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Structure and vibrational frequencies of the peroxymonosulfate ion HSO5−
Journal of Molecular Structure (Theochem), 304 (1994) 13-16
13
0166-1280/94/$07.00 c 1994 ~ Elsevier Science Publishers B.V. All rights reserved
Structure and vibrational frequencies peroxymonosulfate ion HSOY Kimberly
A. Schugart*,
Department of Chemistry CA 90840, USA (Received
28 October
of the
James A. Noblet
and Biochemistry,
1992; accepted
California
State University
Long Beach, Long Beach,
8 July 1993)
Abstract The structure and normal mode vibrational frequencies of the peroxymonosulfate ion HSOF were calculated using ab initio electronic structure theory. The unusual wrap-around structure of the two oxygen and one hydrogen atoms is due to the electronic structure of the ion itself and is not associated with crystal packing forces.
Introduction Peroxymonosulfate ion HSO, is the monoprotic form of Caro’s acid H2S0s, and the anion itself is the species present in the pH range normally found in clouds [l]. It is a powerful oxidizing agent (EHso;/EHso, = 1.82V) [2]. Once formed, peroxymonosulfate can undergo a myriad of reactions important to terrestrial atmospheric chemistry [ 11. The peroxymonosulfate ion is particularly significant because
in the gas phase [4]. From the perspective of the proposed reactants then, the reaction mechanism appears plausible within the context of cloud chemistry. Significantly though, little experimental data and no theoretical studies exist characterizing the peroxymonosulfate anion. These facts are particularly surprising in light of the unusual structure attributed to it through X-ray crystallographic evidence of the anion [5,6]. Consequently, to fully characterize this substance, we under-
it is proposed as an intermediate in atmospheric sulfur compound oxidations in clouds. Theoretical calculations indicate the concen-
took an ab initio study of the structure and vibrational frequencies of the peroxymonosulfate anion.
tration of peroxymonosulfate ion approaches 35% of the total sulfur species in a remote terrestrial cloud [l]. Interestingly, peroxymonosulfate is thought to be a product of the equilibrium between two structural isomers of the bisulfite ions [l]. I70 NMR evidence supports the possibility of aqueous equilibria between these two structures [3], and our ab initio work on the bisulfite ion suggests the two structural forms possess comparable stability * Corresponding SSDZ
author.
0166-1280(93)03425-7
Computational
methods
Calculations were performed using the GAUSSIAN 8s package [7] on two Multiflow Trace 14/300 computers. Geometry optimizations and vibrational frequencies were calculated at the MP2/321 +G* level of theory. The orbital exponents used in this study were those recommended by Hehre et al. [8], namely 0.0845 for oxygen and 0.0405 for sulphur. Preliminary calculations in which a plane
K.A. .Qhugart und J.A. Nobler/J.
14
of symmetry was maintained the HF/3-21G*, MP2/3-21G’
Mol. Strucc. (Throc~hwn) 304 /IW4)
13-16
were performed at and MP2/6-3lG*
levels of theory. Subsequent vibrational frequency calculations indicated that the symmetryconstrained forms were transition states. Therefore, symmetry-relaxed which the total
calculations were performed in energy and geometry were opti-
mized at the MP2/3-21 +G* level of theory. All bond lengths, angles and dihedral angles were allowed to vary. The transition structure optimized at the MP2/3-21G’ level was used as the starting geometry for the symmetry-relaxed calculations. The use of the MP2/3-21 +G* basis set was in response to the excellent performance of this basis set in our previous calculations on bisulfite ion structures. The size of the peroxymonosulfate ion (seven atoms), the large number of variables, and time constraints necessitated the use of a smaller basis set. Results and discussion Structure
und energla calcuhtions
Analogous to our previous work on the bisulfite ion [4], the original symmetry-constrained calculations on the peroxymonosulfate ion produced a transition structure, as indicated by a single negative vibrational frequency (imaginary frequency). The subsequent symmetry-relaxed calculations produced the minimum energy structure shown in Fig. 1. Table 1 lists the calculated structural and total energy data for the peroxymonosulfatc ion and the X-ray crystallographic data for KHSOs . HI0 from two different studies [_5,6]. The calculated data agree well with the cxperimental results. This agreement is a testament to the excellent performance of the diffuse-functionaugmented MP2/3-21 +G* basis set. The interesting wrap-around shape of the [-02 -01 -H] moiety is attributable to a type of intramolecular hydrogen bonding. The calculated 1.995 A distance between 03 and H is somewhat shorter than the typical range of 2.31L3.0A for O-H hydrogen bonding,
Fig. 1. Three views of the minimum peroxymonosulfate ion calculation
energy structure for the at the
MP2/3-21
+G*
level of theory.
and
the
interaction
may
be
more
properly
described as a partial bond with stabilization exceeding the == 10 kcal mol-’ usually associated with short hydrogen bonds [9]. The fact that the calculated structure is virtually identical to the experimentally determined structure from the two crystallographic studies suggests that the interaction is legitimate and not due to crystal packing forces. Vibrational freyuenql
calculutions
The calculated vibrational minimum energy structure
frequency data for the of peroxymonosulfate
K.A. Schugart and J.A. Nohlet/J.
Table 1 Comparison
Mol. Struct.
of calculated and experimental
Parameter”
(Theochem)
structure data for the peroxymonosulfate
Calculated MP2/3-21 +G*
/H-01&02 /SSO2201 102-S-03 /02-SO4 /022SO5 1033SO4 1033SO5 1044-05 /H-O-O-S Total energy
1.0182
1.5765 1.7599 1.5083 1.4888 1.4881 97.262 106.381 100.9232 106.875 98.998 114.357 116.116 116.365 42.13 -169.43696
ion
Experimental Schlemper et aLb
H-01 01-02 s-02 s-03 SO4 SO5
15
304 (1994) 13-16
0.872 1.463 1.634 1.450 1.446 1.440 101.1 109.22 105.69 106.90 99.09 113.09 115.21 114.99 _
Flanagan et al.c
1.460 1.632 1.444 1.437 1.435
109.42 105.91 106.81 99.01 113.11 115.21 115.01
_
a Bond lengths are in angstroms, angles are in degrees and energy is in hartrees. One hartree equals 627.51 kcal mot-‘. b X-ray diffraction data for KHSOs . HZ0 from Ref. 6. ’ X-ray diffraction data for KHSOs . Hz0 from Ref. 7.
in Table 2. In addition, a comparison is made to the experimental spectroscopic data for the solid KHSOs [lo]. Again, significant agreement exists between the experimental and theoretical results for the symmetry-relaxed structure of the peroxymonosulfate ion.
plethora of atmospheric reactions associated with peroxymonosulfate can be seen to be driven by the reactivity associated with this feature of its structure.
Conclusions
All calculations the two Multiflow
ion are presented
The wrap-around
structure
of the peroxymono-
sulfate ion resembles a substituted peroxide structure, indicating that the -02-01-H structure itself predominates in the electronic arrangement and is not influenced by the sulfur. Consequently, the
Acknowledgments in this study were performed on Trace 141300 computers at Cali-
fornia State University, Sacramento. These computers were purchased primarily with a grant from the Chemical Instrumentation Program of the U.S. National Science Foundation (Grant CHE-88227 16).
16
K.A. Schugart and J.A. Noblet;/.
Table 2 Comparison Vibrational mode”
of calculated and experimental
frequency data for the peroxymonosulfate
Calculated frequency (cm- ‘)
Intensityb
II8 243 353 371 441 492 521 564 643
I2 5 4 104 20 71 22 263
823 971
3 109
II67 1230 1321
448 403 64
3181
42
Mol. Strut.
(Theochem)
304 (1994) 13-16
ion Experimental’ frequency (cm-‘)
5
4lOvw 420 VW 545 w 545. 555 w 572 m 605, 615s 750, 770 s 880, 890 w 980 VW 1055~s 1070m 1110,1170vw 1255, 1265~s l3OOw 143ow 2800 VW 3280 m
a The molecule is totally asymmetric; therefore no symmetry of vibration is given. b Intensities are in km mol-’ ‘Data is from Ref. 8 for solid KHSOS in a KBr pellet.
References D.J. Jacob, J. Geophys. Res., 89 (Dl) (1984) 1429. E.A. Betterton and M.R. Hoffmann, J. Phys. Chem., 91 (1987) 3011. D.A. Horner and R.E. Connick, Inorg. Chem., 25 (1986) 2414. J. Noblet and K.A. Schugart, J. Mol. Struct. (Theothem), 304 (I 994) I. E.O. Schlemper, R.C. Thompson, C.K. Fair, F.K. Ross, E.H. Appleman and L.J. Basile, Acta Crystallogr., Sect. C., 40 (1984) 1718. J. Flanagan, W.P. Griffith and A.C. Skapski, J. Chem Sot., Chem Commun., (1984) 1574.
7 M.J. Frisch, M. Head-Fordon, H.B. Schlegel, J. Fox., K. Raghavachari, J.S. Binkley, C. Gonzalez, D.J. DeFrees, R.A. Whiteside, R. Seeger, C.F. Melius, J. Baker, L.R. Kahn, R.L. Martin, J.J.P. Stewart, E.M. Fleuder, S. Topiol and J.A. Pople. GAUSSIAN 88, Gaussian Inc., Pittsburg, PA, 1988. 8 W.J. Hehre, L. Radom, P.v.R. Schleyer and J.A. Pople, Ab lnitio Molecular Orbital Theory, WileyInterscience, New York, 1986. 9 F.A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, 5th Edn., Wiley-Interscience, New York, 1988. 10 (a) J.R. Kyrki, Suom. Kemistil. B, 38 (1965) 51. (b) J.R. Kyrki, Suom. Kemistil. B, 38 (1965) 199.
13
0166-1280/94/$07.00 c 1994 ~ Elsevier Science Publishers B.V. All rights reserved
Structure and vibrational frequencies peroxymonosulfate ion HSOY Kimberly
A. Schugart*,
Department of Chemistry CA 90840, USA (Received
28 October
of the
James A. Noblet
and Biochemistry,
1992; accepted
California
State University
Long Beach, Long Beach,
8 July 1993)
Abstract The structure and normal mode vibrational frequencies of the peroxymonosulfate ion HSOF were calculated using ab initio electronic structure theory. The unusual wrap-around structure of the two oxygen and one hydrogen atoms is due to the electronic structure of the ion itself and is not associated with crystal packing forces.
Introduction Peroxymonosulfate ion HSO, is the monoprotic form of Caro’s acid H2S0s, and the anion itself is the species present in the pH range normally found in clouds [l]. It is a powerful oxidizing agent (EHso;/EHso, = 1.82V) [2]. Once formed, peroxymonosulfate can undergo a myriad of reactions important to terrestrial atmospheric chemistry [ 11. The peroxymonosulfate ion is particularly significant because
in the gas phase [4]. From the perspective of the proposed reactants then, the reaction mechanism appears plausible within the context of cloud chemistry. Significantly though, little experimental data and no theoretical studies exist characterizing the peroxymonosulfate anion. These facts are particularly surprising in light of the unusual structure attributed to it through X-ray crystallographic evidence of the anion [5,6]. Consequently, to fully characterize this substance, we under-
it is proposed as an intermediate in atmospheric sulfur compound oxidations in clouds. Theoretical calculations indicate the concen-
took an ab initio study of the structure and vibrational frequencies of the peroxymonosulfate anion.
tration of peroxymonosulfate ion approaches 35% of the total sulfur species in a remote terrestrial cloud [l]. Interestingly, peroxymonosulfate is thought to be a product of the equilibrium between two structural isomers of the bisulfite ions [l]. I70 NMR evidence supports the possibility of aqueous equilibria between these two structures [3], and our ab initio work on the bisulfite ion suggests the two structural forms possess comparable stability * Corresponding SSDZ
author.
0166-1280(93)03425-7
Computational
methods
Calculations were performed using the GAUSSIAN 8s package [7] on two Multiflow Trace 14/300 computers. Geometry optimizations and vibrational frequencies were calculated at the MP2/321 +G* level of theory. The orbital exponents used in this study were those recommended by Hehre et al. [8], namely 0.0845 for oxygen and 0.0405 for sulphur. Preliminary calculations in which a plane
K.A. .Qhugart und J.A. Nobler/J.
14
of symmetry was maintained the HF/3-21G*, MP2/3-21G’
Mol. Strucc. (Throc~hwn) 304 /IW4)
13-16
were performed at and MP2/6-3lG*
levels of theory. Subsequent vibrational frequency calculations indicated that the symmetryconstrained forms were transition states. Therefore, symmetry-relaxed which the total
calculations were performed in energy and geometry were opti-
mized at the MP2/3-21 +G* level of theory. All bond lengths, angles and dihedral angles were allowed to vary. The transition structure optimized at the MP2/3-21G’ level was used as the starting geometry for the symmetry-relaxed calculations. The use of the MP2/3-21 +G* basis set was in response to the excellent performance of this basis set in our previous calculations on bisulfite ion structures. The size of the peroxymonosulfate ion (seven atoms), the large number of variables, and time constraints necessitated the use of a smaller basis set. Results and discussion Structure
und energla calcuhtions
Analogous to our previous work on the bisulfite ion [4], the original symmetry-constrained calculations on the peroxymonosulfate ion produced a transition structure, as indicated by a single negative vibrational frequency (imaginary frequency). The subsequent symmetry-relaxed calculations produced the minimum energy structure shown in Fig. 1. Table 1 lists the calculated structural and total energy data for the peroxymonosulfatc ion and the X-ray crystallographic data for KHSOs . HI0 from two different studies [_5,6]. The calculated data agree well with the cxperimental results. This agreement is a testament to the excellent performance of the diffuse-functionaugmented MP2/3-21 +G* basis set. The interesting wrap-around shape of the [-02 -01 -H] moiety is attributable to a type of intramolecular hydrogen bonding. The calculated 1.995 A distance between 03 and H is somewhat shorter than the typical range of 2.31L3.0A for O-H hydrogen bonding,
Fig. 1. Three views of the minimum peroxymonosulfate ion calculation
energy structure for the at the
MP2/3-21
+G*
level of theory.
and
the
interaction
may
be
more
properly
described as a partial bond with stabilization exceeding the == 10 kcal mol-’ usually associated with short hydrogen bonds [9]. The fact that the calculated structure is virtually identical to the experimentally determined structure from the two crystallographic studies suggests that the interaction is legitimate and not due to crystal packing forces. Vibrational freyuenql
calculutions
The calculated vibrational minimum energy structure
frequency data for the of peroxymonosulfate
K.A. Schugart and J.A. Nohlet/J.
Table 1 Comparison
Mol. Struct.
of calculated and experimental
Parameter”
(Theochem)
structure data for the peroxymonosulfate
Calculated MP2/3-21 +G*
/H-01&02 /SSO2201 102-S-03 /02-SO4 /022SO5 1033SO4 1033SO5 1044-05 /H-O-O-S Total energy
1.0182
1.5765 1.7599 1.5083 1.4888 1.4881 97.262 106.381 100.9232 106.875 98.998 114.357 116.116 116.365 42.13 -169.43696
ion
Experimental Schlemper et aLb
H-01 01-02 s-02 s-03 SO4 SO5
15
304 (1994) 13-16
0.872 1.463 1.634 1.450 1.446 1.440 101.1 109.22 105.69 106.90 99.09 113.09 115.21 114.99 _
Flanagan et al.c
1.460 1.632 1.444 1.437 1.435
109.42 105.91 106.81 99.01 113.11 115.21 115.01
_
a Bond lengths are in angstroms, angles are in degrees and energy is in hartrees. One hartree equals 627.51 kcal mot-‘. b X-ray diffraction data for KHSOs . HZ0 from Ref. 6. ’ X-ray diffraction data for KHSOs . Hz0 from Ref. 7.
in Table 2. In addition, a comparison is made to the experimental spectroscopic data for the solid KHSOs [lo]. Again, significant agreement exists between the experimental and theoretical results for the symmetry-relaxed structure of the peroxymonosulfate ion.
plethora of atmospheric reactions associated with peroxymonosulfate can be seen to be driven by the reactivity associated with this feature of its structure.
Conclusions
All calculations the two Multiflow
ion are presented
The wrap-around
structure
of the peroxymono-
sulfate ion resembles a substituted peroxide structure, indicating that the -02-01-H structure itself predominates in the electronic arrangement and is not influenced by the sulfur. Consequently, the
Acknowledgments in this study were performed on Trace 141300 computers at Cali-
fornia State University, Sacramento. These computers were purchased primarily with a grant from the Chemical Instrumentation Program of the U.S. National Science Foundation (Grant CHE-88227 16).
16
K.A. Schugart and J.A. Noblet;/.
Table 2 Comparison Vibrational mode”
of calculated and experimental
frequency data for the peroxymonosulfate
Calculated frequency (cm- ‘)
Intensityb
II8 243 353 371 441 492 521 564 643
I2 5 4 104 20 71 22 263
823 971
3 109
II67 1230 1321
448 403 64
3181
42
Mol. Strut.
(Theochem)
304 (1994) 13-16
ion Experimental’ frequency (cm-‘)
5
4lOvw 420 VW 545 w 545. 555 w 572 m 605, 615s 750, 770 s 880, 890 w 980 VW 1055~s 1070m 1110,1170vw 1255, 1265~s l3OOw 143ow 2800 VW 3280 m
a The molecule is totally asymmetric; therefore no symmetry of vibration is given. b Intensities are in km mol-’ ‘Data is from Ref. 8 for solid KHSOS in a KBr pellet.
References D.J. Jacob, J. Geophys. Res., 89 (Dl) (1984) 1429. E.A. Betterton and M.R. Hoffmann, J. Phys. Chem., 91 (1987) 3011. D.A. Horner and R.E. Connick, Inorg. Chem., 25 (1986) 2414. J. Noblet and K.A. Schugart, J. Mol. Struct. (Theothem), 304 (I 994) I. E.O. Schlemper, R.C. Thompson, C.K. Fair, F.K. Ross, E.H. Appleman and L.J. Basile, Acta Crystallogr., Sect. C., 40 (1984) 1718. J. Flanagan, W.P. Griffith and A.C. Skapski, J. Chem Sot., Chem Commun., (1984) 1574.
7 M.J. Frisch, M. Head-Fordon, H.B. Schlegel, J. Fox., K. Raghavachari, J.S. Binkley, C. Gonzalez, D.J. DeFrees, R.A. Whiteside, R. Seeger, C.F. Melius, J. Baker, L.R. Kahn, R.L. Martin, J.J.P. Stewart, E.M. Fleuder, S. Topiol and J.A. Pople. GAUSSIAN 88, Gaussian Inc., Pittsburg, PA, 1988. 8 W.J. Hehre, L. Radom, P.v.R. Schleyer and J.A. Pople, Ab lnitio Molecular Orbital Theory, WileyInterscience, New York, 1986. 9 F.A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, 5th Edn., Wiley-Interscience, New York, 1988. 10 (a) J.R. Kyrki, Suom. Kemistil. B, 38 (1965) 51. (b) J.R. Kyrki, Suom. Kemistil. B, 38 (1965) 199.