Substituent effects in homoleptic iron(II) and ruthenium(II) complexes of 4′-hydrazone derivatives of 2,2′:6′,2″-terpyridine

The synthesis and characterization of eight homoleptic iron(II) and ruthenium(II) complexes containing 4′-hydrazone-substituted 2,2′:6′,2″-terpyridine ligands are described. 1H NMR spectroscopic data illustrate that the coordinated ligands undergo facile rotation about the Cpyridine–Nhydrazone bond when the N atom is methylated, and hindered bond rotation when the hydrazone NH unit is available for hydrogen bonding to solvent molecules. Detailed structural studies illustrate how the flexibility of the backbone of the complexes leads to significant variation in packing. Throughout the series of solid structures, the packing is dictated by a combination of face-to-face aromatic π-stacking, edge-to-face aromatic interactions and classical and non-classical hydrogen bonding.

Graphical abstractSyntheses, solution dynamic behaviour and solid state structural studies of eight homoleptic iron(II) and ruthenium(II) complexes containing 4′-hydrazone-substituted 2,2′:6′,2″-terpyridine ligands are reported. The coordinated ligands undergo facile rotation about the Cpyridine–Nhydrazone bond in N-methylated compounds, and hindered bond rotation when the hydrazone NH unit is available for hydrogen bonding to solvent molecules. In the solid state, the flexibility of the ligand backbone results in significant variation in packing.Figure optionsDownload full-size imageDownload as PowerPoint slide