Synthesis, characterization and conductivity studies of conjugated cyclic Schiff base compounds derived from substituted Salicylaldehyde and Phenylenediamine derivatives

Organic semiconductors have considerable important over the past decades because of its easy preparation. Schiff base ligand is one example of organic semiconductor. Six conjugated Schiff base ligands were synthesized by condensation of phenylenediamine derivatives and substituted salicylaldehyde namely L1, L2, L3, L4, L5 and L6.Metal complexes of L1 and L2 were prepared using cobalt(II) acetate tetrahydrate, copper(II) acetate monohydrate, nickel(II) acetate tetrahydrate and zinc(II) acetate dihydrate by in-situ method. All compounds were characterized by elemental analysis, NMR spectroscopy, infrared spectroscopy, UV-Visible spectroscopy and magnetic susceptibility measurements. Conductivity measurements were done using EIS method. The C=N peaks appeared in the range of 1607 – 1622 cm-1 for all Schiff base ligands indicates the formation of Schiff base ligand. The C=N band is shifted to lower frequency after complexation with metal ions. Complexation occurs by coordination of nitrogen to the metal ion. This was proven by the presence of M-N peak at 500 – 543 cm-1. All metal complexes were suggested to exhibit tetrahedral or square planar geometries based on magnetic susceptibility measurements. Co(II) metal complexes having magnetic moments 3.67 and 3.60 BM for L1Co and L2Co respectively. The magnetic moments of Cu(II) complexes lie in the range 1.83 – 1.87 BM. Conductivity studies and the optical band gap of these compounds were investigated to determine their conductivity values and band gap energy. The conductivity value of synthesized compounds were obtained in the range of 10-8 – 10-5 Scm-1 which include in organic semiconductor range between 10-9 and 103 Scm-1. Both ligands L1 and L2 show higher conductivity value compared to all their metal complexes. Conductivity value of L1 is 1.37 x 10-7 while its metal complexes L1Co, L1Ni, L1Cu and L1Zn are 9.31 x 10-8, 8.97 x 10-8, 7.55 x 10-8 and 1.63 x 10-8 Scm-1respectively. The band gap energy for L1 is 1.56 eV while its metal complexes L1Co, L1Ni, L1Cu and L1Zn are 2.69, 3.17, 2.76 and 2.53 eV respectively. Generally, the optical band gap energy supports the conductivity value as the lower band gap energy indicates higher conductivity value. This study presents a beneficial basis to further apply in electronic industrial application especially in semiconductor.