The crystal and molecular structures of two Re^I tricarbonyl complexes, namely fac-tricarbonylchlorido[1-(4-fluorocinnamoyl)-3-(pyridin-2-yl-κN)pyrazole-κN²]rhenium(I), [ReCl(C₁₇H₁₂FN₃O)(CO)₃], (I), and fac-tricarbonylchlorido[1-(4-nitrocinnamoyl)-3-(pyridin-2-yl-κN)pyrazole-κN²]rhenium(I) acetone monosolvate, [ReCl(C₁₇H₁₂ClN₄O₃)(CO)₃]·C₃H₆O, (II), are reported. The complexes form centrosymmetric dimers that are linked into one-dimensional columns by C-H...Cl and N-O...H interactions in (I) and (II), respectively. C-H...Cl interactions in (II) generate two R₂¹(7) loops that merge into a single R₂¹(10) loop. These interactions involve the alkene, pyrazole and benzene rings, hence restricting the ligand rotation and giving rise to a planar conformation. Unlike (II), complex (I) exhibits a twisted conformation of the ligand and a pair of molecules forms a centrosymmetric dimer with an R₂²(10) loop via C-H...O interactions. The unique supramolecular structures of (I) and (II) are determined by their planarity and weak interactions. The planar conformation of (II) provides a base for appreciable π-π stacking interactions compared to (I). In addition, an N-O...π interaction stabilizes the supramolecular structure of (II). We report herein the first n→π* interactions of Re^I tricarbonyl complexes, which account for 0.33 kJ mol^-1. Intermolecular C-H...Cl and C-H...O interactions are present in both complexes, with (II) showing a greater preference for these interactions compared to (I), with cumulative contributions of 48.7 and 41.5%, respectively. The influence of inductive (fluoro) and/or resonance (nitro) effects on the π-stacking ability was further supported by LOLIPOP (localized orbital locator-integrated π over plane) analysis. The benzene ring of (II) demonstrated a higher π-stacking ability compared to that of (I), which is supported by the intrinsic planar geometry. The HOMA (harmonic oscillator model of aromaticity) index of (I) revealed more aromaticity with respect to (II), suggesting that NO₂ greatly perturbed the aromaticity. The Hirshfeld fingerprint (FP) plots revealed the preference of (II) over (I) for π-π contacts, with contributions of 6.8 and 4.4%, respectively.

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