- Email: [email protected]
The molecular structure of trifluoromethyl manganese pentacarbonyl. A study by gas-phase electron diffraction
Journal of Molecular Structure. 40 (1977) 8 Elsevier Scientific Publishing Company,
296-297 Amsterdam -
Printed in The Netheriands
Short communication
THE MOLECULAR PENTACARBONYL. DIFFRACTTON
B. BEAGLEY
STRUCTURE OF TRIFLUOROMETHYL A STUDY BY GAS-PHASE ELECTRON
MANGANESE
and G_ G. YOUNG
Department of Chemistry. University of Manchester institute of Science and Technology. Sackuille Street, Manchester M60 t QD (Ct. Britain) (Fkceiwzd 7 March 1977)
Trifluoromethyl manganese pentacarbonyl, CFJMn(CO)S, like its methyl analogue [l] can be expected to have manganese in octahedral coordination (Fig. 1). The present study was carried out to ascertain the effect on the molecular dimensions of fluorination of the methyl group. RADIAL
DISTRIBUTION
CURVE
Gas-phase electron diffraction data were collected and processed by routine methods [Z 1. The radial distribution curve obtained is shown in Fig. 2. The C-F and Mn-CF bond distances are clearly indicated as shoulders at the long&stance side of each of the first two peaks, the main components of which are C-G and Mn-CO. From the peak near 3 A it is possible to F distance (and hence LMnCF) because allowance can be deducetheMn=** 0 distances also involved; the Mn* 0 distances can be made for the Mn calculated from the bond distances within the linear Mn-C-G fragments. Of the three remaining independent parameters, LC,MnC, and rFC&#&, l
l
l
l
.F
l
r CFpn~CO)6
Fig. 1. CF,Mn(CQ),
-
m&cular
mod&
Fig. 2. Experimental rad3aI distribution FURY (subscripb:
s 7 short. 1 = low).
were deduced in the subsequent least-squares analysis through the disposition of distances dependent on them. It was doubtful at the outsetwhether- conclusive evidence could be obtained about the difference in the lengths of the axial (a) and equatorial (e) Mn-CO bonds. LEAST-SQUAW&
REFINEMENT
Least-squares refinement of the independent geometrical parameters described above was carried out in the usual way [Z] , comparing the experimental and calculated molecular intensity curves; The final parameters are given in Table 1. To refine vibrational amplitudes, distances were grouped according to the peak in the radial;distribution curve which contained them. The final agreement between experimental (1_,) and calculated(I,,) curves was R = z ll,,--I, icxp I = 0.075.
j/c
RESULTS
AND
DISCUSSION
Table 2 compares the dimensions of the methyl and trifluoromethyl analogues and related molecules. Although in the present work it is not TABLE
1
Structural parameters of h’;Mn (CO), (Distances on r. basis, and amplitudes, in A; angles in degrees; subscripts: e = equatoriaI,_ a = axial, s = short. 1 = long; 1 A = lo-“’ m) Parameter
Distance Value
Independent C-O C-F Mlrc, Ml?C, Mn-CF, LCWC, LMnCF ‘FChC,
parameters 1.143 1.370 1.864 1.874 2.056 92.1 114.0 15a
Dependent distances in @oupa F...F 2.17 I.. 2.6-2.7 c C, Mn..-O/F 2.9-3.0 C .*-o&z, 3:5-3.9 0 ..- 4 4.2-4.4 C ---0,/F, 4.6-5.1 ’ O- --O,F, 5.8-6.0 C/O- -.Fs WriOUS
Amplitude Es-d.
_Value
Es.d.
-* 0.002 0.003 0.007 0.007 1 0.005 0.3 0.2 1
0.031 0.036
- 0.002 0.003
0.074
0.002
-
-
0.048 0.112 0.066 0.16 :0.31-; 0.089 0.135 0.17
0.003 0.010 0.002 0.02 ‘o.g3 . 0.007 O.OO_s,_ 0.02
a
297 TABLE
2
Structural comparison of Xhfn(m),
compounds
(Distances on r, basis in A; angles in degrees)
Molecule
~,MWO
Ref. X
This work CF,
C-G Mn--c, Mn-C,, Mn-CO(av) Mn-X LC,MnC,
1.143 1.864 1.874 1.866 2.056 92.1
1,
f 0.002 * 0.003 f 0.007 f 0.002 +- 0.005 t 0.2
CH,MdCO),
[MnWW,
II
(3C!O),Mn
1.141 1.860 1.820 1.852 2.185 94.7
i 0.002 i 0.004 (ass) f 0.004 +. 0.011 + 1.0
1.147 1.873 1.803 1.859 2.977 93.4
f f 2 r * f
HMn(CO), 4 H
0.002 0.005 0.016 0.006 0.011 0.5
1.139 1.865 1.840 1.860 1.50 96.4
f 2 * ? f f
0.002 0.002 0.002 0.002 0.02 0.5
established with certainty whether the axial and equatorial Mn-CO bonds differ in length, it is quite clear that the axial bond is longer in the trifluoromethyl molecule than in any of the others. As the equatorial Mn-CO bond lengths do not vary significantly, the result is that the trifluoromethyl molecule has the biggest average Mn-CO length. This molecule also has its Mn-CF3 bond shorter than the Mn-CH, bond in the methyl compound. It seems, therefore, that the effect of replacing hydrogen by fluorine is to strengthen the bonding between transition metal and organic ligand and weaken, on average, the metal to carbonyl bonding. A similar conclusion was reached when comparing the ethylene complexes C2H4Fe(CO)J and C1F4Fe(C0)4 [5], and the dimensions of SiHJ Mn(COh [6] and SiF3Mn(CO)S [7] show corresponding trends. REFERENCES H. M. Seip and R. Seip, Acta Chem. Stand., 24 (1970) 3431. B. Beagley, J. J. Monaghan and T. G. Hewitt, J. Mol. Struct., 8 (1971) 401. A. AlmenninGn, G. G. Jacobsen and H. M. Seip, Acta Chem. &and., 23 (1969) 685. A C. Robiette. G. M. Sheldrick and R. N. F. Sim_mon, J. Mol. Struct., 4 (1969) 221. B. Beapley. D. G. Schmidling and D. W. J. Cruickshank. Acta Crystallogr. Sect. B. 29 (1973) 1499. 6 D. W. H. Rankin and A. Robertson, J. Organometal. Chem., 85 (1975) 225. 7 D. W. H. Rankin and A. Robertson, J. Organometal. Chem., 88 (1975) 191. 1 2 3 4 5
296-297 Amsterdam -
Printed in The Netheriands
Short communication
THE MOLECULAR PENTACARBONYL. DIFFRACTTON
B. BEAGLEY
STRUCTURE OF TRIFLUOROMETHYL A STUDY BY GAS-PHASE ELECTRON
MANGANESE
and G_ G. YOUNG
Department of Chemistry. University of Manchester institute of Science and Technology. Sackuille Street, Manchester M60 t QD (Ct. Britain) (Fkceiwzd 7 March 1977)
Trifluoromethyl manganese pentacarbonyl, CFJMn(CO)S, like its methyl analogue [l] can be expected to have manganese in octahedral coordination (Fig. 1). The present study was carried out to ascertain the effect on the molecular dimensions of fluorination of the methyl group. RADIAL
DISTRIBUTION
CURVE
Gas-phase electron diffraction data were collected and processed by routine methods [Z 1. The radial distribution curve obtained is shown in Fig. 2. The C-F and Mn-CF bond distances are clearly indicated as shoulders at the long&stance side of each of the first two peaks, the main components of which are C-G and Mn-CO. From the peak near 3 A it is possible to F distance (and hence LMnCF) because allowance can be deducetheMn=** 0 distances also involved; the Mn* 0 distances can be made for the Mn calculated from the bond distances within the linear Mn-C-G fragments. Of the three remaining independent parameters, LC,MnC, and rFC&#&, l
l
l
l
.F
l
r CFpn~CO)6
Fig. 1. CF,Mn(CQ),
-
m&cular
mod&
Fig. 2. Experimental rad3aI distribution FURY (subscripb:
s 7 short. 1 = low).
were deduced in the subsequent least-squares analysis through the disposition of distances dependent on them. It was doubtful at the outsetwhether- conclusive evidence could be obtained about the difference in the lengths of the axial (a) and equatorial (e) Mn-CO bonds. LEAST-SQUAW&
REFINEMENT
Least-squares refinement of the independent geometrical parameters described above was carried out in the usual way [Z] , comparing the experimental and calculated molecular intensity curves; The final parameters are given in Table 1. To refine vibrational amplitudes, distances were grouped according to the peak in the radial;distribution curve which contained them. The final agreement between experimental (1_,) and calculated(I,,) curves was R = z ll,,--I, icxp I = 0.075.
j/c
RESULTS
AND
DISCUSSION
Table 2 compares the dimensions of the methyl and trifluoromethyl analogues and related molecules. Although in the present work it is not TABLE
1
Structural parameters of h’;Mn (CO), (Distances on r. basis, and amplitudes, in A; angles in degrees; subscripts: e = equatoriaI,_ a = axial, s = short. 1 = long; 1 A = lo-“’ m) Parameter
Distance Value
Independent C-O C-F Mlrc, Ml?C, Mn-CF, LCWC, LMnCF ‘FChC,
parameters 1.143 1.370 1.864 1.874 2.056 92.1 114.0 15a
Dependent distances in @oupa F...F 2.17 I.. 2.6-2.7 c C, Mn..-O/F 2.9-3.0 C .*-o&z, 3:5-3.9 0 ..- 4 4.2-4.4 C ---0,/F, 4.6-5.1 ’ O- --O,F, 5.8-6.0 C/O- -.Fs WriOUS
Amplitude Es-d.
_Value
Es.d.
-* 0.002 0.003 0.007 0.007 1 0.005 0.3 0.2 1
0.031 0.036
- 0.002 0.003
0.074
0.002
-
-
0.048 0.112 0.066 0.16 :0.31-; 0.089 0.135 0.17
0.003 0.010 0.002 0.02 ‘o.g3 . 0.007 O.OO_s,_ 0.02
a
297 TABLE
2
Structural comparison of Xhfn(m),
compounds
(Distances on r, basis in A; angles in degrees)
Molecule
~,MWO
Ref. X
This work CF,
C-G Mn--c, Mn-C,, Mn-CO(av) Mn-X LC,MnC,
1.143 1.864 1.874 1.866 2.056 92.1
1,
f 0.002 * 0.003 f 0.007 f 0.002 +- 0.005 t 0.2
CH,MdCO),
[MnWW,
II
(3C!O),Mn
1.141 1.860 1.820 1.852 2.185 94.7
i 0.002 i 0.004 (ass) f 0.004 +. 0.011 + 1.0
1.147 1.873 1.803 1.859 2.977 93.4
f f 2 r * f
HMn(CO), 4 H
0.002 0.005 0.016 0.006 0.011 0.5
1.139 1.865 1.840 1.860 1.50 96.4
f 2 * ? f f
0.002 0.002 0.002 0.002 0.02 0.5
established with certainty whether the axial and equatorial Mn-CO bonds differ in length, it is quite clear that the axial bond is longer in the trifluoromethyl molecule than in any of the others. As the equatorial Mn-CO bond lengths do not vary significantly, the result is that the trifluoromethyl molecule has the biggest average Mn-CO length. This molecule also has its Mn-CF3 bond shorter than the Mn-CH, bond in the methyl compound. It seems, therefore, that the effect of replacing hydrogen by fluorine is to strengthen the bonding between transition metal and organic ligand and weaken, on average, the metal to carbonyl bonding. A similar conclusion was reached when comparing the ethylene complexes C2H4Fe(CO)J and C1F4Fe(C0)4 [5], and the dimensions of SiHJ Mn(COh [6] and SiF3Mn(CO)S [7] show corresponding trends. REFERENCES H. M. Seip and R. Seip, Acta Chem. Stand., 24 (1970) 3431. B. Beagley, J. J. Monaghan and T. G. Hewitt, J. Mol. Struct., 8 (1971) 401. A. AlmenninGn, G. G. Jacobsen and H. M. Seip, Acta Chem. &and., 23 (1969) 685. A C. Robiette. G. M. Sheldrick and R. N. F. Sim_mon, J. Mol. Struct., 4 (1969) 221. B. Beapley. D. G. Schmidling and D. W. J. Cruickshank. Acta Crystallogr. Sect. B. 29 (1973) 1499. 6 D. W. H. Rankin and A. Robertson, J. Organometal. Chem., 85 (1975) 225. 7 D. W. H. Rankin and A. Robertson, J. Organometal. Chem., 88 (1975) 191. 1 2 3 4 5