Copper nano composites functionalized by bis-benzimidazole diamide ligand: Effect of size, co-anion dependent conductivity and band gap studies

Copper (I) and copper (II) nano composites capped with a bis-benzimidazole diamide ligand were prepared by reverse micelle method and characterized using CHNS, FTIR, 1H NMR, TEM and DLS studies. All particles were spherical ranging between 10 and 70 nm. They displayed a quasi reversible redox wave due to the Cu (II)/Cu (I) reduction process. The Eg1′ values shift anodically as NO3− < Cl− < SCN−. Electrochemical HOMO and LUMO band gap (Eg1′) for the nano composites were +1.80 (NO3−), +2.80 (Cl−) and +4.10 (SCN−) eV, respectively. However, the optical band gap (Eg1) for the nano composites was calculated from their absorption edges and lie between 1.77 and 4.13 eV. Fluorescence studies reveal that nano composites in themselves behave as an enhancer and quencher in respect to ligand, Quantum yield (φ) is varying from 0.008 to 0.02 photon. The activation energies range from 34 to 54 kJ mol−1 and are quite low in comparison to that of the free bis-benzimidazole diamide ligand (137 kJ mol−1). The lower activation energies further re-emphasize the nano size of these composites. At room temperature, the dc conductivity lies between 1 × 10−4–9.33 × 10−4 S cm−1 [NO3− > SCN− > Cl−] indicating them to be on the semiconductor insulator interface. The dielectric constant, dielectric loss and the ac conductivity were measured for all nano at room temperature and below the room temperature for the nano composite containing nitrate as co-anion. The conductivity was found to follow the correlated barrier hopping (CBH) mechanism; the exponent factor (s) varies from 0.5 to 1. -- Highlights: ► Nano composites of copper, capped by bis benzimidazole diamide ligand. ► Such copper nano composites have not been used in conductivity studies before. ► Conductance studies for these thus make this work unique. ► The dc conductivity of these composites is much higher than normal.