Multifunctional Transition Metal Complexes: Design, Synthesis, Luminescent Features, Electrical Behaviour, Nanostructure Morphology and Bioactive Properties with 1,1-Dicyanoethylene-2,2-dithiolate and p-Phenylenediamine Ligands

Abstract

Four new transition metal complexes (1-4) were successfully synthesized through the reaction of M(NO3)2·nH2O (M = Ni, Co, Cd or Zn; n = 6 for Ni, Co, Zn; n = 4 for Cd) with 1,1-dicyanoethylene-2,2-dithiolate (i-MNT2–) and p-phenylenediamine (PPD) ligands. The syntheszed metal complexes were characterized by CHN-analysis, electronic, FTIR and 1H NMR spectroscopic techniques. The electronic transition investigations reveals six coordinate octahedral geometry for Ni(II), distorted octahedral for Co(II), four coordinate tetrahedral geometry for Cd(II) and Zn(II) complexes. All the four metal complexes displayed a significant red shift in the absorption maximum, suggesting their successful assembly. The luminescence behaviour exhibited the prominent fluorescence within the visible range. The current-voltage characteristics revealed that complexes 2 and 3 exhibited ohmic behaviour, displaying a linear curve. On the other hand, complexes 1 and 4 initially maintained a low conducting state (OFF state) until a specific voltage threshold (VTh), beyond which the current sharply increased, transitioning to a higher current state (ON state). The FESEM images of the metal complexes strongly indicated a nano-scale aggregated structure. In terms of antibacterial activity, complexes 3 and 4 demonstrated promising efficacy against various bacterial strains, with complex 3 being particularly potent. The fungicidal activity of all four metal complexes was remarkable against Magnaporthe grisea, Cochliobolus miyabeanus and Synchitrium endobioticum, however, no fungicidal activity was found against Trichophyton mentagrophytes and Candida albicans.