Synthesis and spectroscopic studies of (E)-N−-(1-phenylethylidene)nicotinohydrazide (PNH) and some of its metal complexes

Four metal complexes with the general formula [M (L)2(H2O)x] (where M = Cu(II), Ni(II), Zn(II) or Co(II); L = (E)-N−-(1-phenylethylidene)nicotinohydrazide and x = 0 or 2) have been synthesized and characterized using elemental analyses, spectral analyses (IR, UV–vis, MS, 1H-NMR), thermal analyses, conductance and magnetic measurements. The results showed that; 1:2 metal chelates have been formed. The ligand exists in the keto form while it coordinates in the metal complexes in the enol form. Ni(II) and Zn(II) complexes have a tetrahedral geometry, Cu(II) has a square-planar while Co(II) has an octahedral geometry. Semi-empirical calculations (AM1, PM3 and ZINDO/1) have been used to calculate the vibrational spectra with the purpose to facilitate the assignment of the experimental results. Also, optical band gap (Eg) has been calculated to elucidate the conductivity of the isolated complexes. The optical transition is indirect with (Eg) values equal 2.46, 2.58 and 2.56 eV for Co(II), Ni(II) and Cu(II) complexes, respectively.