Four Different Crystalline Products from One Reaction: Unexpected Diversity of Products of the CuCl2 Reaction with N-(2-Pyridyl)thiourea

Abstract

The reaction of N-(2-pyridyl)thiourea with CuCl₂ in methanol yields four different crystalline products: yellow dimeric complex, [Cu₂Cl₂(µ-Cl)₂(L)₂] (1), red polymeric complex, [Cu₃Cl₈L₂]_n (2), orange crystalline product with ionic structure, L₂[CuCl₄] (3), and colourless ionic compound LCl (4), where L = 2-amino-[1,2,4]thiadiazolo[2,3-a]pyridin-4-ium cation as a result of oxidative cyclization of N-(2-pyridyl)thiourea. The crystal structures of all these crystalline products have been determined by single-crystal X-ray diffraction analysis. Compound 1 involves a copper(I) ion while in 2 and 3 the copper centre is in the divalent state. ¹H NMR spectra for compounds 1–3 are identical and confirm deprotonated thioamide groups of N-(2-pyridyl)thiourea and the formation of a thiadiazolopyridinium cation in solution. The hydrogen bonding and π–π stacking interactions were investigated in the solid state. In addition, all crystalline products 1–4 exhibit also S···Cl bonding interactions which consolidate the complexes into networks. The X-ray diffraction analyses indicate the absence of other crystalline phases in the crude reaction mixture.