Crystal structures of four chiral imine-substituted thiophene derivatives

Abstract

A series of thiophenes substituted in positions 2 and 5 by imine groups have been synthesized using a solvent-free approach, and their crystal structures determined. The substituents are chiral groups, and the expected absolute configuration for each molecule was confirmed by refinement of the Flack parameter. The compounds are 2,5-bis[(S)-(+)-(1,2,3,4-tetrahydronaphthalen-1-yl)imino]thiophene, C26H26N2S, (I), 2,5-bis{[(R)-(-)-1-(4-methoxyphenyl)ethyl]iminomethyl}thiophene, C24H26N2O2S, (II), 2,5-bis{[(R)-(-)-1-(4-fluorophenyl)ethyl]iminomethyl}thiophene, C22H20F2N2S, (III), and 2,5-bis{[(S)-(+)-1-(4-chlorophenyl)ethyl]iminomethyl}thiophene, C22H20Cl2N2S, (IV). A common feature of all four molecules is the presence of twofold symmetry. For (I), which crystallizes in the triclinic space group P1, this symmetry is non-crystallographic, but for (II) in C2 and the isomorphous structures (III) and (IV) that crystallize in P21212, the twofold symmetry is crystallographically imposed with one half of each molecule in the asymmetric unit. The comparable molecular symmetry in the four structures is also reflected in similar packing, with molecules aggregated to form chains through weak C-H⋯S interactions.