N-(acyl)- N < sup > ′ < /sup > -(ferrocenylidene)hydrazines and their nickel(II) complexes: Syntheses, structures and physical properties

Abstract

Abstract: 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· 4H 2O , the Schiff bases (1 and 2) and NaOAc · 3H 2O 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 1H 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-N 2O 2 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). Graphical Abstract : N-(acetyl/benzoyl)-N′-(ferrocenylidene)hydrazines (HFcah and HFcbh) and their diamagnetic nickel(II) complexes [Ni(Fcah) 2] and [Ni(Fcbh) 2], each containing a bent iron(II)-nickel(II)-iron(II) array, were synthesised and characterised by analytical, spectroscopic and electrochemical measurements. Molecular structures of HFcbh and the two trinuclear complexes have been confirmed by X-ray crystallography.[Figure not available: see fulltext.].