N-(acyl)-N'-(ferrocenylidene) hydrazines and their nickel(II) complexes: Syntheses, structures and physical properties

The Schiff bases N-(acyl)-N'-(ferrocenylidene) hydrazines (HFcah (1) and HFcbh (2), where acyl = acetyl in 1 and benzoyl in 2 and H represents the dissociable amide proton) were synthesized in high yields (74 and 81%) by condensation reactions of equimolar amounts of ferrocene-carboxaldehyde and the corresponding acylhydrazines in presence of acetic acid in refluxing methanol. Reactions of Ni(OAc)(2)center dot 4H(2)O, the Schiff bases (1 and 2) and NaOAc center dot 3H(2)O in 1:2:4 mole ratio in refluxing methanol afforded the diamagnetic iron(II)-nickel(II)iron(II) species [Ni(Fcah)(2)] (3) and [Ni(Fcbh)(2)] (4) in 60 and 68% yields, respectively. Both Schiff bases and the two trinuclear complexes were characterized by elemental (CHN) analysis, mass spectrometric, various spectroscopic (IR, UV-Vis and H-1 NMR) and cyclic voltammetric measurements. Molecular structures of 2, 3 and 4 were determined by single crystal X-ray diffraction studies. The cyclopentadienide rings in the ferrocene moieties are essentially in eclipsed conformation in all three structures. Deprotonated Schiff base ligands in each complex (Fcah(-) in 3 and Fcbh(-) in 4) act as five-membered chelate ring forming azomethine-N and amidate-O donors and assemble a square-planar trans-N2O2 coordination environment around the nickel centre. The redox active 1-4 exhibit an iron centred redox couple in the potential range 0.23-0.50 V (vs. Ag/AgCl).