Donor/acceptor organotriiron(II) hydrazone chromophores: structural, spectroscopic and electrochemical properties

Abstract Two new trinuclear organoiron(II) complexes, in which a trans -1,2-ferrocenyl-ferrocenylene ethene unit (electron-donors) is attached to an electron-deficient cationic mixed sandwich via a conjugated hydrazone bridge, giving complexes of the type ( E ) - [ CpFe ( η 5 - C 5 H 4 ) – CH CH – ( η 5 - C 5 H 4 ) Fe ( η 5 - C 5 H 4 ) – CH NNH – ( η 6 - p - RC 6 H 4 ) FeCp ] + PF 6 - ( Cp = η 5 - C 5 H 5 ; R = Me , 4 + PF 6 - ; MeO , 5 + PF 6 - ) , have been prepared. The complexes were fully characterised by 1 H NMR, IR, UV–Vis spectroscopy. Their electrochemical properties have been studied by means of cyclic voltammetry, showing an effective electronic coupling between the two ferrocenyl fragments. The X-ray crystal structure of compound 4 + PF 6 - shows that it adopts the sterically more hindered syn -conformation about the 1,1′-ferrocenediyl core, with a parallel disposition of the conjugated dinucleating ligands, therefore, favouring an efficient electron delocalization through the entire π-framework. At the same time, the (C 5 -ring)Fe moieties adopt an anti , anti -conformation with the iron atoms on the opposite faces of their respective bridging ligand.