SDAS 2002 Vol 81

Proceedings of the South Dakota Academy of Science,Vol. 81 (2002) 181

3- PHOSPHONOSULFONATE(3-) O3PSO3 AND RELATED IONS

Arlen Viste and Kari Lunder Stone Department of Chemistry Augustana College Sioux Falls, SD 57197

ABSTRACT

2- 4- The ions dithionate S2O6 and hypophosphate P2O6 are well known. How- 3- ever the isoelectronic phosphonosulfonate(3-) ion O3PSO3 is not. Neither is the - isoelectronic O3SClO3 ion. Previous experimental study of the oxidation of thio- 3- 3- phosphate ion O3PS suggested the formation of O3PSO3 but the conclusion remains tentative. (Viste 1991) In the present study, HF/6-31G and HF/6- 31G(d) molecular orbital calculations were carried out for each of the four ions, both in the gas phase and solvated in aqueous solution. With Jaguar 4, ge- ometries were optimized for both gas phase and solvated structures for the four ions. In the gas phase in HF/6-31G, Jaguar 4 and Gaussian (94 or 98W) show 4- 2- - 3- stable structures for P2O6 , S2O6 , and O3SClO3 , while gas phase O3PSO3 is cal- - 2- culated to dissociate to planar PO3 and pyramidal SO3 . (Schrödinger 2000, 3- Gaussian 1999) However solvated (aqueous) O3PSO3 is calculated by Jaguar 4 to be stable in HF/6-31G, though with a slightly long S-P bond length of 258 2- pm, compared with 230 pm for S-S in solvated S2O6 and 219 pm for P-P in sol- 4- 4- vated P2O6 . In HF/6-31G solvation also shortens the central X-Y bond in P2O6 2- - and S2O6 but lengthens it in O3SClO3 . Next in HF/6-31G(d) and DFT B3LYP/6- 31G(d), all four ions are calculated to be stable both in the gas phase and in solution. Vibrational frequencies have been calculated in HF/6-31G(d) and DFT B3LYP/6-31G(d) for the normal modes of vibration of the four ions, both gas phase and solvated. Gas phase infrared and Raman intensities have been calculated in HF/6-31G(d). Thus calculations indicate that the phosphonosul- 3- fonate (3-) ion O3PSO3 is stabilized by solvation in HF/6-31G, while all four ions are stable in HF/6-31G(d) and DFT B3LYP/6-31G(d), both gas phase and solvated. Further investigation of protonated species is planned.

Keywords

Phosphonosulfonate(3-), vibrations, Jaguar, Gaussian

INTRODUCTION

3- 3- phosphate ion O3PS suggested the formation of O3PSO3 but the conclusion remains tentative. (Viste 1991) In the present study, HF/6-31G and HF/6- 31G(d) molecular orbital calculations were carried out for each of the four ions, both in the gas phase and solvated in aqueous solution. Structure and vibrations have been investigated through ab initio and DFT molecular orbital calculations, using Jaguar 4 and Gaussian 94 computational chemistry software

COMPUTATIONAL METHODS

Jaguar 4.0 software was used under SuSE 6.4 Linux on a PC. Gaussian 94 software was run under Aix 4.3 on an IBM RS/6000, through a WebMO inter- face. (Schrödinger 2000, Gaussian 2001, WebMO 2001).

RESULTS AND DISCUSSION

Preliminary calculations carried out at the 6-31G level are summarized in 3- Table 1. Note that in the gas phase at this level, the S-P bond of SPO6 breaks, - but is stabilized in aqueous solution, while SClO6 has a longer calculated bond length in solution.

Table 1. 6-31G calculations.

4- 3- 2- - Geometry P2O6 SPO6 S2O6 SClO6

6-31G gas Failed

X-Y, Å 2.525 18.197 2.359 2.871

X-O, Å 1.650 1.576 1.636 1.582

Y-O, Å 1.685 1.948

X-Y-O, deg 108.6 110.89 105.11 105.25

O-X-Y, deg 90.39 96.76

6-31G solvated (aq)

X-Y, Å 2.194 2.578 2.297 3.973

X-O, Å 1.610 1.571 1.622 1.569

Y-O, Å 1.641 1.851 X-Y-O, deg 107 112 104 113 O-X-Y, deg 96 89

** X=lower, Y=higher atomic number

Next, calculations were carried out at the 6-31G* level, also known as 6- 31G(d). The results are presented in Table 2. Note that the addition of d or- 3- bitals in the calculation has stabilized SPO6 in the gas phase. In solution, cal- 4- 3- 2- culated X-Y bond lengths are slightly shorter for P2O6 , SPO6 , and S2O6 , but - longer for SClO6 . Proceedings of the South Dakota Academy of Science,Vol. 81 (2002) 183

Table 2. 6-31G* Calculations in Gaussian 94, Jaguar 4.

4- 3- 2- - Geometry P2O6 SPO6 S2O6 SClO6

6-31G* gas

X-Y, Å 2.315 2.257 2.115 2.848

X-O, Å ** 1.550 1.509 1.455 1.408

Y-O, Å 1.490 1.473

X-Y-O, deg ** 108.4 109.5 105.3 109.3

O-X-Y, deg 103.1 93.8

6-31G* solvated (aq)

X-Y, Å 2.128 2.120 2.075 3.52

X-O, Å 1.521 1.498 1.449 1.404

Y-O, Å 1.469 1.481 X-Y-O, deg 107 108 105 111 O-X-Y, deg 103 89

** X=lower, Y=higher atomic number

Next, DFT (Density Functional Theory) calculations were carried out, at the 6-31G*/B3LYP level. Results are presented in Table 3.

Table 3. 6-31G*/B3LYP (DFT) calculations.

4- 3- 2- - Geometry P2O6 SPO6 S2O6 SClO6

6-31G*/B3LYP gas

X-Y, Å 2.508 2.432 2.255 2.557

X-O, Å 1.582 1.540 1.496 1.47

Y-O, Å 1.533 1.504

X-Y-O, deg 108 109.9 105.4 107

O-X-Y, deg 102.7 108

6-31G*/B3LYP solvated (aq)

X-Y, Å 2.141 2.161 2.165 2.840

X-O, Å 1.545 1.524 1.486 1.453

Y-O, Å 1.504 1.520 X-Y-O, deg 107 108 105 110 O-X-Y, deg 103 92

** X=lower, Y=higher atomic number

4- For comparison, a literature crystal structure containing P2O6 provides these experimental bond length, in Na4P2O6.10H2O. (Emmerson 1973) P-P 2.201 Å, P-O 1.530-1.538 Å, P-P-O 101.5-113.1 deg. The 6-31G* solvated (aq) and the 6-31G*/B3LYP solvated (aq) calculated results are in quite good agreement with these experimental bond lengths and bond angles. 184 Proceedings of the South Dakota Academy of Science,Vol. 81 (2002)

Vibrational calculations were made both for gas phase and solvated species. Table 4 presents results for selected vibrations, calculated in 6-31G*, gas and solvated(aq).

Table 4. Selected Vibrations in 6-31G*, Gaussian 94, Jaguar 4

4- 3- 2- - P2O6 SPO6 S2O6 SClO6

Vibrations (cm-1) A1g, A2u (D3d) and A1 (C3v) 6-31G* gas X-Y stretch (A1g, A1) ** 255 246 317 54 X-Y-O, Y-X-O bend (A2u, A1) 625 618 669 524 X-Y-O, Y-X-O bend (A1g, A1) 713 741 806 655 X-O, Y-O stretch (A2u, A1) 925 1008 1071 1010 X-Y, X-O, Y-O stretch (A1g, A1) 1038 1118 1189 1198

6-31G* solvated (aq) X-Y stretch (A1g, A1) 355 319 366 58 X-Y-O, Y-X-O bend (A2u, A1) 638 549 711 643 X-Y-O, Y-X-O bend (A1g, A1) 835 783 898 775 X-O, Y-O stretch (A2u, A1) 1066 1055 1161 1135 X-Y, X-O, Y-O stretch (A1g, A1) 1201 1186 1292 1274

** X=lower, Y=higher atomic number

Of these selected normal modes of vibration in D3d symmetry, A1g is Ra- man active and A2u is infrared active. In C3v symmetry, A1 is symmetry al- 3- lowed in both Raman and infrared, but calculated intensity patterns in SPO6 4- 2- are still fairly similar to those of P2O6 and S2O6 .

Vibrational calculations were also made in DFT for both gas phase and solvated species. Table 5 presents results for selected vibrations, calculated in 6- 31G*/B3LYP, gas and solvated(aq). Proceedings of the South Dakota Academy of Science,Vol. 81 (2002) 185

Table 5. Selected Vibrations in 6-31G*, Gaussian 94, Jaguar 4

4- 3- 2- - P2O6 SPO6 S2O6 SClO6

Vibrations (cm-1) A1g, A2u (D3d) and A1 (C3v) 6-31G*/B3LYP gas X-Y stretch (A1g, A1) 184 138 272 175 X-Y-O, Y-X-O bend (A2u, A1) 673 525 757 730 X-Y-O, Y-X-O bend (A1g, A1) 721 619 830 782 X-O, Y-O stretch (A2u, A1) 928 903 1075 1062 X-Y, X-O, Y-O stretch (A1g, A1) 1005 966 1154 1102

6-31G*/B3LYP solvated (aq) X-Y stretch (A1g, A1) 306 276 281 120 skew X-Y-O, Y-X-O bend (A2u, A1) 548 500 584 527 X-Y-O, Y-X-O bend (A1g, A1) 723 677 728 647 X-O, Y-O stretch (A2u, A1) 949 956 993 972 X-Y, X-O, Y-O stretch (A1g, A1) 1064 1057 1093 1036

For comparison, experimental vibrational frequencies are summarized in Table 6. (Palmer 1961) The comparison between calculated and observed vibrational frequencies is quite good, particularly for 6-31G*/B3LYP solvated (aq).

Table 6. Comparison with Experiment (Palmer 1961) for Selected Vibrations

4- 3- 2- - P2O6 SPO6 S2O6 SClO6

Vibrations (cm-1) A1g, A2u (D3d) and A1 (C3v) X-X stretch (A1g) 275 293 X-X-O bend (A2u) 562 577 X-X-O bend (A1g) 670 710 X-O stretch (A2u) 942 1000 X-Y, X-O stretch (A1g) 1062 1102

3- Figure 1 shows the electron density with electrostatic potential for SPO6 , calculated in Gaussian 94 6-31G*, as represented by Molekel. (Gaussian 1999, Molekel 2001)

3- Fig. 1. SPO6 electron density with electrostatic potential. 186 Proceedings of the South Dakota Academy of Science,Vol. 81 (2002)

CONCLUSION

3- Calculations indicate that the phosphonosulfonate (3-) ion O3PSO3 is sta- 4- 3- 2- bilized by solvation in HF/6-31G, while all four ions (P2O6 , SPO6 , S2O6 , and - SClO6 ) are stable in HF/6-31G(d) and DFT B3LYP/6-31G(d), both gas phase and solvated. The comparison between calculated frequencies and experimental vibrational frequencies observed by Palmer is quite good, particularly for 6- 31G*/B3LYP solvated (aq). (Palmer 1961) Further investigation of protonated species is planned.

Notes

1. Kari Lunder participated in the beginning of this work as an undergraduate at Augustana College (SD). Kari Lunder Stone is currently a graduate student at Pennsylvania State University. 2. This work was presented in a poster session at the Finnish Symposium on Quantum Chemistry, An International Conference, Kuusamo, Finland, June 11-17, 2001. http://www.chem.helsinki.ﬁ/Research/Kuusamo/ http://inst.augie.edu/~viste/Kuusamo/

LITERATURE CITED

Anderson, Wayne. 2001. Jagconvert1.1.tcl. Bloomsburg University, PA. http://facstaff.bloomu.edu/wpa/ Emmerson, D. S. and D. E. C. Corbridge. 1973. “The crystal structure of tetra-

sodium hypophosphate decahydrate Na4P2O6.10H2O.” Phosphorus. 3: 131. Gaussian, Inc. 2001. Gaussian 94 and 98 software. http://www.gaussian.com/ Laaksonen, Leif. 2000. gOpenMol software. http://www.csc.ﬁ/~laaksone/gopenmol/gopenmol.html Molekel. 2001. Advanced Interactive 3D-Graphics for Molecular Sciences. http://www.cscs.ch/molekel/molekel.html Palmer, W. G. 1961. The vibrational spectra and structures of dithionate, hypophosphate, and related ions. J. Chem. Soc. 1552-1562. Schrödinger, Inc. 2000. Jaguar 4 software. http://www.schrodinger.com/ Viste, Arlen and Jeanne Pfaff. 1991. Oxidation of Thiophosphate. Proc. S.D. Acad. Sci.. 70: 262-263. Abstract. WebMO. 2000. Hope College. Holland, MI. http://www.chem.hope.edu/webmo/ WebMO. 2001. Department of Chemistry, Augustana College, Sioux Falls, SD. http://inst.augie.edu/~spartan/ Proceedings of the South Dakota Academy of Science,Vol. 81 (2002) 187

ACKNOWLEDGMENTS

We thank Hope College for their public-spirited development and provi- sion of the WebMO software. Thanks also to Augustana College and its De- partment of Chemistry for software and hardware support.