Pyridine 1:1 adducts of urea (Z′=1) and thiourea (Z′=8)

During our studies of urea and thiourea adducts, we noticed that no adducts with unsubstituted pyridine had been structurally investigated. The 1:1 adduct of pyridine and urea, C5H5N center dot CH4N2O, crystallizes in the P2(1)/c space group with Z = 4. The structure is of a standard type for urea adducts, whereby the urea molecules form a ribbon, parallel to the a axis, consisting of linked R-2(2)(8) rings, and the pyridine molecules are attached to the periphery of the ribbon by bifurcated (N-H center dot center dot center dot)(2)N hydrogen bonds. The 1:1 adduct of pyridine and thiourea, C5H5N center dot CH4N2S, crystallizes in the P2(1)/n space group, with Z = 32 (Z' = 8). The structure displays similar ribbons to those of the urea adduct. There are two independent ribbons parallel to the b axis at z similar or equal to 0 and 1/2, and three at z similar or equal to 1/4 and 3/4; the latter are crosslinked to form a layer structure by additional long N-H center dot center dot center dot S interactions, which each formally replace one branch of a bifurcated hydrogen-bond system.