Abstract

The influence of the halogen substituent on crystal packing and redox properties is investigated in a series of heteroleptic complexes [Fe(qsal-X)(dipic)]·MeOH (qsal-X = 4-halogen-2-[(8-quinolylimino)methyl]phenolate; dipic = 2,6-pyridinedicarboxylate; X = F1, Cl2, Br3and I4). Compounds1and2exhibit triclinic symmetry (P1̄), whereas3and4crystallise in monoclinicP2<inf>1</inf>/n. The crystal packing shows self-sorting of the ligands with π-π interactions between the qsal-X ligands and overlap of the dipic ligands to form a 1D chain, that is supported by C-HO interactions. In1and2, the cross-section of the 1D chain is square, while for3and4, it is rectangular. In the former, the dipic ligands interact through C Oπ interactions, while π-π interactions are found in3and4. Neighbouring chains are connectedviaπ-π interactions involving the quinoline rings, but their relative position is driven by the preference of1and2, for C-HX interactions, whereas3and4form OX halogen bonds. The nature and topology of the electron density of these interactions have been investigated using molecular electrostatic potential (MEP) mapping, quantum theory of atoms in molecules (QTAIM) and ‘non-covalent interactions’ (NCI) analysis. UV-visible experiments show LMCT bands associated with the qsal-X ligands, confirming the structure is stable in solution. Electrochemical studies reveal slight tuning of the Fe³⁺/Fe²⁺redox couple showing a linear relationship betweenE°′ and the Hammett parameterσ<inf>p</inf>