Copper(ii) hydrazone complexes with different nuclearities and geometries: synthetic methods and ligand substituent effects

Abstract

A series of copper(II) complexes with 4-hydroxybenzhydrazone-related ligands was synthesized by using various methods, including the conventional solution-based method, solvothermal route and electrochemical synthesis. The complexes can be classified as mononuclear [Cu(L^3OMe)(py)] (2py), dinuclear [Cu₂(L^H)₂(py)₂] (1py), [Cu₂(L^H)₂] (1α and 1β), [Cu₂(L^H)₂(py)₂] (1py), [Cu₂(L^4OMe)₂(py)₂] (3py), [Cu₂(L^4OMe)₂] (3), [Cu₂(L^4OMe)₂(MeOH)₂] (3MeOH), [Cu₂(L^4OMe)₂(EtOH)₂] (3EtOH), cubane tetranuclear [Cu₄(L^3OMe)₄]·xsolv (xsolv = 10H₂O·CH₃OH and 2.8EtOH·0.2H₂O for 2MeOH and 2EtOH, respectively), or polynuclear [Cu(L^H)(py)]_n (1py*), where L^H = 2-oxybenzaldehyde 4-hydroxybenzhydrazonato, L^3OMe = 3-methoxy-2-oxybenzaldehyde 4-hydroxybenzhydrazonato, and L^4OMe = 4-methoxy-2-oxybenzaldehyde 4-hydroxybenzhydrazonato ligands. The presented study indicates that complexes having different nuclearities and geometries can be achieved by changing the synthetic conditions and methods. Thermally induced structural transformations of the dinuclear complexes under solvent-free conditions were also investigated. Crystal and molecular structures of 1β, 1py*, 2MeOH, 2EtOH, 2py, 3 and 3MeOH were determined using the single crystal X-ray diffraction method. All complexes were characterized using microanalysis, FT-IR and CW-EPR spectroscopy, thermogravimetric analysis and a powder X-ray diffraction method.