from the diffraction patterns of thallium(I) chloride [lo]. The exposure times were ca. 40 and 70 s for the long and the short-camera-distance photographs, respectively, with an electron-beam current of 0.7 PA. The pressure in the diffraction chamber was 9 X 10e4 Pa during the experiment. Four plates were selected for photographs at each camera distance, and their optical densities were measured at 0.4 mm intervals by a digital microphotometer. The electron diffraction unit and the digital microphotometer used in this study have been described elsewhere [ 111. STRUCTURAL
ANALYSIS
Scattering intensities in the range q = 11.5--51.0 8-l were obtained from the long-camera-distance plates and those in the range q = 28-109 a-l from the short-camera-distance plates (q represents (40/h) sin (e/2), where X is wavelength and 8 is scattering angle). They were levelled by using theoretical backgrounds, and the intensities for each camera distance were averaged. The elastic and inelastic scattering factors were taken from refs. 12 and 13, respectively. The experimental background curve was drawn smoothly, and the experimental molecular intensities obtained are shown in Fig. 1. Figure 2 shows the experimental radial distribution function calculated from the molecular intensities. The molecular model of copper(I) trifluoroacetate is shown in Fig. 3. It was assumed that the molecular skeleton has D,, symmetry and each CF3 group has local C 3v symmetry. Since the shoulder at 3.4 a in the radial distribution function corresponds to the atomic pair of O(1) - * * F(2), the orientation of the CF3 group was considered as one of the C-F bonds lying on the plane perpendicular to the ring plane ($ = 30, 90, 150”, etc.). Here the rotational angle of the CF3 group around the C-C bond, $, is zero at the position where one of the C-F bonds lies on the ring plane. Since the rotational barrier height seemed low because of the Cg symmetry, the molecular intensities were calculated from $ = 60” to 120” at 6” intervals and summed with the weights of the Boltzmann distribution. The peaks of the radial distribution function in the range of 4.4 to 5.1 a are from the
317
,
(a)
1 D i
o-
o-1 -
I
(b)
50
LO
30 q/A-’
20
1 -
-G
E
o-
CT
-1
LO
60
q
/A-’
80
100
Fig. 1. Molecular intensities for gaseous copper(I) trifluoroacetate: (a) long and (b) short camera-distance data. The dots represent the experimental points and the solid curves the theoretical intensities. The curves at the bottom show the residuals.
Fig. 2. Radial distribution curve for gaseous copper(I) trifluoroacetate. The dots represent the experimental curve and the solid line the theoretical curve. The curve at the bottom shows the difference and the vertical bars represent bond distances and their scattering powers.
Fig. 3. Molecular
model
of dimeric
copper(I)
trifluoroacetate
atomic pairs of Cu * * - F. The theoretical radial distribution function did not agree well with the experimental value in this region when it was assumed that the C3” symmetry axis of the CF3 group is coincident with the C-C bond. Thus we assumed that the tilt angle of the CSV axis of the CF3 group is B,, + (l/2)8 1 (1 + cos 64) and the plane including the C-C bond and the CSV axis rotates by 3$1; the CSV axis tilts by f?,, out of the ring plane when l#I = 30, 90, 150”, . . . and by 8 0 + B 1 on the ring plane when $ = 0, 60, 120”, . . . . The molecular parameters were obtained from least-squares analysis of the intensities. The root-mean-square amplitudes and the shrinkage corforce field rections, ra - r, [ 141, were calculated from the Urey--Bradley and were used in the least-squares calculation. The force constants were taken from those of related molecules [4, 151, and were slightly adjusted so that the calculated mean amplitudes agreed with the observed mean amplitudes. The final force constants are listed in Table 1. The calculated mean amplitudes and the shrinkage corrections are listed in Table 2. For the mean amplitudes relating to the harmonic motion of the CF3 group (except the torsional motion) it was assumed that each of the atomic TABLE
1
Urey-Bradley K( cur-Cu’ ) K(Cu-0) K(C--O) W-0 K( C-F) n(C) Y( cu-Cu’ Y(Cu-0)
H(CuCu’0) H(CuOC)
force
field for copper(I) 0.37 1.2 5.0 3.3 3.0 0.62 0.08 0.08 0.14 0.01 0.10
trifluoroacetatea
H(OC0) H(OCC) H( CCF) H(FCF) F(Cu.*.O) F(Cu . . . C)
F(0 . . * 0) F(0 . ‘. C) F(C . . . F) F(F . . F) K
0.10 0.31 0.13 0.13 0.01 0.05 0.50 1.10 1.35 0.3
aUnits of the torsional force constant, Y, the out-of-plane bending force constant, r, and the internal tension of the trifluoromethyl carbon, K, are in lo-” N m, while the F’, was assumed to be -0.1 F. others are in 10’ N mm’ . The linear constant,
319 TABLE
2
Root-mean-square amplitudes fiuoroacetate (in lo-’ A) Atomic
pair
1 1142 728 1450 1029 967 1316 1218 1365 629 460 690 954 745 1126 1471 999 1133 1127 1640
cu-Cu’ cu-O(1) Cu*..O(2) cu. . . C( 1) Cu...C(2) Cu...F(l) Cu...F(2) Cu...F(3) 0(1)*..0(2) 0(1)-C(l) O(l)...C(2) O(l)...F(l) O(l) . ..F(2) O(l)...F(3) O(1) . ..O(l’) 0(1)...0(2’) O(l)...C(l’) O(l)..*C(2’) O(l)*..F(l’)
(I) and shrinkage
r, -r, -34 81 -21 23 73 97 88 87 74 60 135 183 168 167 4 84 35 41 40
corrections
Atomic
pair
O(l).**F(2’) 0(1)...F(3’) C(lW(2) C(l).*.F(l) C(l)...F(2) C(1). . . C(1’) C(l)...C(2’) C(l)...F(l’) C(l).“F(2’) C(2)+(1) C(2)‘..C(2’) C(2)...F(l’) C(2)+--F(2’) F(l)...F(2) F(l)...F(l’) F(l)...F(2’) F(2)...F(2’) F(2)...F(3’)
(ra -
ra)
for copper(I)
tri-
1
ra -ra
1551 1474 484 660 666 998 1031 1637 1469 493 1063 1801 1549 622 1684 2472 1629 1856
40 42 121 185 162 24 20 13 17 114 -10 -31 -22 134 -24 -63 -23 -34
pairs Cu * * * F is equal at every torsional angle. The rotational barrier height of the CF3 group was estimated to be 5.9 f 2.5 kJ mol-1 from the analysis assuming barrier heights of 3.3, 5.0, 6.7 and 8.4 kJ mol-‘. At this stage of analysis a little discrepancy between the theoretical and the experimental radial distributions remained in the ranges 3.6 to 3.9 a and 5.5 to 7.0 8. The latter corresponds to the atomic pairs of O(l), O(2) and C(1) to the atoms in the CF3 group of the other ligands, and the former to the atomic pair of O(1). - * 0( 2’). These discrepancies appear to show the folding motion of the molecule about the Cu-Cu’ line. The analysis taking into account the folding motion by V, = (1/2)h(Aa)‘, where h is the force constant and Acwis the dihedral angle between the ligands, resulted in decrease of the R-factor. Although the R-factor was decreased by 10% by using a k value of 0.15 X lo-‘* N m radm2,it was not so sensitive to the value of the force constant. The least-squares calculations were carried out on a HITAC S-810/20 computer in the Computer Center of the University of Tokyo. RESULTS
AND
DISCUSSION
The final results are listed in Tables 3 and 4. The random errors were 2.6 times the errors estimated in the least-squares calculations. The systematic errors were estimated from the errors in both the measurements of camera
320 TABLE 3 Molecular parameters obtained from least-squares analysis for copper(I) (distances in .&, angles in degrees)
cu-Cu’ cu-o(l) C(l)--Wl) C(l)-C(2) C( 2)--F( 1) O(l)CuO(2’) F(l)C(2)F(2) 88 0:
Rb
r&!
rs
Error
2.561 1.863 1.246 1.529 1.320 170.3 108.0 -0.4 13.6 0.035
2.566 1.874 1.253 1.542 1.333
0.018 0.002 0.004 0.005 0.003 0.6 0.3 0.7 4.2
aThe tilt angle of the C,, axis is defined as e. + (l/2)& rotational angle of the C,, axis (see text). bCw(qMObS -
trifluoroacetate
(1 -t- cos 6o), where o is the
l:bs
. . F( 2)’ CU...F(~)~
0.105 (12) 0.134 (9)
0.122 0.137
aResults obtained by the least-squares analysis. bValues calculated from the force constants in Table 1. ‘The mean amplitudes relating to the harmonic motion (see text).
,
but 0.003
A longer
f
321
ine for hydrogen atoms in the methyl group. However, the lengthening of 0.075 a is significantly smaller than the corresponding difference (0.24 a) between quinoline adducts of copper(I1) trifluoroacetate [ 3 ] and copper(I1) acetate [ 11. This shows that an electronegative atom is not so effective to a monovalent copper atom with filled d orbitals. Lengthening of the Cu--0 distance by the substitution of fluorine is also not large. On the other hand the attraction of electrons by fluorine results in shortening of the C-O bond in the acetate ligand by 0.02 a and lengthening of the C-C bond by 0.03 8. The C-F distance of copper(I) trifluoroacetate, 1.333 ?r 0.003 A is equal to that of CHF3 and CHOCF3 (1.332 a) [ 17, 181. Thus, the m electrons in the conjugated ring of dimeric copper(I) trifluoroacetate appear to move in the ring but not to move out of the ring. Table 5 shows that the radius of monovalent copper is about 0.1 A smaller than that of divalent copper. The values of Ar in Table 5, which represent the degree of strength of the metal-metal bond, are small in monovalent copper acetate complexes, although large in Mo2(02CCF& [19] because of the quadruple bond between molybdenum atoms [ 201. Therefore there may be no bond between the copper atoms of monovalent copper acetate. This is compatible with the fact that the root-mean-square amplitude of the Cu-Cu bond in copper(I) trifluoroacetate is very large (Table 4). The monovalent copper atom has linear two-coordination. The rotational barrier height of the CF, group of copper(I) trifluoroacetate is 5.9 f 2.5 kJ mol-’ , in good agreement with that reported from the NMR study on the benzene adduct of tetrameric copper(I) trifluoroacetate (5.5 kJ mol-’ ) [ 71. The minimum of the barrier is at the position such that one of the C-F bonds lies on the plane perpendicular to the ring ($ = 30, 90, 150”) . . . ), and the tilt angle of the CJV axis is zero within the limits of
TABLE Molecular
5 parameters
of related
2.566 (18) 1.874 (2) 1.253 (4) 1.542 (5) 1.333 (3) 170.3 (6) 128.7 (9) -0.15 This work
‘Ar = 2[r(M oxygen.
-
0)
-
0.661
(distances
in A, angles in degrees)
Cu,(WCH,), gas
Cu,(O,CCH,);2H,O solid
2.491 1.868 1.270 1.506
(3) (2) (2) (3)
2.616 1.969 1.260 1.501
(3) (37) (18) (18)
172.5 125.9 -0.07 5
(1) (2)
168.8 124.8 0.0 16(a)
(6) (18)
Cu,(O,CCF,), gas r(M-M) r(M-0) r(C-0) r(C-C) r( C-F) LOCUO’ LOCO Ara Ref.
molecules
-
r(M-M),
where
0.66
is the covalent
Mo,(O,CCF,), gas 2.105 2.102 1.25 1.54 1.335 176.2 126.9 0.77 19 single-bond
(9) (6) (2) (1) (5) (6) (7)
radius of
322
error. The maximum of the barrier is at the position such that one of the C-F bonds lies on the same plane as the ring ($ = 0,60,120”, . . .), and the C3” axis tilts 13 + 4” to the opposite direction of the C-F bond on the plane. This tilt may reduce the repulsion between the fluorine and the oxygen atoms on the ring plane. REFERENCES 1 T. N. Tarkhova and A. V. Ablov, Kristallografia, 13 (1968) 611. 2 G. Davey and F. S. Stephens, J. Chem. Sot. A, (1970) 2803. 3 J. A. Moreland and R. J. Doedens, J. Am. Chem. Sot., 97 (1975) 508. 4 D. A. Edwards and R. Richards, Inorg. Nucl. Chem. Lett., 8 (1972) 783. 5 K. Iijima, T. Itoh and S. Shibata, J. Chem. Sot., Dalton Trans., (1985) 2555. 6 P. F. Rodesiler and E. L. Amma, J. Chem. Sot., Chem. Commun., (1974) 599. 7 A. Kubo, R. Ikeda, J. A. Sampedra, M. Inoue and D. Nakamura, Bull. Chem. Sot. Jpn., 58 (1985) 2947. 8 R. L. Martin and H. Waterman, J. Chem. Sot., (1957) 2545. 9 D. A. Edwards and R. Richards, J. Chem. Sot., Dalton Trans., (1973) 2463. 10 W. Witt, Z. Naturforsch., Teil A, 19 (1964) 1363. 11 S. Shibata, K. Iijima, R. Tani and I. Nakamura, Rep. Fat. Sci. Shizuoka Univ., 9 (1974) 33. 12 L. Schafer, A. C. Yates and R. A. Bonham, J. Chem. Phys., 55 (1971) 3055. The values for fluorine were taken from H. L. Sellers, L. Schafer and R. A. Bonham, J. Mol. Struct., 49 (1978) 125. 13 D. T. Cromer and J. B. Mann, J. Chem. Phys., 47 (1967) 1892; D. T. Cromer, J. Chem. Phys., 50 (1969) 4857. 14 K. Kuchitsu and S. J. Cyvin, in S. J. Cyvin (Ed.), Molecular Structures and Vibrations, Elsevier, Amsterdam, 1972, Chap. 12. 15 S. Mizushima and T. Shimanouchi, Infrared Absorption and Raman Effect, KyoritsuShuppan, Tokyo, 1963. 16 (a) P. De Meester, S. R. Fletcher and A. C. Skapski, J. Chem. Sot., Dalton Trans., (1973) 2575. (b) V. M. Rao, D. N. Sathyanarayana and H. Manohar, J. Chem. Sot., Dalton Trans., (1983) 2167. 17 S. N. Ghosh, R. Trambarulo and W. Gordy, J. Chem. Phys., 20 (1952) 605. 18 L. E. Sutton, Tables of Interatomic Distances and Configuration in Molecules and Ions, The Chemical Society, London, 1965. 19 C. D. Garner, I. H. Hillier, I. B. Walton and B. Beagley, J. Chem. Sot., Dalton Trans., (1978) 1279. 20 F. A. Cotton and G. G. Stanley, Inorg. Chem., 16 (1977) 2669.
Journal
in The Netherlands
MOLECULAR STRUCTURE OF GASEOUS COPPER(I) TRIFLUOROACETATE AS DETERMINED BY ELECTRON DIFFRACTION
KINYA ILBMA, JUN-ICHI OHKAWA and SHUZO SHIBATA* Department
of Chemistry,
Shizuoka
University,
Oya, Shizuoka
422
(Japan)
(Received 15 September 1986)
ABSTRACT The molecular structure of gaseous copper(I) trifluoroacetate was determined by electron diffraction. The molecule is dimeric and its skeleton is essentially planar. The molecular parameters and the uncertainties are rdCu-Cu) = 2.566 f 0.018 A, ra(Cu-0) = 1.874 + 0.002 A, rg(C-O) = 1.253 + 0.004 A, r&C-C) = 1.542 f 0.005 A, ra(C-F) = 1.333 + 0.003 A and LOCuO’ = 170.3 +_0.6”. The rotational barrier height of the CF, group is 5.9 + 2.5 kd mol’ , and the minimum of the barrier is at the position such that one of the C-F bonds lies on the plane perpendicular to the ring.
INTRODUCTION
Structural studies on dimeric copper(H) complexes of carboxylic acids have shown that the more acidic the carboxylic acid the longer is the metalmetal separation; the Cu-Cu distance of quinoline adduct of copper(I1) acetate is 2.642 A [I], a-picoline adduct of copper(I1) chloroacetate 2.747 A [2] and quinoline adduct of copper(I1) trifluoroacetate 2.886 a [3] . Copper(I) acetate is dimeric in the gas phase [ 41 and the coppercopper separation is 2.491 8, which is the shortest for copper acetates reported so far [5]. We were interested in the effect of halogen substitution on the copper-copper separation of monovalent copper acetate. The crystal structure of copper(I) trifluoroacetate has not yet been determined, but the adduct with benzene was found to be tetrameric in the solid phase [6]. For this compound the orientation of the CF3 groups could not be determined because of the disorder, but the activation energy for the CF3 reorientation has been reported as 5.5 kJ mol-’ from NMR [7] . However, mass spectroscopy has shown that copper(I) trifluoroacetate is dimeric in the gas phase [4] as well as copper(I) acetate. Thus we attempted to determine the molecular structure of copper(I) trifluoroacetate by gasphase electron diffraction and hoped to obtain the orientation and rotational barrier height of the CF3 group though the orientation of the CH3 group of acetate could not be obtained in the study on gaseous copper(I) acetate [5]. 0022-2860/87/$03.50
o 1987 Elsevier Science Publishers B.V.
316 EXPERIMENTAL
Copper(I1) butyrate was prepared from copper carbonate by addition of butyric acid [8]. After the reduction by hydrazine hydrate, copper(I) butyrate was added to trifluoroacetic acid containing a little trifluoroacetic anhydride [9]. The solution was concentrated by pumping in vacua. The white precipitate of copper(I) trifluoroacetate was filtered off and sublimed under vacuum. Electron diffraction photographs were taken by using an r3-sector on Kodak electron-image plates at camera distances of 293.78 and 143.84 mm. The sample was sublimed at 416 K using a high-temperature nozzle. The accelerating voltage was 40 kV and the wavelength was determined from the diffraction patterns of thallium(I) chloride [lo]. The exposure times were ca. 40 and 70 s for the long and the short-camera-distance photographs, respectively, with an electron-beam current of 0.7 PA. The pressure in the diffraction chamber was 9 X 10e4 Pa during the experiment. Four plates were selected for photographs at each camera distance, and their optical densities were measured at 0.4 mm intervals by a digital microphotometer. The electron diffraction unit and the digital microphotometer used in this study have been described elsewhere [ 111. STRUCTURAL
ANALYSIS
Scattering intensities in the range q = 11.5--51.0 8-l were obtained from the long-camera-distance plates and those in the range q = 28-109 a-l from the short-camera-distance plates (q represents (40/h) sin (e/2), where X is wavelength and 8 is scattering angle). They were levelled by using theoretical backgrounds, and the intensities for each camera distance were averaged. The elastic and inelastic scattering factors were taken from refs. 12 and 13, respectively. The experimental background curve was drawn smoothly, and the experimental molecular intensities obtained are shown in Fig. 1. Figure 2 shows the experimental radial distribution function calculated from the molecular intensities. The molecular model of copper(I) trifluoroacetate is shown in Fig. 3. It was assumed that the molecular skeleton has D,, symmetry and each CF3 group has local C 3v symmetry. Since the shoulder at 3.4 a in the radial distribution function corresponds to the atomic pair of O(1) - * * F(2), the orientation of the CF3 group was considered as one of the C-F bonds lying on the plane perpendicular to the ring plane ($ = 30, 90, 150”, etc.). Here the rotational angle of the CF3 group around the C-C bond, $, is zero at the position where one of the C-F bonds lies on the ring plane. Since the rotational barrier height seemed low because of the Cg symmetry, the molecular intensities were calculated from $ = 60” to 120” at 6” intervals and summed with the weights of the Boltzmann distribution. The peaks of the radial distribution function in the range of 4.4 to 5.1 a are from the
317
,
(a)
1 D i
o-
o-1 -
I
(b)
50
LO
30 q/A-’
20
1 -
-G
E
o-
CT
-1
LO
60
q
/A-’
80
100
Fig. 1. Molecular intensities for gaseous copper(I) trifluoroacetate: (a) long and (b) short camera-distance data. The dots represent the experimental points and the solid curves the theoretical intensities. The curves at the bottom show the residuals.
Fig. 2. Radial distribution curve for gaseous copper(I) trifluoroacetate. The dots represent the experimental curve and the solid line the theoretical curve. The curve at the bottom shows the difference and the vertical bars represent bond distances and their scattering powers.
Fig. 3. Molecular
model
of dimeric
copper(I)
trifluoroacetate
atomic pairs of Cu * * - F. The theoretical radial distribution function did not agree well with the experimental value in this region when it was assumed that the C3” symmetry axis of the CF3 group is coincident with the C-C bond. Thus we assumed that the tilt angle of the CSV axis of the CF3 group is B,, + (l/2)8 1 (1 + cos 64) and the plane including the C-C bond and the CSV axis rotates by 3$1; the CSV axis tilts by f?,, out of the ring plane when l#I = 30, 90, 150”, . . . and by 8 0 + B 1 on the ring plane when $ = 0, 60, 120”, . . . . The molecular parameters were obtained from least-squares analysis of the intensities. The root-mean-square amplitudes and the shrinkage corforce field rections, ra - r, [ 141, were calculated from the Urey--Bradley and were used in the least-squares calculation. The force constants were taken from those of related molecules [4, 151, and were slightly adjusted so that the calculated mean amplitudes agreed with the observed mean amplitudes. The final force constants are listed in Table 1. The calculated mean amplitudes and the shrinkage corrections are listed in Table 2. For the mean amplitudes relating to the harmonic motion of the CF3 group (except the torsional motion) it was assumed that each of the atomic TABLE
1
Urey-Bradley K( cur-Cu’ ) K(Cu-0) K(C--O) W-0 K( C-F) n(C) Y( cu-Cu’ Y(Cu-0)
H(CuCu’0) H(CuOC)
force
field for copper(I) 0.37 1.2 5.0 3.3 3.0 0.62 0.08 0.08 0.14 0.01 0.10
trifluoroacetatea
H(OC0) H(OCC) H( CCF) H(FCF) F(Cu.*.O) F(Cu . . . C)
F(0 . . * 0) F(0 . ‘. C) F(C . . . F) F(F . . F) K
0.10 0.31 0.13 0.13 0.01 0.05 0.50 1.10 1.35 0.3
aUnits of the torsional force constant, Y, the out-of-plane bending force constant, r, and the internal tension of the trifluoromethyl carbon, K, are in lo-” N m, while the F’, was assumed to be -0.1 F. others are in 10’ N mm’ . The linear constant,
319 TABLE
2
Root-mean-square amplitudes fiuoroacetate (in lo-’ A) Atomic
pair
1 1142 728 1450 1029 967 1316 1218 1365 629 460 690 954 745 1126 1471 999 1133 1127 1640
cu-Cu’ cu-O(1) Cu*..O(2) cu. . . C( 1) Cu...C(2) Cu...F(l) Cu...F(2) Cu...F(3) 0(1)*..0(2) 0(1)-C(l) O(l)...C(2) O(l)...F(l) O(l) . ..F(2) O(l)...F(3) O(1) . ..O(l’) 0(1)...0(2’) O(l)...C(l’) O(l)..*C(2’) O(l)*..F(l’)
(I) and shrinkage
r, -r, -34 81 -21 23 73 97 88 87 74 60 135 183 168 167 4 84 35 41 40
corrections
Atomic
pair
O(l).**F(2’) 0(1)...F(3’) C(lW(2) C(l).*.F(l) C(l)...F(2) C(1). . . C(1’) C(l)...C(2’) C(l)...F(l’) C(l).“F(2’) C(2)+(1) C(2)‘..C(2’) C(2)...F(l’) C(2)+--F(2’) F(l)...F(2) F(l)...F(l’) F(l)...F(2’) F(2)...F(2’) F(2)...F(3’)
(ra -
ra)
for copper(I)
tri-
1
ra -ra
1551 1474 484 660 666 998 1031 1637 1469 493 1063 1801 1549 622 1684 2472 1629 1856
40 42 121 185 162 24 20 13 17 114 -10 -31 -22 134 -24 -63 -23 -34
pairs Cu * * * F is equal at every torsional angle. The rotational barrier height of the CF3 group was estimated to be 5.9 f 2.5 kJ mol-1 from the analysis assuming barrier heights of 3.3, 5.0, 6.7 and 8.4 kJ mol-‘. At this stage of analysis a little discrepancy between the theoretical and the experimental radial distributions remained in the ranges 3.6 to 3.9 a and 5.5 to 7.0 8. The latter corresponds to the atomic pairs of O(l), O(2) and C(1) to the atoms in the CF3 group of the other ligands, and the former to the atomic pair of O(1). - * 0( 2’). These discrepancies appear to show the folding motion of the molecule about the Cu-Cu’ line. The analysis taking into account the folding motion by V, = (1/2)h(Aa)‘, where h is the force constant and Acwis the dihedral angle between the ligands, resulted in decrease of the R-factor. Although the R-factor was decreased by 10% by using a k value of 0.15 X lo-‘* N m radm2,it was not so sensitive to the value of the force constant. The least-squares calculations were carried out on a HITAC S-810/20 computer in the Computer Center of the University of Tokyo. RESULTS
AND
DISCUSSION
The final results are listed in Tables 3 and 4. The random errors were 2.6 times the errors estimated in the least-squares calculations. The systematic errors were estimated from the errors in both the measurements of camera
320 TABLE 3 Molecular parameters obtained from least-squares analysis for copper(I) (distances in .&, angles in degrees)
cu-Cu’ cu-o(l) C(l)--Wl) C(l)-C(2) C( 2)--F( 1) O(l)CuO(2’) F(l)C(2)F(2) 88 0:
Rb
r&!
rs
Error
2.561 1.863 1.246 1.529 1.320 170.3 108.0 -0.4 13.6 0.035
2.566 1.874 1.253 1.542 1.333
0.018 0.002 0.004 0.005 0.003 0.6 0.3 0.7 4.2
aThe tilt angle of the C,, axis is defined as e. + (l/2)& rotational angle of the C,, axis (see text). bCw(qMObS -
trifluoroacetate
(1 -t- cos 6o), where o is the
l:bs
. . F( 2)’ CU...F(~)~
0.105 (12) 0.134 (9)
0.122 0.137
aResults obtained by the least-squares analysis. bValues calculated from the force constants in Table 1. ‘The mean amplitudes relating to the harmonic motion (see text).
,
but 0.003
A longer
f
321
ine for hydrogen atoms in the methyl group. However, the lengthening of 0.075 a is significantly smaller than the corresponding difference (0.24 a) between quinoline adducts of copper(I1) trifluoroacetate [ 3 ] and copper(I1) acetate [ 11. This shows that an electronegative atom is not so effective to a monovalent copper atom with filled d orbitals. Lengthening of the Cu--0 distance by the substitution of fluorine is also not large. On the other hand the attraction of electrons by fluorine results in shortening of the C-O bond in the acetate ligand by 0.02 a and lengthening of the C-C bond by 0.03 8. The C-F distance of copper(I) trifluoroacetate, 1.333 ?r 0.003 A is equal to that of CHF3 and CHOCF3 (1.332 a) [ 17, 181. Thus, the m electrons in the conjugated ring of dimeric copper(I) trifluoroacetate appear to move in the ring but not to move out of the ring. Table 5 shows that the radius of monovalent copper is about 0.1 A smaller than that of divalent copper. The values of Ar in Table 5, which represent the degree of strength of the metal-metal bond, are small in monovalent copper acetate complexes, although large in Mo2(02CCF& [19] because of the quadruple bond between molybdenum atoms [ 201. Therefore there may be no bond between the copper atoms of monovalent copper acetate. This is compatible with the fact that the root-mean-square amplitude of the Cu-Cu bond in copper(I) trifluoroacetate is very large (Table 4). The monovalent copper atom has linear two-coordination. The rotational barrier height of the CF, group of copper(I) trifluoroacetate is 5.9 f 2.5 kJ mol-’ , in good agreement with that reported from the NMR study on the benzene adduct of tetrameric copper(I) trifluoroacetate (5.5 kJ mol-’ ) [ 71. The minimum of the barrier is at the position such that one of the C-F bonds lies on the plane perpendicular to the ring ($ = 30, 90, 150”) . . . ), and the tilt angle of the CJV axis is zero within the limits of
TABLE Molecular
5 parameters
of related
2.566 (18) 1.874 (2) 1.253 (4) 1.542 (5) 1.333 (3) 170.3 (6) 128.7 (9) -0.15 This work
‘Ar = 2[r(M oxygen.
-
0)
-
0.661
(distances
in A, angles in degrees)
Cu,(WCH,), gas
Cu,(O,CCH,);2H,O solid
2.491 1.868 1.270 1.506
(3) (2) (2) (3)
2.616 1.969 1.260 1.501
(3) (37) (18) (18)
172.5 125.9 -0.07 5
(1) (2)
168.8 124.8 0.0 16(a)
(6) (18)
Cu,(O,CCF,), gas r(M-M) r(M-0) r(C-0) r(C-C) r( C-F) LOCUO’ LOCO Ara Ref.
molecules
-
r(M-M),
where
0.66
is the covalent
Mo,(O,CCF,), gas 2.105 2.102 1.25 1.54 1.335 176.2 126.9 0.77 19 single-bond
(9) (6) (2) (1) (5) (6) (7)
radius of
322
error. The maximum of the barrier is at the position such that one of the C-F bonds lies on the same plane as the ring ($ = 0,60,120”, . . .), and the C3” axis tilts 13 + 4” to the opposite direction of the C-F bond on the plane. This tilt may reduce the repulsion between the fluorine and the oxygen atoms on the ring plane. REFERENCES 1 T. N. Tarkhova and A. V. Ablov, Kristallografia, 13 (1968) 611. 2 G. Davey and F. S. Stephens, J. Chem. Sot. A, (1970) 2803. 3 J. A. Moreland and R. J. Doedens, J. Am. Chem. Sot., 97 (1975) 508. 4 D. A. Edwards and R. Richards, Inorg. Nucl. Chem. Lett., 8 (1972) 783. 5 K. Iijima, T. Itoh and S. Shibata, J. Chem. Sot., Dalton Trans., (1985) 2555. 6 P. F. Rodesiler and E. L. Amma, J. Chem. Sot., Chem. Commun., (1974) 599. 7 A. Kubo, R. Ikeda, J. A. Sampedra, M. Inoue and D. Nakamura, Bull. Chem. Sot. Jpn., 58 (1985) 2947. 8 R. L. Martin and H. Waterman, J. Chem. Sot., (1957) 2545. 9 D. A. Edwards and R. Richards, J. Chem. Sot., Dalton Trans., (1973) 2463. 10 W. Witt, Z. Naturforsch., Teil A, 19 (1964) 1363. 11 S. Shibata, K. Iijima, R. Tani and I. Nakamura, Rep. Fat. Sci. Shizuoka Univ., 9 (1974) 33. 12 L. Schafer, A. C. Yates and R. A. Bonham, J. Chem. Phys., 55 (1971) 3055. The values for fluorine were taken from H. L. Sellers, L. Schafer and R. A. Bonham, J. Mol. Struct., 49 (1978) 125. 13 D. T. Cromer and J. B. Mann, J. Chem. Phys., 47 (1967) 1892; D. T. Cromer, J. Chem. Phys., 50 (1969) 4857. 14 K. Kuchitsu and S. J. Cyvin, in S. J. Cyvin (Ed.), Molecular Structures and Vibrations, Elsevier, Amsterdam, 1972, Chap. 12. 15 S. Mizushima and T. Shimanouchi, Infrared Absorption and Raman Effect, KyoritsuShuppan, Tokyo, 1963. 16 (a) P. De Meester, S. R. Fletcher and A. C. Skapski, J. Chem. Sot., Dalton Trans., (1973) 2575. (b) V. M. Rao, D. N. Sathyanarayana and H. Manohar, J. Chem. Sot., Dalton Trans., (1983) 2167. 17 S. N. Ghosh, R. Trambarulo and W. Gordy, J. Chem. Phys., 20 (1952) 605. 18 L. E. Sutton, Tables of Interatomic Distances and Configuration in Molecules and Ions, The Chemical Society, London, 1965. 19 C. D. Garner, I. H. Hillier, I. B. Walton and B. Beagley, J. Chem. Sot., Dalton Trans., (1978) 1279. 20 F. A. Cotton and G. G. Stanley, Inorg. Chem., 16 (1977) 2669.