The crystal structures, Hirshfeld surface analyses and energy frameworks of 8-{1-[3-(cyclo-pent-1-en-1-yl)benz-yl]piperidin-4-yl}-2-meth-oxy-quinoline and 8-{4-[3-(cyclo-pent-1-en-1-yl)benz-yl]piperazin-1-yl}-2-meth-oxy-quinoline.

The title compounds, 8-{1-[3-(cyclo-pent-1-en-1-yl)benz-yl]piperidin-4-yl}-2-meth-oxy-quinoline, C27H30N2O (I), and 8-{4-[3-(cyclo-pent-1-en-1-yl)benz-yl]piperazin-1-yl}-2-meth-oxy-quinoline, C26H29N3O (II), differ only in the nature of the central six-membered ring: piperidine in I and piperazine in II. They are isoelectronic (CH cf. N) and isotypic; they both crystallize in the triclinic space group P with very similar unit-cell parameters. Both mol-ecules have a curved shape and very similar conformations. In the biaryl group, the phenyl ring is inclined to the cyclo-pentene mean plane (r.m.s. deviations = 0.089 Å for I and 0.082 Å for II) by 15.83 (9) and 13.82 (6)° in I and II, respectively, and by 67.68 (6) and 69.47 (10)°, respectively, to the mean plane of the quinoline moiety (r.m.s. deviations = 0.034 Å for I and 0.038 Å for II). The piperazine ring in I and the piperidine ring in II have chair conformations. In the crystals of both compounds, mol-ecules are linked by C-H⋯π inter-actions, forming chains in I and ribbons in II, both propagating along the b-axis direction. The principal contributions to the overall Hirshfeld surfaces involve H⋯H contacts at 67.5 and 65.9% for I and II, respectively. The major contribution to the inter-molecular inter-actions in the crystals is from dispersion forces (E dis), reflecting the absence of classical hydrogen bonds. © Ullah and Stoeckli-Evans 2021.