- Email: [email protected]
Molecular structure of triiodomethane, CHI3, in the gas phase: an electron diffraction study
Journal of Molecular Structure 657 (2003) 381–384 www.elsevier.com/locate/molstruc
Molecular structure of triiodomethane, CHI3, in the gas phase: an electron diffraction study Hiroshi Takeuchi*, Toshiharu Ozaki, Tsuguhide Takeshima, Toru Egawa, Shigehiro Konaka Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan Received 4 June 2003; revised 30 June 2003; accepted 2 July 2003
Abstract The molecular structure of triiodomethane (iodoform, CHI3) has been determined by gas electron diffraction. The structural ˚ and /a /8) with the estimated limits of error ð3sÞ are: r(C – H) ¼ 1.111 (assumed), r(C – I) ¼ 2.145(8), parameters (rg /A r(I…I) ¼ 3.549(2), /ICI ¼ 111.9(7), /ICH ¼ 107.0(7). Mean amplitudes, l(C – I) and l(I· · ·I), have also been determined. The C– I distance of CHI3 is equal to that of CI4 within experimental uncertainties. q 2003 Elsevier B.V. All rights reserved. Keywords: CHI3; Molecular structure; Electron diffraction
The molecular structure of triiodomethane (iodoform, CHI3) was determined by the visual method of gas ˚ and electron diffraction (GED, r(C –I) ¼ 2.12(4) A /ICI ¼ 113.08) [1] but no precise structural data are available. Recently the geometry of CHI3 has been calculated by MP2, B3LYP and B3PW91 methods, where effective core potentials are used [2 –4]. Precise experimental structure is required for checking the reliability of sophisticated theoretical calculations. In this communication, we report the molecular structure of CHI3 determined by the modern technique of GED, which is compared with the structures of related molecules and the theoretical results. A commercial sample of CHI3 (Aldrich) with a purity of 99% and an apparatus equipped with * Corresponding author. Tel.: þ81-11-706-3533; fax: þ 81-11706-4924. E-mail address: [email protected] (H. Takeuchi).
an r 3 -sector [5] were used for experiment. Diffraction patterns were recorded on 8 £ 8 in. Kodak projector slide plates, which were developed in Kodak Dektol developer diluted 1:1 for 4.5 min. The energy of incident electrons was about 37 keV and the scale factor was determined from the diffraction patterns of ˚ ) [6]. Other carbon disulfide (ra (C – S) ¼ 1.5570 A experimental conditions are as follows: camera distance, 244.5 mm; temperature of nozzle tip [7], ˚ ; exposure 395 K; electron wavelength, 0.06329 A time, 110– 140 s; beam current, 1.5 mA; uncertainties of scale factor, 0.05%; background pressure, ˚ 21. 1.5 £ 1026 Torr; range of s-value, 4.5 – 33.8 A Data reduction was made in the same way as described in Ref. [8] with the exception of the atomic scattering factors used, which were taken from Ref. [9]. The leveled total intensities averaged for four plates were used for data analysis. The molecular
0022-2860/03/$ - see front matter q 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0022-2860(03)00431-9
382
H. Takeuchi et al. / Journal of Molecular Structure 657 (2003) 381–384 Table 1 Observed and calculated vibrational frequencies (in cm21) Species
Mode
Calc1a
Calc2b
Obsc
A1
n1 n2 n3 n4 n5 n6
3256 428 152 1104 583 99
3013 427 152 1067 579 109
3013 425 154 1068 578 110
E
a
Unscaled result (B3LYP/3-21G**). Values obtained from scaled force constants. Values of scale factors for local symmetry coordinates, C – H stretching, CI3 symmetric stretching, CI3 degenerate stretching, CI3 symmetric bending, C –H degenerate bending and CI3 degenerate deformation, are 0.8559, 1.0476, 0.9553, 0.9489, 0.9334 and 1.2467, respectively. c Ref. [11]. b
Fig. 1. Experimental (†) and theoretical (– ) molecular scattering intensities of CHI3: DsMðsÞ ¼ sMðsÞobs 2 sMðsÞcalc :
calculations were transformed into the force constants in symmetry coordinates fij : Resultant quadratic force constants were modified by using scale factors ci so as to reproduce experimental vibrational wavenumbers [11]. Scaled force constants, fijscaled ð¼ ðci cj Þ1=2 fij Þ; were used to calculate mean amplitudes and shrinkage corrections, ra 2 ra ; required for the analysis of GED data. Table 1 compares calculated vibrational wavenumbers with observed ones in the crystal [11]. The mean amplitudes calculated with our program NVMA are listed in Table 2.
scattering intensities of CHI3 are shown in Fig. 1. The leveled total intensities and backgrounds are available from the authors upon request. In order to obtain information on the force field of this molecule, density functional theory calculations were carried out using program GAUSSIAN 98 [10]. Geometry optimization and vibrational calculations were performed at the B3LYP/3-21G** level under the assumption of C3v symmetry. Cartesian force constants obtained from the B3LYP/3-21G**
Table 2 Structural parameters and mean amplitudes of CHI3 with the estimated limits of error ð3sÞ GEDa rg ; /a Interatomic distances (A˚) C –H 1.111e C –I 2.145(8) I· · ·I 3.549(2) I· · ·H 2.680(20)f Bond angles (degrees) ICI 111.9(7)f HCI 107.0(7)f a b c d e f
MP2 ecpb l obs
l calc
0.078e 0.067(7) 0.108(2) 0.122e
0.078 0.063 0.096 0.122
3-21G**
1.092 2.154
112.9 105.8
B3PW91/6-311þ þ G(3df,2pd)/LanL2DZd
B3LYP
1.082 2.193
112.8 105.9
6-31G**/ecpc
1.08 2.17
113 106
1.080 2.156
112.9 105.8
Present study. Index of resolution is 0.90(2). The MP2 calculation using effective core potentials [2]. The B3LYP calculation with the 6-31G** basis set for H and C and effective core potential for I [3]. The B3PW91 calculation with the 6-311þ þG(3df,2pd) basis set for H and C and the LanL2DZ basis set for I [4]. Assumed. Dependent parameter.
H. Takeuchi et al. / Journal of Molecular Structure 657 (2003) 381–384
Fig. 2. Experimental radial distribution curve of CHI3: Df ðrÞ ¼ f ðrÞobs 2 f ðrÞcalc : Atom pairs are indicated by vertical bars.
In the data analysis of GED, the value of rg (C – H) ˚ [12]. Asymmetry was fixed at that of CHBr3, 1.111 A parameters were estimated by the conventional methods [13]. Interatomic distances, r(C – I) and r(I· · ·I), mean amplitudes, l(C – I) and l(I· · ·I), and index of resolution, k; were determined by leastsquares calculations on molecular scattering intensities. The results obtained by GED are listed in Table 2. The experimental radial distribution curve is shown in Fig. 2. Correlation matrix element k=l(I· · ·I) is 0.76 and the absolute values of the other elements are smaller than 0.2. The calculated value of l(I· · ·I) is significantly smaller than the experimental one. We found that calculations in which the wavenumber of n6 was assumed to be 95 cm21 reproduced the experimental value of l(I· · ·I). The assumed value is close to 99(2) cm21, a tentative value of n6 in the gas phase reported by Marquardt et al. [14]. Therefore, the origin of the discrepancy mentioned above is mainly due to the use of the wavenumber measured in the crystal, 110 cm21 [11]. The wavenumbers of other modes reported in the gas phase [14] are different from those in the crystal by less than 3%. These differences do not significantly influence the calculated values of mean amplitudes and thus the determined values of independent parameters. The value of /ICI is larger than the tetrahedral angle. This trend is observed for the gas-phase structures of CHBr3 (/avBrCBr ¼ 111.7(4)8) [12]
383
and CHCl3 (/sClCCl ¼ 111.3(2)8) [15]. These results can be ascribed to non-bonded repulsions between halogen atoms. The value of the rg (C –I) of CI4 is ˚ [16], which is in agreement with that of 2.157(10) A CHI 3 within experimental uncertainties. The differences, rg ðC – IÞ 2 re ðC – IÞ; of CI4 and CHI3 ˚ assuming were roughly estimated to be 0.01 A ˚ 21 in the the anharmonicity parameter a3 to be 2 A 2 approximation, rg 2 re ¼ ð3=2Þa3 l [13]. Therefore, the values of re (C– I) of CI4 and CHI3 are close to the ˚ [17], and the rav (C – I) of re (C – I) of CH3I, 2.1336 A ˚ [18], determined by microwave CH2I2, 2.1364(6) A spectroscopy. As shown in Table 2, the MP2, B3LYP and B3PW91calculations [2 – 4] overestimate the C – I bond length and ICI bond angle.
References [1] O. Bastiansen, Tidsskr. Kjemi Bergv. 6 (1946) 1. [2] S. Roszak, W.S. Koski, J.J. Kaufman, K. Balasubramanian, SAR QSAR Environ. Res. 11 (2001) 383. [3] H. Bock, S. Holl, V. Krenzel, Z. Naturforsch. 56b (2001) 13. [4] H. Lin, L. Yuan, S. He, X. Wang, Chem. Phys. Lett. 332 (2000) 569. [5] S. Konaka, M. Kimura, 13th Austin Symposium on Gas Phase Molecular Structure, The University of Texas, Austin, TX, 12– 14 March 1990, p. S21. [6] A. Tsuboyama, A. Murayama, S. Konaka, M. Kimura, J. Mol. Struct. 118 (1984) 351. [7] N. Kuze, M. Ebizuka, H. Fujiwara, H. Takeuchi, T. Egawa, S. Konaka, G. Fogarasi, J. Phys. Chem. A102 (1998) 2080. [8] H. Takeuchi, J. Enmi, M. Onozaki, T. Egawa, S. Konaka, J. Phys. Chem. 98 (1994) 8632. [9] A.W. Ross, M. Fink, R. Hilderbrandt, J. Wang, V.H. Smith Jr, in: A.J.C. Wilson (Ed.), International Tables for X-Ray Crystallography, Kluwer, Dordrecht, Boston and London, 1995, p. 245. [10] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, V.G. Zakrzewski, J.A. Montgomery Jr., R.E. Stratmann, J.C. Burant, S. Dapprich, J.M. Millam, A.D. Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski, G.A. Petersson, P.Y. Ayala, Q. Cui, K. Morokuma, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J. Cioslowski, J.V. Ortiz, A.G. Baboul, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, J.L. Andres, C. Gonzalez, M. Head-Gordon, E.S. Replogle, J.A. Pople, GAUSSIAN 98 (Revision A.9), Gaussian Inc., Pittsburgh, PA, 1998.
384
H. Takeuchi et al. / Journal of Molecular Structure 657 (2003) 381–384
[11] N. Neto, O. Oehler, R.M. Hexter, J. Chem. Phys. 58 (1973) 5661. [12] K. Tamagawa, M. Kimura, Bull. Chem. Soc. Jpn 52 (1979) 2747. [13] K. Kuchitsu, L.S. Bartell, J. Chem. Phys. 35 (1961) 1945. [14] R. Marquardt, N.S. Gonc¸alves, O. Sala, J. Chem. Phys. 103 (1995) 8391.
[15] M. Jen, D.R. Lide, J. Chem. Phys. 36 (1962) 2525. [16] M. Hargittai, G. Schltz, P. Schwerdtfeger, M. Seth, Struct. Chem. 12 (2001) 377. [17] J. Demaison, L. Margule`s, J.E. Boggs, Struct. Chem. 14 (2003) 159. [18] Z. Kisiel, L. Pszczo´lkowski, L.B. Favero, W. Caminati, J. Mol. Spectrosc. 189 (1998) 283.
Molecular structure of triiodomethane, CHI3, in the gas phase: an electron diffraction study Hiroshi Takeuchi*, Toshiharu Ozaki, Tsuguhide Takeshima, Toru Egawa, Shigehiro Konaka Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan Received 4 June 2003; revised 30 June 2003; accepted 2 July 2003
Abstract The molecular structure of triiodomethane (iodoform, CHI3) has been determined by gas electron diffraction. The structural ˚ and /a /8) with the estimated limits of error ð3sÞ are: r(C – H) ¼ 1.111 (assumed), r(C – I) ¼ 2.145(8), parameters (rg /A r(I…I) ¼ 3.549(2), /ICI ¼ 111.9(7), /ICH ¼ 107.0(7). Mean amplitudes, l(C – I) and l(I· · ·I), have also been determined. The C– I distance of CHI3 is equal to that of CI4 within experimental uncertainties. q 2003 Elsevier B.V. All rights reserved. Keywords: CHI3; Molecular structure; Electron diffraction
The molecular structure of triiodomethane (iodoform, CHI3) was determined by the visual method of gas ˚ and electron diffraction (GED, r(C –I) ¼ 2.12(4) A /ICI ¼ 113.08) [1] but no precise structural data are available. Recently the geometry of CHI3 has been calculated by MP2, B3LYP and B3PW91 methods, where effective core potentials are used [2 –4]. Precise experimental structure is required for checking the reliability of sophisticated theoretical calculations. In this communication, we report the molecular structure of CHI3 determined by the modern technique of GED, which is compared with the structures of related molecules and the theoretical results. A commercial sample of CHI3 (Aldrich) with a purity of 99% and an apparatus equipped with * Corresponding author. Tel.: þ81-11-706-3533; fax: þ 81-11706-4924. E-mail address: [email protected] (H. Takeuchi).
an r 3 -sector [5] were used for experiment. Diffraction patterns were recorded on 8 £ 8 in. Kodak projector slide plates, which were developed in Kodak Dektol developer diluted 1:1 for 4.5 min. The energy of incident electrons was about 37 keV and the scale factor was determined from the diffraction patterns of ˚ ) [6]. Other carbon disulfide (ra (C – S) ¼ 1.5570 A experimental conditions are as follows: camera distance, 244.5 mm; temperature of nozzle tip [7], ˚ ; exposure 395 K; electron wavelength, 0.06329 A time, 110– 140 s; beam current, 1.5 mA; uncertainties of scale factor, 0.05%; background pressure, ˚ 21. 1.5 £ 1026 Torr; range of s-value, 4.5 – 33.8 A Data reduction was made in the same way as described in Ref. [8] with the exception of the atomic scattering factors used, which were taken from Ref. [9]. The leveled total intensities averaged for four plates were used for data analysis. The molecular
0022-2860/03/$ - see front matter q 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0022-2860(03)00431-9
382
H. Takeuchi et al. / Journal of Molecular Structure 657 (2003) 381–384 Table 1 Observed and calculated vibrational frequencies (in cm21) Species
Mode
Calc1a
Calc2b
Obsc
A1
n1 n2 n3 n4 n5 n6
3256 428 152 1104 583 99
3013 427 152 1067 579 109
3013 425 154 1068 578 110
E
a
Unscaled result (B3LYP/3-21G**). Values obtained from scaled force constants. Values of scale factors for local symmetry coordinates, C – H stretching, CI3 symmetric stretching, CI3 degenerate stretching, CI3 symmetric bending, C –H degenerate bending and CI3 degenerate deformation, are 0.8559, 1.0476, 0.9553, 0.9489, 0.9334 and 1.2467, respectively. c Ref. [11]. b
Fig. 1. Experimental (†) and theoretical (– ) molecular scattering intensities of CHI3: DsMðsÞ ¼ sMðsÞobs 2 sMðsÞcalc :
calculations were transformed into the force constants in symmetry coordinates fij : Resultant quadratic force constants were modified by using scale factors ci so as to reproduce experimental vibrational wavenumbers [11]. Scaled force constants, fijscaled ð¼ ðci cj Þ1=2 fij Þ; were used to calculate mean amplitudes and shrinkage corrections, ra 2 ra ; required for the analysis of GED data. Table 1 compares calculated vibrational wavenumbers with observed ones in the crystal [11]. The mean amplitudes calculated with our program NVMA are listed in Table 2.
scattering intensities of CHI3 are shown in Fig. 1. The leveled total intensities and backgrounds are available from the authors upon request. In order to obtain information on the force field of this molecule, density functional theory calculations were carried out using program GAUSSIAN 98 [10]. Geometry optimization and vibrational calculations were performed at the B3LYP/3-21G** level under the assumption of C3v symmetry. Cartesian force constants obtained from the B3LYP/3-21G**
Table 2 Structural parameters and mean amplitudes of CHI3 with the estimated limits of error ð3sÞ GEDa rg ; /a Interatomic distances (A˚) C –H 1.111e C –I 2.145(8) I· · ·I 3.549(2) I· · ·H 2.680(20)f Bond angles (degrees) ICI 111.9(7)f HCI 107.0(7)f a b c d e f
MP2 ecpb l obs
l calc
0.078e 0.067(7) 0.108(2) 0.122e
0.078 0.063 0.096 0.122
3-21G**
1.092 2.154
112.9 105.8
B3PW91/6-311þ þ G(3df,2pd)/LanL2DZd
B3LYP
1.082 2.193
112.8 105.9
6-31G**/ecpc
1.08 2.17
113 106
1.080 2.156
112.9 105.8
Present study. Index of resolution is 0.90(2). The MP2 calculation using effective core potentials [2]. The B3LYP calculation with the 6-31G** basis set for H and C and effective core potential for I [3]. The B3PW91 calculation with the 6-311þ þG(3df,2pd) basis set for H and C and the LanL2DZ basis set for I [4]. Assumed. Dependent parameter.
H. Takeuchi et al. / Journal of Molecular Structure 657 (2003) 381–384
Fig. 2. Experimental radial distribution curve of CHI3: Df ðrÞ ¼ f ðrÞobs 2 f ðrÞcalc : Atom pairs are indicated by vertical bars.
In the data analysis of GED, the value of rg (C – H) ˚ [12]. Asymmetry was fixed at that of CHBr3, 1.111 A parameters were estimated by the conventional methods [13]. Interatomic distances, r(C – I) and r(I· · ·I), mean amplitudes, l(C – I) and l(I· · ·I), and index of resolution, k; were determined by leastsquares calculations on molecular scattering intensities. The results obtained by GED are listed in Table 2. The experimental radial distribution curve is shown in Fig. 2. Correlation matrix element k=l(I· · ·I) is 0.76 and the absolute values of the other elements are smaller than 0.2. The calculated value of l(I· · ·I) is significantly smaller than the experimental one. We found that calculations in which the wavenumber of n6 was assumed to be 95 cm21 reproduced the experimental value of l(I· · ·I). The assumed value is close to 99(2) cm21, a tentative value of n6 in the gas phase reported by Marquardt et al. [14]. Therefore, the origin of the discrepancy mentioned above is mainly due to the use of the wavenumber measured in the crystal, 110 cm21 [11]. The wavenumbers of other modes reported in the gas phase [14] are different from those in the crystal by less than 3%. These differences do not significantly influence the calculated values of mean amplitudes and thus the determined values of independent parameters. The value of /ICI is larger than the tetrahedral angle. This trend is observed for the gas-phase structures of CHBr3 (/avBrCBr ¼ 111.7(4)8) [12]
383
and CHCl3 (/sClCCl ¼ 111.3(2)8) [15]. These results can be ascribed to non-bonded repulsions between halogen atoms. The value of the rg (C –I) of CI4 is ˚ [16], which is in agreement with that of 2.157(10) A CHI 3 within experimental uncertainties. The differences, rg ðC – IÞ 2 re ðC – IÞ; of CI4 and CHI3 ˚ assuming were roughly estimated to be 0.01 A ˚ 21 in the the anharmonicity parameter a3 to be 2 A 2 approximation, rg 2 re ¼ ð3=2Þa3 l [13]. Therefore, the values of re (C– I) of CI4 and CHI3 are close to the ˚ [17], and the rav (C – I) of re (C – I) of CH3I, 2.1336 A ˚ [18], determined by microwave CH2I2, 2.1364(6) A spectroscopy. As shown in Table 2, the MP2, B3LYP and B3PW91calculations [2 – 4] overestimate the C – I bond length and ICI bond angle.
References [1] O. Bastiansen, Tidsskr. Kjemi Bergv. 6 (1946) 1. [2] S. Roszak, W.S. Koski, J.J. Kaufman, K. Balasubramanian, SAR QSAR Environ. Res. 11 (2001) 383. [3] H. Bock, S. Holl, V. Krenzel, Z. Naturforsch. 56b (2001) 13. [4] H. Lin, L. Yuan, S. He, X. Wang, Chem. Phys. Lett. 332 (2000) 569. [5] S. Konaka, M. Kimura, 13th Austin Symposium on Gas Phase Molecular Structure, The University of Texas, Austin, TX, 12– 14 March 1990, p. S21. [6] A. Tsuboyama, A. Murayama, S. Konaka, M. Kimura, J. Mol. Struct. 118 (1984) 351. [7] N. Kuze, M. Ebizuka, H. Fujiwara, H. Takeuchi, T. Egawa, S. Konaka, G. Fogarasi, J. Phys. Chem. A102 (1998) 2080. [8] H. Takeuchi, J. Enmi, M. Onozaki, T. Egawa, S. Konaka, J. Phys. Chem. 98 (1994) 8632. [9] A.W. Ross, M. Fink, R. Hilderbrandt, J. Wang, V.H. Smith Jr, in: A.J.C. Wilson (Ed.), International Tables for X-Ray Crystallography, Kluwer, Dordrecht, Boston and London, 1995, p. 245. [10] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, V.G. Zakrzewski, J.A. Montgomery Jr., R.E. Stratmann, J.C. Burant, S. Dapprich, J.M. Millam, A.D. Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski, G.A. Petersson, P.Y. Ayala, Q. Cui, K. Morokuma, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J. Cioslowski, J.V. Ortiz, A.G. Baboul, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, J.L. Andres, C. Gonzalez, M. Head-Gordon, E.S. Replogle, J.A. Pople, GAUSSIAN 98 (Revision A.9), Gaussian Inc., Pittsburgh, PA, 1998.
384
H. Takeuchi et al. / Journal of Molecular Structure 657 (2003) 381–384
[11] N. Neto, O. Oehler, R.M. Hexter, J. Chem. Phys. 58 (1973) 5661. [12] K. Tamagawa, M. Kimura, Bull. Chem. Soc. Jpn 52 (1979) 2747. [13] K. Kuchitsu, L.S. Bartell, J. Chem. Phys. 35 (1961) 1945. [14] R. Marquardt, N.S. Gonc¸alves, O. Sala, J. Chem. Phys. 103 (1995) 8391.
[15] M. Jen, D.R. Lide, J. Chem. Phys. 36 (1962) 2525. [16] M. Hargittai, G. Schltz, P. Schwerdtfeger, M. Seth, Struct. Chem. 12 (2001) 377. [17] J. Demaison, L. Margule`s, J.E. Boggs, Struct. Chem. 14 (2003) 159. [18] Z. Kisiel, L. Pszczo´lkowski, L.B. Favero, W. Caminati, J. Mol. Spectrosc. 189 (1998) 283.