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. H-1 NMR spectroscopic data illustrate that the coordinated ligands undergo facile rotation about the C-Pyridine-N-hydrazone 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 pi-stacking, edge-to-face aromatic interactions and classical and non-classical hydrogen bonding. (C) 2009 Elsevier Ltd. All rights reserved.