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

Abstract

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 –CF₃) 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.