Deprotonation reactions of 2-thiouracil with [2-(pyridin-2-yl)phenyl]mercury(II) acetate. Structural and spectroscopic effects

Abstract

The reaction of [2-(pyridin-2-yl)phenyl]mercury(II) acetate with 2-thiouracil (H₂tuc) in 1 : 1 and 2 : 1 mole ratio in methanol solution afforded [Hg(C₆H₄C₅H₄N)(H₂tuc)] and [{Hg(C₆H₄C₅H₄N)}₂(tuc)] respectively. The bimetallic complex crystallizes in the monoclinic space group P2₁/n with a= 10.706(1), b= 22.043(3), c= 11.126(1)Å, β= 117.01(1)° and Z= 4. The complex molecules are associated in centrosymmetric dimers by weak intermolecular pyridine N ⋯ Hg bond interactions. Of the two organometallic cations, one is bound to the thiouracil N(3) atom [Hg(1)–N(3) 2.12(1)Å] and the other is S-co-ordinated [Hg(2)–S 2.350(5)Å]. Atom Hg(1) also forms two weak intramolecular bonds with the O and S atoms and another secondary bond with the pyridine nitrogen of the Hg(1)(C₆H₄C₅H₄N) moiety [Hg(1)⋯ N 2.61(2)Å]. This last type of intramolecular bond is also present, though a little longer [Hg(2)⋯ N 2.69(2)Å], in Hg(2)(C₆H₄C₅H₄N), where Hg(2) is located 2.99(1)Å from the non-co-ordinated nitrogen atom of the tuc^2– anion [N(1)]. On the grounds of a vibrational study of the two complexes, a scheme for IR-based diagnosis of the co-ordination of the 2-thiouracilate anions is proposed. The ¹H and ¹⁹⁹Hg NMR spectra of the bimetallic complex in CDCl₃ solution indicate that the N- and S-bound Hg(C₆H₄C₅H₄N) units interchange slowly, while the pyridine intramolecular N ⋯ Hg interactions remain in both CDCl₃ and (CD₃)₂SO solutions.