Synthesis, characterizations, crystal structures, and theoretical studies of copper(II) and nickel(II) coordination complexes

Abstract

In the present study, we report synthesis, characterization, structural and theoretical studies of two copper(II) complexes, [Cu(py)₂(L¹)₂] (1) and [Cu(phen)(Ac)₂-Cu₂(Ac)₄]_n (2), and a nickel(II) complex, [Ni(bipy)(L)(Ac)] (3), where py = pyridine, L¹ = 3,5-dichloro-2-hydroxybenzaldehyde, phen = 1,10-phenanthroline, Ac = acetate ion, bipy = 2,2’-bipyridine and HL = 4-bromo-2-(Z)-(naphthalene-2-ylimino)methyl) phenol. The new complexes were fully characterized using microanalysis, FAB-mas (m/z), FT-IR, UV-Vis and fluorescence spectra, X-band EPR spectroscopy and then by single crystal X-ray diffraction studies. X-ray studies of 1 and 3 revealed distorted octahedral geometries. Complex 2 is a coordination polymer built by an octahedral copper unit Cu(phen)(Ac)₂ alternating with paddle wheel species Cu₂(Ac)₄, located on a crystallographic center of symmetry, where an acetate anion bridges the two crystallographic independent copper ions. The fluorescence intensities and quantum yields of 1 and 2 were found to be more compared to 3. The preliminary tests in the potential application for theoretical biological activities of compounds have also been studied. Furthermore, we also performed quantum chemical calculations to get insights into the structure-property relationships of the synthesized complexes. The quantum chemical calculations were used for theoretical calculations of linear polarizability and third-order nonlinear optical polarizability (γ) for 1, 2 and 3. Besides this, the theoretical calculations, including the analysis of frontier molecular orbitals and electrostatic potential diagrams, are used to highlight the theoretical aspects of metal to ligand charge transfer (MLCT) processes in the studied complexes.

Graphical Abstract

Keywords:

• Metal complexes
• X-ray crystallography
• NLO properties
• polarizability
• third-order polarizability

Acknowledgements

Author thanks the Sophisticated Analytical Instrument Facility (SAIF), IIT Patna for single crystal data collection of 1-3. We thank the Head, Department of Chemistry, NIT Patna and Department of Chemistry, IIT Patna for making available spectral facility.

Additional information

Funding

The authors from King Khalid University acknowledge the financial and technical support of Deanship of Scientific Research (DSR) at King Khalid University of Saudi Arabia through grant No. GRP-69-41. Financial support received from Council of Scientific and Industrial Research, New Delhi, India (Grant No. 01(2856)/16/EMR-II), is gratefully acknowledged. B. Mohan is thankful to CSIR, New Delhi, India for JRF fellowship [Grant No. 01(2856)/16/EMR-II.