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Ab initio molecular orbital calculations on linkage isomers of magnesium difluoride-carbon monoxide adducts
Journal of Molecular Structure (Theochem), 168 (1988) 311-322 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
317
AB INITIO MOLECULAR ORBITAL CALCULATIONS ON LINKAGE ISOMERS OF MAGNESIUM DIFLUORIDE-CARBON MONOXIDE ADDUCTS
ALICIA H. JUBERT Cdtedra de Quimica Inorgcinica, Facultad de Ciencias Exactas, Universidad National de La Plata, 47y 115,190O La P&a (Argentina) SERGIO A. MALUENDES and EDUARDO A. CASTRO* Divisidn Quimica Tedrica, INIFTA, Sucursal4, CC 16,190O Lu Plata (Argentina) KAZUO NAKAMOTO Department of Chemistry, Marquette University, Milwaukee, WI 53233 (U.S.A.) (Received 28 October 1987)
ABSTRACT Ab initio molecular orbital calculations have been performed on the C- and O-bonded adducts of MgF, with CO using MINI-I, MINI-4*, MINI-4**, 3-21G and 6-31G basis sets. In all cases, the O-bonded isomer was found to be more stable than the C-bonded isomer. Mulliken population analysis indicates that the Mg* **0 interaction is mainly ionic as expected from Klopman’s theory.
INTRODUCTION
In the majority of metal carbonyls, carbon monoxide coordinates to the metal via the carbon atom as a terminal or a bridging ligand [ 11. In contrast, only a few reports are available on “isocarbonyl” compounds in which CO is bonded to the metal via the oxygen atom. These include Fez(CzH5)2(C0)42A1(C,H,), (I) [2] and Mn,(CO) (Ph2P(CH2)2PPh2) (II) [3] in which the oxygen atom of the bridging carbonyl is bonded to the metal as shown below.
O\
Al (C2H5j3
I
*To whom correspondence
0166-1280/88/$03.50
II
should be addressed.
0 1988 Elsevier Science Publishers
B.V.
318
The isocarbonyl structure, 0 = C-Au-O = C, was proposed for gold carbonyl [4], the stabilization of this structure is most likely the consequence of the orientational requirements of the CO molecules in CO matrices which prevent the rearrangement to the normal carbon-bonded structure. Thus far, no “genuine” terminal isocarbonyls have been confirmed by spectroscopic or other methods. Isocarbonyl linkage was also proposed between Lewis acids and early transition metals [ 51 with CO. Pearson and co-workers developed the concept of “hard and soft” acids and bases [6,7] which has been widely used to predict linkage isomerism of coordination compounds. Klopman [ 81 developed a quantitative scale of hardness and softness based on molecular orbital theory. Metal atoms in the majority of metal carbonyls are regarded as soft acids since they are in the low oxidation state. Such metals should be bound to the soft end of CO which is evidently the carbon atom. According to Klopman, such soft acid-soft base interaction occurs when there is good energy level matching and orbital overlap between the donor (base) and acceptor (acid) orbital. On the other hand, hard acidhard base interaction occurs when the energy matching and orbital overlap between the donor and acceptor orbitals are poor. In this case, very little electron transfer occurs between them and the interaction is mainly ionic. Typical hard metals such as Mg(I1) and Ca(I1) may form oxygen-bonded CO complexes if these conditions are satisfied. The main objective of this investigation is to elucidate, via ab initio molecular orbital calculations, which structure is more stable, the O-bonded or the C-bonded, in FzMgCO. It should be noted that similar adducts, such as F,CaCO and F2ZnC0, have already been prepared in Ar matrices [ 91. However, no attempt to distinguish between the C- and O-bonded structures has been made. MOLECULAR GEOMETRY
Molecular beam [lo] as well as matrix-isolation IR studies [ 111 indicate that MgFz is linear. This structure was also confirmed by Gole et al. [ 121 who performed non-empirical LCAO MO SCF calculations with different basis sets. We used, as input geometry in our calculations, the following interatomic distances: Mg-F = 1.7701 A [ 131 (linear conformation) and C-O = 1.1282 A [ 141. METHOD OF CALCULATION
We performed ab initio calculations with different basis HONDO-5 and MONSTERGAUSS 84 programs [15]. The those of Pople (3-21 and 6-31G) and Huzinaga and coworkers MINI-4* with polarization function on the Mg, and MINI-4** tion functions over all atoms).
sets basis [ 161 with
using the sets were (MINI-4, polariza-
Geometry optimization was carried out using the gradient method [ 171 on F2Mg, CO and both adducts F2Mg* *CO and F,Mg* **OC. l
RESULTS AND DISCUSSION
For all basis sets, MgF, was predicted to be linear in its ground state. When it interacts with the oxygen-end of CO the F-Mg-F angle was calculated to be 150”, 150”, 158”, 158” and 164” for 3-21G, 6-31G, MINI-4, MINI-4* and MINI4** respectively. The optimized parameters for both C- and O-bonded adducts are listed in Table 1. It is seen that the CO distance increases while the MgF
distance decreases compared with those for the free molecules. This holds regardless of the mode of coordination and the method of calculation. The total energies and energy differences between the 0- and C-bonded structures that have been carried out within the framework of Hartree-Fock theory are listed in Table 2. In all cases the O-bonded adduct is more stable than the C-bonded one. These energies were calculated in terms of single-determinant wavefunctions. However, the neglect of electron correlation effects would lead to an inadequate description of the energy differences on the linkage isomers. To overcome this deficiency a limited direct configuration interaction (CI) calculation was performed on both isomers using the minimal basis set MINI-4. Single and double excitations have been included with respect to the Hartree-Fock single-determinant wavefunction, within the frozen-core approximation [ 181. The Langhoff and Davison [ 191 formula was used in order to approximate the correction to the energy due to the neglect of quadruple substitutions in the multiple-determinant wavefunction. The results are shown at the end of Table 2. It is concluded that at this level of the theory the O-bonded isomer is the more stable one. The total bond energies for both adducts are shown in Table 3. For these adducts the basis set superposition error (BSSE) can be a large amount of the total binding energy. We have estimated the BSSE by calculating CO and MgF, total energies with the complete basis set of F2MgC0 [ 201, then corrected binding energies are obtained. In Table 3 these energies are shown for 3-21G and MINI-4 basis sets (the BSSE is expected to be more important in those calculations performed with the smallest basis sets) and we conclude that this error will not change our prediction that the Mg* **OC adduct is more stable than the Mg* *-CO one. Mulliken population analysis (net charges) obtained from the MINI-4 basis set calculations for the F2Mg*. *OC adduct shows that the 0 atom increases the negative charge ( - 0.36 for free CO and - 0.46 in the adduct). The C and Mg atoms become more positive due to the Mg* *00 intermolecular interaction; their net charges change from 0.36 and 1.69 to 0.47 and 1.70, respectively. The nature of the Mg. **0 bonding seems to be predominatingly ionic as expected
co MgF OMg CMg
F,Mg-OC
MINI-4
1.1282 1.2309 1.7701 1.7489 2.1260
Exp.
2.3760
1.2204 1.7333
F,Mg-CO 1.2313 1.7372 2.1306
F2Mg-OC
MINI-4*
_
.__..
2.5053
1.2195 1.7352
F,Mg-CO 1.1659 1.7140 2.2680
F2Mg-OC
MINI-4**
2.5986
1.1559 1.7159
F2Mg-CO
1.1399 1.7275 2.0597
FzMg-OC
3-21G
2.3671
1.1188 1.7252
FzMg-CO
1.1401 1.7605 2.1082
F,Mg-OC
6-31G
2.4149
1.1210 1.7587
F&g-CO
Experimental data for the fragments and optimized parameters obtained for F,Mg* **CO and F2Mg* **OC from different basis sets (values in A)
TABLE 1
321 TABLE 2 Total energies for F,Mg* **CO and F,Mg* **OC from different basis sets (hartree); A= E FzMr’CO -Er2Mg...oc (ld mol-‘)
3-21G 6-31G MINI-4 MINI-4* MINI-4** MINI-4(CI)”
E F&e.,oc
EF~M~-CO
A
-508.51398 -511.24366 - 510.32421 - 510.34394 -510.45185 -510.43799
- 508.50689 -511.23789 -510.31533 - 510.33645 -510.45139 -510.43535
4.4 3.6 5.6 4.7 0.2 1.3
“The MINI-I(C1) calculation was carried out using the optimized geometry obtained with the MINI-4 basis set. TABLE 3 Total bond energies (Ec ) for F,Mg* - -0C and F2Mg* **CO adducts (kcal mol- ’ )” Basis set
E B(FzM&v.,OC)
3-21G
19.5 (13.5) 14.8 11.8 (11.3) 5.8
6-31G MINI-4 MINI-4**
E B(FzMg..CO) 15.1 (7.5) 11.8 (& 5.5
*Ea values in parentheses are corrected by BSSE.
from Klopman’s theory. Similar results were obtained when using 3-21G, MINI4* and MINI-4** basis sets. ACKNOWLEDGMENTS
The authors thank Prof. R.F. Fenske of University of Wisconsin, Madison, for his valuable comments. K.N. acknowledges the support from CRUN he received during his stay at University of La Plata in March 1983. A.H.J., S.A.M. and E.A.C. thank CONICET and CIC for financial support and CESPI for computational time.
REFERENCES 1
For example, K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, 4th edn., Wiley, New York, 1986.
322 2 3 4 5 6 7 8 9 10 11 12 13 14 15
16 17 18 19 20
N.J. Nelson, N.E. Kime and D.F. Shriver, J. Am. Chem. Sot., 91 (1969) 5173. R. Cohen, C.J. Commons and B.F. Hoskins, J. Chem. Sot., Chem. Commun., (1975) 363. D. McIntosh and G.A. Ozin, inorg. Chem., 16 (1977) 51. E.C. Lisic and B.E. Hanson, Inorg. Chem., 25 (1986) 812. R.G. Pearson, J. Am. Chem. Sot., 85 (1963 ) 3533. R.G. Pearson and J. Songstad, J. Am. Chem. Sot., 89 (1967) 1827. G. Klopman, J. Am. Chem. Sot., 90 (1968) 223. D.A. Van Leirsburg and C.W. Dekock, J. Phys. Chem., 78 (1974) 134. L. Wharton, R.A. Berg and J. Klemperer, Chem. Phys., 39 (1966) 2023. R.H. Hauge, J.L. Margrave and A.S. Kanaan, J. Chem. Sot., Faraday Trans. 2,71 (1975) 1082., J.L.Gole,A.K.Q.SiuandandE.F.Hayes, J.Chem. Phys.,58 (1973) 85. P.A. Akisbin and M. Spiridonov, SW. Phys.-Crystahogr., 2 (1957) 472. L.E. Sutton (Ed. ), Tabtes of Interatomic Distances and Configuration in Molecules and Ions, The Chemical Society, London, 1965. (a) M. Dupuis, J. RysandH.F. King, Q.C.P.E., 13 (1981) 403. (b) M. Peterson and R. Poirier, University of Toronto, Chemistry Department, Toronto, Ontario, Canada. (a) Y. Sakai, H. Tatewaki and S. Huzinaga, J. Comput. Chem., 2 (1981) 100. (b) H. Tatewaki and S. Huzinaga, J. Comput. Chem., 1 (1980) 205. B.A. Murtagh and R.W.H. Sargent, Comput. J., 13 (1970) 185. N.C. Handy, J.D. Goddard and H.F. Schaefer III, J. Chem. Phys., 71 (1979) 426. S.R. Langhoff and E.R. Davidson, Int. J. Quantum Chem., 8 (1974) 61. S.F. Boys and F. Bernard, Mol. Phys., 19 (1970) 553.
317
AB INITIO MOLECULAR ORBITAL CALCULATIONS ON LINKAGE ISOMERS OF MAGNESIUM DIFLUORIDE-CARBON MONOXIDE ADDUCTS
ALICIA H. JUBERT Cdtedra de Quimica Inorgcinica, Facultad de Ciencias Exactas, Universidad National de La Plata, 47y 115,190O La P&a (Argentina) SERGIO A. MALUENDES and EDUARDO A. CASTRO* Divisidn Quimica Tedrica, INIFTA, Sucursal4, CC 16,190O Lu Plata (Argentina) KAZUO NAKAMOTO Department of Chemistry, Marquette University, Milwaukee, WI 53233 (U.S.A.) (Received 28 October 1987)
ABSTRACT Ab initio molecular orbital calculations have been performed on the C- and O-bonded adducts of MgF, with CO using MINI-I, MINI-4*, MINI-4**, 3-21G and 6-31G basis sets. In all cases, the O-bonded isomer was found to be more stable than the C-bonded isomer. Mulliken population analysis indicates that the Mg* **0 interaction is mainly ionic as expected from Klopman’s theory.
INTRODUCTION
In the majority of metal carbonyls, carbon monoxide coordinates to the metal via the carbon atom as a terminal or a bridging ligand [ 11. In contrast, only a few reports are available on “isocarbonyl” compounds in which CO is bonded to the metal via the oxygen atom. These include Fez(CzH5)2(C0)42A1(C,H,), (I) [2] and Mn,(CO) (Ph2P(CH2)2PPh2) (II) [3] in which the oxygen atom of the bridging carbonyl is bonded to the metal as shown below.
O\
Al (C2H5j3
I
*To whom correspondence
0166-1280/88/$03.50
II
should be addressed.
0 1988 Elsevier Science Publishers
B.V.
318
The isocarbonyl structure, 0 = C-Au-O = C, was proposed for gold carbonyl [4], the stabilization of this structure is most likely the consequence of the orientational requirements of the CO molecules in CO matrices which prevent the rearrangement to the normal carbon-bonded structure. Thus far, no “genuine” terminal isocarbonyls have been confirmed by spectroscopic or other methods. Isocarbonyl linkage was also proposed between Lewis acids and early transition metals [ 51 with CO. Pearson and co-workers developed the concept of “hard and soft” acids and bases [6,7] which has been widely used to predict linkage isomerism of coordination compounds. Klopman [ 81 developed a quantitative scale of hardness and softness based on molecular orbital theory. Metal atoms in the majority of metal carbonyls are regarded as soft acids since they are in the low oxidation state. Such metals should be bound to the soft end of CO which is evidently the carbon atom. According to Klopman, such soft acid-soft base interaction occurs when there is good energy level matching and orbital overlap between the donor (base) and acceptor (acid) orbital. On the other hand, hard acidhard base interaction occurs when the energy matching and orbital overlap between the donor and acceptor orbitals are poor. In this case, very little electron transfer occurs between them and the interaction is mainly ionic. Typical hard metals such as Mg(I1) and Ca(I1) may form oxygen-bonded CO complexes if these conditions are satisfied. The main objective of this investigation is to elucidate, via ab initio molecular orbital calculations, which structure is more stable, the O-bonded or the C-bonded, in FzMgCO. It should be noted that similar adducts, such as F,CaCO and F2ZnC0, have already been prepared in Ar matrices [ 91. However, no attempt to distinguish between the C- and O-bonded structures has been made. MOLECULAR GEOMETRY
Molecular beam [lo] as well as matrix-isolation IR studies [ 111 indicate that MgFz is linear. This structure was also confirmed by Gole et al. [ 121 who performed non-empirical LCAO MO SCF calculations with different basis sets. We used, as input geometry in our calculations, the following interatomic distances: Mg-F = 1.7701 A [ 131 (linear conformation) and C-O = 1.1282 A [ 141. METHOD OF CALCULATION
We performed ab initio calculations with different basis HONDO-5 and MONSTERGAUSS 84 programs [15]. The those of Pople (3-21 and 6-31G) and Huzinaga and coworkers MINI-4* with polarization function on the Mg, and MINI-4** tion functions over all atoms).
sets basis [ 161 with
using the sets were (MINI-4, polariza-
Geometry optimization was carried out using the gradient method [ 171 on F2Mg, CO and both adducts F2Mg* *CO and F,Mg* **OC. l
RESULTS AND DISCUSSION
For all basis sets, MgF, was predicted to be linear in its ground state. When it interacts with the oxygen-end of CO the F-Mg-F angle was calculated to be 150”, 150”, 158”, 158” and 164” for 3-21G, 6-31G, MINI-4, MINI-4* and MINI4** respectively. The optimized parameters for both C- and O-bonded adducts are listed in Table 1. It is seen that the CO distance increases while the MgF
distance decreases compared with those for the free molecules. This holds regardless of the mode of coordination and the method of calculation. The total energies and energy differences between the 0- and C-bonded structures that have been carried out within the framework of Hartree-Fock theory are listed in Table 2. In all cases the O-bonded adduct is more stable than the C-bonded one. These energies were calculated in terms of single-determinant wavefunctions. However, the neglect of electron correlation effects would lead to an inadequate description of the energy differences on the linkage isomers. To overcome this deficiency a limited direct configuration interaction (CI) calculation was performed on both isomers using the minimal basis set MINI-4. Single and double excitations have been included with respect to the Hartree-Fock single-determinant wavefunction, within the frozen-core approximation [ 181. The Langhoff and Davison [ 191 formula was used in order to approximate the correction to the energy due to the neglect of quadruple substitutions in the multiple-determinant wavefunction. The results are shown at the end of Table 2. It is concluded that at this level of the theory the O-bonded isomer is the more stable one. The total bond energies for both adducts are shown in Table 3. For these adducts the basis set superposition error (BSSE) can be a large amount of the total binding energy. We have estimated the BSSE by calculating CO and MgF, total energies with the complete basis set of F2MgC0 [ 201, then corrected binding energies are obtained. In Table 3 these energies are shown for 3-21G and MINI-4 basis sets (the BSSE is expected to be more important in those calculations performed with the smallest basis sets) and we conclude that this error will not change our prediction that the Mg* **OC adduct is more stable than the Mg* *-CO one. Mulliken population analysis (net charges) obtained from the MINI-4 basis set calculations for the F2Mg*. *OC adduct shows that the 0 atom increases the negative charge ( - 0.36 for free CO and - 0.46 in the adduct). The C and Mg atoms become more positive due to the Mg* *00 intermolecular interaction; their net charges change from 0.36 and 1.69 to 0.47 and 1.70, respectively. The nature of the Mg. **0 bonding seems to be predominatingly ionic as expected
co MgF OMg CMg
F,Mg-OC
MINI-4
1.1282 1.2309 1.7701 1.7489 2.1260
Exp.
2.3760
1.2204 1.7333
F,Mg-CO 1.2313 1.7372 2.1306
F2Mg-OC
MINI-4*
_
.__..
2.5053
1.2195 1.7352
F,Mg-CO 1.1659 1.7140 2.2680
F2Mg-OC
MINI-4**
2.5986
1.1559 1.7159
F2Mg-CO
1.1399 1.7275 2.0597
FzMg-OC
3-21G
2.3671
1.1188 1.7252
FzMg-CO
1.1401 1.7605 2.1082
F,Mg-OC
6-31G
2.4149
1.1210 1.7587
F&g-CO
Experimental data for the fragments and optimized parameters obtained for F,Mg* **CO and F2Mg* **OC from different basis sets (values in A)
TABLE 1
321 TABLE 2 Total energies for F,Mg* **CO and F,Mg* **OC from different basis sets (hartree); A= E FzMr’CO -Er2Mg...oc (ld mol-‘)
3-21G 6-31G MINI-4 MINI-4* MINI-4** MINI-4(CI)”
E F&e.,oc
EF~M~-CO
A
-508.51398 -511.24366 - 510.32421 - 510.34394 -510.45185 -510.43799
- 508.50689 -511.23789 -510.31533 - 510.33645 -510.45139 -510.43535
4.4 3.6 5.6 4.7 0.2 1.3
“The MINI-I(C1) calculation was carried out using the optimized geometry obtained with the MINI-4 basis set. TABLE 3 Total bond energies (Ec ) for F,Mg* - -0C and F2Mg* **CO adducts (kcal mol- ’ )” Basis set
E B(FzM&v.,OC)
3-21G
19.5 (13.5) 14.8 11.8 (11.3) 5.8
6-31G MINI-4 MINI-4**
E B(FzMg..CO) 15.1 (7.5) 11.8 (& 5.5
*Ea values in parentheses are corrected by BSSE.
from Klopman’s theory. Similar results were obtained when using 3-21G, MINI4* and MINI-4** basis sets. ACKNOWLEDGMENTS
The authors thank Prof. R.F. Fenske of University of Wisconsin, Madison, for his valuable comments. K.N. acknowledges the support from CRUN he received during his stay at University of La Plata in March 1983. A.H.J., S.A.M. and E.A.C. thank CONICET and CIC for financial support and CESPI for computational time.
REFERENCES 1
For example, K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, 4th edn., Wiley, New York, 1986.
322 2 3 4 5 6 7 8 9 10 11 12 13 14 15
16 17 18 19 20
N.J. Nelson, N.E. Kime and D.F. Shriver, J. Am. Chem. Sot., 91 (1969) 5173. R. Cohen, C.J. Commons and B.F. Hoskins, J. Chem. Sot., Chem. Commun., (1975) 363. D. McIntosh and G.A. Ozin, inorg. Chem., 16 (1977) 51. E.C. Lisic and B.E. Hanson, Inorg. Chem., 25 (1986) 812. R.G. Pearson, J. Am. Chem. Sot., 85 (1963 ) 3533. R.G. Pearson and J. Songstad, J. Am. Chem. Sot., 89 (1967) 1827. G. Klopman, J. Am. Chem. Sot., 90 (1968) 223. D.A. Van Leirsburg and C.W. Dekock, J. Phys. Chem., 78 (1974) 134. L. Wharton, R.A. Berg and J. Klemperer, Chem. Phys., 39 (1966) 2023. R.H. Hauge, J.L. Margrave and A.S. Kanaan, J. Chem. Sot., Faraday Trans. 2,71 (1975) 1082., J.L.Gole,A.K.Q.SiuandandE.F.Hayes, J.Chem. Phys.,58 (1973) 85. P.A. Akisbin and M. Spiridonov, SW. Phys.-Crystahogr., 2 (1957) 472. L.E. Sutton (Ed. ), Tabtes of Interatomic Distances and Configuration in Molecules and Ions, The Chemical Society, London, 1965. (a) M. Dupuis, J. RysandH.F. King, Q.C.P.E., 13 (1981) 403. (b) M. Peterson and R. Poirier, University of Toronto, Chemistry Department, Toronto, Ontario, Canada. (a) Y. Sakai, H. Tatewaki and S. Huzinaga, J. Comput. Chem., 2 (1981) 100. (b) H. Tatewaki and S. Huzinaga, J. Comput. Chem., 1 (1980) 205. B.A. Murtagh and R.W.H. Sargent, Comput. J., 13 (1970) 185. N.C. Handy, J.D. Goddard and H.F. Schaefer III, J. Chem. Phys., 71 (1979) 426. S.R. Langhoff and E.R. Davidson, Int. J. Quantum Chem., 8 (1974) 61. S.F. Boys and F. Bernard, Mol. Phys., 19 (1970) 553.