Microwave spectra and gas phase structural parameters for N-hydroxypyridine-2(1H)-thione

The microwave spectrum for N-hydroxypyri-dine-2(1H)-thione (pyrithione) was measured in the frequency range 6 - 18 GHz, providing accurate rotational constants and nitrogen quadrupole coupling strengths for three isotopologues, C ₅H ₄ ³² S ¹⁴NOH, C ₅H ₄ ³²S ¹⁴NOD, and C ₅H ₄ ³⁴ SNOH. Pyrithione was found to be in a higher concentration in the gas phase than the other tautomer, 2-mercaptopyridine-N-oxide (MPO). Microwave spectroscopy is best suited to determine which structure predominates in the gas phase. The measured rotational constants were used to accurately determine the coordinates of the substituted atoms and provided sufficient data to determine some of the important structural parameters for pyrithione, the only tautomer observed in the present work. The spectra were obtained using a pulsed-beam Fourier transform microwave spectrometer, with sufficient resolution to allow accurate measurements of the N nuclear quadrupole hyperfine interactions. Ab initio calculations provided structural parameters and quadrupole coupling strengths that are in very good agreement with measured values. The experimental rotational constants for the parent compound are A = 3212.10(1), B = 1609.328(7), and C = 1072.208(6) MHz, yielding the inertial defect Δ ₀ = - 0.023 amu · Å ² for the C ₅H ₄ ³² S ¹⁴NOH isotopologue. The observed near zero inertial defect clearly indicates a planar structure. The least-squares fit structural analysis yielded the experimental bond lengths R(O - H) = 0.93(2) Å, R(C - S) = 1.66(2) Å, and angle ∠ (N - O - H) = 105(4)° for the ground state structure. (Figure presented)