Synthesis, spectral and single crystal X-ray diffraction studies on Co(II), Ni(II), Cu(II) and Zn(II) complexes with o-amino acetophenone benzoyl hydrazone

doi:10.1016/j.poly.2013.03.048

Polyhedron

Volume 56, 12 June 2013, Pages 71-81

https://doi.org/10.1016/j.poly.2013.03.048 Get rights and content

Abstract

A series of metal complexes of Co(II), Ni(II), Cu(II) and Zn(II) with o-amino acetophenone benzoylhydrazone (HL) have been synthesized. The complexes were characterized by elemental analyses, magnetic susceptibility measurements, electronic, IR, NMR and ESR spectral techniques. The molecular structures of the Co(II) and Ni(II) complexes were determined by single crystal X-ray diffraction studies. The delocalized charge on the five-membered chelate rings of the Co(II) and Ni(II) complexes forms an unusual intra-molecular CH⋯π interaction with the –CH₃ hydrogen. CH⋯π interactions were also observed in the Ni(II) complex between the phenyl ring and phenyl hydrogen. HL acts as a tridentate ligand in most of the complexes, bonding through >C double bond O, >CN and –NH₂ groups. Electronic spectral studies indicate an octahedral geometry for the Co(II) and Ni(II) complexes, but a square planar geometry for the Cu(II) complex. The ESR spectra of the Cu(II) complex also suggest a square planar geometry around the metal ion in the solid state, but a tetragonal distorted octahedral geometry in DMSO solution at LNT due to solvent interactions at the axial positions. The electrochemical study of the Cu(II) complex exhibits reversible redox behaviour. The thermal analyses (TGA and DTA) of a few complexes show an exothermic multi-step decomposition pattern of the bonded ligands.

Graphical abstract

Complexes of Co(II), Ni(II), Cu(II) and Zn(II) with o-amino acetophenone benzoylhydrazone have been synthesized. They were characterized by their magnetic moments together with their electronic, IR, NMR and ESR spectra. The molecular structures of the Ni(II) and Co(II) complexes were determined by single crystal X-ray diffraction studies.

Introduction

Aroylhydrazones readily form stable complexes with transition metals [1], [2], [3], [4], [5], [6], lanthanides [7], as well as main group elements [8], [9], and may provide synthetic interesting models for the metal containing sites in metallo-proteins and metallo-enzymes [10], [11]. The complexes of aroylhydrazones have been found to exhibit therapeutic activity and this is one practical reason for the continuing interest in these materials. The bio-activity of hydrazone ligands may be due to the presence of multi-coordination centres and their ability to form stable chelates with essential metal ions which organisms need in their metabolism.

The coordination behaviour of hydrazones is known to depend on the pH of the medium, the nature of the substituents and also on the position of the hydrazone group relative to other moieties. Moreover, deprotonation of the –NH group, which is readily achieved in the complexed ligand in particular, results in the formation of tautomeric anionic species (–C(O)–NH–N double bond C< ↔ –C(OH)N–NC< ↔ –C(O⁻)N–NC<), having new coordination properties. Structural studies of the complexes specially derived from Schiff base ligands have shown that CH–π and π–π interactions lead to di- or multi-helical topologies of the complexes. Such structures originate from weak inter-molecular face-to-face and edge-to-face π–π interactions between aromatic rings [12]. These complexes can increase their dimensionality and form supramolecular architectures through O–H⋯N and N–H⋯O types of hydrogen bonds [13].

Metal complexes of hydrazones have been proven to show potential applications as catalysts [14], luminescent probes [15] and molecular sensors [16]. Many Schiff base complexes show excellent catalytic activity in various reactions such as oxidation, hydroxylation, aldol condensation and epoxidation [17]. Metal complexes which involve derivatives of salicylaldehyde and diamine act as potential catalysts for the insertion of oxygen into an organic substrate [13]. In view of the significant role played by the metal complexes of aroylhydrazones in biological systems, catalysis and in various other fields, we were motivated to synthesize Co(II), Ni(II), Cu(II) and Zn(II) complexes with o-amino acetophenone benzoylhydrazone and to described their thermogravimetric, electrochemical and spectroscopic properties. The crystal structures of the Co(II) and Ni(II) complexes have also been reported by single crystal X-ray diffraction.

Section snippets

Materials and methods

Commercial reagents have been used without further purification and all experiments were carried out in the open atmosphere. 2-Aminoacetophenone was purchased from Spectrochem Pvt. Ltd., Mumbai (India) and was used as such. Methyl benzoate, hydrazine hydrate (SD Fine Chemicals, India) and solvents (Merck Chemicals, India) were used in the synthesis. The precursor benzoylhydrazine, C₆H₅CONHNH₂, was prepared by the reported procedure [18] by refluxing methyl benzoate with hydrazine hydrate in a

Results and discussion

It appears from the analytical data that although the reactions between metal(II) chlorides and the ligand HL were performed in a 1:2 (M:L) molar ratio, the Cu(II) complex formed a 1:1 complex. The Co(II), Ni(II) and Zn(II) complexes show the general composition [M(HL₂)]Cl·yH₂O, in which one of the two ligand molecules enolizes and deprotonates during complexation with the metal(II) chloride. The reactions may be written as: $2 HL + {MCl}_{2} \cdot x H_{2} O \to [M ({HL}_{2})] Cl \cdot y H_{2} O + HCl$ where, y = 0 for Co(II), 5 for Ni(II), 2

Conclusions

In the present work cobalt(II), nickel(II), copper(II) and zinc(II) complexes of o-amino acetophenone benzoyl hydrazone have been synthesized and characterized. These metal complexes show variations in the mode of bonding and stereochemistry, as inferred from different spectral studies. The single crystal structure of the Ni(II) complex is stabilized by various inter and intra-molecular hydrogen bonding interactions to form a supramolecular structure. The delocalized charge on the five-membered

Acknowledgements

The authors thank the Head, S.A.I.F., Indian Institute of Technology, Mumbai for recording the ESR spectra. The authors V.P.S. and S.S. are grateful to UGC, New Delhi and CSIR, New Delhi, respectively, for financial assistance.

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Synthesis, spectral and single crystal X-ray diffraction studies on Co(II), Ni(II), Cu(II) and Zn(II) complexes with o-amino acetophenone benzoyl hydrazone

Abstract

Graphical abstract

Introduction

Section snippets

Materials and methods

Results and discussion

Conclusions

Acknowledgements

Polyhedron

Spectrochim. Acta, Part A

Pestic. Biochem. Physiol.

J. Organomet. Chem.

Polyhedron

J. Photochem. Photobiol. A: Chem.

J. Luminescence

Sens. Actuators B: Chem.

Coord. Chem. Rev.

Coord. Chem. Rev.

Inorg. Chim. Acta

Spectrochim. Acta, Part A

Inorg. Chim. Acta

Polyhedron

Polyhedron

Polyhedron

Electrochim. Acta

Polyhedron

Polyhedron

J. Organomet. Chem.

Inorg. Chim. Acta

Polyhedron

J. Mol. Struct.

Dalton Trans.

Eur. J. Inorg. Chem.

Biometals