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Mo scf calculations on isocyanates
‘Volume 17,number
1.5 November 19’72
CHEMICAL PHYSICS LETTERS
2
MO SCF CALCULATfONS
ON ISOCYANATES
B.M. RODE
and W. KOSMUS and E. NACHBAUR fustitut fiir Am~anische uud Analjtische Chenie der Universitiit, A SOIO Graz, Austria Rcceivcd
Calculations on some isocyanates NC0 group is found to be nonlinear, bond indices are dkcussd in relation
20 September
h3~1! been performed
1972
by rnwn5 of semi-anpiric;ll hl0 methods (CNDO/Z). The results. Energies, charge densities and
in agreement with recent esperimcntai to the stability of these compounds.
1. Introduction
2. Method of computation
I-WC0 and CINCO are well known compounds and have been investigated by various experimental and thcoretlcal methods [l-6]. MO SCF calculations have proved to be applicable to these compounds and have confirmed the geome tricai data obtained by spectroscopic methods. The eigenvalues resulting from such ca!cuIations enabled a satisfactory interpretation of photoelectron spectra. Most of the caIcu!ations reported however, have been carried out using experimental geometries for nearly ail parameters. The resuits therefore are not very suitable for the discussion of bond energies or charge densities. The preparation of the fluorine compound, FNCO, has not been reported so far. A compound with lithium was prepared (71, but the position of the lithium atom has not as yet been determined (bonding to 0 or N?). Generally, a’quantum chemical treatment cannot give any direct information about the possibility of a synthesis but it may lead to some indications to possible instability factors of a compound. With ok calculations we intended to obtain information about chemical bonding, enargy data and charge densities within this seiies of related compounds.
All calculations have been carried out by the CNDO/Zprogram QCPE 141 * adapted to the CDC 3300 computer of the University of Innsbruck in the original parametrization [S] . Geometrical parameters have been varied with respect to lowest total energy.
186
3. Results and discussion The obtained CNDO minimum values for the geometrical parameters are listed in table 1. Variation of the dihedral angles (X-N/C-O) did not lead to any energy minimum. All calculations therefore were carried out for planar configurations. For the Cl-N-C angle in ClNCO no miminum could be obtained. Therefore we used the experimental value of 118.2’ for all further calculations on this molecule. The diffkulty in obtaining 3 minimum angle is supposed to arise from the imperfect parametrization for second-row elements in the CNDO method. The same difficulty is found, however, when attempt* Quantum Chemistry Indiana, USA.
Pro&m
Exchange,
Bioomington,
.,
I
17, number
Volume
2
CHEMICAL
PHYSICS
15 November
LETTERS
1972
Table 1 Geometrical parameters Compound
X-N
HNCO
1.06 1.25 1.58 1.93 2.03 (Li-0)
FNCO CLNCO LWCO LiOCN
a) Experimental
value. b) Parameter
(A)
has not
N-C
been
(A)
c-o
1.26 1.26 1.26 1.25
1.23 1.23 1.23 1.23
1.18
1.33
varied. c) No minimum
(A)
XNC
NC0
119.2” 134.8” L18.Z03) 125.8” 180.0’ C)
172.8” 165.4” 176.1° !80” b) 180.0
obtained.
ing to obtain the minimum Li-O-C angle in !iOCN. No satisfactory explanation for this phenomenon can
lesser
be @ven at the moment.
still
The most striking result of these calculations is, that the N-C-O group is found to be nonlinear for all compounds. This agrees well with experimental results for CINCO, obtained by electron diffraction [b]. N-C and C-O bond lengths are found to be almost identical within the compounds investigated. The calculated values of the electronic, total and binding energies (listed in table 2) do not allow any conclusions in regard to special instabilities for FNCO of LiNCO. They do show, however, LiNCO to be energetically favoured in comparison to LiOCN. However the bond index [9], listed in table 3, gives some indication in regard to LiNCO. It shows an Li-N bond to be rather weak because of an exceptionally small value of 0.147. The indices for the N-C and C-O bonds in ihis compound are also significantly smaller compared to other isocyanates. Comparison of the bond indices for the Li-N and Li-0 bonds in LiNCO and LiOCY, respectively, seems to favour the second compound, quite opposite to the energy data. A Further reason for an instability of LiNCO may be the strongly ionic character of the Li-N and, to a
formation obtained by the calculations reported here does not allow a clear decision between LiNCO or LiOCN in the gaseous phase, however considering the
extent, the C-O bond as indicated by charge densities (table 4). As to be expected, LiOCN shows more ionic character
more significant
data we believe
The in-
LiNCO to be
more stable, although the Li-N bond being rather weak. The apolar character of the F-N and Cl-N bonds deserves special attention. It is confirmed for ClNCO by the quadrupole coupling constant found for chiorine by microwave methods [lo]. The calculations performed, however do not give any explanation for the apparent instability of FNCO. Table 3 Bond Indices Compound
X-N
N-C
c-o ----
HNCO
0.896
1.909
1.805
FNCO CWCO LiNCO
0.973 1.188 0.147
1.890 1.793 1.571
1.898 1.986
LiOCN
0.785 (Li-0)
2.744
1.191
Table 2 Energy values (au) Compound
energy
in all of its bonds.
1.655
Tab!c 4 Charge densities
EIcctronic
TOId
UlCIgy
energy
Binding energy
Compound
qX
qN
qc
40 6.263
HNCO
-
67.28604
-37.63656
-1.67400
HNCO
0.854
5.313
3.570
FNCO CINCO LiNCO
-117.41177 - 102.24047 - 65.29435
-64.68784 -53.10159 -37.23783
-1.81488 -1.73106 -1.68180
FNCO
7.076
5.072
3.604
6.249
ClNCO
7.037
5.172
3.530
6.261
LiNCO
0.612
5.337
3.627
6.394
LiOCN
- 64.73979
-37.11633
-1.56030
LiOCN
0.451
5.349
3.79
6.450
187
Volume
17, number
2
CHEMICAL
Difficulties with the preparation of this compound probably have their origin in factors not taken into account by such calculations, e.g., decomposition to more stable molecules. The relative order of the eigenvalucs for HNCO is in good agreement with photoelectron spectra [l l] . For CINCO, PE spectra are not reported yet, but hopefully will be available soon. Our results are in good agreement with ab initio &tlculations on HNCO reported recently [ 121, proving the CND0/2 method to be successfully applicable to studies of such compounds. This was also confirmed by calculations on reIated compounds, which will be published later.
Acknowledgement The authors are greatly indebted to the “Rechenzentrum” of the University of Innsbruck for generously supplying them with computer time. They are very grateful to Dr. P. Schuster and Dr. W. Jakubetz for many helpful discussions.
PHYSICS LETTERS
15 November
1972
References E.H. Eyster, R.H. Gillette and L.O. Brockway, J. Am. Chem. Sot. 62 (1940) 3236. L.H. Jones, J.N. Shoolcry and R.G. Shulman, J. Chem. Phys. 18 (1950) 990. R.N. Dixon and G.H. Kirby, Trans. Faraday Sot. 64 (1968) 2002. J.W. Rabalais, J.R. ZricDomId and S.P. ;Cl&lynn, J. Chem. Phys. 51 (1969) 5103. H.H. Eysel and B. Nachbaur, Z. Anorp. Allg. Chem. 381 (1971) 71. H. Oberhammer, Z. Naturforsch. 26a (1971) 280. K. Rossmanith, hlonatsh. Chem. 98 (1967) 501. I.A. Pople, D.P. Sentry and G.A. Sgal, J. Chem. Phys. 43 (1965) 129; J.A. Pople and G.A. Segai, J. Chem. Phys 43 (1965) 136; 44 (1966) 3289. (91 K.B. Wiberg, Tetrahedron 24 (1968) 1083. [lo] W.H. Hockine and M.C.L. Gerry, Chem. Commun. (1970) 448. IllI W. Kosmus, B.hl. Rode zqd E. Nachbnur, to be published. FL21 R. Bonnccorsi, C. Petrolorgo, E. Scrocco and J. Tomzsi. J. Chem. Phys. 48 (1968) 1500.
1.5 November 19’72
CHEMICAL PHYSICS LETTERS
2
MO SCF CALCULATfONS
ON ISOCYANATES
B.M. RODE
and W. KOSMUS and E. NACHBAUR fustitut fiir Am~anische uud Analjtische Chenie der Universitiit, A SOIO Graz, Austria Rcceivcd
Calculations on some isocyanates NC0 group is found to be nonlinear, bond indices are dkcussd in relation
20 September
h3~1! been performed
1972
by rnwn5 of semi-anpiric;ll hl0 methods (CNDO/Z). The results. Energies, charge densities and
in agreement with recent esperimcntai to the stability of these compounds.
1. Introduction
2. Method of computation
I-WC0 and CINCO are well known compounds and have been investigated by various experimental and thcoretlcal methods [l-6]. MO SCF calculations have proved to be applicable to these compounds and have confirmed the geome tricai data obtained by spectroscopic methods. The eigenvalues resulting from such ca!cuIations enabled a satisfactory interpretation of photoelectron spectra. Most of the caIcu!ations reported however, have been carried out using experimental geometries for nearly ail parameters. The resuits therefore are not very suitable for the discussion of bond energies or charge densities. The preparation of the fluorine compound, FNCO, has not been reported so far. A compound with lithium was prepared (71, but the position of the lithium atom has not as yet been determined (bonding to 0 or N?). Generally, a’quantum chemical treatment cannot give any direct information about the possibility of a synthesis but it may lead to some indications to possible instability factors of a compound. With ok calculations we intended to obtain information about chemical bonding, enargy data and charge densities within this seiies of related compounds.
All calculations have been carried out by the CNDO/Zprogram QCPE 141 * adapted to the CDC 3300 computer of the University of Innsbruck in the original parametrization [S] . Geometrical parameters have been varied with respect to lowest total energy.
186
3. Results and discussion The obtained CNDO minimum values for the geometrical parameters are listed in table 1. Variation of the dihedral angles (X-N/C-O) did not lead to any energy minimum. All calculations therefore were carried out for planar configurations. For the Cl-N-C angle in ClNCO no miminum could be obtained. Therefore we used the experimental value of 118.2’ for all further calculations on this molecule. The diffkulty in obtaining 3 minimum angle is supposed to arise from the imperfect parametrization for second-row elements in the CNDO method. The same difficulty is found, however, when attempt* Quantum Chemistry Indiana, USA.
Pro&m
Exchange,
Bioomington,
.,
I
17, number
Volume
2
CHEMICAL
PHYSICS
15 November
LETTERS
1972
Table 1 Geometrical parameters Compound
X-N
HNCO
1.06 1.25 1.58 1.93 2.03 (Li-0)
FNCO CLNCO LWCO LiOCN
a) Experimental
value. b) Parameter
(A)
has not
N-C
been
(A)
c-o
1.26 1.26 1.26 1.25
1.23 1.23 1.23 1.23
1.18
1.33
varied. c) No minimum
(A)
XNC
NC0
119.2” 134.8” L18.Z03) 125.8” 180.0’ C)
172.8” 165.4” 176.1° !80” b) 180.0
obtained.
ing to obtain the minimum Li-O-C angle in !iOCN. No satisfactory explanation for this phenomenon can
lesser
be @ven at the moment.
still
The most striking result of these calculations is, that the N-C-O group is found to be nonlinear for all compounds. This agrees well with experimental results for CINCO, obtained by electron diffraction [b]. N-C and C-O bond lengths are found to be almost identical within the compounds investigated. The calculated values of the electronic, total and binding energies (listed in table 2) do not allow any conclusions in regard to special instabilities for FNCO of LiNCO. They do show, however, LiNCO to be energetically favoured in comparison to LiOCN. However the bond index [9], listed in table 3, gives some indication in regard to LiNCO. It shows an Li-N bond to be rather weak because of an exceptionally small value of 0.147. The indices for the N-C and C-O bonds in ihis compound are also significantly smaller compared to other isocyanates. Comparison of the bond indices for the Li-N and Li-0 bonds in LiNCO and LiOCY, respectively, seems to favour the second compound, quite opposite to the energy data. A Further reason for an instability of LiNCO may be the strongly ionic character of the Li-N and, to a
formation obtained by the calculations reported here does not allow a clear decision between LiNCO or LiOCN in the gaseous phase, however considering the
extent, the C-O bond as indicated by charge densities (table 4). As to be expected, LiOCN shows more ionic character
more significant
data we believe
The in-
LiNCO to be
more stable, although the Li-N bond being rather weak. The apolar character of the F-N and Cl-N bonds deserves special attention. It is confirmed for ClNCO by the quadrupole coupling constant found for chiorine by microwave methods [lo]. The calculations performed, however do not give any explanation for the apparent instability of FNCO. Table 3 Bond Indices Compound
X-N
N-C
c-o ----
HNCO
0.896
1.909
1.805
FNCO CWCO LiNCO
0.973 1.188 0.147
1.890 1.793 1.571
1.898 1.986
LiOCN
0.785 (Li-0)
2.744
1.191
Table 2 Energy values (au) Compound
energy
in all of its bonds.
1.655
Tab!c 4 Charge densities
EIcctronic
TOId
UlCIgy
energy
Binding energy
Compound
qX
qN
qc
40 6.263
HNCO
-
67.28604
-37.63656
-1.67400
HNCO
0.854
5.313
3.570
FNCO CINCO LiNCO
-117.41177 - 102.24047 - 65.29435
-64.68784 -53.10159 -37.23783
-1.81488 -1.73106 -1.68180
FNCO
7.076
5.072
3.604
6.249
ClNCO
7.037
5.172
3.530
6.261
LiNCO
0.612
5.337
3.627
6.394
LiOCN
- 64.73979
-37.11633
-1.56030
LiOCN
0.451
5.349
3.79
6.450
187
Volume
17, number
2
CHEMICAL
Difficulties with the preparation of this compound probably have their origin in factors not taken into account by such calculations, e.g., decomposition to more stable molecules. The relative order of the eigenvalucs for HNCO is in good agreement with photoelectron spectra [l l] . For CINCO, PE spectra are not reported yet, but hopefully will be available soon. Our results are in good agreement with ab initio &tlculations on HNCO reported recently [ 121, proving the CND0/2 method to be successfully applicable to studies of such compounds. This was also confirmed by calculations on reIated compounds, which will be published later.
Acknowledgement The authors are greatly indebted to the “Rechenzentrum” of the University of Innsbruck for generously supplying them with computer time. They are very grateful to Dr. P. Schuster and Dr. W. Jakubetz for many helpful discussions.
PHYSICS LETTERS
15 November
1972
References E.H. Eyster, R.H. Gillette and L.O. Brockway, J. Am. Chem. Sot. 62 (1940) 3236. L.H. Jones, J.N. Shoolcry and R.G. Shulman, J. Chem. Phys. 18 (1950) 990. R.N. Dixon and G.H. Kirby, Trans. Faraday Sot. 64 (1968) 2002. J.W. Rabalais, J.R. ZricDomId and S.P. ;Cl&lynn, J. Chem. Phys. 51 (1969) 5103. H.H. Eysel and B. Nachbaur, Z. Anorp. Allg. Chem. 381 (1971) 71. H. Oberhammer, Z. Naturforsch. 26a (1971) 280. K. Rossmanith, hlonatsh. Chem. 98 (1967) 501. I.A. Pople, D.P. Sentry and G.A. Sgal, J. Chem. Phys. 43 (1965) 129; J.A. Pople and G.A. Segai, J. Chem. Phys 43 (1965) 136; 44 (1966) 3289. (91 K.B. Wiberg, Tetrahedron 24 (1968) 1083. [lo] W.H. Hockine and M.C.L. Gerry, Chem. Commun. (1970) 448. IllI W. Kosmus, B.hl. Rode zqd E. Nachbnur, to be published. FL21 R. Bonnccorsi, C. Petrolorgo, E. Scrocco and J. Tomzsi. J. Chem. Phys. 48 (1968) 1500.