Synthesis and spectral studies of copper complexes using a N-octylated bis benzimidazole diamide ligand

Monomeric Cu(II) and Cu(I) complexes bound to a tetradentate bis-benzimidazole diamide ligand N,N′-bis(N-octyl benzimidazolyl-2yl)(methyl)pentane diamide (O-GBGA) have been isolated and characterized. X-Band EPR spectra of the copper(II) complexes in CH2Cl2 were recorded in a frozen solution as solvent at liquid nitrogen temperature. Solution spectra typically indicate a dx2−y2 ground state (g|| > g⊥ > 2.0023) and show less than four nuclear hyperfine lines with broadening of g⊥ line in some cases, thus indicating distorted tetragonal geometry. One of the copper(II) complexes shows a five line N-SHF structure (16 ± 1 G) implying the binding of imine nitrogen of the benzimidazole to copper ion. α2 ranges from 0.57-0.97 indicating considerable amount of covalent character in Cu-L bond. Anodic shifts in E1/2 values indicate the retention of anion in the coordination sphere of Cu(II), E1/2 values becoming anodic in the order C6H5COO− < SCN− < Cl−. The fluorescence quantum yield of complexes was found to be lower than that of the ligand O-GBGA (Φ = 0.029) and the relative fluorescence data reveals that fluorescence of such compounds could distinguish between small and large anions.