MICROWAVE INVESTIGATIONS OF $C_{5}H_{5}N-SO_{3}$ AND $HCCCN-SO_{3}$: THE PRINCIPLE OF HARD AND SOFT ACIDS AND BASES APPLIED TO PARTIALLY BONDED SYSTEMS

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2000

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Ohio State University

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The Lewis acid-base adducts $C_{5}H_{5}N-SO_{3}$ and $HCCCN-SO_{3}$ have been studied by Fourier transform microwave spectroscopy. The spectrum of $C_{5}H-5N-SO_{3}$ indicates a short N-S bond length of $1.91540(66)$ \AA and free rotation of the $SO_{3}$ unit. In contrast, $HCCCN-SO_{3}$ is more weakly bound with an N-S distance of $2.5676(76)$ \AA, only slightly less than the expected van der Waals interaction distance. The NSO angles are $98.9212(45)^{\circ}$ and $91.89(36)^{\circ}$ for $C_{5}H_{5}N-SO_{3}$ and $HCCCN-SO_{3}$ respectively. A Townes and Dailey analysis of the $^{14} N$ quadrupole coupling constant of $C_{5}H_{5}N-SO_{3}$ indicates a transfer of 0.54 electrons upon formation of the dative bond. This is physical measurement of the ``soft'' portion of the chemical interaction and comparisons are made with other adducts of $SO_{3}$. Bonding is considered in light of Pearson's concept of Hard and Soft Acids and $Bases,^{a}$ nothing the correlation of adduct properties, such as electron transfer and bond length, with the energy gap between the donor and acceptor orbital.

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$^{a}$R.G. Pearson J. Am. Chem. Soc. 85, 3533 (1963).
Author Institution: Department of Chemistry, University of Minnesota

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