- Email: [email protected]
An indo investigation of the structure and bonding in malondialdehyde and lithium malondialdehyde
101 Journal of Molecular
Structure,
G
Publishing
Elsevier Scientific
2.5 (1975)
101-107
Company,
Amsterdam
- Printed in The Netherlands
AN INDO INVESTIGATION OF THE STRUCTURE AND BONDING IN MALONDIALDEHYDE AND LITHIUM MALONDIALDEHYDE
F. J. MARSH, Deparrment
(Received
B. G. THOMAS of Chemistry,
AND
North
M. S. GORDON
Dakota
State
University,
Fargo,
North
Dakota
58102 (U.S.A.)
15 April 1974)
ABSTRACT
The geometries of the enol forms of malondialdehyde and its lithium analog have been investigated usin g the INDO MO method in its original parametrization The former molecule is predicted to have a planar, symmetric structure nearly identical with that of acetylacetone. Optimization of the geometry of lithium malondialdehyde yielded questionable results. The covalent bonding in both molecules is discussed with the aid of localized molecular orbitals and calculated interference energies.
INTRODUCTION
In the second paper in this series [l] an investigation of the structure and bonding in acetylacetone (ACAC) and trifluoroacetylacetone (TFA) was carried out using the semi-empirical INDO molecuIar orbital method [2]. It was concluded from these calculations that the former molecule is pIanar and symmetric, in agreement with a number of experimental findings [3, 41 but at variance with the CNDO/2 calculations [S] of Schuster on maIondialdehyde [6] (HM). The latter differs from ACAC only in the substitution of two hydrogens for methyl groups; thus Schuster’s conclusion that HM is strongly asymmetric is somewhat disconcerting. Apart from the substituent difference of the two moIecules, the two calculations also differed in that the INDO results were obtained by a complete geometry optimization, whiIe Schuster assumed a planar, symmetric ring and only optimized the position of the bridging hydrogen. The present work is an attempt to unravel the discrepancy between these two calculations by carrying out INDO calculations on malondialdehyde in a manner analogous to those performed on ACAC.
102 In addition, Schuster,found that, under the same geometric restrictions as were placed on HM, substitution of lithium for the hydroxyl hydrogen resulted in a pIanar symmetric ring. The effect of complete geometric freedom on this conclusion is of interest; thus INDO calculations on lithium malondialdehyde (LiM) have also been carried out.
MALONDlALDEHYDE
To minimize the possibility of prejudicing the final result, the starting geometry of HM was chosen to be planar and asymmetric with typical CC and CO single and doubIe bond lengths and 120” ring angles (see Fig. 1 for structure). AI1 bond Iengths and angles, including dihedral angles, were allowed to vary independentIy with initial step sizes of 0.01 8, and O.IO”, respectively, using an adaptation of Powell’s conjugate directions program [7]. The minimum-energy geometry is predicted to be pIanar and symmetric, in agreement with previous results [I] for ACAC. As for the Iatter molecule, it should be pointed out that while a11dihedral angles were allowed to vary, a complete search for a non-pIanar minimum was not carried out.
Fig. 1. Numbering system and coordinate axes. X = H (HM,
TABLE
OF MALONDIALDEHYDE
Bondiengrirs
AND
GEOMETRIES=
Angles (deg.) ACAP
cc
1.383
1.395
co
1.310
1.324
OH
1.178
1.174
CL&
1.113
1.115 -
1.125
ACETYLACETONE
(A)
HM
GH,
Li (LiM).
1
COMPARISON
Bond
ACAC),
3 Numbering system refers to Fig. I. b See ref. 1.
HM
ACACb
ccc
113.21
116.82
cc0
122.78
COH CCHe OH0
105.09 123.39 151.10
119.47 106.02
121.39 152.18
103 The geometries of malondialdehyde and acetyiacetone are compared in Table 1, and are strikingly similar. The CO and CC bond lengths are both 0.01 L& shorter in malondialdehyde, the other bond lengths remaining essentially the same. The most noticeable changes are the decrease (increase) in the CCC (CCO) angles by 3.6 (3.3”), resulting in a 0.07 A decrease in the C,C, distance. As a check on the finaf geometry, the OH distance was varied from 1.03 A to 1.38 A in steps of 0.05 A, alfowing the COH angle to re-optimize at each bond Iength. Due to computer time restrictions, the remaining geometry was held constant. This procedure (Fig. 2) resuhs in a continual increase in energy with deviation from C,, symmetry as expected, the energy variation being essentially the same as that found for ACAC Since displacing R,, tends to increase the COH angle, we also forced successive 5” decreases in the latter, optimize. Again this resulted in an energy increase.
alfowing
Ron to re-
100 t
80s ” I 2
60-
t.i8
1.10
1.15
105
103
ROH
Fig. 2. Energy of maiondialdehyde relative to equi1ibrim-ngeometry as a function of OH bond length. TABLE
2
CALCULATED
BOND ENERGIES
(ev)
IN MALONDIALDEHYDE,
ACETOSE
Bond
cc co OH
3 See ref. I.
Sorzd enetgv HM
ACAC”
LiM
5.12
4.96
5.39 3.00
5.13 3.03
5.10 5.50 -
LITHIUM
MALONDIALDEHYDE
AND ACETYL-
104 Theoretical bond energies, obtained in a manner described previously [I J, were calculated for HM and are listed in Table 2. The increase in the CC and CO bondstrengths reffects the bond Iength changes discussed above. Those bond energies not listed are virtually unaffected by methyl substitution.
LITHIUM
MALONDIALDEHYDE
Initially, a geometry optimization procedure was carried out for LiM in a manner analogous to previous molecules. The starting geometry was simiIar to that for malondialdehyde with the exception of the LiO bond length and COLi angle. The latter were taken from Schuster [6]. The geometry optimization for this molecule was not very well behaved. The two oxygens twisted out of the XZ plane (Fig. 1) in opposite directions. At the same time, the Li Y coordinate increased faster than that of oxygen 4, giving rise to a COLi
distance angle approaching 80”. Further, the Li-C2 internuclear became smaIIer than that for Li-05, with the CCC bond angle opening to more
than 130”. This behavior is not compIeteIy surprising since similar resuIts [8] have been obtained for LiOH and Li,O, both of which INDO predicts to form three-membered ring structures_ Experimentally, Li,O has been found [9-l 1 ] to be nearly linear, while an ab initio molecular orbital calculation [12] predicts LiOH to be linear as well. In view of this, it is not clear whether the tendency of LiM to become nonplanar is real or a result of the inability of INDO to adequateIy describe lithium. Because of these results, further geometry optimization of lithium malondial
dehyde was not pursued. Instead, for the purpose of comparison with calculated bond energies and IocaIized orbitals (see below) of HM and ACAC, an assumed geometry was chosen in which a11 angIes and bond lengths are identical to those of HM except the Li-0 bond length of 2.21 A. The latter was taken from Schuster [6] and results in an 0-Li-0 angle of 62.16”, very close to Schuster’s value and 90” smaller than the corresponding angle calculated for HM and ACAC. The CC and CO bond energies, listed in Table 2, are similar to those of HM, although it is interesting to note the increase in the CO energy in view of the fact that the corre-
sponding
LOCALIZED
bond lengths of the two molecules
are the same.
ORBITALS
Energy-localized molecular orbitals 1131 (LMO’s) were calcuiated for both molecules by the Edmiston-Ruedenberg procedure_ Of particular interest are those LMO’s directly involved in the ring (&-& in ref. 1). For both maIondiaIdehyde
and its lithium analog the CC 0 bonds &),
CCC z bond (Aa), and CO bonds (&)
105 TABLE
3
LOCALIZED
Cl
ORBITAL5
A#t
43
0.0224 -0_0740 0.0 -0.0655
-0.0007 -0.0004 -0.0846 0.0038
-0.0010
0.0024 0.1114 -0.0053
0.0026 0.0071 -0.0552 -0.0119
-0.0028 -0.0041 -0.0329 0.0040
0.0174 -0.0040 0.0 -0.0153
0.0203 0.0102 -0.0609 0.0143
-0.0027 -0.0019 0.0696 0.0035
-00.0228 -0.0131 -0.0369 -oo.oo23
0.0326 0.0141 -0.0222 0.0210
-0.0133 -0.0223 0.0 -0.0039
-0.0019 0.0308 0.2765 0.0355
0.0056 0.0283 -0.3670 -0.0373
-0.0335 -0.0279 0.1780 -00.0846
0.0051 0.0569 0.1055 0.0735
PZ
-00.4624 -OS931 0.0 -0.4914
0.0021 0.000 1 0.0336 0.0025
-0.0094 -00.0026 -0.0360 -0.0074
-0.0229 -0.0051 0.0195 -oo.oI1o
0.0014 -00.0052 0.0117 -0.0049
S 9V p, PZ
0.0477 -0.0385 0.0 -0.0694
0.5187 0.4434 0.6416 0.1735
0.4226 0.0930 -0.7613 -0.1860
0.5130 -0.1305 0.3731 -0.6888
0.5261 0.6444 0.2215 0.4488
s
-0.4102
0.0835 -0.0374 -0.1431 0.1180
0.1238 -0_0970 0.0705 0.1607
0.0821 0.0431 0.0419 0.1413
S
S
PZ S 9U PI
PZ
Xb
MALONDIALDEHYDE
Litldumtnalondiafdelyde
PY
05
LITHIUhI
‘-5
PA.
0-L
AND
MaIoadiaIdelyde
PZ
C3
MALONDIALDEHYDE
A3
9Y PY
G
IN
S PIPI
PI PI
pz
-0.0196
-I See test for description. h X = H or Li.
are essentially the same as those pubhshed previously [l] and will not be repeated here. These orbitals make essentially the same contributions to the corresponding bond energies as in ACAC. The significant differences between the hydrogen and lithium analogs occur in the OH bonds and oxygen lone pairs and are listed in Table 3. For HM these LMO’s are similar to those found for ACAC, %., being one of two equivalent OH bond orbitals and 1, one of four equivalent oxygen Ione pairs (two on each oxygen). The lone pairs are substantially delocalized into the K orbital of the adjacent carbon, thus making a significant (19 %) contribution to the CO bond energy. The “OH bond” orbitals account for virtually a11 of the bond energy between these two atoms. The electron density on oxygen in these two orbitals is 1.6142 and 1.8150, respectively. For Iithium malondialdehyde the situation is more complicated, there being three inequivalent LMO’s on O5 (&, 2,, A,-) with an identical set on 04. These
106 appear to be somewhat of a mixture of i., and ,iL5; although LA, with an oxygen density of 1.6029, is most simiIar to A,, and & and A, are Iess delocalized with oxygen densities of 1.7877 and 1.8851, respectively. Such an analogy is misleading, however, since the greatest Iithium electron density as we11 as the greatest contribution to Li-0 constructive interference is in &, while E., and Jc give approximately the same contribution (about half that of RB). The sum of these three LMO’s contribute 25 o/0of the CO bond energy, again principaily due to delocalization into the K orbital on the adjacent carbon. Part of the interest in replacing the hydrogen by a metal is to determine the extent to which the 7~orbital on the metal can interact with those in the rest of the ring. To investigate this we have calculated the contribution of Li-0 K-X interaction to the overall Li-0 interference energy. We find this contribution to be less than 10 %. In contrast the s--s and s-p cr contributions to Li-0 binding are 20 and 54 T!, respectiveIy.
CONCLUSIONS
The principal concIusion of the current work is that TNDO predicts malondialdehyde, like acetyIacetone, to be planar and symmetric with CZ, symmetry: thus the CNDO results of Schuster are likely to be due to incomplete optimization of geometry_ The geometry of lithium malondialdehyde, we feel. remains somewhat questionable. It is difficult to feel comfortable with INDO geometry optimizations of molecules containing Li; however, the geometry assumed by Schuster (and in the present work as well) results in an extremeIy small (62”) 0-Li-0 angle. Nonempirica calculations are needed to resolve this question. Finally, with the assumed geometry in mind, we find little n-type contribution to the Li-0 bonding.
ACKNOWLEDGEMENTS
The authors gratefuIIyacknowIedge the generous support of this work by the North Dakota State University Computer Center. The work was also supported in part by a grant from Research Corporation.
REFERENCES 1 M. S. Gordon
2 3 4 5 6
and R. D. Koob, J. Amer. Chem. Sm., 95 (1973) 5863. J. A. Pople, D. L. Beveridge and P. A. Dobosh, J. Chem. Phys., 47 (1967) 2026. H. Junge, M. Kuhr and H. Musso, Angew. Chem., Internat. Edn., 10 (1971) 225. A. H. Lowery, C. George, P. D’Antonio and J. Karle, J. Anzer. Chenz. SOL, 93 (1971) J. A. Pople and G. A. Segal, J. Chem. Phys., 44 (1966) 3289. P. Schuster, Chem. Php. Lett., 3 (1969) 433.
6399.
107 7 M. J. D. Powell, QrranrunzChemistry Program Exchange, Program No. 60. 8 M. S. Gordon, unpublished results. 9 A. Buchler, J. L. Stauffer, W. Klemperer and L. Wharton, J. Chenz. Phys., 39 (1963) 2299. 10 D. White, K. S. Seshadri, D. F. Dever, D. E. Mann and M. J. Linevsky, J. Clrem. HITS., 39 (1963) 2463. I1 K. S. Seshadri, D. White and D_ E. Mann, J. Chem. PJps., 45 (1966) 4697. 12 R. J. Buenker and S. D. Peyerimhoff, J. Chenz. Phys., 45 (1966) 3682. 13 C. Edmiston and K. Ruedenberg, Rer. Mod. Phys., 35 (1963) 457.
Structure,
G
Publishing
Elsevier Scientific
2.5 (1975)
101-107
Company,
Amsterdam
- Printed in The Netherlands
AN INDO INVESTIGATION OF THE STRUCTURE AND BONDING IN MALONDIALDEHYDE AND LITHIUM MALONDIALDEHYDE
F. J. MARSH, Deparrment
(Received
B. G. THOMAS of Chemistry,
AND
North
M. S. GORDON
Dakota
State
University,
Fargo,
North
Dakota
58102 (U.S.A.)
15 April 1974)
ABSTRACT
The geometries of the enol forms of malondialdehyde and its lithium analog have been investigated usin g the INDO MO method in its original parametrization The former molecule is predicted to have a planar, symmetric structure nearly identical with that of acetylacetone. Optimization of the geometry of lithium malondialdehyde yielded questionable results. The covalent bonding in both molecules is discussed with the aid of localized molecular orbitals and calculated interference energies.
INTRODUCTION
In the second paper in this series [l] an investigation of the structure and bonding in acetylacetone (ACAC) and trifluoroacetylacetone (TFA) was carried out using the semi-empirical INDO molecuIar orbital method [2]. It was concluded from these calculations that the former molecule is pIanar and symmetric, in agreement with a number of experimental findings [3, 41 but at variance with the CNDO/2 calculations [S] of Schuster on maIondialdehyde [6] (HM). The latter differs from ACAC only in the substitution of two hydrogens for methyl groups; thus Schuster’s conclusion that HM is strongly asymmetric is somewhat disconcerting. Apart from the substituent difference of the two moIecules, the two calculations also differed in that the INDO results were obtained by a complete geometry optimization, whiIe Schuster assumed a planar, symmetric ring and only optimized the position of the bridging hydrogen. The present work is an attempt to unravel the discrepancy between these two calculations by carrying out INDO calculations on malondialdehyde in a manner analogous to those performed on ACAC.
102 In addition, Schuster,found that, under the same geometric restrictions as were placed on HM, substitution of lithium for the hydroxyl hydrogen resulted in a pIanar symmetric ring. The effect of complete geometric freedom on this conclusion is of interest; thus INDO calculations on lithium malondialdehyde (LiM) have also been carried out.
MALONDlALDEHYDE
To minimize the possibility of prejudicing the final result, the starting geometry of HM was chosen to be planar and asymmetric with typical CC and CO single and doubIe bond lengths and 120” ring angles (see Fig. 1 for structure). AI1 bond Iengths and angles, including dihedral angles, were allowed to vary independentIy with initial step sizes of 0.01 8, and O.IO”, respectively, using an adaptation of Powell’s conjugate directions program [7]. The minimum-energy geometry is predicted to be pIanar and symmetric, in agreement with previous results [I] for ACAC. As for the Iatter molecule, it should be pointed out that while a11dihedral angles were allowed to vary, a complete search for a non-pIanar minimum was not carried out.
Fig. 1. Numbering system and coordinate axes. X = H (HM,
TABLE
OF MALONDIALDEHYDE
Bondiengrirs
AND
GEOMETRIES=
Angles (deg.) ACAP
cc
1.383
1.395
co
1.310
1.324
OH
1.178
1.174
CL&
1.113
1.115 -
1.125
ACETYLACETONE
(A)
HM
GH,
Li (LiM).
1
COMPARISON
Bond
ACAC),
3 Numbering system refers to Fig. I. b See ref. 1.
HM
ACACb
ccc
113.21
116.82
cc0
122.78
COH CCHe OH0
105.09 123.39 151.10
119.47 106.02
121.39 152.18
103 The geometries of malondialdehyde and acetyiacetone are compared in Table 1, and are strikingly similar. The CO and CC bond lengths are both 0.01 L& shorter in malondialdehyde, the other bond lengths remaining essentially the same. The most noticeable changes are the decrease (increase) in the CCC (CCO) angles by 3.6 (3.3”), resulting in a 0.07 A decrease in the C,C, distance. As a check on the finaf geometry, the OH distance was varied from 1.03 A to 1.38 A in steps of 0.05 A, alfowing the COH angle to re-optimize at each bond Iength. Due to computer time restrictions, the remaining geometry was held constant. This procedure (Fig. 2) resuhs in a continual increase in energy with deviation from C,, symmetry as expected, the energy variation being essentially the same as that found for ACAC Since displacing R,, tends to increase the COH angle, we also forced successive 5” decreases in the latter, optimize. Again this resulted in an energy increase.
alfowing
Ron to re-
100 t
80s ” I 2
60-
t.i8
1.10
1.15
105
103
ROH
Fig. 2. Energy of maiondialdehyde relative to equi1ibrim-ngeometry as a function of OH bond length. TABLE
2
CALCULATED
BOND ENERGIES
(ev)
IN MALONDIALDEHYDE,
ACETOSE
Bond
cc co OH
3 See ref. I.
Sorzd enetgv HM
ACAC”
LiM
5.12
4.96
5.39 3.00
5.13 3.03
5.10 5.50 -
LITHIUM
MALONDIALDEHYDE
AND ACETYL-
104 Theoretical bond energies, obtained in a manner described previously [I J, were calculated for HM and are listed in Table 2. The increase in the CC and CO bondstrengths reffects the bond Iength changes discussed above. Those bond energies not listed are virtually unaffected by methyl substitution.
LITHIUM
MALONDIALDEHYDE
Initially, a geometry optimization procedure was carried out for LiM in a manner analogous to previous molecules. The starting geometry was simiIar to that for malondialdehyde with the exception of the LiO bond length and COLi angle. The latter were taken from Schuster [6]. The geometry optimization for this molecule was not very well behaved. The two oxygens twisted out of the XZ plane (Fig. 1) in opposite directions. At the same time, the Li Y coordinate increased faster than that of oxygen 4, giving rise to a COLi
distance angle approaching 80”. Further, the Li-C2 internuclear became smaIIer than that for Li-05, with the CCC bond angle opening to more
than 130”. This behavior is not compIeteIy surprising since similar resuIts [8] have been obtained for LiOH and Li,O, both of which INDO predicts to form three-membered ring structures_ Experimentally, Li,O has been found [9-l 1 ] to be nearly linear, while an ab initio molecular orbital calculation [12] predicts LiOH to be linear as well. In view of this, it is not clear whether the tendency of LiM to become nonplanar is real or a result of the inability of INDO to adequateIy describe lithium. Because of these results, further geometry optimization of lithium malondial
dehyde was not pursued. Instead, for the purpose of comparison with calculated bond energies and IocaIized orbitals (see below) of HM and ACAC, an assumed geometry was chosen in which a11 angIes and bond lengths are identical to those of HM except the Li-0 bond length of 2.21 A. The latter was taken from Schuster [6] and results in an 0-Li-0 angle of 62.16”, very close to Schuster’s value and 90” smaller than the corresponding angle calculated for HM and ACAC. The CC and CO bond energies, listed in Table 2, are similar to those of HM, although it is interesting to note the increase in the CO energy in view of the fact that the corre-
sponding
LOCALIZED
bond lengths of the two molecules
are the same.
ORBITALS
Energy-localized molecular orbitals 1131 (LMO’s) were calcuiated for both molecules by the Edmiston-Ruedenberg procedure_ Of particular interest are those LMO’s directly involved in the ring (&-& in ref. 1). For both maIondiaIdehyde
and its lithium analog the CC 0 bonds &),
CCC z bond (Aa), and CO bonds (&)
105 TABLE
3
LOCALIZED
Cl
ORBITAL5
A#t
43
0.0224 -0_0740 0.0 -0.0655
-0.0007 -0.0004 -0.0846 0.0038
-0.0010
0.0024 0.1114 -0.0053
0.0026 0.0071 -0.0552 -0.0119
-0.0028 -0.0041 -0.0329 0.0040
0.0174 -0.0040 0.0 -0.0153
0.0203 0.0102 -0.0609 0.0143
-0.0027 -0.0019 0.0696 0.0035
-00.0228 -0.0131 -0.0369 -oo.oo23
0.0326 0.0141 -0.0222 0.0210
-0.0133 -0.0223 0.0 -0.0039
-0.0019 0.0308 0.2765 0.0355
0.0056 0.0283 -0.3670 -0.0373
-0.0335 -0.0279 0.1780 -00.0846
0.0051 0.0569 0.1055 0.0735
PZ
-00.4624 -OS931 0.0 -0.4914
0.0021 0.000 1 0.0336 0.0025
-0.0094 -00.0026 -0.0360 -0.0074
-0.0229 -0.0051 0.0195 -oo.oI1o
0.0014 -00.0052 0.0117 -0.0049
S 9V p, PZ
0.0477 -0.0385 0.0 -0.0694
0.5187 0.4434 0.6416 0.1735
0.4226 0.0930 -0.7613 -0.1860
0.5130 -0.1305 0.3731 -0.6888
0.5261 0.6444 0.2215 0.4488
s
-0.4102
0.0835 -0.0374 -0.1431 0.1180
0.1238 -0_0970 0.0705 0.1607
0.0821 0.0431 0.0419 0.1413
S
S
PZ S 9U PI
PZ
Xb
MALONDIALDEHYDE
Litldumtnalondiafdelyde
PY
05
LITHIUhI
‘-5
PA.
0-L
AND
MaIoadiaIdelyde
PZ
C3
MALONDIALDEHYDE
A3
9Y PY
G
IN
S PIPI
PI PI
pz
-0.0196
-I See test for description. h X = H or Li.
are essentially the same as those pubhshed previously [l] and will not be repeated here. These orbitals make essentially the same contributions to the corresponding bond energies as in ACAC. The significant differences between the hydrogen and lithium analogs occur in the OH bonds and oxygen lone pairs and are listed in Table 3. For HM these LMO’s are similar to those found for ACAC, %., being one of two equivalent OH bond orbitals and 1, one of four equivalent oxygen Ione pairs (two on each oxygen). The lone pairs are substantially delocalized into the K orbital of the adjacent carbon, thus making a significant (19 %) contribution to the CO bond energy. The “OH bond” orbitals account for virtually a11 of the bond energy between these two atoms. The electron density on oxygen in these two orbitals is 1.6142 and 1.8150, respectively. For Iithium malondialdehyde the situation is more complicated, there being three inequivalent LMO’s on O5 (&, 2,, A,-) with an identical set on 04. These
106 appear to be somewhat of a mixture of i., and ,iL5; although LA, with an oxygen density of 1.6029, is most simiIar to A,, and & and A, are Iess delocalized with oxygen densities of 1.7877 and 1.8851, respectively. Such an analogy is misleading, however, since the greatest Iithium electron density as we11 as the greatest contribution to Li-0 constructive interference is in &, while E., and Jc give approximately the same contribution (about half that of RB). The sum of these three LMO’s contribute 25 o/0of the CO bond energy, again principaily due to delocalization into the K orbital on the adjacent carbon. Part of the interest in replacing the hydrogen by a metal is to determine the extent to which the 7~orbital on the metal can interact with those in the rest of the ring. To investigate this we have calculated the contribution of Li-0 K-X interaction to the overall Li-0 interference energy. We find this contribution to be less than 10 %. In contrast the s--s and s-p cr contributions to Li-0 binding are 20 and 54 T!, respectiveIy.
CONCLUSIONS
The principal concIusion of the current work is that TNDO predicts malondialdehyde, like acetyIacetone, to be planar and symmetric with CZ, symmetry: thus the CNDO results of Schuster are likely to be due to incomplete optimization of geometry_ The geometry of lithium malondialdehyde, we feel. remains somewhat questionable. It is difficult to feel comfortable with INDO geometry optimizations of molecules containing Li; however, the geometry assumed by Schuster (and in the present work as well) results in an extremeIy small (62”) 0-Li-0 angle. Nonempirica calculations are needed to resolve this question. Finally, with the assumed geometry in mind, we find little n-type contribution to the Li-0 bonding.
ACKNOWLEDGEMENTS
The authors gratefuIIyacknowIedge the generous support of this work by the North Dakota State University Computer Center. The work was also supported in part by a grant from Research Corporation.
REFERENCES 1 M. S. Gordon
2 3 4 5 6
and R. D. Koob, J. Amer. Chem. Sm., 95 (1973) 5863. J. A. Pople, D. L. Beveridge and P. A. Dobosh, J. Chem. Phys., 47 (1967) 2026. H. Junge, M. Kuhr and H. Musso, Angew. Chem., Internat. Edn., 10 (1971) 225. A. H. Lowery, C. George, P. D’Antonio and J. Karle, J. Anzer. Chenz. SOL, 93 (1971) J. A. Pople and G. A. Segal, J. Chem. Phys., 44 (1966) 3289. P. Schuster, Chem. Php. Lett., 3 (1969) 433.
6399.
107 7 M. J. D. Powell, QrranrunzChemistry Program Exchange, Program No. 60. 8 M. S. Gordon, unpublished results. 9 A. Buchler, J. L. Stauffer, W. Klemperer and L. Wharton, J. Chenz. Phys., 39 (1963) 2299. 10 D. White, K. S. Seshadri, D. F. Dever, D. E. Mann and M. J. Linevsky, J. Clrem. HITS., 39 (1963) 2463. I1 K. S. Seshadri, D. White and D_ E. Mann, J. Chem. PJps., 45 (1966) 4697. 12 R. J. Buenker and S. D. Peyerimhoff, J. Chenz. Phys., 45 (1966) 3682. 13 C. Edmiston and K. Ruedenberg, Rer. Mod. Phys., 35 (1963) 457.