Two Related Thienoquinolizidines and Their Crystal, Molecular Structure and Electronic Properties

Abstract

Two crystals of quinolizidine compounds; systematic name: (rac)-(7,8,9,9a)-tetrahydro-4H-thieno[2,3-b]quinolizine-6,10-dione, (I), and (rac)-(9a,10)-10-hydroxy-8,9,9a,10-tetrahydro-4H-thieno[2,3-b]quinolizin-6(7H)-one, (II), have been compared and characterized by single-crystal X-ray diffraction and electronic analysis. N-heterocyclic rings in both structures are not planar and adopt a half-chair conformation. The molecules of (I) are linked via weak C–H···O hydrogen bonds into chains along c axis. While the crystal stacks in compound (II) are formed by strong O–H···O hydrogen bonds the molecules link into infinite zig-zag chains along the b axis. In both crystal structures, π–π stacking and C–H···π interactions are also observed. Calculation of the net atomic charges shows that O atoms in both compounds carry a relatively large negative charges, in comparison with the corresponding H atoms. Crystal, molecular and electronic structures of these compounds, which are influenced by hydrogen-bonded assemblies in the molecular crystals, are discussed in detail. Crystal, molecular and electronic structures of two related tricyclic compounds containing thienoquinolizidine ring skeleton, both structures have similar quinolizine ring moieties assuming conformations resembling half-chair.