Transition metal coordination polymers: Microwave-assisted synthesis, morphology, conductivity, and decomposition kinetics by TG/DTA techniques

ABSTRACT

Five novel transition metal coordination polymers (CPs) or commonly called as CPs based on chelating ligand 1-(2, 4-dihydroxy-5-(1-(hydroxyamino)ethyl)-3-bromophenyl) ethanoneoxime (DHBO) (L) with different transition metal ions were synthesized by microwave-assisted technique, viz. {[Mn(L)(H₂O)₂]^.2H₂O}_n (1), {[Co(L)(H₂O)₂]^.2H₂O}_n (2), {[Ni(L)]^.H₂O}_n (3), {[Cu(L)]^.H₂O}_n (4), and {[Zn(L)(H₂O)₂]^.2H₂O}_n (5). As-synthesized CPs were characterized by elemental analyses, Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy, diffused reflectance spectroscopy, magnetic measurements, and thermogravimetric property (TG/DTA) to find out their structures and geometries. The morphological behaviours of polymers were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM investigations reveal different shapes and structures, although they were synthesized from a single ligand. Captivatingly, spectroscopic and magnetic measurements revealed octahedral geometry for 1, 2, and 5, while 3 and 4 exhibited a square planar. Six coordinated geometries were constructed due to a tetradentate chelating ligand (L) and two coordinated water molecules, while square planar geometry constructed by only a tetradentate ligand. Furthermore, the main aim of this article is to find out the comparative thermal stability and electrical conductivity of 1–5. Also, kinetic parameters like activation energy, order of reaction, enthalpy change , entropy change, and free energy change were evaluated using Freeman-Carroll method.

KEYWORDS:

• Coordination polymers
• microwave-assisted synthesis
• diffused reflectance spectroscopy
• TEM
• thermal stability
• activation energy

Acknowledgments

Authors are thankful to the Head, Post Graduate Department of Chemistry, Rashtrasant Tukadoji Maharaj Nagpur University, Nagpur for providing the laboratory facilities. Authors are grateful to Birla Institute of Technology, Ranchi, Jharkhand for thermal analysis and STIC Cochin University, Kerala for SEM and TEM analyses of CPs..

Disclosure statement

The authors declare that they have no competing interest.