- Email: [email protected]
Vibrational spectroscopy of maleimide
ARTICLE IN PRESS
Physica B 350 (2004) e591–e593
Vibrational spectroscopy of maleimide C. Corsaroa,*, S.F. Parkerb a
Dipartimento di Fisica, Universita" di Messina, S. Agata 98166, Messina, Italy b ISIS Facility, Rutherford Appleton Lab. Chilton, Oxon OX11 0QX, UK
Abstract Vibrational spectroscopy represents an important analysis tool for the characterization of different molecular systems. In the present work a model compound, maleimide, has been characterized by means of inelastic neutron scattering measurements and theoretical calculations. r 2004 Elsevier B.V. All rights reserved. PACS: 25.40.Fq; 29.30.Hs; 71.15.Pd; 78.20.Bh Keywords: INS vibrational spectroscopy; Electronic structure calculations
1. Introduction Substituted maleimides are a convenient molecular system for the production of thermally cured and/or photo cured polymers with a wide range of properties and applications. In addition, a substituted maleimide is an intermediate in the crosslinking reactions of PMR-15, a leading candidate for high temperature resins for aerospace applications [1]. Maleimide (see Fig. 1 for the structure) has been characterized by infrared and Raman spectroscopies [2,3]. The assignments were made assuming that maleimide could be treated as an isolated system. However, a recent single crystal X-ray diffraction study [4] showed that the triclinic unit cell of maleimide actually contains eight molecules which form four centrosymmetric hydrogen-bonded dimers. The aim of the work is to *Corresponding author. Fax: +39090395004. E-mail address: [email protected] (C. Corsaro).
understand the vibrational spectroscopy of the simplest possible maleimide as a basis to understand the spectroscopy of more industrially relevant and complex systems. In the present work we assign the solid state inelastic neutron scattering (INS) spectrum of maleimide using a density functional theory (DFT) calculation of the dimer.
2. Experimental Maleimide (Aldrich, 99%) was used as received. INS spectra were recorded using the high-resolution time of flight spectrometer TOSCA [5] at ISIS (Rutherford Appleton Laboratory, UK). IR and Raman calculated frequencies of maleimide are in agreement with the literature values. The DFT calculations of the monomer and dimer were made using GAUSSIAN98 [6] with the 6-31++G(d,p) basis set and the B3LYP functional. The output of the calculation includes the optimised geometry,
0921-4526/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2004.03.158
ARTICLE IN PRESS e592
C. Corsaro, S.F. Parker / Physica B 350 (2004) e591–e593
Fig. 1. Experimental INS spectrum of maleimide (centre) with the calculated spectra of the isolated monomer (top) and the isolated dimer (bottom).
all the normal modes of the molecules and the displacements of the atoms in each mode, these were used to generate the INS spectrum with a-CLIMAX [7].
3. Results Fig. 1 shows a comparison of the experimental data (centre) with the calculated spectra of the isolated monomer (top) and the isolated dimer (bottom). It is apparent that the dimer provides a much better model for this system. This is supported by inspection of the crystallographically determined geometry and that calculated by DFT. For the dimer, all the bond distances are within ( and most are within 0:05 A ( and the bond 0:1 A angles are within 2 of those in the crystal. In particular, the dimer calculation reproduces the different C–N and CQO bondlengths observed in the crystal structure whereas this is not seen for the monomer. The INS spectrum can be divided into two regions: 0–160 and 160–4000 cm1 : These correspond to modes that involve whole body motions of the individual molecules and modes that involve changes in bondlengths/angles of the
molecules respectively. The latter region is well represented by the dimer calculation and allows a complete assignment of the modes as given in Table 1. That there is some interaction between the dimers is shown by the factor group splitting which accounts for the doubling of some of the bands. This is most noticeable for the out-ofphase, out-of-plane CQO bend at 301 and 307 cm1 and the out-of-phase, out-of-plane N– H bend at 763 and 787 cm1 : The whole body motion region is very complex. This reflects the fact that there are 24 librational, 21 translational and 3 acoustic modes present. Of these, 24 (=6 modes per dimer 4 dimers) can be considered as internal modes of the dimers where each molecule moves with respect to its partner, so these are calculated by DFT for the dimer. Although the frequency agreement is poorer than for the internal modes, it can be seen that a significant part of the total area would be accounted for by these modes. To fully analyse this region, and to take proper account of the factor group splitting, a more sophisticated analysis that takes account of all the intermolecular interactions, such as periodic-DFT, is required. This work is in-progress.
ARTICLE IN PRESS C. Corsaro, S.F. Parker / Physica B 350 (2004) e591–e593
e593
Table 1 Frequency assignment scheme for Maleimide. i.p. stands for in phase while o.p. stands for out phase; b is bending, d is deformation and s is stretching C2h character
Calculated frequencies
INS frequencies
Calculated/INS
Description
Ag Ag Ag Ag Ag Ag Ag Ag Ag Ag Ag Au Au Au Au Au Au Au Bg Bg Bg Bg Bg Bg Bg Bu Bu Bu Bu Bu Bu Bu Bu Bu Bu
546 642 944 1083 1157 1326 1369 1411 1645 1775 1832 156 296 627 764 793 839 969 158 296 621 767 770 837 969 414 950 1084 1160 1325 1366 1407 1645 1780 1839
554 650 949 1074 1163 1308 1369 1398 1645 1753 1825 180 300 643 781 769 865 986 184 308 637 781 726 859 991 424 954 1079 1166 1307 1365 1395 1645 1758 1830
0.986 0.987 0.995 1.009 0.995 1.014 1 1.009 1 1.012 1.004 0.865 0.988 0.976 0.979 1.031 0.97 0.983 0.861 0.962 0.975 0.982 1.061 0.975 0.978 0.976 0.996 1.004 0.995 1.014 1 1.009 1 1.012 1.005
o.p. ring b o.p. ring d o.p. asym C–N–C s i.p. sym C–H b o.p. asym C–N–C s o.p. asym C–H b o.p. sym C–N–C s o.p. N–H b i.p. CQC s o.p. asym CQO s o.p. sym CQO s i.p. OQC–N–CQO b o.p. CQC b i.p. sym C–H b i.p. C–N–CþCQC b i.p. N–H b i.p. sym C–H b i.p. asym C–H b o.p. OQC–N–CQO b i.p. CQC b o.p. sym C–H b o.p. C–N–CþCQC b o.p. N–H b o.p. sym C–H b o.p. asym C–H b i.p. CQO b i.p. asym C–NQC s o.p. sym C–H b i.p. asym C–N–C s i.p. asym C–H b i.p. sym C–N–C s i.p. N–H b o.p. CQC s i.p. asym CQO s i.p. sym CQO s
Acknowledgements The Rutherford Appleton Laboratory thanked for access to neutron beam facilities.
is
References [1] D. Wilson, Br. Polym. J. 20 (1988) 405. [2] T. Woldbaek, P. Klaeboe, C.J. Nielsen, J. Mol. Struct. 27 (1975) 283.
[3] B. Fortunato, M.G. Giorgini, P. Mirrone, Atti Soc. Nat. Mat. Di Modena 106 (1975) 89. [4] P.J. Cox, S.F. Parker, Acta Crystallogr. C 52 (1996) 2578. [5] D. Colognesi, M. Celli, F. Cilloco, R.J. Newport, S.F. Parker, V. Rossi-Albertini, F. Sacchetti, J. Tomkinson, M. Zoppi, Appl. Phys. A 74 (Suppl.) (2002) S64. [6] Gaussian Inc., Pittsburgh, PA, USA, http://www.gaussian.com. [7] The a-CLIMAX program and its accompanying documentation can be downloaded from: http://www.isis.rl.ac.uk/ molecularSpectroscopy/aclimax/.
Physica B 350 (2004) e591–e593
Vibrational spectroscopy of maleimide C. Corsaroa,*, S.F. Parkerb a
Dipartimento di Fisica, Universita" di Messina, S. Agata 98166, Messina, Italy b ISIS Facility, Rutherford Appleton Lab. Chilton, Oxon OX11 0QX, UK
Abstract Vibrational spectroscopy represents an important analysis tool for the characterization of different molecular systems. In the present work a model compound, maleimide, has been characterized by means of inelastic neutron scattering measurements and theoretical calculations. r 2004 Elsevier B.V. All rights reserved. PACS: 25.40.Fq; 29.30.Hs; 71.15.Pd; 78.20.Bh Keywords: INS vibrational spectroscopy; Electronic structure calculations
1. Introduction Substituted maleimides are a convenient molecular system for the production of thermally cured and/or photo cured polymers with a wide range of properties and applications. In addition, a substituted maleimide is an intermediate in the crosslinking reactions of PMR-15, a leading candidate for high temperature resins for aerospace applications [1]. Maleimide (see Fig. 1 for the structure) has been characterized by infrared and Raman spectroscopies [2,3]. The assignments were made assuming that maleimide could be treated as an isolated system. However, a recent single crystal X-ray diffraction study [4] showed that the triclinic unit cell of maleimide actually contains eight molecules which form four centrosymmetric hydrogen-bonded dimers. The aim of the work is to *Corresponding author. Fax: +39090395004. E-mail address: [email protected] (C. Corsaro).
understand the vibrational spectroscopy of the simplest possible maleimide as a basis to understand the spectroscopy of more industrially relevant and complex systems. In the present work we assign the solid state inelastic neutron scattering (INS) spectrum of maleimide using a density functional theory (DFT) calculation of the dimer.
2. Experimental Maleimide (Aldrich, 99%) was used as received. INS spectra were recorded using the high-resolution time of flight spectrometer TOSCA [5] at ISIS (Rutherford Appleton Laboratory, UK). IR and Raman calculated frequencies of maleimide are in agreement with the literature values. The DFT calculations of the monomer and dimer were made using GAUSSIAN98 [6] with the 6-31++G(d,p) basis set and the B3LYP functional. The output of the calculation includes the optimised geometry,
0921-4526/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2004.03.158
ARTICLE IN PRESS e592
C. Corsaro, S.F. Parker / Physica B 350 (2004) e591–e593
Fig. 1. Experimental INS spectrum of maleimide (centre) with the calculated spectra of the isolated monomer (top) and the isolated dimer (bottom).
all the normal modes of the molecules and the displacements of the atoms in each mode, these were used to generate the INS spectrum with a-CLIMAX [7].
3. Results Fig. 1 shows a comparison of the experimental data (centre) with the calculated spectra of the isolated monomer (top) and the isolated dimer (bottom). It is apparent that the dimer provides a much better model for this system. This is supported by inspection of the crystallographically determined geometry and that calculated by DFT. For the dimer, all the bond distances are within ( and most are within 0:05 A ( and the bond 0:1 A angles are within 2 of those in the crystal. In particular, the dimer calculation reproduces the different C–N and CQO bondlengths observed in the crystal structure whereas this is not seen for the monomer. The INS spectrum can be divided into two regions: 0–160 and 160–4000 cm1 : These correspond to modes that involve whole body motions of the individual molecules and modes that involve changes in bondlengths/angles of the
molecules respectively. The latter region is well represented by the dimer calculation and allows a complete assignment of the modes as given in Table 1. That there is some interaction between the dimers is shown by the factor group splitting which accounts for the doubling of some of the bands. This is most noticeable for the out-ofphase, out-of-plane CQO bend at 301 and 307 cm1 and the out-of-phase, out-of-plane N– H bend at 763 and 787 cm1 : The whole body motion region is very complex. This reflects the fact that there are 24 librational, 21 translational and 3 acoustic modes present. Of these, 24 (=6 modes per dimer 4 dimers) can be considered as internal modes of the dimers where each molecule moves with respect to its partner, so these are calculated by DFT for the dimer. Although the frequency agreement is poorer than for the internal modes, it can be seen that a significant part of the total area would be accounted for by these modes. To fully analyse this region, and to take proper account of the factor group splitting, a more sophisticated analysis that takes account of all the intermolecular interactions, such as periodic-DFT, is required. This work is in-progress.
ARTICLE IN PRESS C. Corsaro, S.F. Parker / Physica B 350 (2004) e591–e593
e593
Table 1 Frequency assignment scheme for Maleimide. i.p. stands for in phase while o.p. stands for out phase; b is bending, d is deformation and s is stretching C2h character
Calculated frequencies
INS frequencies
Calculated/INS
Description
Ag Ag Ag Ag Ag Ag Ag Ag Ag Ag Ag Au Au Au Au Au Au Au Bg Bg Bg Bg Bg Bg Bg Bu Bu Bu Bu Bu Bu Bu Bu Bu Bu
546 642 944 1083 1157 1326 1369 1411 1645 1775 1832 156 296 627 764 793 839 969 158 296 621 767 770 837 969 414 950 1084 1160 1325 1366 1407 1645 1780 1839
554 650 949 1074 1163 1308 1369 1398 1645 1753 1825 180 300 643 781 769 865 986 184 308 637 781 726 859 991 424 954 1079 1166 1307 1365 1395 1645 1758 1830
0.986 0.987 0.995 1.009 0.995 1.014 1 1.009 1 1.012 1.004 0.865 0.988 0.976 0.979 1.031 0.97 0.983 0.861 0.962 0.975 0.982 1.061 0.975 0.978 0.976 0.996 1.004 0.995 1.014 1 1.009 1 1.012 1.005
o.p. ring b o.p. ring d o.p. asym C–N–C s i.p. sym C–H b o.p. asym C–N–C s o.p. asym C–H b o.p. sym C–N–C s o.p. N–H b i.p. CQC s o.p. asym CQO s o.p. sym CQO s i.p. OQC–N–CQO b o.p. CQC b i.p. sym C–H b i.p. C–N–CþCQC b i.p. N–H b i.p. sym C–H b i.p. asym C–H b o.p. OQC–N–CQO b i.p. CQC b o.p. sym C–H b o.p. C–N–CþCQC b o.p. N–H b o.p. sym C–H b o.p. asym C–H b i.p. CQO b i.p. asym C–NQC s o.p. sym C–H b i.p. asym C–N–C s i.p. asym C–H b i.p. sym C–N–C s i.p. N–H b o.p. CQC s i.p. asym CQO s i.p. sym CQO s
Acknowledgements The Rutherford Appleton Laboratory thanked for access to neutron beam facilities.
is
References [1] D. Wilson, Br. Polym. J. 20 (1988) 405. [2] T. Woldbaek, P. Klaeboe, C.J. Nielsen, J. Mol. Struct. 27 (1975) 283.
[3] B. Fortunato, M.G. Giorgini, P. Mirrone, Atti Soc. Nat. Mat. Di Modena 106 (1975) 89. [4] P.J. Cox, S.F. Parker, Acta Crystallogr. C 52 (1996) 2578. [5] D. Colognesi, M. Celli, F. Cilloco, R.J. Newport, S.F. Parker, V. Rossi-Albertini, F. Sacchetti, J. Tomkinson, M. Zoppi, Appl. Phys. A 74 (Suppl.) (2002) S64. [6] Gaussian Inc., Pittsburgh, PA, USA, http://www.gaussian.com. [7] The a-CLIMAX program and its accompanying documentation can be downloaded from: http://www.isis.rl.ac.uk/ molecularSpectroscopy/aclimax/.