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The molecules of the (pyrazinecarbonyl)hydrazones of the heterocyclic aldehydes RCHO with R = pyrrol-2-yl, furan-2-yl, thien-2-yl and pyridin-2-yl corresponding to compounds ( 2:  X = NH), ( 2:  X = O), ( 2:  X = S)  and  3 , respectively, are formally rather similar. Despite this the molecular packing and intermolecular interactions show unexpectedly wide variation throughout the series. In  2  hydrogen-bonds link the planar molecules edge to edge to form chains or, in one case, planar ribbons while  3  exhibits zig-zag chain connectivity. Three-dimensional connectivity is attained by intermolecular hydrogen-bonds alone in  ortho -( 2:  X = S), the orthorhombic polymorph of ( 2:  X = S)  and by intermolecular hydrogen-bonds combined with π···π interactions in ( 2:  X = O) and  3 . No more than two-dimensional layer connectivity is found in ( 2:  X = NH) and the monoclinic polymorph,  mono -( 2:  X = S) of ( 2:  X = S).

zeitschrift für kristallographie - crystalline materials

(Pyrazinecarbonyl)hydrazones of heteroarenealdehydes: crystal structures formed from N—H···O, N—HN, C—H···O hydrogen-bonds, C—H···π and π···π interactions