STRUCTURE OF THE GAS PHASE ZWITTERION OF SULFAMIC ACID: MICROWAVE SPECTRUM $H_{3}N-SO_{3}$
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Date
1995
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Publisher
Ohio State University
Abstract
The microwave spectrum of $H_{3}N-SO_{3}$ has been observed by pulsed-nozzle Fourier transform microwave spectroscopy. The N-S distance is $1.971(1) {\AA}$ and the NSO angle is $98.0(1)^{\circ}$. The complex is the gas phase form of the $NH_{3} ^{+}SO_{3}$ zwitterion which comprises the crystalline form of sulfamic acid. However, the structure of the complex changes dramatically upon formation of the solid: The N-S bond length in the gas phase is $0.207(21) {\AA}$ longer than that in the crystal, and the NSO angle is $5.2(6)^{\circ}$ smaller. These results are in reasonable agreement with recent predictions by self consistent reaction field $theory^{1}$. Also the gas phase system appears to be intermediate in character between a weakly bound complex and a chemically bonded species. For example, the $N-S$ bond length, while $0.2 {\AA}$ longer in the gas phase than in the crystal is still about $0.6 {\AA}$ shorter than that observed in the gas phase complex $HCN-SO_{3}$. Similarly, the $8^{\circ}$ out-of-plane distortion of the $SO_{3}$ in the gaseous adduct lies between the $0^{\circ}$ value expected for a weakly bound system and the $13^{\circ}$ distortion found in solid sulfamic acid. The centrifugal distortion constant is somewhat small, indicating a large stretching force constant for the N-S bond, and analysis of the nitrogen quadrupole coupling constant indicates about a quarter of an electron transferred in forming the dative bond. The general connection between partial bonding in the gas phase and large gas-solid structure differences will be discussed.
Description
1. M.W. Wong, K.B. Wiberg, and M.J. Frisch, J. Am. Chem. Soc., 114, 523 (1992)
Author Institution: University of Minnesota, Minneapolis, MN 55455
Author Institution: University of Minnesota, Minneapolis, MN 55455