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, C 5 H 5 N·CH 4 N 2 O, crystallizes in the P 2 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…) 2 N hydrogen bonds. The 1:1 adduct of pyridine and thiourea, C 5 H 5 N·CH 4 N 2 S, crystallizes in the P 2 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 ≃ 0 and , and three at z ≃ and ; the latter are crosslinked to form a layer structure by additional long N—H…S interactions, which each formally replace one branch of a bifurcated hydrogen‐bond system.