Green chemistry synthesis: 2-amino-3-[(E)-(2-pyridyl)methylideneamino]but-2-enedinitrile monohydrate and 5-cyano-2-(2-pyridyl)-1-(2-pyridylmethyl)-1H-imidazole-4-carboxamide

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The title compounds, C(10)H(9)N(5)O.H(2)O (L1.H(2)O) and C(16)H(12)N(6)O (L2), were synthesized by solvent-free aldol condensation at room temperature. L1, prepared by grinding picolinaldehyde with 2,3-diamino-3-isocyanoacrylonitrile in a 1:1 molar ratio, crystallized as a monohydrate. L2 was prepared by grinding picolinaldehyde with 2,3-diamino-3-isocyanoacrylonitrile in a 2:1 molar ratio. By varying the conditions of crystallization it was possible to obtain two polymorphs, viz. L2-I and L2-II; both crystallized in the monoclinic space group P2(1)/c. They differ in the orientation of one pyridine ring with respect to the plane of the imidazole ring. In L2-I, this ring is oriented towards and above the imidazole ring, while in L2-II it is rotated away from and below the imidazole ring. In all three molecules, there is a short intramolecular N-H...N contact inherent to the planarity of the systems. In L1.H(2)O, this involves an amino H atom and the C=N N atom, while in L2 it involves an amino H atom and an imidazole N atom. In the crystal structure of L1.H(2)O, there are N-H...O and O-H...O intermolecular hydrogen bonds which link the molecules to form two-dimensional networks which stack along [001]. These networks are further linked via intermolecular N-H...N(cyano) hydrogen bonds to form an extended three-dimensional network. In the crystal structure of L2-I, symmetry-related molecules are linked via N-H...N hydrogen bonds, leading to the formation of dimers centred about inversion centres. These dimers are further linked via N-H...O hydrogen bonds involving the amide group, also centred about inversion centres, to form a one-dimensional arrangement propagating in [100]. In the crystal structure of L2-II, the presence of intermolecular N-H...O hydrogen bonds involving the amide group results in the formation of dimers centred about inversion centres. These are linked via N-H...N hydrogen bonds involving the second amide H atom and the cyano N atom, to form two-dimensional networks in the bc plane. In L2-I and L2-II, C-H...pi and pi-pi interactions are also present.