New rhenium-tricarbonyl complexes bearing halogen-substituted bidentate ligands: Structural, computational and Hirshfeld surfaces studies

A series of ten rhenium tricarbonyl complexes (C1-C10), bearing halogen-substituted bidentate N,N-donor ligands with halogens or trifluoromethyl groups (X = -F, -Cl, -Br, and -CF ₃) in different positions on the aromatic rings were synthesized and characterized by FT-IR and ¹H-NMR spectroscopy and their solid-state structures were determined by single crystal X-ray diffraction. The resultant complexes Re(CO) ₃(N,N)X display an octahedral coordination geometry around the central Re atom, and in all the complexes the Re(CO) ₃ unit adopts a fac geometry. The metal-bound halogen atoms along with the halogen-substituted ligands were used to fine-tune the electron density of the halogen σ-hole on the coordinated halide that is involved in halogen-halogen and other intermolecular interactions. This series of compounds was used to explore the range of possible intermolecular interactions involving rhenium coordinated halides. These supramolecular interactions include: (i) halogen bonding through the metal-bound halogen with the carbon-bound halogen (Re-X⋯X-C), (ii) halogen bonding through the carbon-bound halogen with another carbon-bound halogen (C-X⋯X-C), (iii) dipolar interactions through carbonyl-carbonyl (CO⋯CO), (iv) C-H⋯X hydrogen bonding interactions, (v) C-H⋯O hydrogen bonding interactions, (vi) halogen (X)⋯heteroatom (N, O) interactions and (vii) metal-bond carbonyl lone pair with aromatic π-ring interaction, Re-CO(lone pair)⋯π(aromatic ring). In each case the molecular electrostatic potential and non-covalent interaction index were calculated. Crystal packing analyses using Hirshfeld surface calculation confirmed that metal-bound halogen is more effective than carbon-bound halogen in the formation of intermolecular interactions. Complexes C8 and C10 featured interesting intramolecular Re-CO(lone pair)⋯π interactions, the presence of which were confirmed by molecular orbital and non-covalent interaction index (NCI) calculations.